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Invasive, naturalized and casual alien plants in southern Africa: A summary based on the Southern African Plant Invaders Atlas (SAPIA)
Abstract
The primary objective of this publication is to provide an overview of the species identity, invasion status, geographical extent, and abundance of alien plants in South Africa, Swaziland and Lesotho, based on fi eld records from 1979 to the end of 2000. The dataset is all the species records for the study area in the Southern African Plant Invaders Atlas (SAPIA) database during this time period. A total of 548 naturalized and casual alien plant species were catalogued and invasion was recorded almost throughout the study area. Most invasion, in terms of both species numbers and total species abundance, was recorded along the southern, southwestern and eastern coastal belts and in the adjacent interior. This area includes the whole of the Fynbos and Forest Biomes, and the moister eastern parts of the Grassland and Savanna Biomes. This study reinforces previous studies that the Fynbos Biome is the most extensively invaded vegetation type in South Africa but it also shows that parts of Savanna and Grassland are as heavily invaded as parts of the Fynbos. The Fabaceae is prominent in all biomes and Acacia with 17 listed species, accounts for a very large proportion of all invasion. Acacia mearnsii was by far the most prominent invasive species in the study area, followed by A. saligna, Lantana camara, A. cyclops, Opuntia fi cus-indica, Solanum mauritianum, Populus alba/×canescens, Melia azedarach, A. dealbata and species of Prosopis.
... S.E. Blake (Asteraceae: Heliantheae), is increasing its invasive status in South Africa, with extensive monospecific stands in over 42 quarter degree squares inhabiting roadsides, agroecosystems, rivers and natural systems (Henderson 2007(Henderson , 2020Mawela et al. 2022). Five out of South Africa's nine provinces, namely Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga and North West support populations of T. rotundifolia (Henderson 2007(Henderson , 2020Simelane et al. 2011;Mawela and Simelane 2021;Mawela et al. 2022). ...
... Blake (Asteraceae: Heliantheae), is increasing its invasive status in South Africa, with extensive monospecific stands in over 42 quarter degree squares inhabiting roadsides, agroecosystems, rivers and natural systems (Henderson 2007(Henderson , 2020Mawela et al. 2022). Five out of South Africa's nine provinces, namely Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga and North West support populations of T. rotundifolia (Henderson 2007(Henderson , 2020Simelane et al. 2011;Mawela and Simelane 2021;Mawela et al. 2022). A biological control programme was thus initiated in 2007 (Mawela and Simelane 2021) and culminated in release of two leaf-feeding beetles, Zygogramma piceicollis (Stål) and Zygogramma signatipennis (Stål) (Coleoptera: Chrysomelidae), from 2014 to 2019 (Mawela et al. 2022). ...
... The objective of this study was to predict the potential for Z. signatipennis and Z. piceicollis to establish and spread throughout the invaded range of T. rotundifolia in South Africa. Tithonia rotundifolia remains a major invasive weed in five provinces of South Africa (Henderson 2007). While there might be scepticism towards the release of almost identical biocontrol agents that attack the same niche, the realized distributions of Z. signatipennis and Z. piceicollis were different in Mexico. ...
Two Mexican leaf-feeding beetles, Zygogramma piceicollis (Stål) and Zygogramma signatipennis (Stål) (Coleoptera: Chrysomelidae), were released in South Africa for the biological control of the invasive species Tithonia rotundifolia (Mill.) S.E. Blake (Asteraceae: Heliantheae). The aim of this study was to predict the potential of these beetles to establish and spread in South Africa, using MaxEnt climate modelling that incorporated locality data recorded in Mexico between 2008 and 2019 and data from the Global Biodiversity Information Facility. Zygogramma signatipennis displayed a wider distribution than Z. piceicollis in Mexico, with some overlap between the two species. The average receiver operating characteristic curves obtained for Z. piceicollis and Z. signatipennis predicted high mean area under curve values of 0.910 and 0.885, respectively. Jackknife tests revealed that mean annual temperature had the highest gain when used in isolation for Z. piceicollis , compared with minimum precipitation of the driest month for Z. signatipennis . These tests also revealed that the highest and lowest contributing environmental variables for Z. piceicollis and Z. signatipennis were minimum precipitation of the driest month (37.9 and 46.7%) and maximum annual temperature of the warmest month (3.8 and 12.3%), respectively. MaxEnt modelling predicted that at least six of South Africa’s nine provinces provide regions that would support the proliferation of both beetles, with conditions best suited for Z. piceicollis . Despite predictions that both beetles should establish throughout the range of T. rotundifolia in South Africa, their realized establishment has so far been poor. Other factors, besides climate, including release size, site destructions, drought, soil moisture and texture could be constraining establishment.
... In countries like South Africa, poplar species are common in many landscapes and are only legally permitted in certain areas under controlled conditions [9]. Dense stands of cottonwood formed through rooting can narrow and block water channels, leading to flooding and increased siltation [10]. ...
... These studies were geographically distributed in over 20 countries, where poplar is either native or invasive, and their wide distribution is shown in Figure 4. Most studies were conducted in China (34), followed by the United States of America (22), Italy (21), France (13), and Canada (12), accounting for over two-thirds of the studies. The remaining publications came from Sweden (6) For emphasis, note that despite reported cases in countries like South Africa, where it is classified as a Category 2 (occurring throughout/in part of South Africa and allowed [9], no studies have been conducted on the African continent. This underscores the need for rigorous research, particularly when the studied species is invading (e.g., South Africa and Africa). ...
... Although not yet used in poplar studies, spectral angle mapper classifiers are also associated with better discrimination of floral invasive species [69]; hence, they are also recommended for future use. Many of these computations were performed using Matlab (17), Python (13), ArcMap (9), RStudio (14), ENVI (version 5.0) (9), and other software ( Table 2). ...
Given the ability of remote sensing to detect distinctive plant traits, it has emerged in recent decades as a useful and attractive research tool for forest trees such as poplars. Although poplars have been extensively studied using remote sensing over the past thirty years, no reviews have been conducted to understand the results of multiple applications. Here, we present a review and synthesis of poplar studies in this regard. We searched the Scopus, Google Scholar, and Science Direct databases and found 266 published articles, of which 148 were eligible and analyzed. Our results show a rapid increase in remote sensing-based poplar publications over the period of 1991-2022, with airborne platforms, particularly LiDAR, being predominantly used, followed by satellite and ground-based sensors. Studies are widespread in the Global North, accounting for more than two-thirds of studies. The studies took place mainly in agricultural landscapes, followed by forest areas and riparian areas, with a few in mountain and urban areas. Commonly studied biophysical parameters were mostly obtained from LiDAR data. On the other hand, spectral indicators have been widely used to monitor the health and vitality of poplar trees, integrating various machine learning algorithms. Overall, remote sensing has been widely used in poplar studies, and the increasing use of free satellite data and processing platforms is expected to pave the way for data-poor countries to monitor poplar in the Global South, where resources are mainly limited.
... The genus Cestrum is native to Central and South America where it thrives in montane forests (Monro, 2012). The abundant, attractive and fragrant flowers of this genus are the reason it has been introduced as an ornamental plant in many regions, where it has subsequently become naturalized, and in several cases, turned invasive, including in parts of Africa, Asia, Australia and multiple oceanic islands (Henderson, 2007;Harvey et al., 2012;Junaedi, 2012;Gardener et al., 2013;Padmanaba et al., 2017;Makokha, 2018). In the Indian subcontinent, C. aurantiacum has been reported across many montane regions including the Himalaya, the Western Ghats and in Sri Lanka (Kunwar, 2003;Sajeev et al., 2012;Wijesundara, 2012;Moktan and Das, 2013;Mandal and Joshi, 2015;Nayak et al., 2020). ...
... bear berries with small seeds that remain viable in the seed bank and are bird-dispersed (Marambe et al., 2001;Geldenhuys, 2004;Gardener et al., 2013). They are also shadetolerant (Geldenhuys, 2004), drought-tolerant, capable of growing on poor soils and have invaded a range of habitats from coastal dunes to savannahs, grasslands, plantations and closed forest (Henderson, 2007). Most are quite toxic to livestock, native mammals and humans (de Rojas and D'Arcy, 1998;Makokha, 2018). ...
... Most are quite toxic to livestock, native mammals and humans (de Rojas and D'Arcy, 1998;Makokha, 2018). For these reasons, they are labelled as noxious weeds with moderate to high invasive potential (Nel et al., 2004;Henderson, 2007). In South Africa and Australia, extensive programs have been undertaken to clear areas of Cestrum species (Macdonald and Jarman, 1985;Stockard, 1996;Marais and Wannenburgh, 2008). ...
In the montane forest-grassland mosaics of the Western Ghats, land cover conversion to silviculture and agriculture over the last five decades has resulted in both loss of natural habitats and widespread invasion of remnant habitat patches. While invasion of the grassland habitats of the mosaic has been relatively well studied, there have been few attempts to understand the extent to which forest habitats (locally known as sholas) have been affected by the spread of exotic species. Here we examine the patterns and impacts of invasion of shola forest understoreys by Cestrum aurantiacum Lindl., an exotic shrub species. At the landscape scale, we demonstrate that the presence and abundance of this invasive in shola understories is negatively related to distance from tea plantations. Further, the intensity of invasion is higher in areas with greater seasonality of temperature and lower mean annual precipitation. At the patch scale, invasion is greatest at shola edges and away from stream courses. We find that C. aurantiacum abundance has negatively affected the regeneration of native shola tree species as well as the abundance of native shola understorey shrubs. Fifty three percent of invaded plots had no native shrubs present. In plots where both C. aurantiacum and native shrubs were present in large enough numbers, we found evidence of negative spatial dependence between stem locations of C. aurantiacum and native shrubs. Our findings have important implications for the management and conservation of these mosaics.
... Invasive plant species occupy more than 20 million hactares of South Africa (Wynberg, 2003). Invaded lands in South African include forest, fynbos, savannah and grassland biomes (Henderson, 2007). The most prevalent invasive plant species over the biomes of South Africa are the Fabaceae family, which are Acacia mearnsii, Acacia saligna and Acacia cyclops (Henderson, 2007). ...
... Invaded lands in South African include forest, fynbos, savannah and grassland biomes (Henderson, 2007). The most prevalent invasive plant species over the biomes of South Africa are the Fabaceae family, which are Acacia mearnsii, Acacia saligna and Acacia cyclops (Henderson, 2007). There are, however, many more species that are becoming increasingly problematic. ...
... Nonnative species commonly encountered were tickberry Lantana camara and guava Psidium guajava. Both of these species are native to tropical central and southern America and are categorised as fully invasive in South Africa (Henderson, 2007;Gaertner et al. 2016). In the region these invasive species are well-known to have a substantial negative impact on native plant species through competition and replacement (Richardson and van Wilgen, 2004;Vardien et al., 2012;Urquía et al., 2019). ...
