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Effects of forest fragment management on vegetation condition and maintenance of canopy composition in a New Zealand pastoral landscape
Abstract
Residual forest fragments in areas dominated by pastoral agriculture can have high value for biodiversity conservation but are still subject to ongoing degradation as (i) processes initiated by fragmentation continue to operate, for example, changes in canopy replacement probabilities; and (ii) deleterious processes impinge upon them from the surrounding matrix, for example, browsing and trampling by vagrant livestock. Responses by management to slow or reverse these processes require evaluation. Stock (mainly cattle and sheep) exclusion by fencing and mammal pest (mainly Trichosurus vulpecula (brushtail possum)) control are currently used as management tools to maintain or improve the vegetation condition of fragments in New Zealand. We examined the effectiveness of these tools by sampling vegetation composition, forest structure and regeneration of woody species in 41 old-growth fragments dominated by Beilschmiedia tawa, selected to populate a factorial design that included four different fencing classes (unfenced, fenced 2–10, 10–20 and >20 years ago), with and without sustained mammal pest control. Fencing for more than 10 years led to higher abundances of native ground ferns and shrubs, and lower abundances and numbers of mostly adventive herbaceous ground cover species. In contrast, lianes were less abundant with mammal pest control, whereas herbs were more abundant. Fencing led to a high-density pulse of seedlings and saplings of woody species within 10 years that then thinned. Mammal pest control allowed increases in abundance of some species palatable to T. vulpecula, and increased the ratio of canopy to subcanopy seedlings in the regeneration pulse caused by fencing. Neither treatment, however, led to the restoration of indigenous species richness to reference forest levels, nor allowed densities of juveniles of shade-tolerant canopy species to establish to levels commensurate with replacement of existing canopy trees. Most woody seedlings that established following fencing were of short-lived subcanopy species. These management actions will therefore slow but not reverse the long-term degradation of these forest fragments, which will eventually differ substantially from continuous forest under current management regimes. Additional measures such as replanting may be necessary not only to ensure replacement of some current species but also to restore lost species.
... The use of fencing assumes that following the exclusion of undesirable animals post-dispersal processes will return to their prefragmentation state (Spooner et al., 2002). However, the effects of herbivore exclusion also depend on the type of vegetation and history of the fragment (Spooner et al., 2002;Burns et al., 2011); the contrasting outcomes that occur after fencing (e.g. compare Aronson andHandel, 2011 with Spooner et al., 2002) suggest that its success is habitat-dependent. ...
... However, the effect of fencing in facilitating the recovery of these forest fragments remains unclear. Burns et al. (2011) found that fencing restored neither the richness of native species to unfragmented forest levels nor the density of seedlings of shadetolerant species in sufficient numbers to replace adult canopy trees. On the other hand, Smale et al. (2005) and Dodd et al. (2011) concluded that fencing could positively affect native plant regeneration and canopy tree populations. ...
... In the unfenced fragments all canopy tree species, including B. tawa, and sub-canopy species will become less prevalent, potentially due to herbivory. Evidence suggests that the prevalence of species other than B. tawa indicates a change in composition and structure that differs from an unfragmented forest (Spooner et al., 2002;Burns et al., 2011). Burns et al. (2011) suggested that a site's history may be as important as protection against large herbivores, and the inconsistent response of fragments to fencing that we observed re-emphasises the importance of site-level effects and contingencies in community dynamics. ...
... The off-site effects of livestock grazing and trampling in native habitat remnants within pastoral land have been less well studied than effects on the pasture itself, but nevertheless can be severe (Close, Davidson & Watson 2008;Dodd et al. 2011). The importance of these off-site effects for understorey plant communities (Naeth et al. 1991;Burns et al. 2011) and soils (Pietola, Horn & Yli-Halla 2005;Jeddi & Chaieb 2010) is reflected in the extensive evidence for differences in biodiversity between fenced and unfenced forest remnants (Bromham et al. 1999;Didham et al. 2009). Consequently, world-wide, fencing to exclude livestock is an increasingly common management option for the conservation of native habitat remnants embedded within production landscapes (Hayward & Kerley 2009;Burns et al. 2011). ...
... The importance of these off-site effects for understorey plant communities (Naeth et al. 1991;Burns et al. 2011) and soils (Pietola, Horn & Yli-Halla 2005;Jeddi & Chaieb 2010) is reflected in the extensive evidence for differences in biodiversity between fenced and unfenced forest remnants (Bromham et al. 1999;Didham et al. 2009). Consequently, world-wide, fencing to exclude livestock is an increasingly common management option for the conservation of native habitat remnants embedded within production landscapes (Hayward & Kerley 2009;Burns et al. 2011). However, in many other regions where livestock still have access to native remnants, the off-site or 'spillover' effects of livestock grazing and trampling are only likely to become more significant in the future as livestock densities increase. ...
... In many parts of the world, there is extensive evidence that unfenced forest remnants embedded within farmland can be severely damaged by livestock trampling (Close, Davidson & Watson 2008;Hayward & Kerley 2009;Burns et al. 2011). However, the relationship between the intensity of livestock trampling and the magnitude of ecological effect has been poorly quantified. ...
Land‐use intensification is increasing dramatically in production systems world‐wide. Livestock production is an important component of production land use, and increases in livestock densities have had a wide range of negative consequences. The off‐site effects of livestock grazing and trampling on native vegetation adjacent to pastoral land have received less attention than on‐farm effects. Moreover, where significant ecological effects of livestock spillover have been identified, the mechanistic determinants of these effects have not typically been investigated.
Here, we tested the mechanistic drivers of livestock trampling effects on land snail communities in forest remnants using simulated trampling under field conditions. We used a factorial combination of leaf‐litter manipulation and trampling treatments to partition different causal drivers of livestock impacts on land snail communities and related them to five environmental variables that are altered by livestock.
We show that even very low frequency trampling caused severe changes to land snail communities. Land snail density, even under the lowest trampling frequency, declined by an average of 42 individuals m ⁻² and land snail species richness decreased by an average of 10 species per plot compared with control plots.
The underlying drivers of changes in land snail communities varied, but were primarily linked to leaf‐litter mass, rather than soil compaction.
Synthesis and applications . Overall, these results suggest that even minimal disturbance by livestock has large effects on land snail communities, but the underlying drivers of these effects require further investigation in longer duration and more intensive studies. Our results provide strong support for livestock exclusion as an important management tool for native forest remnants embedded within production landscapes.
... The composition, structure and spatial arrangement of native biodiversity in those parts of New Zealand where pastoral agroecosystems dominate is different to those in areas with extensive public conservation lands. With some exceptions, native habitats tend to be small, isolated, and modified to varying degrees by grazing (domestic and feral), historic logging, plant invasions and edge effects resulting in changes to their composition and structure (Timmins & Williams 1991;Burns et al. 2000;Smale et al. 2008;Burns et al. 2011;Ruffell & Didham 2017). While some of these native habitats are protected through covenants or as part of the public conservation estate, most do not have any formal protection (Norton & Pannell 2018). ...
... Protection of all that remains of our original old-growth forests and wetlands, and the extensive areas of regenerating native forest is essential ). The sustainability of remnants of the original old growth forests is critical even when they might have been impacted in some manner through historic logging, grazing animals or the effects of adjacent agricultural activities (Smale et al. 2008;Burns et al. 2011;Didham et al. 2015). These remnants are the direct connections with the past and the source of propagules (plant, animal, fungal) for the future. ...
... These findings are of particular importance as B. tawa is endemic to New Zealand and has been affected by a lack of recruitment (Burns et al. 2011) where germination rates are as low as 4%, even when herbivores are excluded. In contrast, in undisturbed forests mass germination has been reported (Knowles & Beveridge 1982). ...
... In addition, podocarp-tawa forests are under pressure from exotic predators (e.g. deer, possum), and the reduced seed dispersal by the native pigeon kererū (Hemiphaga novaeseelandiae) (Knowles & Beveridge 1982;Mander et al. 1998;Burns et al. 2011). Hemiphaga novaeseelandiae plays an important role in B. tawa regeneration as a seed disperser (Campbell & Atkinson 2002) and seeds that pass through its digestive system germinate faster (West 1986;Burrows 1999;Robertson et al. 2006). ...
In northern New Zealand, Beilschmiedia tawa has shown recruitment failure in some sites. The Beilschmiedia genus has been shown to contain allelopathic compounds in its leaves and bark. In addition, the distribution of the main seed disperser for tawa, the kererū (Hemiphaga novaeseelandiae), has declined in recent years. In this study I assessed whether B. tawa leaf leachate can affect recruitment of B. tawa, particularly in disturbed sites. I also tested whether simulated endozoochory (removal of mesocarp) had an effect on germination. Results show that under laboratory conditions, leachate can have either a negative or a positive effect, depending on the concentration. At high concentrations (1:1), higher than normally experienced in the field, radicles were shorter than in the less concentrated treatment. At lower concentrations (1:50) there was a 50% higher germination index compared with the control and high concentration (1:1) treatments. Using soils from sites with different levels of anthropogenic disturbance did not have an effect on germination or hypocotyl length. Removal of the mesocarp positively affected germination (1.5-fold). Based on the results of this study, inhibition of germination and growth of B. tawa is unlikely to be caused by phytotoxicity of their own leachate under field conditions.
... Grazing is known to reduce the presence of those species that are most palatable to livestock and least resilient to herbivory, whilst favouring an increase in unpalatable and resilient species (Pettit et al. 1995;Burns et al. 2011). Given that all member sites of the mature forest cluster were known to be inaccessible to cattle, while most disturbed vegetation sites were not, it appears that grazing is a major edge effect that alters forest communities within the upper Papallacta valley. ...
... Protecting large forest areas from further clearance should be a priority for the conservation of high montane cloud forest throughout the Ecuadorian Andes. It would also help to encourage farmers to keep livestock out of forested areas because this would eliminate the edge effects caused by grazing (Burns et al. 2011). If large forest areas cannot be protected, then some of the loss of biodiversity caused by clearing forest for pasture could be mitigated by retaining scattered trees and forest fragments. ...
