Fig 4 - uploaded by Faiz Bebawi
Content may be subject to copyright.
(a) Germination and (b) viability response of gamba grass seed to burial duration and burial depth. Vertical bars indicate the l.s.d. at P = 0.05.
Source publication
Gamba grass (Andropogon gayanus Kunth.) is a highly invasive, naturalised Weed of National Significance in Australia due to its economic, environmental and social impacts. It outcompetes native pastures and fuels intense fires in northern Australian rangelands. To aid management of current infestations and to better understand its potential distrib...
Contexts in source publication
Context 1
... seed viability (percent of total seed number) averaged 64.3 AE 1.0% (Fig. 4b). Following burial, viability was significantly affected by burial duration (P < 0.001) (Fig. 4b) and burial depth (P < 0.05) (Fig. 5), with a significant soil type ? level of pasture cover interaction (P < 0.05) also occurring (Fig. ...
Context 2
... seed viability (percent of total seed number) averaged 64.3 AE 1.0% (Fig. 4b). Following burial, viability was significantly affected by burial duration (P < 0.001) (Fig. 4b) and burial depth (P < 0.05) (Fig. 5), with a significant soil type ? level of pasture cover interaction (P < 0.05) also occurring (Fig. ...
Context 3
... seed germination averaged 58.6 AE 1.1% (Fig. 4a). Following burial, a significant interaction (P < 0.05) in germination was detected between burial depth and burial duration (Fig. 4a). Germination declined rapidly over the first three months across all treatments, but a greater proportion germinated after three months when buried at 10-and 20-cm depth (average of 11.5%) compared with those located on the soil surface or buried only 2.5 cm below ground (average of 3.5%). Thereafter germination remained low (<4% germination) at all burial depths until no germination was recorded at 30 months after ...
Context 4
... seed germination averaged 58.6 AE 1.1% (Fig. 4a). Following burial, a significant interaction (P < 0.05) in germination was detected between burial depth and burial duration (Fig. 4a). Germination declined rapidly over the first three months across all treatments, but a greater proportion germinated after three months when buried at 10-and 20-cm depth (average of 11.5%) compared with those located on the soil surface or buried only 2.5 cm below ground (average of 3.5%). Thereafter germination remained low (<4% germination) at all burial depths until no germination was recorded at 30 months after ...
Similar publications
Core Ideas
Broomsedge increases in low‐fertility tall fescue pastures.
Phosphorus fertilization limits broomsedge increase in tall fescue pastures.
Lime application limits broomsedge increase in tall fescue pastures.
Applying recommended rates of lime and phosphorus increases tall fescue and limits broomsedge.
Most Missouri tall fescue ( Schedonor...
Weed invasion is a major threat to Australian tropical savannas, and controlling weeds is essential for successful re‐establishment of native species on disturbed sites. Gamba Grass (Andropogon gayanus) is an African grass which has invaded large areas of tropical savanna across northern Australia. Current management strategies in northern Australi...
The introduction of a new tropical forage grass, Andropogon gayanus, on pastures of degraded Panicum maximum is studied in traditional agriculture.
Andropogon gayanus worked well to rehabilitate a herbaceous fallow, without weeding or fertilizer contribution. Its cover increases from 3 to 70 % in the first year and remain around this value the next...
Andropogon gayanus Kunth is a highly invasive grass, but the importance of the seed reproduction for its spread has not been evaluated in Cerrado. This study measured the seed reproduction of A. gayanus by assessing parameters from seed production to seed establishment. The study used replicates in three natural reserves located near Brasília. In e...
Citations
... It is notably absent from the central African rainforest (Foster 1962;Bowden 1964;Ojo et al. 2021; Royal Botanic Gardens, Kew 2022). Andropogon gayanus is considered a weed of national significance in Australia, spreading mostly in the northernmost regions (Bebawi et al. 2018) (Fig. 1e, f ). ...
... As part of a broader program of experimenting and introducing tropical forages, A. gayanus was included in experiments during the 1970s to introduce grasses that would offer cattle improved pastures in the Cape York Peninsula in North Queensland, with results describing the species as an aggressive coloniser (Jones 1979;Anning 1982;Cook and Dias 2006). Grains for A. gayanus were later released to cattle farmers throughout northern Australia in the 1980s and 1990s (Oram 1987;Cameron 2000). ...