Leaf litter contributes to the functioning of aquatic ecosystems through allochthonous inputs of carbon, nitrogen and other elements. In many freshwater ecosystems, leaf litter inputs are among the most important cross-ecosystem nutrient contributions. However, native plant communities are under threat from invasive plant species, with largely unexplored consequences for recipient aquatic ecosystems. Broadly, ecological impacts of invasive alien species can be unpredictable and simultaneously span multiple habitat types and taxonomic groups. Invasive alien plants can have particularly severe ecological impacts, and plant inputs into aquatic environments can alter abiotic and biotic aquatic dynamics. Lakes and reservoir ecosystems are regarded as heterotrophic detritus-based habitats which are dependent upon allochthonous organic matter for the majority of energy inputs. Allochthonous detritus is extremely important for the trophic dynamics of the microbial organisms, macroinvertebrates and benthic plants in lakes and reservoirs. In the present study, leaf litter nutrient inputs, decomposition and colonisation associated with four plant species was examined using a combination of mesocosm and field experimental approaches. Native sycamore fig Ficus sycomorus L., and silver cluster–leaf Terminalia sericea Burch. ex DC. decomposition dynamics were compared to invasive tickberry Lantana camara L and guava Psidium guajava L., whereby phosphate, nitrate, nitrite, silicate and ammonium releases were quantified over time. Leaf inputs significantly reduced pH, with reductions most marked by invasive L. camara. Conductivity was heightened by all leaf input treatments, excepting native T. sericea. Leaf inputs significantly affected all nutrient levels monitored in the water over time, except for silicate. In particular, leaf litter from invasive L. camara drove significantly increased nutrient concentrations compared to other native plant species, whilst effects of invasive P. guajava were less statistically clear. The end weights of the leaf litter demonstrated decomposition differences among the species types, following a decreasing order of P. guajava > T. sericea > F. sycomorus > L. camara, further suggesting high organic inputs from invasive L. camara. Furthermore, ex-situ larval mosquito colonisation of with the above-mentioned native and invasive species leaves were assessed. Larval mosquito abundances differed significantly accordingly to leaf treatment, whilst no mosquitoes colonised leaf-free controls. Leaf litter from the invasive L. camara, invasive P. guajava and native F. sycomorus drove significant increases in mosquito abundances relative to native T. sericea. In situ macroinvertebrate colonisation, and quantify decomposition rates, of four species of native and invasive terrestrial plants was also assessed. Leaf treatments had a significant, group-specific effect on abundances and composition among focal macroinvertebrates. Invasive leaves reduced Physidae and Oligochaeta abundances, yet Ostracoda were significantly more abundant in the presence of invasive P. guajava. Chironomidae relative abundances increased under invasive L. camara treatments, whilst differences among leaf treatment effects on Coenogrionidae abundances were not statistically clear. In turn, macroinvertebrate diversity did not differ significantly among plant treatment groups, but the contributing taxa varied. The decomposition rate of the leaf litter demonstrated differences among the species types, following a decreasing order of L. camara > F. sycomorus > T. sericea > P. guajava. The study results highlight that differential leaf litter decomposition rates of …
... South Africa has one of the biggest problems of alien plant invasions globally, with the largest number of invasive plant species occurring in the Fynbos Biome [3,[41][42][43]. Applications of remote sensing to map invasive species within the Fynbos Biome have primarily focused on invasive trees such as those from the genera Eucalyptus, Pinus and Acacia that impact riparian zones and mountain slopes, and pose a threat to water security [44,45]. ...
... The CFR, with its high native species richness and levels of endemism, is a biodiversity hotspot [74,75]; it is the smallest, but most biologically diverse of all the world's six plant kingdoms, and is recognized as a UNESCO world heritage site [76,77]. The Fynbos Biome is one of the most species-rich floristic regions in the world [78]; however, it is also the most invaded of all biomes in South Africa [3,41]. The Fynbos Biome is characterized by a Mediterranean-type climate with hot, dry summers and mild wet winters, and has a mean annual precipitation of 480 mm [79]. ...
... Geomatics 2023, 3, FOR PEER REVIEW 4 native species richness and levels of endemism, is a biodiversity hotspot [74,75]; it is the smallest, but most biologically diverse of all the world's six plant kingdoms, and is recognized as a UNESCO world heritage site [76,77]. The Fynbos Biome is one of the most species-rich floristic regions in the world [78]; however, it is also the most invaded of all biomes in South Africa [3,41]. The Fynbos Biome is characterized by a Mediterranean-type climate with hot, dry summers and mild wet winters, and has a mean annual precipitation of 480 mm [79]. ...
Invasive alien plants (IAPs) pose a serious threat to biodiversity, agriculture, health, and economies globally. Accurate mapping of IAPs is crucial for their management, to mitigate their impacts and prevent further spread where possible. Remote sensing has become a valuable tool in detecting IAPs, especially with freely available data such as Sentinel-2 satellite imagery. Yet, remote sensing methods to map herbaceous IAPs, which tend to be more difficult to detect, particularly in shrubland Mediterranean-type ecosystems, are still limited. There is a growing need to detect herbaceous IAPs at a large scale for monitoring and management; however, for countries or organizations with limited budgets, this is often not feasible. To address this, we aimed to develop a classification methodology based on optical satellite data to map herbaceous IAP's using Echium plantagineum as a case study in the Fynbos Biome of South Africa. We investigate the use of freely available Sentinel-2 data, use the robust non-parametric classifier Random Forest, and identify the most important variables in the classification, all within the cloud-based platform, Google Earth Engine. Findings reveal the importance of the shortwave infrared and red-edge parts of the spectrum and the importance of including vegetation indices in the classification for discriminating E. plantagineum. Here, we demonstrate the potential of Sentinel-2 data, the Random Forest classifier, and Google Earth Engine for mapping herbaceous IAPs in Mediterranean ecosystems.
... We identified 428 naturalized alien species in Nigeria, which is a major update of the 102 previously reported in the GRIIS database (Borokini et al. 2021). This naturalized flora can be compared, in terms of richness, with 436 naturalized species in the Democratic Republic of Congo (Bordbar and Meerts 2022), 113 in Sudan and South Sudan (Omer et al. 2021), 108 in Algeria (Meddour et al. 2020), 548 in Southern Africa (Henderson 2007 (Henderson 2007;Witt et al. 2018;Ansong et al. 2019;Bordbar and Meerts 2020;Meddour et al. 2020;Omer et al. 2021). However, compared to only 20% of alien plants in Fabaceae that have become invasive in Nigeria, over 80% of alien plants in Poaceae have become invasive, making it the family with the largest percentage of invasive species in Nigeria. ...
... We identified 428 naturalized alien species in Nigeria, which is a major update of the 102 previously reported in the GRIIS database (Borokini et al. 2021). This naturalized flora can be compared, in terms of richness, with 436 naturalized species in the Democratic Republic of Congo (Bordbar and Meerts 2022), 113 in Sudan and South Sudan (Omer et al. 2021), 108 in Algeria (Meddour et al. 2020), 548 in Southern Africa (Henderson 2007 (Henderson 2007;Witt et al. 2018;Ansong et al. 2019;Bordbar and Meerts 2020;Meddour et al. 2020;Omer et al. 2021). However, compared to only 20% of alien plants in Fabaceae that have become invasive in Nigeria, over 80% of alien plants in Poaceae have become invasive, making it the family with the largest percentage of invasive species in Nigeria. ...
Biological invasions remain one of the greatest threats to biodiversity and livelihoods, and are predicted to increase due to climate change and globalization. In this study, we produced a comprehensive checklist of alien plants in Nigeria from online flora databases, herbarium records, published field surveys, and questionnaires administered to botanical gardens. The resulting alien flora was classified into naturalized, invasive, and cultivated plants. We then fitted a random forest model to identify the attributes which facilitate the naturalization of alien plants in Nigeria. We also used separate chi-squared tests to investigate if the frequency of these attributes is significantly different between the naturalized and invasive plants. The results include 1,381 alien plant taxa, comprising 238 naturalized, 190 invasive, and 953 cultivated species. The naturalized and invasive plants (428 species) are from 91 families, with Fabaceae and Poaceae having the highest representations. The random forest model showed that life forms and local economic uses were the most important drivers of alien plant naturalization in Nigeria. Chi-squared tests revealed a non-random distribution of life forms, higher frequencies of naturalized plants from the Indomalaya and the Neotropics, greater introductions during the British colonial rule, and that naturalized species are mostly used for medicinal, ornamental, food, or animal fodder purposes. Naturalized and invasive plants were recorded in all regions of Nigeria and are mostly found in urban and agricultural landscapes. This baseline information can support further ecological studies and conservation actions in Nigeria.
... In semi-arid districts of southern Zimbabwe where rainfall limits crop production, people's livelihoods are directly dependent on livestock production (Chenje et al. 1998). However, these semi-arid areas are prone to invasion by several cacti species in particular Opuntia fulgida, which is unpalatable (Henderson 2007). The invasion of semi-arid areas by O. fulgida constitutes a serious threat to the security of farmers who depend on rangelands as a key source of forage for their livestock and this deserves research attention. ...
... These stems detach easily to form new individual plants. The species is native to South America but was introduced into tropical countries as an ornamental shrub (Coates-Palgrave 2002, Henderson 2007). Due to its ability to naturalise, escape cultivation and spread rapidly, it is now classified as a serious invasive species in many countries. ...
... In semi-arid districts of southern Zimbabwe where rainfall limits crop production, people's livelihoods are directly dependent on livestock production (Chenje et al. 1998). However, these semi-arid areas are prone to invasion by several cacti species in particular Opuntia fulgida, which is unpalatable (Henderson 2007). The invasion of semi-arid areas by O. fulgida constitutes a serious threat to the security of farmers who depend on rangelands as a key source of forage for their livestock and this deserves research attention. ...
... These stems detach easily to form new individual plants. The species is native to South America but was introduced into tropical countries as an ornamental shrub (Coates-Palgrave 2002, Henderson 2007). Due to its ability to naturalise, escape cultivation and spread rapidly, it is now classified as a serious invasive species in many countries. ...
... We identified 428 naturalized alien species in Nigeria, which is a major update of the 102 previously reported in the GRIIS database (Borokini et al. 2019). This naturalized flora can be compared, in terms of richness, with 436 naturalized species in the Democratic Republic of Congo (Bordbar and Meerts 2022), 113 in Sudan and South Sudan (Omer et al. 2021), 108 in Algeria (Meddour et al. 2020), 548 in Southern Africa (Henderson 2007), 129 in Egypt (El-Beheiry et al. 2020), 291 in Ghana (Ansong et al. 2019), and over 180 in Angola (Figueiredo and Smith 2022). ...
... Fabaceae was also cited as having the highest number of representatives among naturalized plants in Algeria, Sudan and South Sudan, the Democratic Republic of Congo, South Africa, Ghana, and Eastern Africa (Henderson 2007;Witt et al. 2018;Ansong et al. 2019;Bordbar and Meerts 2020;Meddour et al. 2020;Omer et al. 2021). However, compared to only 20% of alien plants in Fabaceae that have become invasive in Nigeria, over 80% of alien plants in Poaceae have become invasive, making it the family with the largest percentage of invasive species in Nigeria. ...
Biological invasions remain one of the greatest threats to biodiversity and livelihoods, and this is predicted to increase due to climate change and globalization. In this study, we produced a comprehensive checklist of alien plants in Nigeria from online flora databases, herbarium records, published field surveys, and questionnaires administered to botanical gardens. The resulting alien flora was classified into naturalized, invasive, and cultivated plants. We then fitted a random forest model to identify the attributes which facilitate the naturalization of alien plants in Nigeria. We also used separate chi-squared tests to investigate if the frequency of these attributes is statistically significant between the naturalized and invasive plants. The results include 1,381 alien plant taxa, comprising 238 naturalized, 190 invasive, and 953 cultivated species. The naturalized and invasive plants (428 species) spread across 91 families, with Fabaceae and Poaceae having the highest representations. The random forest model showed that life forms and local economic uses were the most important drivers of alien plant naturalization in Nigeria. Chi-squared tests revealed a non-random distribution of life forms (P < 0.001), higher frequencies of naturalized plants from the Indomalaya (P = 0.006) and the Neotropics (P = 0.04), greater introductions during the British colonial rule, and are used mostly for medicinal, ornamental, food, and fodder. Naturalized and invasive plants were recorded in all regions of Nigeria and are mostly found in urban ruderal and agricultural landscapes. This baseline information can support further ecological studies and conservation actions in Nigeria.
... Gleditsia triacanthos L., Species Plantarum 2: 1056 (1753) (Leguminosae) is a deciduous tree species of Eastern USA that has been introduced and spread in some warm temperate areas as Argentina, Uruguay, Australia, South Africa and Central and SE continental Europe (Henderson 2007;Batianoff and Butler 2002;Keighery and Longman 2004;Richardson et al. 2006;Grbić et al. 2007;Fernandez et al. 2017). It usually has large, rigid spines (except in var. ...