High Andean cloud forests are home to a diversity of unique wildlife and are important providers of ecosystem services to people in the Andean regions. The extent of these cloud forests has been widely reduced through conversion to pasture for livestock, which threatens the forests’ ability to support biodiversity and provide ecosystem services. This paper explores whether impacts on woody plant biodiversity and four ecosystem properties (woody plant species richness, juvenile timber tree abundance, soil organic matter content and soil moisture) from converting forest to pasture can be mitigated if some woody forest vegetation is maintained within pastures. Woody vegetation in pastures was found to conserve those woody plant species that are more tolerant to exposure and grazing, but conservation of the high montane cloud forest community required areas of forest from which livestock were restricted. The sampled sites clustered according to woody plant species cover; these clusters represented a gradient from pasture with patches of shrubs to mature forest. Clusters differed in both woody plant species richness and number of juvenile timber trees whereas soil organic matter and soil moisture were observed to be similar among all clusters. This suggests that the different habitats may have some equivalent ecosystem properties. We conclude that the presence of woody vegetation in pastures may reduce some of the impacts of converting forest to pasture, but should not be considered a substitute for protecting large areas of forest, which are essential for maintaining woody plant species diversity in high Andean cloud forest.
... Bird species responses to forest patch size and edge effects may also differ according to their native or exotic origin, which can be reflected in their distinct life-histories and habitat preferences (Cassey 2001; van Heezik et al. 2008). The native forests of New Zealand have experienced a long history of fragmentation and are nowadays occurring throughout much of the country as forest patches of various sizes within a landscape matrix dominated by exotic grasslands and pine plantations (Clout and Gaze 1984; Deconchat et al. 2009; Burns et al. 2011). Together with predation by introduced mammals, the loss of habitat due to the clearing of natural forest and the expansion of agriculture and other modified land cover resulted in major extinction events among the native avifauna (Holdaway 1989). ...
... This pattern is consistent with the fact that functional richness increases avian predation rates through life-trait complementation among predatory birds (Philpott et al. 2009). Such coexistence may also contribute to maintain ecosystem services provided by birds in New Zealand native forests (Clout and Hay 1989; Murphy and Kelly 2003; Wenny et al. 2011), especially in changing mosaic landscapes of native and exotic forests and open habitats (Tscharntke et al. 2007; Zamora et al. 2010; Burns et al. 2011). However, further functional extinction of keystone endemics will strongly affect ecosystem services, as demonstrated by reduced bird pollination of native shrubs in the mainland compared to island sanctuaries (Anderson et al. 2011). ...
Disentangling the confounded effects of edge and area in fragmented landscapes is a recurrent challenge for landscape ecologists, requiring the use of appropriate study designs. Here, we examined the effects of forest fragment area and plot location at forest edges versus interiors on native and exotic bird assemblages on Banks Peninsula (South Island, New Zealand). We also experimentally measured with plasticine models how forest fragment area and edge versus interior location influenced the intensity of avian insectivory. Bird assemblages were sampled by conducting 15 min point-counts at paired edge and interior plots in 13 forest fragments of increasing size (0.5–141 ha). Avian insectivory was measured as the rate of insectivorous bird attacks on plasticine models mimicking larvae of a native polyphagous moth. We found significant effects of edge, but not of forest patch area, on species richness, abundance and composition of bird assemblages. Exotic birds were more abundant at forest edges, while neither edge nor area effects were noticeable for native bird richness and abundance. Model predation rates increased with forest fragmentation, both because of higher insectivory in smaller forest patches and at forest edges. Avian predation significantly increased with insectivorous bird richness and foraging bird abundance. We suggest that the coexistence of native and exotic birds in New Zealand mosaic landscapes enhances functional diversity and trait complementation within predatory bird assemblages. This coexistence results in increased avian insectivory in small forest fragments through additive edge and area effects.
... A limitation of modelling the realised climatic niche is that we cannot be certain our estimates are an accurate representation of the species true realised niche, as biotic and historical factors may have a strong influence on the fill and distribution of the species, within its broad climatic niche. Since human arrival, New Zealand's forests have also been shaped by an extensive history of anthropogenic disturbance including fire (Perry et al., 2014;McWethy et al., 2014), selective logging (Burns et al., 2011), grazing by livestock (Dodd & Power, 2007) and ...
Aim
Species severely under‐represented in fossil pollen records leave gaps in interpretations and reconstructions of past vegetation. These ‘silent taxa’ leave little or no trace due to low pollen production, dispersal, preservation and taxonomic resolution. An approach for including them is through associating them with other species with reliable pollen representation. Here, we demonstrate a method for selecting such a proxy species for the Holocene using modern vegetation data.
Location
New Zealand.
Taxon
Beilschmiedia tawa (A.Cunn.) Benth. & Hook. F. ex Kirk (Lauraceae).
Methods
We used vegetation plot data to perform a pairwise co‐occurrence analysis of the New Zealand indigenous forest metacommunity to identify species with a strong positive association with Beilschmiedia tawa (tawa), a common tree severely under‐recorded in the pollen record. For those species, we then modelled their realised climatic niches to identify species with high niche overlap. We discuss how well those species could be interpreted from the Holocene fossil pollen record based on the representation of their pollen taxa.
Results
Knightia excelsa (rewarewa; Proteaceae) is a potential proxy for B. tawa in Holocene fossil pollen records, and other, range‐limited species may provide community‐specific proxies. We show combining resampling with sub‐sampling is a robust method for reducing the high false positive rate associated with large co‐occurrence analyses (1000+ sites) by limiting the sample size to 100 sites.
Main Conclusions
We show that the palaeoecology of silent taxa can be studied via proxy species, allowing their past distributions to be better understood. We highlight the importance of modelling many aspects of the realised niche to understand the usefulness and limitations of the silent–proxy association. Future research should focus on testing the underlying assumptions of the silent–proxy relationship so that models built on modern data can confidently be applied to palaeoecological data.
... This could be due to varying establishment rates of woody vegetation. The initial establishment issues could be due to a variety of factors, such as a lack of viable seed, competition amongst species, animal grazing, the soil environment, climate, or a mixture of factors [20,22,36,37]. ...
Abstract: The New Zealand Emissions Trading Scheme allows landowners to be remunerated for
the carbon sequestration capabilities of eligible forests established post 1990. For afforested areas
of 100 hectares or fewer, carbon sequestration is estimated with the use of default carbon look-up
tables administered by the Ministry for Primary Industries. However, a disparity exists between
exotic pines (Pinus radiata), where carbon sequestration predictions are regionally differentiated,
and native species, where carbon sequestration estimations are neither distinguished by species or
locality. This paper aims to highlight this inequality by comparing the calculated carbon storage
of endemic tree species with the ‘Indigenous Forest’ category in the carbon look-up tables. The
carbon storage of 12-year-old naturally regenerated tea trees (Leptospermum scoparium and Kunzea
ericoides) was calculated using allometric measurements and compared to the look-up tables. The
results suggest that carbon look-up tables underestimate the carbon sequestration of native tea trees
by 81.8%. A bimodal data distribution suggests that carbon sequestration is heavily dependent on
light interception levels. It is recommended that carbon sequestration data for specific native species
in different environments are collected and integrated into such tables.
... In addition to concentrations of cellulose and phenolics, Bee et al. (2011) concluded that season and associated species can also influence diet selection. Exclusion of cattle in forests in Westland resulted in an increase in abundance of woody species (Buxton et al., 2001) and where sheep and cattle were excluded from forest fragments in the Waikato region, abundance of woody species including Coprosma grandiflora, Schefflera digitate, and M. ramiflorus increased (Burns et al., 2011). The preference of species to ruminants was categorized by Sweetapple and Nugent (2004) who found that highly preferred species included C. grandiflora, Coprosma lucida, G. littoralis, M. ramiflorus, and S. digitata. ...
Steep, uncultivable hill country below 1,000 m comprises about 40% of New Zealand's land surface area. Hill country farmers require options to increase the resilience of their farms to climatic and economic extremes while addressing soil conservation and water quality issues. We profile and discuss two options that can assist in transforming hill country. The first comprises a simple approach to grazing management in hill country pastures to increase pasture resilience and the second approach focuses on including selected forage shrubs (and trees) to create grazed pasture-shrublands. Deferred grazing, the cessation of grazing from flowering until seed dispersal of the desirable species in a pasture, is an old practice which has novel applications to improve resilience of hill country farming systems. We draw on current research and practitioner experience to demonstrate the impact of deferred grazing on the resilience of the deferred pasture and the farm system. We propose that deferred grazing will: (i) increase resilience of a pasture by enabling it to better recover from biotic and abiotic stresses and (ii) reduce the risk of nutrient and sediment losses in hill country by increasing ground cover, rooting depth and soil structural stability. Introducing woody forage shrubs into hill country pastures is another option that can improve farm profitability and resilience to current and future economic and climatic variabilities. The extensive root networks of shrubs can increase soil structural stability and reduce the risk of soil erosion. In addition, shrubs can supply many other ecosystem services, such as forage and shelter for livestock. In this paper, we discuss: (i) the potential benefits of a grazed pasture-shrubland at farm, landscape and national scales; (ii) candidate woody exotic and indigenous forage species; and (iii) priorities for research.
... The discrepancy between model predictions and field observations is, at least in part, due to the lack of regeneration in B. tawa at some sites as reported by Burns et al. (2011), Morales (2015), Morales et al. (2016). In addition, the discrepancies between model predictions and the available empirical data could arise from differences in the site characteristics (e.g. ...
Understanding the interactive effects of fragmentation and invasive species on forest dynamics requires a long-term perspective because they are difficult to assess in the medium- to long-term using observational or experimental data alone. In such settings ecological models have an important role to play. Here we describe the implementation of a spatially explicit individual-based model (SEIBM) representing the dynamics of small forest fragments in northern New Zealand based on empirical data collected in the region. In addition, we performed a baseline analysis to determine how well the model captured podocarp-tawa forest dynamics, and compared its performance with stand structure data obtained from an unfragmented forest in northern New Zealand. We used sensitivity analysis to determine how sensitive the model was to changes in the input parameters. In addition, we simulated different scenarios under diverse management conditions to explore the model’s potential as a management tool. The model captures the stand structural characteristics of the fragments reasonably well but under-predicts stand basal area, suggesting that it does not represent the long-term suppression of some canopy tree species adequately. Although some refinement is needed to improve its performance, we believe that the model presented here is a useful tool for management purposes and for the assessment of the long term viability of forest fragments. The model can help inform managers and decision-makers regarding the long-term persistence of podocarp-tawa forest patches.