Context Andropogon gayanus, commonly known as gamba grass, is one of the declared weeds of national significance in Australia. Past studies have focused on gross morphology of root structures, biogeochemical behaviour, and ecology, but there has been limited work on comparative descriptions of leaf micromorphology and anatomy. Aims We investigated and described its leaf micromorphology and anatomy to understand weed biology and ecophysiology. Methods Optical and scanning electron microscope examination of the adaxial and abaxial leaf surfaces of A. gayanus was carried out. We identified and generated a list of morphological characters that were used to compare several dried herbarium specimens of A. gayanus. Key results The leaf characters were consistent across all specimens examined, with minor differences in leaf pubescence, indicating this could be a plastic trait. Conclusions Andropogon gayanus leaves are well adapted to wet and dry tropical conditions. Plasticity in leaf surface pubescence possibly enhances its adaptability, increasing its success as a weed in Australian ecosystems. The success of A. gayanus in Australia could be because the environment compares favourably with the native environment of the species in Africa, where it has adapted to extremes of wet and dry conditions over a large geographical range. Implications Plant morphological and taxonomic studies of A. gayanus focused on describing characters of spikelets and caryopses are recommended to understand how reproductive structures aid in its successful proliferation.
... Is an excellent forage for both livestock and wildlife due to its palatability and high biomass which are important characteristics for the selection of monocultures suitable for grassland establishment or extensive grazing practices (USDA-NRSC, 2002) ( Figure 2). (Bebawi et al., 2018). Akinyemi et al. (2021) studied the genetic diversity of 9 different Andropogon spp. ...
Pastures are very important for agriculture since the main feeding source of the enormous cattle herd in the world is through forage. Pastures comprise plants from several genera of grasses and legumes. In terms of physical variety, ecology, and economic significance, the Poaceae is among the most significant families of Angiosperms. Regarding stress tolerance, species within this family exhibit a very wide range of variation. In recent years, the importance of using molecular markers in phylogenetic analyses of numerous organisms has increased. The development of genomic technologies and infrastructure has progressed sufficiently for their use in marker- aided selection (MAS) to be studied in several important perennial fodder species. Differences can be directly attributed to minor variations in the genetic code such as phenotype, single sequence repeats (SSRs), and single nucleotide polymorphisms (SNPs). Therefore, breeders can benefit greatly from the development and characterization of new genetic markers. Here in this paper, a brief analysis of some international studies on some minor Poacea forages is given.
... Observed persistence in the field is influenced by multiple factors, including the microhabitat of the seed as determined by the position of the seed within the seedbank [13]. Reduced seed viability is observed in seeds with shallow burial depth and increased duration of burial compared to seeds with deeper burial [19,20]. Seed predation is another factor which affects seed persistence in the soil, especially in the shallow soil layers [21]. ...
Navua sedge (Cyperus aromaticus (Ridley) Mattf. & Kukenth) is a significant agricultural and environmental weed found in tropical island countries including north Queensland, Australia. It is a prolific seed producer and consequently forms a high-density seedbank, and therefore understanding the longevity and persistence of the seeds can provide critical information required for the management of this species. A laboratory-controlled artificial ageing experiment was conducted where the seeds were exposed to a temperature of 45 °C and 60% relative humidity for 125 days. Seeds were removed at various times (1, 2, 5, 9, 20, 30, 50, 75, 100 and 125 days) and their viability determined through standard germination tests. It took 20 days in the artificial ageing environment for the seeds to decline to 50% viability which indicates that Navua sedge has relatively short-lived persistent seeds. These findings will assist in developing a better understanding of the seedbank dynamics of this invasive species, allowing managers to tactically implement control strategies and prepare budgets for ongoing treatments, and have implications for the duration and success of management programs.
... Poaceae Buried trials show Andropogon gayanus Kunth. forms a very short-lived seed bank with viability dropping to below 10% after 6 months, 1% after 12 months and 0% after 30 months (Bebawi et al. 2018b). The results in Table 1 fit into the transient category. ...
Longevity of weed seeds in the soil drives the cost and duration of weed control activities. Traditional methods for estimating weed seed longevity, such as repeated field soil sampling and buried packet trials can take many years and substantial resources to complete. A laboratory process, a Controlled Ageing Test (CAT) exposes seeds to and 'ageing environment' of 45 oC temperatures and 60% humidity. Data from this test is used to sort species into relatively transient, short lived or long-lived categories of weed seed longevity.