... Average annual precipitation in its natural area ranges from 500 to 1,800 mm and the frostfree period varies from 140 to 300 days (Gold and Hanover 1993). It is extremely invasive in certain areas of South America (Fernandez et al. 2017), Australia (Randall 2017) and South Africa (Henderson 2007). The review of literature on invaded areas shows that the species has become invasive mainly under Cfa and Cfb climate types and mathematical models show that it may marginally colonise Csa and BSk types as well (Csurhes and Kriticos 1994;State of Queensland 2016;Fernandez et al. 2017; State of Victoria 2020). ...
... Gleditsia triacanthos L., Species Plantarum 2: 1056 (1753) (Leguminosae) is a deciduous tree species of Eastern USA that has been introduced and spread in some warm temperate areas as Argentina, Uruguay, Australia, South Africa and Central and SE continental Europe (Henderson 2007;Batianoff and Butler 2002;Keighery and Longman 2004;Richardson et al. 2006;Grbić et al. 2007;Fernandez et al. 2017). It usually has large, rigid spines (except in var. ...
... Average annual precipitation in its natural area ranges from 500 to 1,800 mm and the frostfree period varies from 140 to 300 days (Gold and Hanover 1993). It is extremely invasive in certain areas of South America (Fernandez et al. 2017), Australia (Randall 2017) and South Africa (Henderson 2007). The review of literature on invaded areas shows that the species has become invasive mainly under Cfa and Cfb climate types and mathematical models show that it may marginally colonise Csa and BSk types as well (Csurhes and Kriticos 1994;State of Queensland 2016;Fernandez et al. 2017; State of Victoria 2020). ...
... Gleditsia triacanthos L., Species Plantarum 2: 1056 (1753) (Leguminosae) is a deciduous tree species of Eastern USA that has been introduced and spread in some warm temperate areas as Argentina, Uruguay, Australia, South Africa and Central and SE continental Europe (Henderson 2007;Batianoff and Butler 2002;Keighery and Longman 2004;Richardson et al. 2006;Grbić et al. 2007;Fernandez et al. 2017). It usually has large, rigid spines (except in var. ...
... Average annual precipitation in its natural area ranges from 500 to 1,800 mm and the frostfree period varies from 140 to 300 days (Gold and Hanover 1993). It is extremely invasive in certain areas of South America (Fernandez et al. 2017), Australia (Randall 2017) and South Africa (Henderson 2007). The review of literature on invaded areas shows that the species has become invasive mainly under Cfa and Cfb climate types and mathematical models show that it may marginally colonise Csa and BSk types as well (Csurhes and Kriticos 1994;State of Queensland 2016;Fernandez et al. 2017; State of Victoria 2020). ...
... Gleditsia triacanthos L., Species Plantarum 2: 1056 (1753) (Leguminosae) is a deciduous tree species of Eastern USA that has been introduced and spread in some warm temperate areas as Argentina, Uruguay, Australia, South Africa and Central and SE continental Europe (Henderson 2007;Batianoff and Butler 2002;Keighery and Longman 2004;Richardson et al. 2006;Grbić et al. 2007;Fernandez et al. 2017). It usually has large, rigid spines (except in var. ...
... Average annual precipitation in its natural area ranges from 500 to 1,800 mm and the frostfree period varies from 140 to 300 days (Gold and Hanover 1993). It is extremely invasive in certain areas of South America (Fernandez et al. 2017), Australia (Randall 2017) and South Africa (Henderson 2007). The review of literature on invaded areas shows that the species has become invasive mainly under Cfa and Cfb climate types and mathematical models show that it may marginally colonise Csa and BSk types as well (Csurhes and Kriticos 1994;State of Queensland 2016;Fernandez et al. 2017; State of Victoria 2020). ...
... Gleditsia triacanthos L., Species Plantarum 2: 1056 (1753) (Leguminosae) is a deciduous tree species of Eastern USA that has been introduced and spread in some warm temperate areas as Argentina, Uruguay, Australia, South Africa and Central and SE continental Europe (Henderson 2007;Batianoff and Butler 2002;Keighery and Longman 2004;Richardson et al. 2006;Grbić et al. 2007;Fernandez et al. 2017). It usually has large, rigid spines (except in var. ...
... Average annual precipitation in its natural area ranges from 500 to 1,800 mm and the frostfree period varies from 140 to 300 days (Gold and Hanover 1993). It is extremely invasive in certain areas of South America (Fernandez et al. 2017), Australia (Randall 2017) and South Africa (Henderson 2007). The review of literature on invaded areas shows that the species has become invasive mainly under Cfa and Cfb climate types and mathematical models show that it may marginally colonise Csa and BSk types as well (Csurhes and Kriticos 1994;State of Queensland 2016;Fernandez et al. 2017; State of Victoria 2020). ...
... Gleditsia triacanthos L., Species Plantarum 2: 1056 (1753) (Leguminosae) is a deciduous tree species of Eastern USA that has been introduced and spread in some warm temperate areas as Argentina, Uruguay, Australia, South Africa and Central and SE continental Europe (Henderson 2007;Batianoff and Butler 2002;Keighery and Longman 2004;Richardson et al. 2006;Grbić et al. 2007;Fernandez et al. 2017). It usually has large, rigid spines (except in var. ...
... Average annual precipitation in its natural area ranges from 500 to 1,800 mm and the frostfree period varies from 140 to 300 days (Gold and Hanover 1993). It is extremely invasive in certain areas of South America (Fernandez et al. 2017), Australia (Randall 2017) and South Africa (Henderson 2007). The review of literature on invaded areas shows that the species has become invasive mainly under Cfa and Cfb climate types and mathematical models show that it may marginally colonise Csa and BSk types as well (Csurhes and Kriticos 1994;State of Queensland 2016;Fernandez et al. 2017; State of Victoria 2020). ...
... Gleditsia triacanthos L., Species Plantarum 2: 1056 (1753) (Leguminosae) is a deciduous tree species of Eastern USA that has been introduced and spread in some warm temperate areas as Argentina, Uruguay, Australia, South Africa and Central and SE continental Europe (Henderson 2007;Batianoff and Butler 2002;Keighery and Longman 2004;Richardson et al. 2006;Grbić et al. 2007;Fernandez et al. 2017). It usually has large, rigid spines (except in var. ...
... Average annual precipitation in its natural area ranges from 500 to 1,800 mm and the frostfree period varies from 140 to 300 days (Gold and Hanover 1993). It is extremely invasive in certain areas of South America (Fernandez et al. 2017), Australia (Randall 2017) and South Africa (Henderson 2007). The review of literature on invaded areas shows that the species has become invasive mainly under Cfa and Cfb climate types and mathematical models show that it may marginally colonise Csa and BSk types as well (Csurhes and Kriticos 1994;State of Queensland 2016;Fernandez et al. 2017; State of Victoria 2020). ...
... Gleditsia triacanthos L., Species Plantarum 2: 1056 (1753) (Leguminosae) is a deciduous tree species of Eastern USA that has been introduced and spread in some warm temperate areas as Argentina, Uruguay, Australia, South Africa and Central and SE continental Europe (Henderson 2007;Batianoff and Butler 2002;Keighery and Longman 2004;Richardson et al. 2006;Grbić et al. 2007;Fernandez et al. 2017). It usually has large, rigid spines (except in var. ...
... Average annual precipitation in its natural area ranges from 500 to 1,800 mm and the frostfree period varies from 140 to 300 days (Gold and Hanover 1993). It is extremely invasive in certain areas of South America (Fernandez et al. 2017), Australia (Randall 2017) and South Africa (Henderson 2007). The review of literature on invaded areas shows that the species has become invasive mainly under Cfa and Cfb climate types and mathematical models show that it may marginally colonise Csa and BSk types as well (Csurhes and Kriticos 1994;State of Queensland 2016;Fernandez et al. 2017; State of Victoria 2020). ...
Invasive species are one of the main causes of biodiversity loss worldwide. As introduced, populations may increase in abundance and expand geographical range, so does the potential for negative impacts on native communities. As such, it is necessary to understand the processes driving range expansion, before a species becomes established in new areas. Through an investigation into capacity for population growth and range expansion of introduced populations of a non-native lizard, we aimed to demonstrate how multi-scale factors influence spatial spread, population growth, and invasion potential in introduced species. The Italian Wall Lizard (Podarcis siculus) was introduced multiple times to the United States with extant populations in California, Kansas, New Jersey, and New York. Recently, a single specimen was discovered in British Columbia, Canada, and unstudied populations are on Orcas Island and Missouri (USA). We used phylogenetic analysis of mtDNA sequences (cytb gene) of individuals sampled from these introduced populations and across the native range to identify potential source populations. Our phylogenetic analysis result with documentation of the introductions revealed that the Canadian individual is derived from the Tuscany clade (together with samples from Kansas and New York). The New Jersey population is likely from the Adriatic clade and the Californian one from Sicily. The Orcas Island and Missouri populations still require study. Consequently, humans are key drivers of the distribution of alien reptiles in North America, but the distributions are determined by a complex interplay between human activities, geographic factors and species features. Genetic evidence is essential for reliable biogeographic assessment of invasive species, particularly in systems with a long history of human influence.
... In South Africa, a total of 559 taxa have been identified as serious alien invasive species that require compulsory control under the Alien and Invasive Species regulations of South Africa (van Wilgen et al., 2020). American bramble (Rubus cuneifolius) is one of the most prominent and aggressive alien invasive plants in the grassland biome of South Africa (Henderson, 2007). Bramble forms dense stands where it invades and threatens plant species richness and endemic grassland birds (Reynolds and Symes, 2013), pollinating insects (Hansen et al., 2018), soil arthropods and soil recovery (Eckert et al., 2019), as well as large bodied Caelifera grasshoppers (Theron et al., 2022). ...
... Plants only become invasive when they can survive and spread at new locations (Blackburn et al., 2011). Bramble does this remarkably well within the grasslands of South Africa (Henderson, 2007), especially at lower elevations on eastern slopes where the air is warm and moist (Ndlovu et al., 2018). However, very little research has focused on the mechanisms and drivers of bramble invasion (Erasmus, 1984;Denny, 2005). ...
Alien invasive plant species are one of the main drivers of global biodiversity loss. Methods for monitoring the spread of alien invasive plants are needed to improve management and mitigate impact on local biodiversity. Recent advances in deep learning and image fusion holds great potential for mapping and managing alien invasive plants. One such method is super-resolution image reconstruction, where a neural network learns to downscale images from coarse to fine resolution. Within the commercial timber production landscape of KwaZulu-Natal, endangered grassland corridors are threatened by American bramble invasion, impacting plants, birds, arthropods, and soil restoration. Here we aim to improve our understanding of bramble invasion dynamics through using super-resolved satellite mosaics. Bramble was classified with very high accuracies (85%) from the super-resolved satellite mosaic, compared to other conventional satellite imagery with different spectral and spatial resolutions. Using landscape analyses, we identified plantation tree harvesting and prescribed burning to be major drivers increasing bramble cover within the landscape. Bramble cover was highest one year following plantation tree harvesting. Continuous prescribed burning positively influenced bramble. Bramble cover was also high close to streams, and under future invasion projections, bramble will severely impact Ensifera species alongside low priority grasshopper species habitat. Results also indicate that bramble has a significant negative impact on intermediate priority grasshoppers and plant species richness. For controlling bramble invasion within commercial timber production landscapes, we recommend the adoption rotational harvesting, as harvesting entire plantation blocks throughout the landscape will dramatically increase invasion potential of bramble. Current bramble removal programmes should prioritize riparian areas. Special attention is needed to control bramble one year after timber harvesting, as this is when bramble cover is highest. We show the benefits of using super-resolved mosaics to gain new insights into alien invasive species dynamics, while further development of this technique will aid in managing invasive alien plant species at local scales.