... In New Zealand, 71% of indigenous forest is gone, much of it from the accessible lowlands (Ewers et al. 2006;Walker et al. 2006). Remaining forest remnants typically have a suite of non-native plants and mammals present (Jane 1983;Timmins & Williams 1991;Craig et al. 2000;King 2005), which can exacerbate biodiversity loss and impede ecosystem recovery (Didham et al. 2007;Hutchison 2008;Burns et al. 2011). Lowland forest remnants are particularly susceptible to invasion by non-native plants for several reasons. ...
Globally, lowland forests have been depleted, fragmented, and degraded by land clearance and conversion by humans. Many remnants are also invaded by non-native plants and mammals, which can exacerbate biodiversity loss and impede ecosystem recovery. We examined the effects of non-native ground cover weeds and mammals on the seedling recruitment of native woody plants in lowland forests in northern New Zealand by following establishment over 2 years at sites experiencing different levels of weed cover, with or without supplemental seed addition, and with or without mammal exclusion. In general, native seedling recruitment was highest where seeds had been added and mammals excluded. Native seedling recruitment was negatively correlated with weed cover at sites invaded by Asparagus scandens or Tradescantia fluminensis, but only where seeds had been added. These results suggest that attempts to facilitate native seedling recruitment by sowing native seeds will be most successful where ground cover weeds and introduced mammals are low in abundance. Seedling recruitment was highest for Piper excelsum, Myrsine australis and Melicytus ramiflorus, so these species could be good options for lowland-forest restoration projects where ground cover weeds are present.
... Ground cover weeds are associated with a reduction in both native abundance and native species richness in New Zealand lowland forests, particularly where weed volume is high. In the long term, this could compromise the health of these forests, particularly since many are highly fragmented and under threat from other invasive species such as possums (Trichosurus vulpecula) (Burns et al. 2011). However, it is only in high light environments, such as the forest edge or in canopy gaps, that these weeds attain the highest volumes. ...
Ecological impacts of three weed species of similar life form, Asparagus scandens, Plectranthus ciliatus and Tradescantia fluminensis, were investigated in six lowland forest remnants in New Zealand. All three species form dense, ground-covering mats of vegetation, and are tolerant of a broad range of light environments. Relationships between canopy openness, weed volume, native plant abundance and native species richness were investigated. Volume of all three weed species increased as canopy openness increased. Tradescantia fluminensis appeared to be most detrimental to native vegetation, with both native abundance and native species richness decreasing sharply as weed volume increased. Plectranthus ciliatus and Asparagus scandens were also associated with declines in native abundance and native species richness, but the correlations were less pronounced and were inconsistent across sites. Regression tree analyses on data from individual sites suggested a potential threshold of weed volume for Tradescantia fluminensis, beyond which both native abundance and native species richness declined abruptly. A threshold was also evident when data from all sites were analysed together. Where native species richness did decline in association with increasing weed volume, there did not appear to be any particular native species that were more likely to be excluded than others. All three ground cover weed species are associated with declines in native plant abundance and native species richness, particularly under high light conditions where the weeds are most abundant.
... For example, of the 145,000 ha of native forest that existed in the Waipa district prior to human settlement, only 6% now remains [59]. Because vegetation clearing was selective, most of the remaining native forest is in areas that were considered less valuable for agriculture such as gullies, steep slopes and rocky terrain [60]. Furthermore, a high proportion of remaining forest remnants are small (<5 ha) and dominated by tawa (Beilschmiedia tawa (A.Cunn.) ...
Land-use intensification is a central element in proposed strategies to address global food security. One rationale for accepting the negative consequences of land-use intensification for farmland biodiversity is that it could 'spare' further expansion of agriculture into remaining natural habitats. However, in many regions of the world the only natural habitats that can be spared are fragments within landscapes dominated by agriculture. Therefore, land-sparing arguments hinge on land-use intensification having low spillover effects into adjacent protected areas, otherwise net conservation gains will diminish with increasing intensification. We test, for the first time, whether the degree of spillover from farmland into adjacent natural habitats scales in magnitude with increasing land-use intensity. We identified a continuous land-use intensity gradient across pastoral farming systems in New Zealand (based on 13 components of farmer input and soil biogeochemistry variables), and measured cumulative off-site spillover effects of fertilisers and livestock on soil biogeochemistry in 21 adjacent forest remnants. Ten of 11 measured soil properties differed significantly between remnants and intact-forest reference sites, for both fenced and unfenced remnants, at both edge and interior. For seven variables, the magnitude of effects scaled significantly with magnitude of surrounding land-use intensity, through complex interactions with fencing and edge effects. In particular, total C, total N, δ15N, total P and heavy-metal contaminants of phosphate fertilizers (Cd and U) increased significantly within remnants in response to increasing land-use intensity, and these effects were exacerbated in unfenced relative to fenced remnants. This suggests movement of livestock into surrounding natural habitats is a significant component of agricultural spillover, but pervasive changes in soil
... The discrepancy between model predictions and field observations is, at least in part, due to the lack of regeneration in B. tawa at some sites as reported by Burns et al. (2011), Morales (2015), Morales et al. (2016). In addition, the discrepancies between model predictions and the available empirical data could arise from differences in the site characteristics (e.g. ...
... Further management actions may be required, such as exclusion of domestic livestock, control of invasive predators, herbivores, and weeds (e.g. 124,125). Consequently, ecological restoration activities required to improve ecosystem services such as water quality or carbon storage may often be insufficient to enhance biodiversity (Figure 3;60). ...
... (3) Nonnative species would have a greater effect under lower canopy cover, given that many grasses and other nonnative species (e.g., Jager and Kowarik, 2010 ;Burns et al., 2011 ;Weller et al., 2011 ), very few studies have targeted rare or endangered ferns for restoration (but see Zenkteler, 2002 ;Aguraiuja, 2011 ). There is a need for ecological studies on which to base conservation and restoration of fern species. ...
Premise of the study:
Conserving endangered plants is a complex task, and practitioners must often use a "triage" approach, addressing only immediate needs. Ecologists can improve this process by conducting sound science upon which to base management. Marsilea villosa is an endangered, endemic Hawaiian fern with seven remaining populations in ephemerally flooding drylands. Among its uncommon traits are long-lived sporocarps, requiring flood and drought to complete its sexual life cycle, and extensive vegetative growth.
Methods:
We conducted a 3-yr ecological field study, measuring percent cover of M. villosa and associated species, flooding depth, and canopy cover, to identify ecological factors with the greatest impact on M. villosa growth.
Key results:
Maximum flooding depth and canopy cover had strong positive relationships with M. villosa growth, and all plots with >50% threshold of either variable reached 100% cover of M. villosa by the end of the study. Interaction effects explained nuances of these relationships, including synergy between the two variables. Percent cover of nonnative functional groups (graminoids and nongraminoids) each had negative relationships with M. villosa growth, but interactions showed that nongraminoid cover was driven by particular species, and that time since flooding had greater influence on M. villosa growth than graminoid cover.
Conclusions:
We recommend planting reintroduced populations in flood-prone areas with moderate shade, experimental outplanting of native plants with M. villosa, and management of graminoids as a functional group, while nongraminoid management should be species-specific. These practices will promote self-sustaining populations and reduce the need for labor-intensive management.
... We conclude that broadcast seeding in combination with pre-sowing seed treatments can contribute to lowland forest restoration in heavily modified landscapes where avian seed dispersers or seed sources are limited. This may apply to urban forest fragments (Sullivan et al. 2009; MacKay et al. 2011) or forests in agricultural landscapes suffering reduced native bird occupancy and insufficient regeneration of canopy species (Burns et al. 2011). However, we emphasize the importance of controlling non-native mammalian seed predators alongside revegetation efforts to successfully restore native forest habitat. ...
Forest restoration in urban areas often occurs in isola-tion from remnant forest, limiting the chances for recol-onization by native species. Plants with bird-dispersed seeds can be particularly vulnerable to dispersal limitation and regeneration can be further impeded by non-native seed predators. We used a factorial experiment to inves-tigate broadcast seeding as a method to reintroduce trees with large seeds and fleshy fruits into early successional forests. We assessed rates of seed and fruit loss, germina-tion and seedling establishment in three seed treatments: (1) caging to exclude introduced mammalian seed preda-tors; (2) removal of fleshy fruit pericarp; and (3) placing seeds in nutritionally enriched clay balls. Across all species (Beilschmiedia tawa, Elaeocarpus dentatus, and Litsea cali-caris) seeds and fruits accessible to mammalian predators suffered significantly greater loss (58%) than those pro-tected by cages (4%). However, seed and fruit loss in the presence of predators was reduced to only 35% across all species by the treatment combining the removal of fruit flesh and clay ball application to seeds. Establishment of B. tawa seedlings after 1 year was significantly enhanced by the clay ball treatment (12% of seeds sown vs. 6% with-out clay balls). Very low establishment rates were recorded for E. dentatus and L. calicaris. Broadcast seeding was found to be a viable method of improving regeneration of large-seeded late successional trees and may be a cost-effective alternative to planting saplings. Seedling estab-lishment can be improved with fruit flesh removal and clay ball treatments, especially in the presence of mammalian seed predators.
... This paper describes part of a wider study of the interactive effects of routine management (stock fencing and pest control) on key ecological processes on pastoral land around rural Waikato, New Zealand. Elsewhere we have described the vegetation (Burns et al. 2010) and abundance of invertebrates (Didham et al. 2009) in 53 forest fragments managed under different combinations of strategies (Dodd et al. 2011), and the abundance of ship rats in eight (Innes et al. 2010b). ...