This paper reports on examples from a series of trials that seek to correlate the data from CAT batches with longevity data from buried packet trials.
... Seed predation is also increased at shallow depths [32]. Due to these factors, it has been observed that seeds that are buried deeper into the soil profile are better protected from a range of devitalising disturbances and persist in the seedbank for a longer period of time compared to those buried closer to the surface [14,29]. The trade-off, however, is that at increased depths, seed dormancy is usually prolonged, particularly for photoblastic seeds [33], leading to observations that with increased depth, successful emergence is reduced, particularly in smaller seeds with less energy reserves [34]. ...
The ability to produce highly dense and persistent seedbanks is a major contributor to the successful widespread establishment of invasive plants. This study seeks to identify seed persistence and seedbank longevity for the invasive tussock grass Nassella trichotoma (Nees.) Hack. ex Arechav in order to recommend management strategies for preventing re-emergence from the seedbank. To determine the seedbank longevity and persistence, two experiments were conducted: (i) seeds were buried at four depths (0, 1, 2, and 4 cm) and collected and assessed for viability, seed decay, and in-field germination after 6, 9, 12, 15, and 18 months of field burial; and (ii) seeds were exposed to artificial ageing conditions (60% RH and 45 °C) for 1, 2, 5, 9, 20, 30, 50, 75, 100, and 120 days, and viability was determined through germination tests and tetrazolium tests. Less than 10% of the seeds collected after 12 months of in-field burial were viable. The artificial ageing treatment found germination declined to 50% after 5.8 days, further suggesting that N. trichotoma seeds are short lived. The results from both experiments indicate that N. trichotoma has a transient seedbank, with less than 10% of the seeds demonstrating short-term persistence. It is likely the persistent seeds beyond 12 months were exhibiting secondary dormancy as viable seeds did not germinate under optimal germination conditions. The “Best Practice Guidelines” recommend monitoring for seedbank recruitment for at least three years after treating N. trichotoma infestations. The results of this study support this recommendation as a small proportion of the seeds demonstrated short-term persistence.
... Seed biology of A. gayanus may also contribute to the invasion success of this weed in northern Australia. Bebawi et al. (2018) noted that seed persistence is supported by deeper burial of the seed, relative to shallow placement of seed which leads to loss of viability within 1 year of seed shedding in dry tropics of northern Australia. Andropogon gayanus typically germinates and persists well in cooler climates and has strong potential to expand across southern parts of Australia, particularly if predicted changes in Australia's climatic zones are realised. ...
Australia’s separation from other land masses has resulted in the evolution of flora and fauna in relative isolation. The arrival of Europeans some 230 years ago marked the beginning of a mass invasion of the continent by alien plant (and animal) species from across the globe. These mass invasions have had profound effects on the Australian landscape and its native species and have required significant management interventions. In this chapter, we present an overview of the history of alien plant invasions in Australia and the scope of the current situation in terms of the number of species introduced. Seven case studies illustrate the nature of the invasive weed issues and the actions undertaken towards management. Case studies include Australian Weeds of National Significance (WoNS) (Chrysanthemoides monilifera subsp. rotundata, Lantana camara) and environmental and agriculturally important invasive plants (Opuntia inermis, Opuntia stricta, Echium plantagineum, Cucumis myriocarpus, Citrullus lanatus, Andropogon gayanus) as well as recent incursions (Bassia scoparia). Each case study outlines the impacts and risks associated with the invasion and presents the unique management approaches adopted - asset protection, biological control, successful eradication and ecosystem transformation. Several case studies draw comparisons between the establishment and persistence of alien plants in Australia and their native ranges and provide important clues on key traits that contribute to their successful invasion. Results to date have shown that the number of introduced plants to Australia has increased exponentially across most states and territories, particularly in recent years. Targeted control strategies for some WoNS such as Chrysanthemoides monilifera subsp. rotundata have been successful due to significant investment in the study of weed biology and physiology and subsequent development of effective integrated weed management strategies. The management strategies for several WoNS and invasive plants are evolving, through continued involvement of local, state and federal government and nongovernmental agencies and researchers to identify more effective control strategies. Lastly, future management challenges are described, including the expanding alien flora, the potential impact of climate change and risk management associated with weed incursion. Unique Australian insights can provide potential examples for other countries facing similar challenges as alien plants are now a global problem.