... Records were obtained from the two most comprehensive occurrence species datasets available-the Southern African Plant Invaders Atlas (SAPIA) and iNaturalist recordsfor both high and low elevation mountain areas (Fig. 14.2). The SAPIA and iNaturalist databases vary in how records are obtained, being roadside surveys (Henderson, 2007) and citizen science observations, respectively (Unger et al., 2020). These different approaches are reflected in the variation in IAP records between the databases. ...
... A different suite of IAPs dominate the higher and thus moister and colder montane areas (>1600 m), mostly comprising of the eastern Great Escarpment and higher reaches of the Cape Fold Mountains (Figs. 14.1 and 14.2). High-elevation areas have distinct environmental conditions such as large temperature fluctuations, higher rainfall, and the occurrence of freezing conditions, including on occasion snow (Henderson, 2007;. These features are favourable only to certain types of IAPs that can withstand such extremes, thus excluding many common lowland tropical species. ...
... Records were obtained from the two most comprehensive occurrence species datasets available-the Southern African Plant Invaders Atlas (SAPIA) and iNaturalist recordsfor both high and low elevation mountain areas (Fig. 14.2). The SAPIA and iNaturalist databases vary in how records are obtained, being roadside surveys (Henderson, 2007) and citizen science observations, respectively (Unger et al., 2020). These different approaches are reflected in the variation in IAP records between the databases. ...
... A different suite of IAPs dominate the higher and thus moister and colder montane areas (>1600 m), mostly comprising of the eastern Great Escarpment and higher reaches of the Cape Fold Mountains (Figs. 14.1 and 14.2). High-elevation areas have distinct environmental conditions such as large temperature fluctuations, higher rainfall, and the occurrence of freezing conditions, including on occasion snow (Henderson, 2007;. These features are favourable only to certain types of IAPs that can withstand such extremes, thus excluding many common lowland tropical species. ...
... Records were obtained from the two most comprehensive occurrence species datasets available-the Southern African Plant Invaders Atlas (SAPIA) and iNaturalist recordsfor both high and low elevation mountain areas (Fig. 14.2). The SAPIA and iNaturalist databases vary in how records are obtained, being roadside surveys (Henderson, 2007) and citizen science observations, respectively (Unger et al., 2020). These different approaches are reflected in the variation in IAP records between the databases. ...
... A different suite of IAPs dominate the higher and thus moister and colder montane areas (>1600 m), mostly comprising of the eastern Great Escarpment and higher reaches of the Cape Fold Mountains (Figs. 14.1 and 14.2). High-elevation areas have distinct environmental conditions such as large temperature fluctuations, higher rainfall, and the occurrence of freezing conditions, including on occasion snow (Henderson, 2007;. These features are favourable only to certain types of IAPs that can withstand such extremes, thus excluding many common lowland tropical species. ...
Significance Statement
Globally, marine ecosystems and indigenous cultures continue to collapse, prompting a need for a paradigm shift in conservation and marine planning. While top-down processes of marine and cultural conservation have widely been shown to be unsuccessful, this chapter shows how to carry out participatory methods for marine conservation planning, through eliciting traditional ecological knowledge and mapping with fisheries communities. Drawing on work in Manquemapu and Caulin Indigenous Marine Areas located in Chile, it considers how different communities identify ecological threats from overfishing and aquaculture, and how researchers can advance the integration of their evidence through participatory GIS. The chapter explores how different valuations of nature are expressed, specifically in Mapuche -Huichille first nation culture and conservation science; and how they can work together.
... Records were obtained from the two most comprehensive occurrence species datasets available-the Southern African Plant Invaders Atlas (SAPIA) and iNaturalist recordsfor both high and low elevation mountain areas (Fig. 14.2). The SAPIA and iNaturalist databases vary in how records are obtained, being roadside surveys (Henderson, 2007) and citizen science observations, respectively (Unger et al., 2020). These different approaches are reflected in the variation in IAP records between the databases. ...
... A different suite of IAPs dominate the higher and thus moister and colder montane areas (>1600 m), mostly comprising of the eastern Great Escarpment and higher reaches of the Cape Fold Mountains (Figs. 14.1 and 14.2). High-elevation areas have distinct environmental conditions such as large temperature fluctuations, higher rainfall, and the occurrence of freezing conditions, including on occasion snow (Henderson, 2007;. These features are favourable only to certain types of IAPs that can withstand such extremes, thus excluding many common lowland tropical species. ...
Significance Statement
In the management of natural resources and biodiversity, humans and nature have traditionally been considered as two distinct systems, one controlling the other. The concept of socio-ecosystems allows a more integrated approach, in which humans and nature are recognized as interdependent. However, this new perspective does not necessarily eliminate a distinction between humans and nature, or even a hierarchy of humans over nature. This chapter aims to raise awareness of the potential human–nature dualism in socio-ecosystem approaches. Other research fields have adopted different approaches regarding human–nature integration versus dualism, offering a window on the advantages and limitations of various positions. We also discuss how methodological choices are important to translate human–nature integration or dichotomy depending on the study aim.
... The Southern African Plant Invaders Atlas (SAPIA) (n = 32) (Henderson, 2007), field surveys (n = 23), Botanical Database of Southern Africa (n = 13) (SANBI, 2016), the Global Biodiversity Information Facility (GBIF) (GBIF.org, 2023) (n = 3878), and a citizen science project iNaturalist (n = 49) (Nugent, 2018) were used as sources of C. pallida occurrence records. ...
The emerging alien cactus Cylindropuntia pallida (Rose) F.M. Knuth originates from northern Mexico and introduced into South Africa in 1940s as an ornamental plant. Multiple populations of C. pallida have been detected in various areas of South Africa. C. pallida has effective propagule dispersal and rapid recruitment making it a likely key future invader, and thus, is a target for eradication in South Africa. To eradicate C. pallida populations, a foliar spray (i.e. using a 2% concentration of herbicide with fluroxypyr and triclopyr) has been applied to plants in nine populations, with population sizes ranging between 535 and 2701 plants and populations covering areas of 100 –1000 ha. The aims of the study were to investigate the efficacy of the foliar spray method used to eradicate C. pallida; to investigate the impacts of C. pallida invasions on native vegetation integrity; to apply species distribution models (SDMs) to identify suitable climates for C. pallida in South Africa; and to document the biomes vulnerable to the negative impact of C. pallida in South Africa. Results show that foliar spray killed many C. pallida plants (mean percentage of dead plants ± SE, 83.3 ± 6.4; n = 9; range, 70–96%), with adult plants taking about 2 months to die completely. The efficacy of the herbicide was not affected by plant size or the concentration of the herbicide used. The invaded site had significantly greater vegetation cover which persisted across winter compared to the uninvaded site, but the latter site’s vegetation cover significantly dropped in winter. Also, the invaded site had lower plant species diversity than the uninvaded site and was dominated by species in the Poaceae and Asteraceae plant families. Additionally, a normalised difference vegetation index (NDVI) analysis shows that the uninvaded site has higher vegetation cover and health than the invaded site wherein a notable decline in vegetation health was observed between 2019 and 2022. A large area (> 15 million hectares) was predicted to be suitable for invasion by C. pallida in provinces with arid and warm temperate climates - the fynbos and grassland biomes are the most vulnerable. Because of the observed negative impacts, high environmental compatibility, and high cost of clearing large infestations, we advocate for considering the biocontrol method for effectively managing C. pallida invasion in South Africa.
... The natural habitat of the species is tropical or subtropical environments including Florida, Mexico, Brazil, and West Indies (Jones, 1987). In some cases, it has escaped from cultivation and invaded geographic locations beyond its native habitats (de Almeida and Freitas, 2006;Henderson, 2007). It appears to be a relatively stable and successful plant in the natural environment and is currently listed as "Least Concern" (LC) by the IUCN Red List (Bárrios and Copeland, 2021). ...
... In South Africa, Populus alba and Populus canescens are classified as a Category 2 weed under the National Environmental Management and Biodiversity Act (NEMBA) (No. 10 of 2004) and Conservation of Agricultural Resources Act (CARA) (No. 43 of 1983) of South Africa's Invasive Species Legislation (Henderson 2007). This means that poplars (Category 2) plants may not occur on land or inland water surfaces other than a demarcated area or a biological control reserve (Roy, Pauchard & Stoett 2023). ...
Poplars (Populus alba, Populus canadensis, Populus canescens, Populus deltoides, Populus fremontii, Populus nigra and Populus simonii) are found throughout the world and are invasive in South Africa, where they are spatially permitted in certain areas under controlled conditions, as specified in the country’s invasive species legislation. To better trace their geographic distribution, this study predicts the potentially suitable habitat of poplar trees in South Africa based on generalised linear model (GLM), Random Forests (RF) and Support Vector Machines (SVM) models and also assesses the climatic variables with the greatest impact on prediction performance. The results show excellent performance for all models (Area Under the Receiver Operation Characteristics Curve [AUC] > 0.9) in predicting the poplar distribution, with RF achieving the best performance (r = 0.83 and AUC = 0.965), followed by SVM (r = 0.72 and AUC = 0.959) and then GLM (r = 0.65 and AUC = 0.937). In a geographical perspective, all models show a similar pattern, with the highest concentrations being in the south-western parts of the Western Cape, the Southern Cape on the Garden Route, the central-eastern Free State, Mpumalanga, and the southern parts of Limpopo. The evaluation of the relative
importance of the bioclimates used showed that the warmest and driest quarter’s precipitation and annual precipitation significantly contribute to the poplar population. These results demonstrate the power of machine learning and regression models for predicting suitable habitats and extracting valuable environmental-climatic knowledge for monitoring and managing invasive tree species such as poplars.
... A subspecies of M. tenuifolium (M. tenuifolium subspecies montanum) was considered present in South Africa, an assumption has been perpetuated in the literature (Blanchard, 2004;Henderson, 2007). However, this taxon in South Africa has since been resolved to M. montanum (M. ...
Myoporum is a genus of trees and shrubs native to the Northern Hemisphere that has been introduced to many parts of the world, mainly for ornamental purposes. We assessed the introduction history, distribution, and extent of naturalization/invasion for Myoporum species in South Africa. Information was collated to determine key events associated with the introduction, establishment, and nat-uralization of Myoporum in South Africa. Data were collated to determine the current distribution of the genus in South Africa. Twenty sites in the Western Cape were sampled to determine correlates of naturalization. Myoporum was first recorded in South Africa in 1934. Three species were confirmed to be present in South Africa: M. insulare, M. laetum and M. montanum (37 %, 25 % and 24 % of all iNaturalist records respectively). Most records are from the Western Cape (91 %) and small parts of the Eastern Cape; isolated populations occur in Gauteng and the Northern Cape. We could not confirm the presence M. petiolatum, M. tenuifolium or M. tetrandrum. Field surveys revealed widespread naturalization of M. insulare (46 % of all Research Grade observations in iNaturalist); this species was categorized code D1 in the introduction-naturalization-invasion continuum. Myoporum laetum (C3) and M. montanum (C2) are also widely naturalized but over smaller areas. Naturalized populations comprised predominantly juvenile M. insulare plants occurring in highly disturbed (transformed) habitats. Formal risk analyses for all Myoporum species in South Africa are needed as the basis for re-evaluation of their status in national legislation.
... Similarly, the invasive Acacia species in Madagascar and South Africa have been introduced to provide timber, pulp for paper, bark for tannins and fuel wood (de Neergaard et al. 2005;Kull et al. 2007). Opuntia ficus-indica in South Africa is mainly used as fodder and food source (Henderson 2007;Shackleton et al. 2011). ...