Reinvasions provide prime examples of source-sink population dynamics, and are a major reason for failure of eradications
of invasive rats from protected areas. Yet little is known about the origins and population structure of the replacement population
compared with the original one. We eradicated eight populations of ship rats from separate podocarp-broadleaved forest fragments
surrounded by open grassland (averaging 5.3ha, scattered across 20,000ha) in rural landscapes of Waikato, New Zealand, and
monitored the- re-establishment of new populations. Rats were kill-trapped to extinction during January to April 2008, and
then again after reinvasion in April–May (total n=517). Rats carrying Rhodamine B dye (n=94), available only in baits
placed 1–2months in advance in adjacent source areas located 170–380m (average 228m edge to edge) away, appeared in 7 of
the 8 fragments from the first day of the first eradication. The distribution of age groups, genders and proportions of reproductively
mature adults (more immature juvenile males and fewer fully mature old females) was different among marked rats compared with
all other rats (P=0.001, n=509); in all rats caught on days 7+ of the first eradication compared with on days 1–6 (P=0.000); and in the total sample collected in fragments by trapping to and after local extinction compared with in brief,
fixed-schedule sampling of populations in continuous forests (P=0.000). Genotyping of 493 carcases found no significant population-level differentiation among the 8 fragments, confirming
that the rats in all fragments belonged to a single dynamic metapopulation. Marked rats of both genders travelled up to 600m
in a few days. Conservation of forest fragments is compromised by the problem that ship rats cannot be prevented from rapidly
reinvading any cleared area after eradication.
KeywordsInvasive predators–Reinvasion–Roof rat–Black rat–Forest fragment–Genetic differentiation–Eradication units
... The system dynamics model indicated that a number of key ecosystem variables would provide information on dynamic responses to perturbation release, particularly with respect to plant regeneration, plant canopy cover, palatable plant biomass, litter mass, litter decomposition rate, invertebrate density, soil fertility and bird populations. The semi-quantitative data derived from the empirical data in the forest fragment resilience study (Didham et al. 2009;Burns et al. in press), with quantitative approximations, are shown in Table 1. ...
A number of factors have combined to diminish ecosystem integrity in New Zealand indigenous lowland forest fragments surrounded by intensively grazed pasture. Livestock grazing, mammalian pests, adventive weeds and altered nutrient input regimes are important drivers compounding the changes in fragment structure and function due to historical deforestation and fragmentation. We used qualitative systems modelling and empirical data from Beilschmiedia tawa dominated lowland forest fragments in the Waikato Region to explore the relevance of two common resilience paradigms – engineering resilience and ecological resilience – for addressing the conservation management of forest fragments into the future. Grazing by livestock and foraging/predation by introduced mammalian pests both have direct detrimental impacts on key structural and functional attributes of forest fragments. Release from these perturbations through fencing and pest control leads to partial or full recovery of some key indicators (i.e. increased indigenous plant regeneration and cover, increased invertebrate populations and litter mass, decreased soil fertility and increased nesting success) relative to levels seen in larger forest systems over a range of timescales. These changes indicate that forest fragments do show resilience consistent with adopting an engineering resilience paradigm for conservation management, in the landscape context studied. The relevance of the ecological resilience paradigm in these ecosystems is obscured by limited data. We characterise forest fragment dynamics in terms of changes in indigenous species occupancy and functional dominance, and present a conceptual model for the management of forest fragment ecosystems.
The incorporation of native, woody vegetation into New Zealand’s agricultural ecosystems offers a “nature-based solution” approach for mitigating poor environmental outcomes of land use practices, biodiversity loss, and the accelerating effects of climatic change. However, to achieve this at scale requires a systematic framework for scoping, assessing, and targeting native revegetation opportunities in a way that addresses national-scale priorities, supports landscape-scale ecological processes, and recognises that land use decisions
are made at farm-scales by landowners. In this forum discussion, we outline the requirements for a spatial decision support system for native revegetation; we provide illustrations of national-, landscape-, and farm-scale components of this framework and outline a range of organisational, societal, and scientific challenges that must be addressed to enable effective and targeted revegetation across the country. Our primary motivation is to provide a focus for discussions among scientists, policy makers, hapū, iwi, landowners, communities, and other interested parties who are invested in restoring biodiverse and resilient agroecosystems.
Invasive exotic tree and shrub species (woody weeds) form dense, monospecific stands in many areas of New Zealand. At some sites, the weed dies out naturally and is replaced by native species as succession proceeds, but at others the weed persists indefinitely. The ability to distinguish between these different trajectories is critical to effective weed management, but the conditions that determine successional outcomes remain poorly understood. However, clues to the successional trajectory at any given woody weed site can be found in the understory, because understory plants represent the potential future plant community (in the absence of disturbance). Of key relevance is whether the woody weed species is regenerating under its own canopy, because this enables it to replace individuals as they die, and thus persist as succession proceeds. Conversely, if the understory is comprised entirely of native species, there is potential for the natives to take over the community as the weed dies out. This process is often termed "passive restoration", because native vegetation is restored without any active management other than (in some cases) the removal of environmental stressors or degrading processes. The likelihood of a native understory developing is affected by site-specific traits such as the natural (historical) vegetation type, proximity to native seed sources, climate, stand age and the presence of herbivores. We present a framework to help land managers use their observations of understory vegetation to assess likely successional trajectories in woody weed stands.
Data on 15 reserve characteristics were derived from surveys of 234 reserves. The most important characteristics influencing the number of problem weeds in reserves are proximity to towns, distance from roads and railway lines, human use, reserve shape, and habitat diversity. Reserves with the most weeds are narrow remnants on fertile soils with clearings and a history of modification, and those close to towns or sites of high human activity. -from Authors
Vegetation was sampled in kahikatea (Dacrycarpus dacrydioides)-dominant forest fragments having different recovery periods since grazing ceased in the Waikato region, North Island, New Zealand. Changes in vegetation were modeled against recovery periods ranging from 0-74 y and in relation to position within fragment (edge or interior). Indigenous plant species richness increased and adventive plant species (mostly pasture herbs) richness declined with increasing recovery period; small tree and sapling density and seedling ground cover increased. Fragment edges had higher adventive species richness, lower basal area, more established seedlings, lower litter cover and higher grass ground cover, than interior plots. Some indigenous species (e.g. Laurelia novaezealandiae and Myrsine australis) increased with recovery period while some adventive species (e.g. Solanum pseudocapsicum) declined. The relative basal area of Alectryon excelsus increased significantly with recovery period at edges, and that of Melicytus ramiflorus everywhere. Twenty years represents a turning point in the recovery period, with the end of the loss phase of adventive pasture species, the start of the re-establishment phase of indigenous ground layer and understorey species, and significant recovery of population structures of major species. In relatively non-weedy rural environments, retirement from grazing may be sufficient to ensure a return to near-natural states in 40-50 y.
Despite the importance of forest edges in ecology, only one study has previously been carried out in New Zealand on the modification of climate across forest edges. We measured light exposure, wind speed, air and soil temperature, and vapour pressure deficit (VPD) perpendicular to a north-south aligned, mature, edge of native broadleaf rainforest adjoining grazed pasture. At a point 80 m into the forest from the edge, light was only c. 0.7% and wind speed c. 20% of that in the open, and there was much less diurnal fluctuation in soil temperature, air temperature and VPD. The gradient of microclimate near the edge, as measured with a third (mobile) weather station, was abrupt for soil temperature and similar to the pattern of light exposure, with almost complete change over about 10 m. The gradient was less steep for wind speed, air temperature and VPD, with at least 40 m being required to stabilise these variables when wind was directed into the forest. These findings suggest that forest buffers of at least 40 m may be needed to protect forest reserves and streams from climatic exposure.
Small isolated patches of native forest surrounded by extensive pastoral grasslands, characteristic of many New Zealand rural landscapes, represent an important reservoir of lowland biodiversity. Improved management of them is a major focus of biodiversity conservation initiatives in New Zealand. We quantified the long-term impacts of grazing on indigenous forest remnants in hill country at Whatawhata, western Waikato, North Island. Structure and composition were compared between forest fragments grazed for >50 years and nearby ungrazed continuous forest. Grazed fragments had shorter and less shady canopies, sparser understoreys, tree populations with larger mean diameters, and ground layers with lower cover of litter and higher cover of vegetation and bare soil than continuous forest. Fragments also had lower indigenous-plant species richness, especially in sapling and seedling populations, and almost no palatable indigenous shrubs, terrestrial orchids, and ferns that require high humidity (e.g. Hymenophyllum spp.), but contained many indigenous and adventive herbaceous species. A transition appears to be occurring in grazed fragments from tall, long-lived trees like Beilschmiedia tawa and Dysoxylum spectabile to short and shorter-lived trees like Kunzea ericoides, Melicytus ramiflorus, and Dicksonia squarrosa. Because grazing inhibits most regeneration processes, unfenced remnants of conifer-broadleaved forest are unlikely to be maintained in grazed pasture in the long term.