... Seed biology of A. gayanus may also contribute to the invasion success of this weed in northern Australia. Bebawi et al. (2018) noted that seed persistence is supported by deeper burial of the seed, relative to shallow placement of seed which leads to loss of viability within 1 year of seed shedding in dry tropics of northern Australia. Andropogon gayanus typically germinates and persists well in cooler climates and has strong potential to expand across southern parts of Australia, particularly if predicted changes in Australia's climatic zones are realised. ...
The persistence of weeds is directly influenced by their capacity to interfere with other plants, either through competition for resources or through chemical interference mediated by plant‐produced secondary metabolites, a phenomenon known as allelopathy. Recent research has focused on critically assessing the role of allelochemicals in plant succession and invasion, in both native and invaded ecosystems and their associations with other plants and the soil microbiome. The use of sensitive and accurate metabolomics and advanced genomics platforms has led to new advances in the identification of allelochemicals and biotic interactions, biosynthetic pathways associated with their production, and determination of specific impacts on target plant species. In this chapter, we describe the chemistry, biosynthesis, and modes of action of selected groups of allelochemicals associated with persistent and invasive plants and the biotic and abiotic stressors regulating allelochemical production and release. Selected case studies of persistent weeds of global significance exhibiting significant production of allelochemicals are presented, which include the following species: (i) Echium plantagineum , (ii) Centaurea solstitialis , (iii) Sorghum halepense , (iv) Reynoutria japonica , and (v) Parthenium hysterophorus . The use of metabolic profiling technologies has enhanced opportunities for identification and study of the biological activity of these invasive weeds and associated organs, with respect to biosynthesis, persistence, and mode of action. The future profiling of allelochemicals in rhizosphere soils will also provide additional proof of concept of the impact of allelochemicals on microbial diversity and establishment of invasive plants in novel ecosystems.
... Germination occurs after the first rains of the storm or wet season after which dormancy rates are either low (Bebawi et al. 2018) or absent (Felippe et al. 1983). Drivers of germination are temperature and the availability of water; light has no effect on germination (Felippe et al. 1983). ...
... Drivers of germination are temperature and the availability of water; light has no effect on germination (Felippe et al. 1983). Germination takes place under a wide range of constant (~15 -40°C, (Felippe et al. 1983, Bebawi et al. 2018) and alternating day/night temperatures (16/12 -47/39°C). Germination success declines towards the two extremes. ...
... At temperatures below ~15°C, seeds enter into dormancy with no effect on viability. Maximum seed viability is maintained at lower temperatures with a gradual decline in viability with increasing temperature (Bebawi et al. 2018). At temperatures above ~40°C both dormancy and loss of seed occurs and above 43°C seeds are rendered unviable within weeks. ...
Andropogon gayanus (gamba grass) is a high-biomass grass native to tropical and subtropical Africa and introduced into Australia as a pasture grass. Under well-managed grazing conditions, gamba grass has proven a useful and palatable addition to tropical cattle pastures. However, it has also become a significant environmental weed and is considered an ecosystem transformer. In recognition of the significant threat posed by gamba grass, it has been listed (along with 4 other invasive grasses) as a key threatening process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).
One of the major problems limiting the effective management of gamba grass once established as an environmental weed is the lack of registered herbicides for use in natural systems and conservation areas. Glyphosate is the primary herbicide in use in northern Australia.
There are several current and emerging issues which make a reliance on glyphosate for gamba grass control problematic. Application of glyphosate is logistically difficult in wet and remote areas, it has no residual action and largely relies on follow-up treatments, and there are emerging resistance issues. In addition, there is growing concern that glyphosate may be linked to carcinogenicity, genotoxicity and epidemiological disorders. Alternative herbicides are critical to allow long-term, effective and timely control of gamba grass in the environments encountered on Cape York Peninsula and across northern Australia.
The goal of this project was to collate existing knowledge related to control and management of gamba grass and test alternative herbicide options for use in natural areas of Cape York Peninsula. Three herbicides were tested alongside glyphosate in field trials and 10 residual pre-emergence herbicides were tested in pot trials. Neither the field nor pot trials identified a clear suitable alternative to glyphosate that selectively controlled gamba grass with low off-target effects in the contexts in which we tested them. However, there are several herbicides that warrant further testing at a range of additional application rates and in a range of environments (flupropanate, clomazone, oxyfluorfen, imazapyr and indaziflam). In particular, the granular form of flupropanate is worthy of further experimentation because of its portability in the field and flexibility in application, and because it showed the most promising results in the field trials.