There is an inextricable link between ecosystem integrity and the potential for achieving sustainable development goals (SDG). This chapter highlights key ecosystem threats and their drivers within the southern African regional context to emphasize the role of earth system science in supporting the achievement of regional sustainable development goals. It describes how some major anthropogenic threats have unfolded in terrestrial, aquatic and marine ecosystems of the region. Earth system science is increasingly contributing to understanding how globally driven climate and environmental changes threaten these ecosystems, and in turn how these impact people’s livelihoods. Long-term changes in rainfall variability, concomitant disruption of hydrological balances, impacts on ocean chemistry, together with more immediate impacts on the frequency and magnitude of extreme climate events are some of the critical global change drivers. While terrestrial ecosystems are already faced with encroachment by novel species, characterized by the proliferation of both invasive alien and endemic woody species, freshwater and marine ecosystems appear more immediately threatened by more local impacts, such as the accumulation of contaminants. Overall, predicted climate and environmental changes are projected to hamper development trajectories and poverty reduction efforts, and possibly exacerbate adverse impacts on human livelihoods.
... Later on, it was adopted by cattle herders for fencing their bomas before the park was gazette a National Park and large number of nomadic Maasai being shifted to Ngorongoro Conservation Area Authority in 1959. However, the invasion of African savannas by numerous alien plant species is a key environmental problem confronting natural resource managers (Henderson, 2007). Alien species is a species, subspecies, or lower tax on introduced outside its normal past or present distribution, whereas an invasive alien species is an alien species whose establishment and/or spread threaten ecosystems, habitats or species with economic or environmental harm (Koike et al., 2004). ...
Invasive alien plant species are increasingly invading natural habitats
posing a major threat to sustainable biodiversity conservation (Pauchard
et al., 2009). Opuntia species have invade the Serengeti National Park
since the 1950s (Bukombe et al., 2017). However, their distribution, extent
and effects on natural habitat have less beesn investigated. The park was
surveyed to map and assessed the level of Opuntia spp infestion in terms
of cover and diversity within the park. Point Centered Quadrant sampling
method was used where by 50 x 50 m & nested quadrant of 2 x 2 m for
soil sampling. Five Quadrates were established in each hectare plot in
infected and uninfected sites. In each quadrant, Opuntia species were
identified and their canopy cover visually estimated.The total cover of all
two species was approximately 6.9 km2 in the five different sites. It was
further found that each of the two invasive species suppressed the growth
of native plant species within the nearby sites as the diversity of native
herbaceous species was far lower in plots that were located closer to
Opuntia patches. For this case the p-value was (4.34E-09≤0.05) indicating
strong evidence against the null hypothesis. The p-value is less than the
significance level thus the null hypothesis was rejected and concluded that
there is a significant difference in the effectiveness of methods used to
eradicate Opuntia species in Serengeti National Park. The management of
the park should put more commitment on the management to controlling
the two species and other exotics in order to avoid any further negative
impact on the ecosystem.
... According to previous research, its impact on water resources is also significant in South Africa. The most prominent invasive species from this taxon are P. glandulosa (honey mesquite), P. velutina (velvet mesquite) as well as their hybrids [29,30]. It is evident that these species have similar environmental requirements. ...
Invasive alien plants are one of the main causes for the decline of native biodiversity worldwide. Hence, it is crucial to understand the dynamics of invasive plants in the context of a changing climate. The main aim of this study was to evaluate the potential distribution of two major invasive alien plants, Prosopis spp and Acacia mearnsii, under current and future climate change scenarios across South Africa. The maximum entropy (MaxEnt) model was used with species occurrence data and bioclimatic variables. The Species occurrence data was obtained from the Global Biodiversity Information Facility (GBIF), while the bioclimatic variables were downloaded from the WorldClim database. The model evaluation metrics for training and test samples were the area under curve (AUC) of 0.76 and 0.77 for Prosopis spp, and 0.91 and 0.89 for A. mearnsii, respectively. It showed that MaxEnt performed well in mapping the distribution of both species. Model results indicated that the near-current potential distribution of Prosopis spp and A. mearnsii in South Africa is significant (93.8% and 9.7% of the total land area, respectively). With the projected climate, Prosopis spp showed an inconsistent result across the General Circulation Models (GCMs), projection times and climate change scenarios. However, with respect to the current potential distribution, the geographical ranges of A. mearnsii will significantly contract (by about 75%) due to climate change. Therefore, it is imperative that policy makers, environmental managers and other stakeholders implement integrated management and control strategies to restrict the distribution of Prosopis spp.
... Its invasive potential is high; it has asexual and sexual reproduction, a high rate of fructi cation, seed production and germination and short juvenile stages (Marco and Páez 2000). It is dispersed by hydrocory and zoochory, mainly cattle (Henderson 2007). ...
Riparian systems are highly threatened by alterations in its hydrological regimen and biological invasions. To guide its conservation is important to understand the relationships established between biological invasions and abiotic conditions affected by the hydrological regimen. We analyze the relationship between the distribution pattern of soil sand content and the invasive process of the woody invasive Gleditsia triacanthos in riparian forests of the Esteros de Farrapos and Islands of Uruguay River National Park, zoning the study area according to the type of relationship between both variables. We integrate the use of regression trees and geographic information systems to zone this relationship. This is a novel approach to study the relationships between an invasive species and its environment. Areas with lower sand content were found to be favorable for the development of the invasive species, and areas with higher sand content were found to limit its spread. No relationship was found between the intermediate sand content and the progress of the invasive process. This work highlights the complexity inherent to the definition of causal relationships in highly heterogeneous systems such as riparian ecosystems. Spatial analysis techniques are a useful tool for this approach.
... Su potencial invasivo es alto; presenta reproducción asexual y sexual tiene una alta tasa de fructificación, producción de semillas y germinación y estadios juveniles cortos (Marco and Páez, 2000). Sus frutos oscilan entre los 20-40cm de largo y 2,5 de ancho (Sabattini et al., 2009), se dispersa por hidrocoria y zoocoría fundamentalmente ganado (Henderson, 2007). ...
Los ecosistemas fluviales presentan alta vulnerabilidad. Su degradación se asocia fundamentalmente a alteraciones del régimen hídrico afectando la deposición y consecuentemente las condiciones edáficas determinantes del establecimiento de la vegetación pudiendo afectar procesos invasivos de especies vegetales reconocidos como otra importante amenaza. Por tanto, resulta relevante comprender la relación entre las condiciones edáficas y los procesos invasivos. Este trabajo evalúa la relación entre el contenido de arena y la distribución de la leñosa invasora Gleditsia triacanthos en un bosque del Río Uruguay. Se caracterizó el patrón espacial de la variación en la textura del suelo, el patrón de distribución de G.triacanthos y las relaciones existentes entre éste y el contenido de arena del suelo. Se detectó variación en la textura del suelo en el eje norte-sur y en el eje este-oeste. Se detectó una relación compleja entre la abundancia de G.triacanthos y el contenido de arena del suelo.
... The invasive nature of the weed is exacerbated by the decline in soil fertility caused by mono-cropping and limited use of external inputs that improve the soils, such as the use of fertilizers and organic manure (Emeghebe et al., 2004;Midega et al., 2015). Consequently, this causes the invasive plants to successfully outcompete the native plant species for nutrients, water, and sunlight (Henderson, 2007;Ikegawa et al., 2019). ...
Food insecurity continues to affect more than two-thirds of the population in sub‐Saharan Africa (SSA), particularly those depending on rain-fed agriculture. Striga, a parasitic weed, has caused yield losses of cereal crops, immensely affecting smallholder farmers in SSA. Although earlier studies have established that Striga is a constraint to crop production, there is little information on the spatial extent of spread and infestation severity of the weed in some SSA countries like Malawi and Zambia. This study aimed to use remotely sensed vegetation phenological (n = 11), climatic (n = 3), and soil (n = 4) variables to develop a data-driven ecological niche model to estimate Striga (Striga asiatica) spatial distribution patterns over Malawi and Zambia, respectively. Vegetation phenological variables were calculated from 250-m enhanced vegetation index (EVI) timeline data, spanning 2013 to 2016. A multicollinearity test was performed on all 18 predictor variables using the variance inflation factor (VIF) and Pearson’s correlation approach. From the initial 18 variables, 12 non-correlated predictor variables were selected to predict Striga risk zones over the two focus countries. The variable “start of the season” (start of the rainy season) showed the highest model relevance, contributing 26.8% and 37.9% to Striga risk models for Malawi and Zambia, respectively. This indicates that the crop planting date influences the occurrence and the level of Striga infestation. The resultant occurrence maps revealed interesting spatial patterns; while a very high Striga occurrence was predicted for central Malawi and eastern Zambia (mono-cultural maize growing areas), lower occurrence rates were found in the northern regions. Our study shows the possibilities of integrating various ecological factors with a better spatial and temporal resolution for operational and explicit monitoring of Striga-affected areas in SSA. The explicit identification of Striga “hotspot” areas is crucial for effectively informing intervention activities on the ground.
... When assessed at a national scale, plant invasions appear to have continued to grow in range and abundance over the past 20 years. The clearest indication of this comes from the Southern African Plant Invaders Atlas (SAPIA) which was launched in 1994 (Henderson, 2007), and currently (2020) holds 96,000 georeferenced records of ~850 alien plant taxa growing outside of cultivation. Henderson and Wilson (2017) reported that 773 alien plant species had been recorded on SAPIA by 2016, 172 of which were first recorded between 2006 and 2016, suggesting that the number of recorded naturalised alien plant species was increasing. ...
Large sums of money are spent globally on invasive alien plant control projects, but their effectiveness in the medium to long term is seldom reported. Here we review the cost, extent and effectiveness of the management of plant invasions by South Africa's “Working for Water” program between 1998 and 2020. We use a broad framework of indicators for assessing the inputs, outputs, and outcomes of alien plant control interventions at a national level. Our study is based on (1) spatially explicit data on efforts that targeted selected sites and species for control; (2) surveys of the extent of invasion; and (3) case studies of control effectiveness. An average of ZAR310 million (adjusted to 2020 values) was spent annually, creating the equivalent of 8113 full-time jobs, with expenditure rising rapidly between 1998 and 2003 and again between 2009 and 2015, dropping more recently. Control efforts were directed at 178 species, with 15 taxa receiving two thirds of the total expenditure. Control was conducted on ~76,000 sites covering 2.7 million ha, which is ~14 % of the estimated invaded area. Over a quarter of the control was not in priority areas for biodiversity and/or water conservation. The effectiveness of control operations has not been monitored regularly, but a few studies at local scales have found reductions in alien plant cover, and it is likely that “Working for Water” has had a role in limiting invasion. Nonetheless, national surveys suggest that plant invasions have continued to grow—the problem is too large to expect that control can be achieved everywhere. We recommend that, to bring plant invasions under control at priority sites, a national strategy should be based on conservation triage, focussing on clearly defined priority sites, improving planning and monitoring, and increasing operational efficiency.
... As such, healthy urbans street trees like Jacaranda provide societal, health and environmental benefits and monitoring their phenology is one way to ensure these benefits are protected. What is more, although, Jacaranda mimosifolia is widely planted across the globe [21] in its native range it is considered vulnerable [70] and in parts of South Africa [71] and Queensland, Australia [72], it is considered an invasive species that can potentially out-compete native species [21,72]. Future work should also explore reproduction and seed dispersal of J. mimosifolia if we are to improve its conservation status, as well as its invasion risk and apply effective means of control. ...
In the absence of historical information on phenology available in Australia, expert opinion was used for selecting indicator species that would be suitable for monitoring phenology on a continental scale as part of ClimateWatch—a citizen science program. Jacaranda mimosifolia being the most frequently observed species was used in this study to test expert opinion and the adequacy of citizen science records in detecting the influence of climatic conditions on this species’ flowering phenology. Generalised Additive Models for Location Scale and Shape were used to explore the occurrence and intensity of flowering of Jacaranda in relation to rainfall, temperature, and sun exposure. Jacaranda flowering onset was influenced by winter cold exposure, while flowering intensity was related to increasing sun exposure as spring progresses, and both were influenced by the conditions for flowering in the former flowering seasons (i.e., sun exposure and highest temperatures reached, respectively). Our models provide the first attempt to describe the climate drivers for Jacaranda mimosifolia flowering in the southern hemisphere and identify where climatic changes will most likely alter this tree’s phenology in Australia and benefit or challenge its reproductive ability. They also support the choice of species for citizen science programs based on expert opinion.