Forest dwelling browsing mammals, notably feral goats and deer, have been introduced to New Zealand over the past 220 years; prior to this such mammals were absent from New Zealand. The New Zealand forested landscape, therefore, presents an almost unique opportunity to determine the impacts of introduction of an entire functional group of alien animals to a habitat from which that group was previously absent. We sampled 30 long-term fenced exclosure plots in indigenous forests throughout New Zealand to evaluate community- and ecosystem-level impacts of introduced browsing mammals, emphasizing the decomposer subsystem. Browsing mammals often significantly altered plant community composition, reducing palatable broad-leaved species and promoting other less palatable types. Vegetation density in the browse layer was also usually reduced. Although there were some small but statistically significant effects of browsing on some measures of soil quality across the 30 locations, there were no consistent effects on components of the soil microfood web (comprising microflora and nematodes, and spanning three consumer trophic levels); while there were clear multitrophic effects of browsing on this food web for several locations, comparable numbers of locations showed stimulation and inhibition of biomasses or populations of food web components. In contrast, all microarthropod and macrofaunal groups were consistently adversely affected by browsing, irrespective of trophic position. Across the 30 locations, the magnitude of response of the dominant soil biotic groups to browsing mammals (and hence their resistance to browsers) was not correlated with the magnitude of vegetation response to browsing but was often strongly related to a range of other variables, including macroclimatic, soil nutrient, and tree stand properties. There were often strong significant effects of browsing mammals on species composition of the plant community, species composition of leaf litter in the litter layer, and composition of various litter-dwelling faunal groups. Across the 30 locations, the magnitude of browsing mammal effects on faunal community composition was often correlated with browser effects on litter layer leaf species composition but never with browser effects on plant community composition. Browsing mammals usually reduced browse layer plant diversity and often also altered habitat diversity in the litter layer and diversity of various soil faunal groups. Across the 30 locations, the magnitude of browser effects on diversity of only one faunal group, humus-dwelling nematodes, was correlated with browser effects on plant diversity. However, browser effects on diversity of diplopods and gastropods were correlated with browser effects on habitat diversity of the litter layer. Reasons for the lack of unidirectional relationships across locations between effects of browsers on vegetation community attributes and on soil invertebrate community attributes are discussed. Browsing mammals generally did not have strong effects on C mineralization but did significantly influence soil C and N storage on an areal basis for several locations. However the direction of these effects was idiosyncratic and presumably reflects different mechanisms by which browsers affect soil processes. While our study did not support hypotheses predicting consistent negative effects of browsing mammals on the decomposer subsystem through promotion of plant species with poorer litter quality, our results still show that the introduction of these mammals to New Zealand has caused far-ranging effects at both the community and ecosystem levels of resolution, with particularly adverse effects for indigenous plant communities and populations of most groups of litter-dwelling mesofauna and macrofauna.
Summary Fencing remnant native vegetation has become a widespread activity for arresting declines in biodiversity in agricultural landscapes. However, few data are available on the effectiveness of this approach. The present study investigated the short-term effects of fencing to exclude livestock on dominant tree and shrub recruitment, plant species cover, litter and soil characteristics in remnant grassy woodlands in southern NSW. Vegetation and soil surveys were undertaken at 47 sites fenced by Greening Australia (NSW) for 2–4 years. Fenced and unfenced areas at each site were compared using split-plot sampling. Woodlands sampled were dominated by Yellow Box/Blakely’s Red Gum (Eucalyptus melliodora/Eucalyptus blakelyi), Grey Box (Eucalyptus microcarpa) or White Cypress-pine (Callitris glaucophylla). Significantly higher numbers of tree recruits were found in the fenced sites, with tree recruitment found in 59% of fenced sites compared with 13% of unfenced sites. Fenced sites also had significantly greater cover of native perennial grasses, less cover of exotic annual species and less soil surface compaction. However, outcomes varied among woodland ecosystems and individual sites. Where tree recruitment occurred, there was significantly more tree recruitment where there was greater perennial grass cover and less regeneration where exotic annual grass cover or overstorey crown cover was dense. Few shrubs recruited in fenced or unfenced areas, reflecting the lack of mature shrubs in most sites. Fencing is an important first step for conserving threatened grassy woodlands, but more active management may be needed to enhance woodland recovery, particularly in sites where few or no recruits were found.
Key words bush regeneration, fencing, grazing exclusion, rehabilitation, woodland restoration.
In many agricultural landscapes, significant biodiversity gains can be made by improving the ecological condition of degraded remnants of semi‐natural habitat. Recent emphasis has been on the level of management intervention required to initiate vegetation recovery in small forest remnants, but no comparable emphasis has been placed on benefits for invertebrate communities. In the Waikato region, New Zealand, we tested the effects of livestock exclusion, mammalian pest control, and their interaction, on leaf‐litter invertebrate communities in 30 forest remnants, using a space‐for‐time substitution approach. A total of 87 376 invertebrates were extracted from 964 leaf‐litter samples. Invertebrate density was an order of magnitude lower in remnants than in nearby large forest reserves. For key taxa, such as Diplopoda, Isopoda, Coleoptera and Mollusca, 10‐ to 100‐fold lower densities were recorded in remnants with no pest control, particularly where livestock were not excluded. By contrast, other taxa such as Thysanoptera and For‐micidae (Hymenoptera) had up to 100‐fold greater densities in remnants with recent stock exclusion and pest control. These changes led to a significant livestock exclusion x pest control interaction effect on the degree of invertebrate community dissimilarity between forest remnants and forest reserves. Using structural equation modelling, we found that treatment effects were largely mediated by a cascading series of indirect causal paths involving altered soil chemistry, vegetation composition, and litter mass relative to large forest reserves, although the livestock exclusion × pest control interaction was inadvertently confounded with differing slopes and areas of remnants in different treatments. Livestock exclusion and mammalian pest control have significant, but contrasting, effects on invertebrates in the first 10–20 years following livestock exclusion from forest remnants, with mammalian pest control having limited benefit for the leaf‐litter invertebrate fauna without livestock exclusion.
Making use of existing fences as ready-made exclosures, this study aimed to assess the long-term effects of cattle grazing on forest margins. Results indicated: 1) that cattle browsing and trampling has an impact on vegetation species composition, structure and regeneration; 2) that the effects of a particular grazing regime may take many decades to dissipate; and 3) that the impacts of cattle change with stock intensity. Some plant species appeared to be highly palatable to cattle and only occurred on sites without cattle. Such species included pate (Schefflera digitata), broadleaf (Griselinia littoralis), pigeonwood (Hedycarya arborea), supplejack (Ripogonum scandens), mahoe (Melicytus ramiflorus), milk tree (Streblus heterophyllus), lancewood (Pseudopanax crassifolius) and hen and chickens fern (Asplenium bulbiferum). A small group of plants appeared to regenerate better under cattle than in their absence, particularly mountain horopito (Pseudowintera colorata) and prickly shield fern (Polystichum vestitum). A few species were encouraged by cattle at one site but suppressed by them at another: kahikatea (Dacrycarpus dacrydioides), wheki (Dicksonia squarrosa), Coprosma rhamnoides and Blechnum fluviatile. The impact of cattle on most other plant species was not discernible. The results of this study, while somewhat equivocal, indicate that future grazing licences in South Westland should restrict stock to low numbers and be confined to already modified sites where damage to conservation values would be
Seedlings were grown under 2 light intensities. Three species from open habitats, Coprosma robusta, Dodonaea viscosa and Crataegus monogyna, had the highest mean relative growth rates in 66% daylight and 16% daylight, but their ranking for other parameters was variable. Acer pseudoplatanus and Plagianthus regius had particularly fast height growth. Carpodetus serratus was the fastest growing species of early successional vegetation on weakly to moderately leached soils, and it grew as well in 16% daylight as in 66% daylight. Many species had significantly faster height growth in 16% daylight, eg Melicytus ramiflorus and Pittosporum tenuifolium, and several species had faster height growth rates overall in 16% daylight, eg Myrsine australis, Melicytus ramiflorus, and Pittosporum eugenioides. Griselinia littoralis, from moderately to strongly leached soils, had the slowest height growth rates in both light levels. All species had lower root:shoot ratios and a greater proportion of dry weight in leaves in 16% daylight. Such responses may contribute to the slow establishment of these species in secondary vegetation experiencing summer drought in the seedlings' rooting zone. -from Authors
The second-generation anticoagulant brodifacoum is currently used for possum and rodent control on the New Zealand mainland, and for rodent eradication on offshore islands. To investigate whether these uses have produced undesirable effects in localised wild rat populations (anticoagulant resistance) or in birds (effects on blood coagulation times), blood clotting response tests utilising small-volume sampling were established using albino laboratory rats ( Rattus norvegicus, Wistar) and domestic chickens ( Gallus domesticus ). These tests were then used on blood samples taken from wild rats ( R. norvegicus ) and kiwi ( Apteryx australis mantelli ). During the development of the blood-clotting test in laboratory rats we observed a reduced anticoagulant response after a second dose of 0.1 mg/kg of brodifacoum, compared with the initial exposure. There was no evidence of anticoagulant resistance in rats from areas where there was a history of 2.5 years. use of brodifacoum. Statistical differences were found in the clotting times of kiwi from areas with a history of anticoagulant use and those from areas where brodifacoum has not been used, but the clotting times were the opposite of what would be expected if they were interpreted on the basis of exposure history alone. These results highlight uncertainties regarding resistance, sub-lethal effects, threshold concentrations in the liver and the toxicodynamics of anticoagulants in mammals and birds.
ABSTRACT: In many agricultural landscapes, significant biodiversity gains can be made by improving the ecological condition of degraded remnants of semi‐natural habitat. Recent emphasis has been on the level of management intervention required to initiate vegetation recovery in small forest remnants, but no comparable emphasis has been placed on benefits for invertebrate communities. In the Waikato region, New Zealand, we tested the effects of livestock exclusion, mammalian pest control, and their interaction, on leaf‐litter invertebrate communities in 30 forest remnants, using a space‐for‐time substitution approach. A total of 87 376 invertebrates were extracted from 964 leaf‐litter samples. Invertebrate density was an order of magnitude lower in remnants than in nearby large forest reserves. For key taxa, such as Diplopoda, Isopoda, Coleoptera and Mollusca, 10‐ to 100‐fold lower densities were recorded in remnants with no pest control, particularly where livestock were not excluded. By contrast, other taxa such as Thysanoptera and For‐micidae (Hymenoptera) had up to 100‐fold greater densities in remnants with recent stock exclusion and pest control. These changes led to a significant livestock exclusion x pest control interaction effect on the degree of invertebrate community dissimilarity between forest remnants and forest reserves. Using structural equation modelling, we found that treatment effects were largely mediated by a cascading series of indirect causal paths involving altered soil chemistry, vegetation composition, and litter mass relative to large forest reserves, although the livestock exclusion × pest control interaction was inadvertently confounded with differing slopes and areas of remnants in different treatments. Livestock exclusion and mammalian pest control have significant, but contrasting, effects on invertebrates in the first 10–20 years following livestock exclusion from forest remnants, with mammalian pest control having limited benefit for the leaf‐litter invertebrate fauna without livestock exclusion.