Ultimately, land managers may need to trade-off significant, short-term, off-target effects for longer term, more effective and permanent control of gamba grass with herbicides.
... Each plant produces large quantities of seeds (2000-70 000 seeds/m 2 ; Setterfield et al. 2004;Flores et al. 2005), which are easily spread via wind and water . Gamba Grass seeds rapidly loose viability with <1% surviving after twelve months (Bebawi et al. 2018); however, sufficient seedstock persists in the soil seed bank up to 2 years to re-establish Gamba infestations after local eradication (Setterfield et al. 2004). Propagule pressure and soil seed banks are a major driver for grass infestations in disturbed areas (Smith et al. 2000;Bellairs et al. 2006;Fensham et al. 2013). ...
Weed invasion is a major threat to Australian tropical savannas, and controlling weeds is essential for successful re‐establishment of native species on disturbed sites. Gamba Grass (Andropogon gayanus) is an African grass which has invaded large areas of tropical savanna across northern Australia. Current management strategies in northern Australia focus on fire and glyphosate to effectively control mature plants; however, re‐establishment of infestations from the soil seed bank remains a major challenge to eradication efforts. This study focused on the effects of soil seed bank treatments on Gamba Grass recruitment on a mine site in northern Australia. Adult Gamba Grass plants within test plots were killed with glyphosate to exclude resource competition. Chemical, physical and biological treatments were then applied, and the treatment effects on subsequent Gamba Grass seedling emergence and survival quantified. Seedling emergence was significantly reduced by three of the four residual herbicide treatments tested. The most effective herbicide treatments, dalapon and sulfometuron, reduced emergence by 90% compared to the standard glyphosate treatment alone. This equated to a reduction in Gamba Grass seedling emergence from 1 seedling/m2 to 1 seedling 10 m−2, a major improvement for Gamba Grass management. These residual herbicide treatments significantly reduced the population density of Gamba Grass for at least 5 months after emergence. The physical and biological treatments did not have a significant effect on seedling emergence. This significant reduction in Gamba Grass seedling emergence and survival can substantially improve Gamba Grass management. Reducing re‐colonisation from the soil seed bank using residual herbicides provides a valuable management tool for land managers, integrating readily with established strategies for controlling the mature plants.
Globally, invasive grasses are a major threat to protected areas (PAs) due to their ability to alter community structure and function, reduce biodiversity, and alter fire regimes. However, there is often a mismatch between the threat posed by invasive grasses and the management response. We document a case study of the spread and management of the ecosystem-transforming invasive grass, Andropogon gayanus Kunth. (gamba grass), in Litchfield National Park; an iconic PA in northern Australia that contains significant natural, cultural and social values. We undertook helicopter-based surveys of A. gayanus across 143,931 ha of Litchfield National Park in 2014 and 2021-2022. We used these data to parametrise a spatially-explicit spread model, interfaced with a management simulation model to predict 10-year patterns of spread, and associated management costs, under three scenarios. Our survey showed that between 2014 and 2021-22 A. gayanus spread by 9463 ha, and 47%. The gross A. gayanus infestation covered 29,713 ha of the total survey area, making it the largest national park infestation in Australia. A. gayanus had not been locally eradicated within the Park's small existing 'gamba grass eradication zone', and instead increased by 206 ha over the 7-year timeframe. Our modelled scenarios predict that without active management A. gayanus will continue spreading, covering 42,388 ha of Litchfield within a decade. Alternative scenarios predict that: (i) eradicating A. gayanus in the small existing eradication zone would likely protect 18% of visitor sites, and cost ∼AU$825,000 over 5 years - more than double the original predicted cost in 2014; or (ii) eradicating A. gayanus in a much larger eradication zone would likely protect 86% of visitor sites and several species of conservation significance, and cost ∼AU$6.6 million over 5 years. Totally eradicating A. gayanus from the Park is no longer viable due to substantial spread since 2014. Our study demonstrates the value of systematic landscape-scale surveys and costed management scenarios to enable assessment and prioritisation of weed management. It also demonstrates the increased environmental and financial costs of delaying invasive grass management, and the serious threat A. gayanus poses to PAs across northern Australia.