... So long as conditions for lantana growth are favourable, mortality of the invasive in its naturalized range is low [ 14,22 ]. Where lantana successfully establishes itself, it can outcompete indigenous species and alter the hydrology, carbon sequestration, nutrient cycling and fire regimes of invaded ecosystems [7] . ...
Alien plant invasions are a major ecological and management problem facing many parts of southern Africa. Invasive plants spread rapidly, negatively impacting native flora and fauna, agriculture and livelihoods. Lantana camara has invaded most parts of the Zaka District, a semi-arid communal area in Zimbabwe and the aim of this study was to assess and document the invasion status of the plant in the district. Mapping the occurrence of L. camara provides useful information for planning clearing efforts, modelling the invasion patterns and budgeting costs. We report the results of a study conducted in February 2015 where a combination of remote sensing and ground-based data collection was used to record lantana presence. Field assessment was done at 140 sampling sites (across seven land cover types), with sites chosen using a stratified random strategy. At each site the percent canopy cover of lantana was assessed by visual estimation and the data used to map the occurrence of lantana in each land cover type. Cover of lantana was highest in drainage lines (21.5 %) and lowest in agricultural fields on grey and red soils (12 %). Analysis of variance showed that differences in lantana cover among land cover types were not statistically significant, indicating that lantana is a generalist invader capable of thriving in various habitats within its range. Notwithstanding, habitat-specific invasion patterns were apparent and, as such, habitat targeted control efforts are advisable to achieve best results. We recommend cutting, stumping and onsite burning of lantana as the management method of choice and the periodic monitoring of the invasive plant in the district.
... Psidium cattleyanum was introduced to South Africa in 1948 (http://posa.sanbi.org/). The species currently invades habitats in the Fynbos, Grassland, and Savanna biomes, mainly along watercourses, in wetlands, and on forest margins (Baard and Kraaij, 2014;Henderson, 2007). The species was declared a Category 1b in the Alien and Invasive Species Regulations of the National Environmental Management: Biodiversity Act in South Africa (for the most recent lists see: South African Department of Environment, Forestry and Fisheries, 2020). ...
Psidium cattleyanum (Myrtaceae) is a widespread invasive species in several countries, particularly on oceanic islands. The species was first recorded in South Africa in 1948 and has since established self-sustaining populations. We present the first comprehensive evaluation of the invasiveness of P. cattleyanum in South Africa by: 1) mapping the current distribution of the species; 2) estimating its potential range using species distribution models in MaxEnt; 3) analysing the risk posed to South Africa using the risk analysis for alien taxa framework; and 4) developing recommendations for regulation. Psidium cattleyanum was recorded at 52 sites in four provinces across South Africa, with the population in the Western Cape being the first substantial invasive population reported from a temperate winter-rainfall region globally. Invasive populations were assessed in detail at four sites: Newlands Forest (Western Cape; n=2193 plants; covering ∼12 ha), Eshowe (KwaZulu-Natal; n=1561, ∼7.6 ha), Southbroom (KwaZulu-Natal; n = 449, ∼2.9 ha), and George (Western Cape; n=214, ∼2.4 ha). At all four sites the species is self-sustaining and there is evidence of spread. In South Africa, the east coast is climatically suitable for the species to expand its range. Although damaging invasions of P. cattleyanum have only been recorded on several islands to date, we find no reason to suggest that climatically suitable continental regions (including parts of South Africa) will not suffer harmful impacts if invasions progress unmanaged. As such, we support the current regulation of P. cattleyanum in South Africa, whereby the species must be controlled as part of a national management plan (category 1b) noting that while it is advisable to ban cultivation, the forcible removal of plants from people's gardens should perhaps only be prioritised if such plantings clearly pose a high risk (i.e., in climatically suitable regions near to riparian areas or natural areas).
This study reviews various aspects of the genus Quercus in South Africa. We determine the number of oak species present, assess their introduction status, map their distribution, highlight areas of putative naturalisation, elucidate environmental factors that can mediate invasibility in a riparian zone, and evaluate the usefulness of the community science platform iNaturalist for assessing these factors.
A literature search was conducted to review events associated with the introduction, cultivation and naturalisation of oaks and associated pests and diseases in South Africa. Records of Quercus species in South Africa were collated from herbaria, arboreta, the Southern African Plant Invader Atlas, the Plants of Southern Africa database and iNaturalist. A field study was conducted along the Eerste River in Stellenbosch to elucidate the role of environmental factors in mediating naturalisation.
We found records of 47 Quercus taxa in South Africa which were refined to a list of 22 to 34 species likely present. The earliest record was for Quercus robur in 1656 but first records for most species date from between the late 1800s to the early 1900s. More than 99% of presence and naturalisation records were of the ten commonly cultivated species. Quercus palustris, Q. robur, and Q. suber were categorised as invasive, and naturalisation was documented for Q. acutissima, Q. canariensis, Q. cerris, Q. ilex, and Q. nigra. Most naturalisation occurred at the urban-wildland interface and in riparian vegetation in Cape Town and Stellenbosch. Steepness of the riverbank was found to affect seedling recruitment in riparian areas. iNaturalist records shed new light on the presence, distribution, and introduction status of Quercus species in South Africa. However, taxonomic complexity and data quality complicated attempts to develop a robust inventory of Quercus in South Africa. Molecular studies are needed to achieve better resolution. Nonetheless, this study has greatly improved our understanding of the distribution and status of oaks in South Africa, with implications for their management.
Invasive alien species represent one of the main threats to biodiversity and species extinction. This is the case for the genus Prosopis, among which Prosopis velutina is the most invasive and common tree species along the Molopo River in the North-West Province, impacting native plant communities. However, its impact on the composition and diversity of native woody species remains poorly investigated in the area. Thus, this study aimed to assess the impact of P. velutina on native woody plant composition and diversity across three sites along the Molopo River. At each site, five quadrats of 20 × 20 m2 were randomly established in invaded and adjacent uninvaded stands. A comparative methodological approach was adopted, and the woody plants in invaded and uninvaded stands with similar site conditions were sampled. The results showed that native woody species density differed significantly (p < 0.05) between invaded and uninvaded stands, except for Bray sites, where there was a marginal difference (p = 0.6). The overall native woody species density decreased by 79.7% in the invaded stand. However, non-metric multidimensional scaling (nMDS) and analysis of similarity (ANOSIM) indicated significant differences in native tree composition between invaded and uninvaded stands at all sites. In all three sites, all ecological indices had significantly lower values in invaded stands compared to uninvaded stands. The decrease in all ecological indices in invaded over uninvaded stands indicated that P. velutina invasion reduced the diversity of native woody plant species. Due to the incessant spread of P. velutina, it may become a long-term dominant species with an increasing impact on the native vegetation. Therefore, the findings of this study call for urgent management and appropriate control measures against the ongoing spread of this invader within the riparian zones of the Molopo River in North-West Province.
This datasheet on Acacia decurrens covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Management, Genetics and Breeding, Economics, Further Information.
This datasheet on Acacia saligna covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Management, Economics, Further Information.
This datasheet on Sonchus oleraceus covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
This datasheet on Ricinus communis covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Management, Genetics and Breeding, Economics, Further Information.
This datasheet on Tithonia rotundifolia covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
This datasheet on Lygodium japonicum covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
This datasheet on Pittosporum undulatum covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
This datasheet on Schizolobium parahyba covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Dispersal, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Management, Genetics and Breeding, Further Information.
This datasheet on Buddleja madagascariensis covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
The role of climate change in enhancing bio-invasions in natural environments needs to be assessed to provide baseline information for effective species management and policy formulations. In this study, potential habitat suitability maps were generated through Ecological Niche Modeling for five problematic alien and native species in current and future climate simulations for the periods 2050s and 2070s under RCP2.6, RCP4.5, and RCP8.5 emission scenarios. Projected current binary suitability maps showed that 67%, 40%, 28%, 68%, and 54% of the total study area ~ 3318 Km ² is suitable for C . decapetala , L . camara , O . stricta , S . didymobotrya and S . campylacanthum species, respectively. Assuming unlimited species dispersal, two of these species, C . decapetala and S . didymobotrya , were observed to have consistent gradual increase in potential habitats and no habitat losses under the three RCPs by the end of the 2050 and 2070 future periods. The highest recorded relative potential habitat increase was observed for O . stricta at ~205% under RCP2.6 and ~223% under RCP8.5. Although L . camara and O . stricta were observed to have habitat losses, the losses will be very low as compared to that of S . campylacanthum . L . camara and O . stricta relative habitat losses were predicted to be between ~1% under RCP2.6 to ~4.5% under RCP8.5 by 2070 while that of S . campylacanthum was between ~50% under RCP2.6 to ~68% under RCP8.5 by the year 2070. From this study we conclude that the target study species are expected to remain a big threat to inhabited areas as well as biodiversity hotspot areas especially in the Mt. Kenya and the Aberdare forest and national park reserves under climate change. The information generated through this study can be used to inform policy on prioritizing management of these species and subsequent determination of their absolute distributions within the area.
Opuntia engelmannii Salm‐Dyck (Cactaceae:Opuntioideae) is a morphologically variable cactus that has invaded pasture lands in South Africa and Kenya. Biological control of invasive Opuntia species can be very successful when the correct agent is matched with the appropriate host. This research investigated the similarity (morphological and genetic) between several populations of O. engelmannii and a morphologically uniform, O. stricta, that occur in South Africa and Kenya to help understand the identity of the target weed. Spine and cladode morphology showed that the Limpopo (South African) and Kenyan populations were most similar, while the spiny Eastern Cape (South African) population was more similar to Opuntia stricta. Multivariate analysis showed that spine morphometry was a useful diagnostic character in identifying different putative O. engelmannii populations in the field. In addition, we used amplified fragments length polymorphisms to estimate genetic similarity and genetic structure among populations that represent the morphologically variable populations. There was relatively little differentiation in the population structure between the Limpopo and Kenyan populations. The spiny Eastern Cape population showed moderate genetic differentiation (FST = 0.05 − 0.15) relative to other O. engelmannii populations and was genetically more similar to the O. stricta population. These results will facilitate the search for suitable biocontrol agents by directing future collections of the appropriate biotype of Dactylopius opuntiae Cockerell (Hemiptera: Dactylopiidae) to relevant populations of O. engelmannii in its home range. In addition, given the genetic similarity of the spiny Eastern Cape population to O. stricta, we recommend the efficacy of D. opuntiae ‘stricta’ biotype be tested on the spiny Eastern Cape population as a potential biocontrol agent.
For several decades, the control of plant diseases and pests were mainly based on the frequent use of pesticides. However, as science advances, the importance of mitigating the exposure of plants, animals, and humans to hazardous chemicals is better understood. Many conventional synthetic pesticides have become of concern, even if they are presumed to have reached the required level of "safety". The repeated and continuous use of pesticides based on the same active ingredient considerably promotes the development of resistant populations of harmful organisms, resulting in an additional need for pesticides.
Plant derivatives represent effective alternatives to synthetic chemicals and provide very promising results. It is now widely recognized that certain fungal, bacterial, nematode, weed, and insect control agents derived from plants can be developed into commercial products suitable for integrated pest management. Plant extracts and essential oil-based pesticide products are selective in their target, while no harm is made to non-target organisms and the environment. These pesticides act differently depending on the types of plant pathogens and pests and can be applied to the plant in the same way as conventional pesticides. Many plant extracts and essential oils are already screened for their effectiveness against a wide range of pathogens and pests, further confirmed by field studies.