HABITAT destruction is the major cause of species extinctions13. Dominant species often are considered to be free of this threat because they are abundant in the undisturbed fragments that remain after destruction. Here we describe a model that explains multispecies coexistence in patchy habitats4 and which predicts that their abundance may be fleeting. Even moderate habitat destruction is predicted to cause time-delayed but deterministic extinction of the dominant competitor in remnant patches. Further species are predicted to become extinct, in order from the best to the poorest competitors, as habitat destruction increases. More-over, the more fragmented a habitat already is, the greater is the number of extinctions caused by added destruction. Because such extinctions occur generations after fragmentation, they represent a debta future ecological cost of current habitat destruction.
Introduced rodents and possums in New Zealand eat flowers, fruits, seeds and seedlings, but little is known about their impact on forest regeneration. We investigated seedling establishment in exclosures with mesh of two different sizes to exclude (1) possums and (2) possums and rats, at two mainland forest sites (beech– podocarp–broadleaved and second-growth broadleaved–podocarp) near Dunedin. We recorded all new woody seedlings that established over the next 2 years. The number of seedlings with true leaves differed significantly between treatments after 1.5 years at both sites and after 2 years in beech–podocarp–broadleaved forest. This effect was broadly consistent across all species including pepper tree (Pseudowintera colorata), whose adult foliage is unpalatable to possums. Cotyledonous seedlings were relatively ephemeral, but differed significantly in abundance between treatments in second-growth broadleaved–podocarp forest after 1.5 and 2 years. In second-growth broadleaved–podocarp forest, possums were present throughout the study but rats were rare. Numbers of seedlings did not differ significantly between exclosures with different mesh sizes which admitted or excluded rats. In beech–podocarp–broadleaved forest, rats were present periodically throughout the study, but possums may have been scarce during the final 7 months as a result of pest control. At this location, 80 seedlings with true leaves occurred in exclosures that excluded possums and rats, 3.6 times as many as on control plots and 2.1 times as many as in exclosures that deterred only possums. The consequences of these pest impacts on seedling recruitment for forest regeneration must be confirmed in longer-term studies. Exclosures can be effectively used to experimentally separate the impacts of different herbivores on seedling establishment.
Research on fragmented ecosystems has focused mostly on the biogeograpbic consequences of the creation of habitat “islands” of different sizes and has provided little of practical value to managers. However, ecosystem fragmentation causes large changes in the physical environment as well as biogeograpbic changes. Fragmentation generally results in a landscape that consists of remnant areas of native vegetation surrounded by a matrix of agricultural or other developed land. As a result fluxes of radiation, momentum (La, wind), water, and nutrients across the landscape are altered significantly. These in turn can have important influences on biota within remnant areas, especially at or near the edge between the remnant and the surrounding matrix. The isolation of remnant areas by clearing also has important consequences for the biota. These consequences vary with the time since isolation distance from other remnants, and degree of connectivity with other remnants. The influences of physical and biogeographic changes are modified by the size, shape, and position in the landscape of individual remnant, with larger remnants being less adversely affected by the fragmentation process. The Dynamics of remnant areas are predominantly driven by factors arising in the surrounding landscape. Management of, and research on, fragmented ecosystems should be directed at understanding and controlling these external influences as much as at the biota of the remnants themselves. There is a strong need to develop an integrated approach to landscape management that places conservation reserves in the context of the overall landscape
Although forest edges have been studied extensively as an important consequence of fragmentation, a unifying theory of edge influence has yet to be developed. Our objective was to take steps toward the development of such a theory by (1) synthesizing the current knowledge of patterns of forest structure and composition at anthropogenically created forest edges, (2) developing hypotheses about the magnitude and distance of edge influence that consider the ecological processes influencing these patterns, and (3) identifying needs for future research. We compiled data from 44 published studies on edge influence on forest structure and composition in boreal, temperate, and tropical forests. Abiotic and biotic gradients near created forest edges generate a set of primary responses to edge creation. Indirect effects from these primary responses and the original edge gradient perpetuate edge influence, leading to secondary responses. Further changes in vegetation affect the edge environment, resulting in ongoing edge dynamics. We suggest that the magnitude and distance of edge influence are a direct function of the contrast in structure and composition between adjacent communities on either side of the edge. Local factors such as climate, edge characteristics, stand attributes, and biotic factors affect patch contrast. Regional factors define the context within which to assess the ecological significance of edge influence (the degree to which the edge habitat differs from interior forest habitat). Our hypotheses will help predict edge influence on structure and composition in forested ecosystems, an important consideration for conservation. For future research on forest edges in fragmented landscapes, we encourage the testing of our hypotheses, the use of standardized methodology, complete descriptions of study sites, studies on other types of edges, synthesis of edge influence on different components of the ecosystem, and investigations of edges in a landscape context.
Fencing incentive programmes have been widely used throughout Australia to assist landholders to fence remnant woodland vegetation, to control grazing and improve native vegetation condition. This study investigated vegetation and soil condition in remnant woodlands fenced for 7–9 years in the Murray catchment area in southern New South Wales. Surveys were undertaken at 42 sites, where vegetation condition was assessed in paired fenced and unfenced sites. Semi‐structured interviews were also conducted with landholders to gather management information. Woodlands surveyed were Yellow Box/Blakely's Red Gum ( Eucalyptus melliodora/E. blakelyi , 15 sites), Grey Box ( E. microcarpa , 13 sites) and White Cypress Pine ( Callitris glaucophylla, 14 sites).
Fencing resulted in a range of responses which were highly variable between sites and vegetation types. In general, fenced sites had greater tree regeneration, cover of native perennial grasses, less cover of exotic annual grasses and weeds, and less soil compaction than unfenced sites. However, there was greater tree recruitment in remnants to the west of the study area, and tree recruitment was positively correlated with time since fencing. Within sites, tree recruitment tended to occur in more open areas with a good cover of native perennial grasses, as compared to sites with a dense tree canopy, or dominated by exotic annuals grasses or weeds. Forty‐eight per cent of fenced sites had no tree regeneration. There was a significant decline in native perennial grasses, and increase of several unpalatable weeds in many fenced areas, suggesting certain ecological barriers may be preventing further recovery. However, drought conditions and associated grazing are the most likely cause of this trend. A range of grazing strategies was implemented in fenced sites which require further research as a conservation management tool. Continued long‐term monitoring is essential to detect key threats to endangered woodland remnants.
Historically, New Zealand was dominated by forest below the alpine treeline, but about 1000 years of Polynesian and European colonisation has resulted in the destruction of nearly three-quarters of the indigenous forest cover. In this study, the historical patterns of deforestation and forest fragmentation were assessed in relation to major topographical, climatic and anthropogenic variables that may drive forest loss. Deforestation has occurred almost equally on the two main islands, the North and South Islands, although the remaining indigenous forest is more fragmented in the North Island. Most deforestation has occurred in regions with a high-density of road networks, although gradients in climatic water availability and soil fertility also had weak effects. Deforestation rates over the period 1997–2002 were very low (nationwide deforestation rate of just −0.01% p.a.), but varied widely among political districts. Expansion of plantation forestry was the single most important driver of recent deforestation. Only 10 of 73 political districts are afforded long-term protection of native forest cover (having more than 30% forest cover that is managed by the Department of Conservation). Forest cover in the majority of New Zealand landscapes has been reduced below the level of an expected ‘extinction threshold’ (circa 30% native habitat cover) in 55 political districts, and long-term trajectories predict that ongoing deforestation threatens to force another five districts below the critical threshold within the next 45 years. Except for the most heavily deforested regions, relatively modest annual rates of habitat restoration could bring forest cover back above the extinction threshold by the year 2050.
In the early 1980s, a strategy for graphical representation of multivariate (multi-species) abundance data was introduced into marine ecology by, among others, Field, et al. (1982). A decade on, it is instructive to: (i) identify which elements of this often-quoted strategy have proved most useful in practical assessment of community change resulting from pollution impact; and (ii) ask to what extent evolution of techniques in the intervening years has added self-consistency and comprehensiveness to the approach. The pivotal concept has proved to be that of a biologically-relevant definition of similarity of two samples, and its utilization mainly in simple rank form, for example ‘sample A is more similar to sample B than it is to sample C’. Statistical assumptions about the data are thus minimized and the resulting non-parametric techniques will be of very general applicability. From such a starting point, a unified framework needs to encompass: (i) the display of community patterns through clustering and ordination of samples; (ii) identification of species principally responsible for determining sample groupings; (iii) statistical tests for differences in space and time (multivariate analogues of analysis of variance, based on rank similarities); and (iv) the linking of community differences to patterns in the physical and chemical environment (the latter also dictated by rank similarities between samples). Techniques are described that bring such a framework into place, and areas in which problems remain are identified. Accumulated practical experience with these methods is discussed, in particular applications to marine benthos, and it is concluded that they have much to offer practitioners of environmental impact studies on communities.
We evaluated the importance of small (<5 ha) forest patches for the conservation of regional plant diversity in the tropical rainforest of Los Tuxtlas, Mexico. We analyzed the density of plant species (number of species per 0.1 ha) in 45 forest patches of different sizes (1-700 ha) in 3 landscapes with different deforestation levels (4, 11, and 24% forest cover). Most of the 364 species sampled (360 species, 99%) were native to the region, and only 4 (1%) were human-introduced species. Species density in the smallest patches was high and variable; the highest (84 species) and lowest (23 species) number of species were recorded in patches of up to 1.8 ha. Despite the small size of these patches, they contained diverse communities of native plants, including endangered and economically important species. The relationship between species density and area was significantly different among the landscapes, with a significant positive slope only in the landscape with the highest deforestation level. This indicates that species density in a patch of a given size may vary among landscapes that have different deforestation levels. Therefore, the conservation value of a patch depends on the total forest cover remaining in the landscape. Our findings revealed, however, that a great portion of regional plant diversity was located in very small forest patches (<5 ha), most of the species were restricted to only a few patches (41% of the species sampled were distributed in only 1-2 patches, and almost 70% were distributed in 5 patches) and each landscape conserved a unique plant assemblage. The conservation and restoration of small patches is therefore necessary to effectively preserve the plant diversity of this strongly deforested and unique Neotropical region.
Despite continued forest conversion and degradation, forest cover is increasing in countries across the globe. New forests
are regenerating on former agricultural land, and forest plantations are being established for commercial and restoration
purposes. Plantations and restored forests can improve ecosystem services and enhance biodiversity conservation, but will
not match the composition and structure of the original forest cover. Approaches to restoring forest ecosystems depend strongly
on levels of forest and soil degradation, residual vegetation, and desired restoration outcomes. Opportunities abound to combine
ambitious forest restoration and regeneration goals with sustainable rural livelihoods and community participation. New forests
will require adaptive management as dynamic, resilient systems that can withstand stresses of climate change, habitat fragmentation,
and other anthropogenic effects.
The diet of Trichosurus vulpecula in mixed hardwood forests, described from analysis of plant cuticle fragments and seeds in their faeces, included forest and pasture foliage, buds, and fruits of >100 species, although most were eaten infrequently. Foliage was taken most often from woody forest species (88%), with 3 canopy species, kamahi Weinmannia racemosa, southern rata Metrosideros umbellata and mahoe Melicytus ramiflorus, providing 69% of the leaf intake. Pasture species formed 12% of the diet of possums living within 300 m of the forest edge, with 90% of this being clovers Trifolium and grasses. Fruit was taken from a wide range of forest species. Males ate more pasture foliage and less ferns than females and differed significantly in their use of many of the major woody species. Woody species were favoured most in winter and spring, ferns and fruits in autumn and winter, and pasture species in autumn. Pasture species were eaten only by possums denning within 1000 m of the forest/pasture margin, and high-altitude species by possums denning nearby. Only 15 forest species (10 frequently) were eaten as much as or more than expected from their relative abundance. Preferred species showed clear evidence of possum browse and were often represented by many dead stems, demonstrating the adverse effects of possums in such mixed hardwood forests. -from Authors Trichosurus vulpecula rata Metrosideros umbellata kamahi Weinmannia racemosa mahoe Melicytus ramiflorus
Regeneration in gaps and under closed high canopy, representing the gap and mature phases of the forest growth cycle, was investigated in 2 small areas within forest dominated by Beilschmiedia tawa. Significant differences in regeneration occurred between phases, and within phases diameter distributions varied among species. Results suggest differing replacement strategies among species, largely reflecting differences in shade-tolerance. Of the 4 major regenerating species, shade-tolerant tawa and Dysoxylum spectabile commonly develop to advanced stages beneath closed canopies; relatively intolerant Litsea calicaris and Knightia excelsa seldom do, apparently requiring gap formation for development to maturity. In the area where tawa and Dysoxylum were co-dominant in the canopy, they tended to replace each other, thus maintaining their co-dominance. In forests where the gap phase is important, replacement trends may best be gauged from gap regeneration alone. Of the indices of species' relative importance tested, 4 juveniles of largest diameter appeared to most appropriate predictor of future canopy occupation in gaps.-from Authors
Habitat fragmentation is a major cause of biodiversity erosion in tropical forests. The Brazilian Atlantic forest has both high species richness and a long history of anthropogenic disturbance, beginning with colonial agriculture in the sixteenth century. Here we examine the species composition and guild structure of woody plants within five montane Atlantic forest fragments of the Tiet River basin, State of São Paulo, southeastern Brazil, ranging from 5 to 7900 ha in area. We found a negative relationship between fragment size and the relative importance of tree and shrub species that (1) depend on abiotic modes of seed dispersal, (2) are shade-intolerant, and (3) occupy the forest canopy. As fragment size decreased, there was a marked rise in the relative importance of ruderal species, primarily in the Compositae, Euphorbiaceae, Solanaceae, and Leguminosae. There also was a 9% average decline in smaller fragments in relative importance of Myrtaceae, Lauraceae, Sapotaceae, and Rubiaceae, which are the main sources of fleshy fruits for vertebrate frugivores in these forests. Our results suggest that predictable shifts in plant guild structure occur as tropical forest fragments are reduced in size, and that small fragments may become dominated by edges and the surrounding habitat matrix. We suggest that small forest fragments will be unlikely to preserve intact plant and animal assemblages of Brazil's Atlantic coastal forest
Beilschmiedia tawa (Lauraceae) is a common canopy tree which is often dominant in lowland forests in the North Island and northern South Island of New Zealand. The sustainability of B. tawa-dominated forests was investigated at Pureora Forest Park, west of Lake Taupo, central North Island, where a range of sites with different extents of disturbance by logging was studied. Demographic studies-estimates of seedfall, recruitment, growth, and mortality rates-yielded data for life history tables. Based on these, Leslie matrix models were used to determine the rate of increase of five populations. Of these, three logged populations were apparently declining, whereas unlogged forest showed moderate population increase. These population studies suggested that B. tawa is a K-selected species capable of regeneration only within forest. The smaller size-classes are shade tolerant and stems accumulate in the stripling size-class. High light conditions are needed for growth from this class to the sapling class.
Clematis vitalba, Lonicera japonica, and Passiflora mollissima are three introduced vine species which have become naturalised in New Zealand. Their light requirements and growth rates were compared with those of two common native vine species (Muehlenbeckia australis and Parsonsia heterophylla) by growing plants under irradiance levels corresponding to 40%, 7%, 3.5%, and 2% of available sunlight (expressed as relative irradiance (% RI)). Weedy vines are characterised by a high degree of shade tolerance and a rapid growth rate in high-light environments. Clematis vitalba and Lonicera japonica have their light compensation points at 1.0% RI and 0.9% RI, respectively, and both species show high maximum growth rates. The native vine Parsonsia heterophylla has the lowest light compensation point (
Fragmentation of natural vegetation is one of the most pervasive changes in terrestrial ecosystems across the Earth. Developing a general understanding of how fragmentation affects plant and animal populations is essential to meet the pressing need for guidelines for the management of fragmented systems. Nevertheless, this general understanding has to take account of differences in ecosystem types and different biogeographic, evolutionary and ecological backgrounds against which fragmentation impacts are played out in different parts of the world. Here, we examine fragmentation impacts on plant populations by considering the processes underlying fragmentation. We suggest that it is critical to focus on the key processes that are important in particular situations, rather than assuming that the same factors are likely to be important everywhere. In other words, there are inevitable limits to generalisation because of the idiosyncratic nature of the geography, history and biota of different regions. Studies on the effects of fragmentation on plant populations have focused on a limited subset of plant types and have concentrated heavily on reproductive output rather than actual regeneration success. These studies have indicated a clear impact of fragmentation on fecundity, but there is no clear signal in terms of the actual importance of this in relation to population viability. Other factors including local habitat conditions, disturbance and competition from weeds may be just as important as the classical biogeographical impacts of fragmentation. Generalisations based on a clear assessment of key life-history processes may be valuable tools in developing management responses to ecosystem fragmentation, but this requires considerably more emphasis on factors affecting successful recruitment as well as factors affecting fecundity.
Aim
The impact of fragmentation on a eucalypt forest was investigated by examining the effects of fragment size, time since fragmentation, degree of anthropogenic disturbance to fragment interiors, and time since fire, on native and exotic plant species richness per unit area.
Location
Two areas of dry open‐forest were studied on the central coast of New South Wales in south‐eastern Australia. Fifty forest fragments were located at Tomago, an area progressively fragmented over the last 60 years, most recently by clearing for sand‐mining. Also at Tomago were six very large blocks of forest that were used as reference sites. The second area at Myall Lakes National Park (50 km north of Tomago) had four very large areas of intact forest that were also used as reference sites.
Methods
Fragments were allocated into (1) three size classes: small (<1 ha), medium (1 to <10 ha) and large (10 to <100 ha); (2) two classes of age since fragmentation: young (up to 10 years) and old (10 years or more); (3) two classes of disturbance (minor, major) based on the degree and extent of human‐induced disturbance to the fragment interior; and (4) two classes of time since fire (between 5 and 6 years; 10 years or more). Reference sites belonged to a very large size class (>100 ha). Mean plant species richness per 25 m ² area was determined for each fragment and analysed separately for native and exotic species.
Results
The most significant effects observed resulted from anthropogenic disturbance. In fragments with major disturbance, native species richness per unit area was significantly reduced in small‐sized young and medium‐sized old fragments. A significant increase was also observed for exotic species richness in fragments with major disturbance. With minor disturbance, native species richness in small fragments declined significantly with time since fragmentation, in contrast to medium and large fragments. Among recently created fragments, those recently burned had significantly more native species per unit area than those burned 10 or more years ago.
Main conclusions
Anthropogenic disturbance coupled with fragmentation had a stronger and more immediate effect in reducing native species richness and increasing exotic species richness than did fragmentation alone. In the absence of major disturbance, small fragments had fewer native species than larger size classes, but only after 10 or more years since fragmentation, confirming the importance of controlling for age of fragments when examining species–area relationships. This study has not tested whether differences in area were the direct cause of this loss of species over time; other factors that are correlated with area (such as edge effects) may also be involved. The increase in native species richness following fire was consistent with other studies of fire in unfragmented eucalypt forest. This study thus shows that in addition to the factors emphasized in classical island biogeography models, fragment age, disturbance and fire history are important in explaining species richness in fragmented eucalypt forests.