The frequency and abundance o ;f exotic, woody plant invaders were recorded in 60% of the quarter degree squares in the study area. Sixty-one invaders were encountered o f which the most important and aggressive were Acacia dealbaia, Populus spp., Melia azedarach, Opuntia ficus-indica, Salix babylonica and Acacia mearnsii. Invasion patterns are discussed and an attempt is made to correlate distribution with environmental factors. Attention is drawn to the areas of greatest invasion and the areas that are liable to show the greatest expansion in the future.
The frequency and abundance of invasive alien woody plants were recorded along roadsides and at watercourse crossings in 87% (152/175) of the quarter degree squares in the study area. The survey yielded BO species of which the most prominent species (in order of prominence) in roadside and veld habitats were: Chromolaena odoruta, Solatium mauritianum, Psidium guajava, Rubus spp., Acacia meamsu and Lantana camara The most prominent species (in order of prominence) in streambank habitats were: Acacia dealbata, A. meamsii and Salix babylonica.The greatest intensity of invasion was recorded in the Natal midlands and in the coastal belt of southern Natal, including the metropolitan areas of Pietermaritzburg and Durban. There was relatively little invasion in the north-eastern lowlands of Natal but the potential for expansion is great. Little invasion was recorded in the north-eastern Orange Free State except along some watercourses.
The frequency and abundance of invasive alien plants were recorded along roadsides and at watercourse crossings in 82.9% (145/175) of the quarter degree squares in the study area (31-35°S, 17-25°E and covering ± 90 000 km2). The survey yielded 102 species of which the most prominent (in order of prominence) in roadside and veld (natural and modified) habitats were: Acacia cyclops, A. saligna and A. mearnsii. The most prominent species (in order of prominence) in streambank habitats were: A. mearnsii, A. saligna and Populus x canescens. The greatest intensity of invasion was recorded in forest and fynbos vegetation types in the relatively narrow belt stretching from the coastline to the tops of the coastal mountain ranges. In the coastal lowlands Acacia cyclops and A. saligna form the most extensive and continuous stands of alien vegetation recorded anywhere in South Africa. In the arid interior invasion was largely confined to watercourses.
A prime aim of invasion biology is to predict which species will become invasive, but retrospective analyses have so far failed to develop robust generalizations. This is because many biological, environmental, and anthropogenic factors interact to determine the distribution of invasive species. However, in this paper we also argue that many analyses of invasiveness have been flawed by not considering several fundamental issues: (1) the range size of an invasive species depends on how much time it has had to spread (its residence time); (2) the range size and spread rate are mediated by the total extent of suitable (i.e. potentially invasible) habitat; and (3) the range size and spread rate depend on the frequency and intensity of introductions (propagule pressure), the position of founder populations in relation to the potential range, and the spatial distribution of the potential range. We explored these considerations using a large set of invasive alien plant species in South Africa for which accurate distribution data and other relevant information were available.
Species introduced earlier and those with larger potential ranges had larger current range sizes, but we found no significant effect of the spatial distribution of potential ranges on current range sizes, and data on propagule pressure were largely unavailable. However, crucially, we showed that: (1) including residence time and potential range always significantly increases the explanatory power of the models; and (2) residence time and potential range can affect which factors emerge as significant determinants of invasiveness. Therefore, analyses not including potential range and residence time can come to misleading conclusions. When these factors were taken into account, we found that nitrogen‐fixing plants and plants invading arid regions have spread faster than other species, but these results were phylogenetically constrained. We also show that, when analysed in the context of residence time and potential range, variation in range size among invasive species is implicitly due to variation in spread rates, and, that by explicitly assuming a particular model of spread, it is possible to estimate changes in the rates of plant invasions through time.
We believe that invasion biology can develop generalizations that are useful for management, but only in the context of a suitable null model.
Copyright: 2004 Acad Science South Africa This paper provides estimates of the costs of clearing important species of invasive alien plants, as well as of progress made with clearing, based on data from a recently developed GIS-based project information system. Before the deployment of the system, managers were unable to record, in any detail, information relating to the costs associated with areas cleared at different densities for a range of species. As a result of this, only superficial estimates of the impact of the Working for Water programme have been possible hitherto. While the system is not yet in full operation, data for about 60% of project expenditure from the 2002/03 financial year were available, and we used this information on which to base our analysis. These data show that the costs of clearing rise sharply with the density of invasion, reaching more that R2000/ha in some cases. These amounts do not include expenditure on herbicides, which can reach over R1000/ha for dense infestations of sprouting species. A large proportion (57%) of the costs was incurred in clearing large trees, which are perceived to have a significant influence on water resources. Large sums were also justifiably spent on species that probably are not substantial water users, including lantana, triffid weed and cacti. These plants affect biodiversity, catchment stability, and the agricultural potential of land. Some of the species on which large amounts have been spent, however, are arguably not a priority. Good progress has been made with clearing certain species. At current rates of clearing, however, many other species will not be brought under control within the next half century. This underscores both the importance of biological control as a sustainable, effective and inexpensive solution to the most intractable of the invasive alien plant problems, and the need for landowners to share the responsibility for clearing. Our estimates are preliminary, given the incomplete data on the project management system, and should be treated as such.
Many invasive alien plant species in South Africa are already well-established and cause substantial damage, while scores of others are at the early stages of invasion (only recently introduced and/or entering a phase of rapid population growth). Management programmes must target well-established invaders, but must also give appropriate attention to emerging problems. Protocols for objectively prioritizing species in the two groups for management action are lacking. To this end, the authors describe the objective derivation of two lists of invasive alien plants in South Africa, using available quantitative data and expert knowledge on current patterns of distribution and abundance, life-history traits, and (for emerging invaders) estimates of potential habitat. 'Major invaders' are those invasive alien species that are well-established, and which already have a substantial impact on natural and semi-natural ecosystems. 'Emerging invaders' currently have less influence, but have attributes and potentially suitable habitat that could result in increased range and consequences in the next few decades. We describe the derivation of lists that contain 117 major invaders (categorized into groups based on geographical range and abundance) and 84 emerging invaders (categorized into groups based on current propagule-pool size and potentially invasible habitat). The main lists, and groupings within them, provide a useful means for prioritizing species for a range of management interventions at national, regional and local scales.
Every country has weed species whose presence conflicts in some way with human management objectives and needs. Resources for research and control are limited, so priority should be given to species that are the biggest problem. The prioritization system described in this article was designed to assess objectively research and control priorities of invasive alien plants at a national scale in South Africa. The evaluation consists of seventeen criteria, grouped into five modules that assess invasiveness, spatial characteristics, potential impact, potential for control, and conflicts of interest for each plant species under consideration. Total prioritization scores, calculated from criterion and module scores, were used to assess a species' priority. Prioritization scores were calculated by combining independent assessments provided by several experts, thus increasing the reliability of the rankings. The total confidence score, a separate index, indicates the reliability and availability of data used to make an assessment. Candidate species for evaluation were identified and assessed by several experts using the prioritization system. The final ranking was made by combining two separate indices, the total prioritization score and the total confidence score. This approach integrates the plant's perceived priority with an index of data reliability. Of the 61 species assessed, those with the highest ranks (Lantana camara, Chromolaena odorata and Opuntia ficus-indica) had high prioritization and high confidence scores, and are thus of most concern. Those species with the lowest ranks, for example, Harrisia martinii, Opuntia spinulifera and Opuntia exaltata, had low prioritization scores and high confidence scores, and thus are of least concern. The authors approach to ranking weeds offers several advantages over existing systems because it is designed for multiple assessors based on the Delphi decision-making technique, the criteria contribute equally to the total score, and the system can accommodate incomplete data on a species. Although the choice of criteria may be criticized and the system has certain limitations, it appears to have delivered credible results.
Although invasive alien species (IAS) are a major threat to biodiversity, human health, and economy, our understanding of the factors controlling their distribution and abundance is limited. Here, we determine how environmental factors, land use, life-history traits of the invaders, residence time, origin, and human usage interact to shape the spatial pattern of invasive alien plant species in South Africa. Relationships between the environmental factors and the extrinsic and intrinsic attributes of species were investigated using RLQ analysis, a multivariate method for relating a species-attribute table to an environmental table by way of a species presence/absence table. We then clustered species according to their position on the RLQ axes, and tested these groups for phylogenetic independence. The first three axes of the RLQ explained 99% of the variation and were strongly related to the species attributes. The clustering showed that, after accounting for environmental factors, the spatial pattern of IAS in South Africa was driven by human uses, life forms, and reproductive traits. The seven clusters of species strongly reflected geographical distribution, but also intrinsic species attributes and patterns of human use. Two of the clusters, centered on the genera Acacia and Opuntia, were phylogenetically non-independent. The remaining clusters comprised species of diverse taxonomic affinities, but sharing traits facilitating invasion in particular habitats. This information is useful for assessing the extent to which the potential spread of recent introductions can be predicted by considering the interaction of their biological attributes, region of origin, and human use.
The frequency and abundance of invasive alien woody plants were recorded along roadsides and at watercourse crossings in 31% (90/286) of the quarter degree squares in the study area. The survey yielded 23 species of which the most prominent invaders were Prosopis spp. The most prominent remaining species were: Opuntia ficus-indica, Nicotiana glauca and Melia azedarach.
The greatest abundance and diversity of alien invader plants were recorded near human settlements. More than half of the total recorded species have invaded perennial riverbanks. The episodic Molopo and Kuruman Rivers have been invaded almost exclusively by Prosopis spp., which in places have formed extensive stands.
The first biological control project against invasive alien plants in South Africa was in 1913. Initially, invasive cactus species were the only plants in South Africa targeted for biological control. By the early 1960s, the emphasis expanded to include problem plants that threatened the 'Fynbos' biome, and latterly to invasive species in other types of natural habitats. Many of the South African projects have been innovative, for example: the use of gall-forming and seed-feeding insect species that have not been used elsewhere; the emphasis on weeds in conservation areas; and the predominance of woody invaders that have been targeted for biological control. Most of these woody plants originated as forestry or agro-forestry introductions, which has created a relatively high incidence of conflicts of interest between conservationists and growers. Recent benefit:cost analyses have demonstrated exceptionally high returns on investment for biological control, even for the least successful of the projects. The inception of the Working for Water programme in 1995 has significantly enhanced biological weed control in South Africa. The benefits include: sustainable funding; investment in research on emerging weeds; a well-organized implementation programme that has increased the impact of biological control in the field; improved international cooperation, particularly in Africa, in concert with the NEPAD initiative; and the recent re-organization of research personnel into cooperative teams that include entomologists, plant pathologists, resource economists and plant ecologists.
Acacia saligna was regarded as the most troublesome invasive alien weed in the Cape Floristic region. The gall-forming rust fungus Uromycladium tepperianum was introduced into South Africa in 1987, and it established throughout the range of the weed. Five populations of the weed were monitored annually from 1991 to 2005. Tree density and stem diameter were recorded in each of four permanent transects at each site. Tree density declined by between 87% and 98% for the period 1991–2005 at these five sites. Average annual mortality rate (±SE) of infected trees dying was 18% (±2%) during the same period. Canopy mass and age were determined by destructively sampling trees at 19 sites. Canopy mass at all sites was lower than data published before introduction of U. tepperianum, and the longer since the last major disturbance (fires or clearing operations), the greater the reduction. Average age of trees in these sites was between 2.2 and 6.1 years, despite the last major disturbance being at least 10–20 years previous at 11 of the sites. Pod and seed production were determined, and seed fall calculated, at each of four sites in 2004. These data were compared to the same variables gathered in 1989. Seed fall in 2004 was reduced compared to that recorded earlier. Results show that U. tepperianum remains a highly effective biological control agent against A. saligna in South Africa.
The number of studies dealing with plant invasions is increasing rapidly, but the accumulating body of knowledge has unfortunately also spawned increasing confusion about terminology. Invasions are a global phenomenon and comparison of geographically distant regions and their introduced biota is a crucially important methodological approach for elucidation of the determinants of invasiveness and invasibility. Comparative studies of alien floras provide substantial new insights to our understanding of general patterns of plant invasions. Such studies, using information in previously published floras and checklists, are fundamentally dependent on the quality of the assessment of particular species with respect to their taxonomic identity, time of immigration and invasion status. Three crucial decisions should be made when defining the status of a plant species in a given region: (1) whether the taxon is native or alien to that region (origin status); (2) what is its position in the invasion process, i.e., when was it introduced (residence status); and (3) what is the degree of its naturalization and possible invasion (invasion status). Standard floras differ hugely in their treatment of non-native species and those with appropriate categorization of alien species according to their status are rather rare. The present paper suggests definitions of terms associated with plant invasions and places these into the context of floras. Recommendations are outlined on how to deal with the issue of plant invasions in standard floras with the aim of contributing to a better understanding between taxonomists and ecologists and allowing more detailed comparative analyses of alien floras of various regions of the world.
Cette étude explore les patrons géographiques de la richesse en espèces chez les plantes exotiques de l'Afrique du Sud au sein de zones ayant une superficie approximative de 675 km2 (25 × 27 km). Nous avons tenu compte de toutes les espèces exotiques pour lesquelles nous avions une mention et d'un sous-ensemble de celles-ci, soit les espèces qui envahissent la végétation naturelle et semi-naturelle. Nous avons utilisé comme principale source d'informations une banque de données nationale constituée à l'aide de spécimens d'herbier. Les données spécifiques aux espèces exotiques envahissantes proviennent d'un projet d'atlas national. Nous avons d'abord évalué l'importance de la disponibilité en énergie et l'hétérogénéité de l'habitat en tant qu'indicateurs de la richesse des espèces indigènes, exotiques et envahissantes. Les modèles de régression linéaire montrent que la richesse en espèces des trois groupes de plantes est expliquée par les mêmes variables. Les deux groupes de variables les plus importants sont les facteurs climatiques et le relief. Nous avons également examiné le role des espèces indigènes, de plusieurs variables environnementales et d'autres variables associées aux activités humaines pour expliquer la richesse des espèces exotiques et envahissantes. Les résultats révèlent une interaction entre les caractéristiques naturelles et les variables qui quantifient l'importance des activités humaines. Lorsque la richesse des espèces indigènes est ignorée, les variables associées aux activités humaines sont plus fortement corrélées à la richesse des espèces exotiques qu'avec celle des espèces envahissantes. Le nombre d'espèces exotiques et d'espèces envahissantes au sein de chaque zone de 675 km2 est corrélé de façon significative avec la richesse des espèces indigènes, un phénomène qui a été observé ailleurs dans le monde. L'analyse des résidus des valeurs observées et des valeurs prédites montre que les patrons diffèrent toutefois selon les biomes. Les résultats peuvent servir à planifier des politiques d'intervention à long terme, à l'échelle nationale. Ils suggèrent que les secteurs riches en espèces indigènes seront plus susceptibles d'être colonisés de façon soutenue par des plantes exotiques envahissantes et que des mesures d'atténuation devront être prises pour en diminuer les impacts.
Much confusion exists in the English-language literature on plant invasions concerning the terms ‘naturalized’ and ‘invasive’ and their associated concepts. Several authors have used these terms in proposing schemes for conceptualizing the sequence of events from introduction to invasion, but often imprecisely, erroneously or in contradictory ways. This greatly complicates the formulation of robust generalizations in invasion ecology.
Based on an extensive and critical survey of the literature we defined a minimum set of key terms related to a graphic scheme which conceptualizes the naturalization/invasion process. Introduction means that the plant (or its propagule) has been transported by humans across a major geographical barrier. Naturalization starts when abiotic and biotic barriers to survival are surmounted and when various barriers to regular reproduction are overcome. Invasion further requires that introduced plants produce reproductive offspring in areas distant from sites of introduction (approximate scales: > 100 m over < 50 years for taxa spreading by seeds and other propagules; > 6 m/3 years for taxa spreading by roots, rhizomes, stolons or creeping stems). Taxa that can cope with the abiotic environment and biota in the general area may invade disturbed, seminatural communities. Invasion of successionally mature, undisturbed communities usually requires that the alien taxon overcomes a different category of barriers.
We propose that the term ‘invasive’ should be used without any inference to environmental or economic impact. Terms like ‘pests’ and ‘weeds’ are suitable labels for the 50–80% of invaders that have harmful effects. About 10% of invasive plants that change the character, condition, form, or nature of ecosystems over substantial areas may be termed ‘transformers’.
The impact of an introduced, gall-forming rust fungus,Uromycladium tepperianum,on an invasive treeAcacia salignawas evaluated in the Western Cape Province. The number of infected trees, rust galls per tree, state of trees (dead or alive), stem diameter of trees, and number of seeds in the soil were recorded along transects at yearly intervals from 1991 to 1996 at eight sites where the fungus had been inoculated during 1988 or 1989. The levels of disease increased rapidly after 1992 at all sites. By 1995, the mean number of galls per tree varied from 5 to approximately 1500 per tree depending on tree size. Tree density decreased by at least 80% at all sites over the period, although young seedlings started to grow at some sites. The seed number in the soil seed bank stabilized after 1992 at most sites, except where fires occurred which reduced the number of seeds.U. tepperianumtherefore is proving to be a highly effective biological control agent, as shown by greatly reduced population densities ofA. salignain South Africa.
Copyright: 2004 Blackwell Publishing Ltd Most national or regional initiatives aimed at managing biological invasions lack objective protocols for prioritizing invasive species and areas based on likely future dimensions of spread. South Africa has one of the most ambitious national programmes for managing plant invasions in the world. There is, however, no protocol for assessing the likely future spread patterns needed to inform medium- to long-term planning. This paper presents an assessment of the climatic correlates of distribution of 71 important invasive alien plants, and an analysis of the implications of these findings for future invasions in different vegetation types in South Africa, Lesotho and Swaziland over the next few decades. We used a variant of climatic envelope models (CEMs) based on the Mahalanobis distance to derive climatic suitability surfaces for each species. CEMs were developed using the first three principal components derived from an analysis of seven climatic variables. Most species are currently confined to 10% or less of the region, but could potentially invade up to 40%. Depending on the species, between 2% and 79% of the region is climatically suitable for species to invade, and some areas were suitable for up to 45 plant invaders. Over one third of the modelled species have limited potential to substantially expand their distribution. About 20% of the vegetation types have low invasion potential where fewer than five species can invade, and about 10% have high invasion potential, being potentially suitable for more than 25 of the plant invaders. Author’s results suggest that management of the invasive plant species that are currently most widespread should focus on reducing densities, for example through biological control programmes, rather than controlling range expansions. The authors also identify areas of the region that may require additional management focus in the future.
Plant Protection Research Institute initiatives: Southern African Plant Invaders Atlas (SAPIA) phase II
HENDERSON, L. 2006a. Plant Protection Research Institute initiatives: Southern African Plant Invaders Atlas (SAPIA) phase II.
Plant Protection News 68: 5.
Malvaceae, Cretan holly- hock parvifl ora L., Malvaceae, small mallow Malvastrum coromandelianum (L.) Garcke, Malvaceae, prickly malvastrum Mangifera indica L
- M F Ray
Malva
dendromorpha M.F.Ray (= Lavatera arborea L.), Malvaceae, tree
mallow
linnaei M.F.Ray (= Lavatera cretica L.), Malvaceae, Cretan holly-
hock
parvifl ora L., Malvaceae, small mallow
Malvastrum coromandelianum (L.) Garcke, Malvaceae, prickly
malvastrum
Mangifera indica L., Anacardiaceae, mango
Manihot
esculenta Crantz (= M. utilissima Pohl), Euphorbiaceae, bitter
cassava
grahamii Hook. (= M. dulcis (J.F.Gmel.) Pax var. multifi da (Graham)
Pax), Euphorbiaceae, hardy cassava #
Invasive alien plants of the Orange Free State
HENDERSON, L. 1991a. Invasive alien plants of the Orange Free
State. Bothalia 21: 73–89.
Comparisons of invasive plants in southern Africa originating from southern temperate, northern temperate and tropical regions
HENDERSON, L. 2006b. Comparisons of invasive plants in southern
Africa originating from southern temperate, northern temperate
and tropical regions. Bothalia 36: 201–222.
Pompom weed—an invader of grasslands that threatens conservation and agriculture in South Africa
- L Goodall
- J M Klein
HENDERSON, L., GOODALL, J.M. & KLEIN, H. 2003. Pompom
weed—an invader of grasslands that threatens conservation
and agriculture in South Africa. Pamphlet produced by Gauteng
Department of Agriculture, Conservation, Environment and
Land Affairs (DACEL) in collaboration with the Agricultural
Research Council (ARC).
Asteraceae, Singapore daisy Spiraea cantoniensis Lour., Rosaceae, Cape may # Stellaria media (L.) Vill., Caryophyllaceae, chickweed Stenocarpus sinuatus Endl
- L Sonchus Oleraceus
- Asteraceae
- Sophora
Sonchus oleraceus L., Asteraceae, sowthistle
Sophora cf. davidii (Franch.) Skeels, Fabaceae #
Sorghum halepense (L.) Pers. (= S. almum Parodi), Poaceae, Johnson
grass
Spartium junceum L., Fabaceae, Spanish broom
Spathodea campanulata P.Beauv., Bignoniaceae, African fl ame tree
Sphagneticola trilobata (L.) Pruski (= Thelechitonia trilobata (L.)
H.Rob. & Cuatrec, Wedelia trilobata (L.) Hitchc.), Asteraceae,
Singapore daisy
Spiraea cantoniensis Lour., Rosaceae, Cape may #
Stellaria media (L.) Vill., Caryophyllaceae, chickweed
Stenocarpus sinuatus Endl., Proteaceae, fi rewheel tree ?#
Styphnolobium japonicum (L.) Schott (= Sophora japonica L.),
Fabaceae, Japanese pagoda tree ?#
Symphyotrichum subulatum (Michx.) G.L.Nesom var. squamatum
(Spreng.) S.D.Sundb. (= Aster squamatus (Spreng.) Hieron.),
Asteraceae, swamp aster
Syncarpia glomulifera (Sm.) Nied. (= S. laurifolia Ten.), Myrtaceae,
turpentine tree
Syzygium
cumini (L.) Skeels, Myrtaceae, jambolan
jambos (L.) Alston, Myrtaceae, rose apple
paniculatum Gaertn. (= Eugenia myrtifolia Sims), Myrtaceae,
Australian water pear
Alien plant invasions Vegetation of southern Africa
- D M Macdonald
- I A W Hoffmann
- J H Henderson
RICHARDSON, D.M., MACDONALD, I.A.W., HOFFMANN, J.H. &
HENDERSON, L. 1997. Alien plant invasions. In R.M. Cowling,
D.M. Richardson & S.M. Pierce, Vegetation of southern Africa.
Cambridge University Press, Cambridge.
Fabaceae, alfalfa Melaleuca hypericifolia Sm., Myrtaceae, red-fl owering tea tree wilsonii F
- L Medicago Sativa
Medicago sativa L. (= M. falcata L.), Fabaceae, alfalfa
Melaleuca
hypericifolia Sm., Myrtaceae, red-fl owering tea tree
wilsonii F.Muell., Myrtaceae, violet honey-myrtle #
Invasive alien plants in South Africa: macroecological patterns, with special emphasis on the Cape Floristic region
- D M Rouget
- M Henderson
- L Nel
RICHARDSON, D.M., ROUGET, M., HENDERSON, L. & NEL, J.L.
2004b. Invasive alien plants in South Africa: macroecological
patterns, with special emphasis on the Cape Floristic region.
In M. Arianoutsou & V. Papanastasis, Proceedings of the 10th
MEDECOS Conference, April 25–May 1, 2004, Rhodes, Greece.
Millpress, Rotterdam.