Population trends of colonising brushtail possums Trichosurus vulpecula were monitored between 1981 and 1993 at Waipoua Forest in Northland, New Zealand. Canopy defoliation and possum-related damage to eight plant indicator species were assessed annually for four years after an aerial poison operation in 1990, to determine whether the operation had reduced possum numbers and halted possum-related damage to the vegetation. Trap catch estimates of possum density increased by over 70% during the 1980s. The poison operation killed 87% of possums, and ongoing leg-hold trapping (1991–1993) maintained population levels at 7–9% trap catch. Reduction of the possum population did not produce a significant positive short-term vegetation response, but did halt the continuing downward trend in vegetation condition evident in nearby forested areas where possum densities were not reduced. Other measures of possum impact (browsed foliage, stem damage) improved significantly within a year of the poison operation, and may prove more sensitive short-term indicators of reduced possum-related damage. The apparent ability of residual possum populations to retard vegetation recovery has important implications for forest health strategies based on intermittent poison operations. While a large initial population reduction is required to halt vegetation decline, an ability to maintain residual possum populations at very low levels appears necessary for significant vegetation recovery. Targetting the increased resources now available for reducing possum populations to fewer areas of higher conservation value may well return greater ecological dividends than attempts to sustain long-term reduction of possum populations over large areas of more modified indigenous forest
It is in the nature of today's world that interventionist, rather than protectionist, management strategies are likely to be in greater demand, because an enormous area of the earth's habitable surface has already been transformed by human action. [Holdgate, M.W., 1986. Summary and conclusions: characteristics and consequences of biological invasions. In: Kornberg, H., Williamson, M.H. (Eds), Quantitative aspects of the ecology of biological invasions. The Royal Society, London, pp. 733–742]Progress with ecological restoration in New Zealand is reviewed. A useful goal for restoration is that of rebuilding, as far as possible, the evolutionary and ecological context of species in the system, i.e. reinstating earlier selection regimes. Opportunities for restoring biological components of these regimes are greater than those available for restoring physical conditions. In this country, effective ecological restoration is not possible without control or eradication of introduced mammals. Descriptive models of systems to be restored are also a necessity for achieving goals. A particular problem is that caused by past extinctions of animal species. Replacement of some extinct species, within particular trophic guilds, with ecologically appropriate and related extant species, is suggested as a possible response to this problem.
Morphological and anatomical descriptions of Beilschmiedia tawa are given together with information relevant to its ecology, a distribution map based on its presence or absence in grid squares, and bibliographic references to other informaion. B. tawa is one of the main canopy-forming trees in the lowland and low hill forests of the North Island and is also one of the main merchantable hardwoods. It has a good capacity to regenerate in shade or small canopy gaps, but is sensitive to exposure, tending to deteriorate in intensively logged forests.
Summary Tawa (Beilschmiedia tawa)-dominated forest fragments on farms within the Rotorua Basin were surveyed to quantify the likely recovery processes following exclusion of domestic livestock grazing, using a space-for-time substitution approach. Vegetation structure, plant diversity and soil fertility were measured at 24 sites within 15 forest fragments on six farms, covering a range in time since exclusion from grazing of 1–53 years. The forest fragments were compared with a large area of ungrazed forest in the nearby Lake Okataina Scenic Reserve. As time since exclusion from grazing increased, indigenous plant species diversity increased (up to 30–35 years); ground fern and epiphyte abundance increased (up to 30–35 years); tree seedling and sapling numbers, and litter cover also increased (up to 10–15 years); and overall tree numbers increased, while average tree diameter at breast height and overall tree basal area did not differ significantly. The soil fertility status was highly variable, obscuring clear patterns, although Olsen P status decreased with time since grazing exclusion. Once grazing of forest fragments ceases, significant changes in their diversity, structure and soil characteristics can be expected, which indicate recovery of these plant communities towards the conditions observed in ungrazed forest.
Abstract Although the potential impacts of rising water tables and secondary salinization on agricultural land in southern Australia have been recognized for some time, it is only recently that the impacts on native vegetation have been considered. Despite the likely extent and severity of the problem, no comprehensive approach to assessing the impact of salinity upon native vegetation has been attempted to date. In the present paper, we discuss the causes and impacts of rising water tables and dryland salinity, assess the levels of risk in different ecosystem types and consider the possibilities for the maintenance of biodiversity and ecosystem function in vegetation at risk. We examine the salinity risk to woodland vegetation in the Western Australian (WA) wheatbelt, and consider both broad-scale context and finer-scale variation within individual patches of vegetation. From this information, we develop a set of conceptual models of the potential impacts of shallow saline water tables on ecosystem structure and processes in remnant vegetation in agricultural areas, particularly in the WA wheatbelt. First, we suggest that fine-scale variability in surface topography and soil characteristics may play an important role in limiting the impacts of rising saline water tables. The outcome will depend on the interaction of the heterogeneity of the impact, species distribution in relation to small-scale environmental heterogeneity and variation in species response to hydrological change. Second, we suggest that shallow saline water tables can be considered to cause an ‘edge effect’, which moves inwards from the edge of remnants of native vegetation. Finally, we consider how saline surface flows exacerbate the effects of shallow saline water tables and hasten vegetation decline in remnant areas. We put these models forward as hypotheses to be tested in different situations. We contrast the situation of secondary salinization in Australian vegetation with that of naturally saline systems in Australia and elsewhere, and suggest that these systems may provide important signposts toward developing management approaches for vegetation at risk. In conclusion, we consider the need to set priorities for the protection and restoration of natural vegetation at risk from altered hydrology, based on an assessment of relative threat and probability of persistence or recovery. We highlight the urgency for action that protects native vegetation from the increasing risks of rising water tables.
Ensuring the regeneration of selectively harvested canopy tree species remains challenging in mixed forests where species have different requirements for successful recruitment. Mature conifer trees (Podocarpaceae) have been selectively harvested from parts of New Zealand's North Island conifer–angiosperm forests. Forest managers require guidance on podocarp restoration, given current dominance by the shade-tolerant angiosperm Beilschmiedia tawa. We surveyed seedling densities of podocarps and B. tawa ca. 40 years after harvesting and found that B. tawa seedlings outnumbered the combined total of podocarp seedlings by approximately 3:1. There were significant, positive associations between seedlings of most species suggesting that safe sites for establishment were similar, in part, for the suite of study species. These sites are the same as those where adult podocarp trees are reported to occur. We developed and tested candidate models predicting the influence of environmental factors on seedling regeneration; these focused on the roles of soil nutrients, landform, canopy openness, tree fern cover, ground cover by ferns and disturbance. We found the most support for models that used a combination of soil nutrients, canopy composition, landform index and disturbance type to predict seedling occurrence. A positive relationship was found between soil nitrogen (N) and seedling occurrence of all species surveyed, and this relationship alone had most support in explaining the occurrence of Prumnopitys taxifolia and Dacrycarpus dacrydioides seedlings. We found little difference in the current sites of young Prumnopitys ferruginea and B. tawa; both species occur in dense stands of adult B. tawa, although in contrast to B tawa, P. ferruginea seedling occurrence declined with increasing soil phosphorus (P). Dacrydium cupressinum also declined with increasing soil P. Given that the studied forest fits the apparent global trend for angiosperm ascendancy we suggest that manipulations will be required to restore podocarps. Possible interventions are planting seedlings and/or removing some of the B. tawa canopy. Given that podocarp seedlings were found on soils with low soil P, but high soil N concentrations, soil nutrient status should be taken into account during management.
Grazing by domestic livestock in native woodlands can have major effects on ecosystem functioning by the removal of plant species that form important functional groups. This paper documents the changes in floristics in a large group of remnants of native woodland left after agricultural clearing in southwestern Australia. Species richness and diversity were significantly reduced in remnants and the proportion of exotic species increased. Detrended Correspondence Analysis (DCA) was used to identify floristic and environmental patterns among plots and identified two distinct groups based on grazing intensity. This indicated that the significance of the relationship between grazing effects and DCA floristic axes was greater than edaphic characteristics that normally influence floristic patterns. Floristic characteristics of sites that were influencing the position of plots on the ordination diagram included proportion of exotic species and proportion of native perennial shrubs and herbs. Numbers of species of native shrubs and perennial herbs were significantly reduced in grazed plots and numbers of exotic annual grasses and herbs were significantly higher. Other life form groups such as native perennial grasses and geophytes were not significantly affected by grazing. Reproductive strategies of perennial species showed a significant decrease in numbers of resprouters and a significant increase in numbers of facultative seeder/sprouters. Exclosure plots showed increases in number and cover of perennial shrubs and herbs after three years whereas number and cover of exotic species did not change. Time series DCA showed that the floristic composition of exclosure plots in grazed sites became closer to that of the ungrazed sites.
House mice Mus musculus and other introduced rodents represent a novel source of predation on tree seeds in New Zealand forests. In the northern temperate forests where these rodents are native, spatial and temporal variation in tree seed production can result in dramatic fluctuations in the distribution and abundance of seed predators, with subsequent feedbacks on the distribution and abundance of seedlings. We use neighbourhood models to examine variation in rodent predation on seeds of 4 tree species of the temperate rainforests of New Zealand as a function of 1) spatial variation in local canopy composition and 2) spatial and temporal variation in mouse activity. We placed seeds throughout mapped stands of mixed forests in alluvial valley bottoms and on elevated marine terraces in the Waitutu Forest, South Island. The risk of predation on seeds of 2 dominant canopy trees – rimu Dacrydium cupressinum and mountain beech Nothofagus solandri var. cliffortioides– peaked in neighbourhoods dominated by those species and by silver beech N. menziesii, particularly in a year of plentiful seed rain from these species. The risk of predation on rimu and beech seed was also related to measures of local mouse activity. These relationships suggest that the highest local abundance of mice was concentrated in rimu and beech neighbourhoods because of the food provided by seed rain from those trees. Predation on seed of miro Prumnopitys ferruginea, which is eaten by rats but not mice, was low in rimu neighbourhoods and where mouse activity was high. These patterns may reflect spatial segregation in the activity of rats versus mice within stands. Our results suggest that the spatial distribution of canopy trees translates into predictable patterns of variation in mouse activity and seed predation. Heterogeneity in rodent activity and seed predation within stands may have important implications for tree population dynamics.
To evaluate the impact of fragmentation on forest regeneration, I measured the abundance of shade‐tolerant, mature‐phase tree seedlings (individuals 5–100 cm tall) in unfragmented and fragmented vegetation in three sites near Manaus, Brazil. The habitats studied were (1) continuous forest (control, n = 5); (2) 100‐ha fragments (n = 2); (3) 10‐ha fragments (n = 4); and (4) 1‐ha fragments (n = 5). For 10‐ and 100‐ha fragments, seedling density was measured in the center, the edge, and the corner of the fragments, and at 20‐m intervals up to 100 m away from the fragment’s edge. The density of seedlings declined significantly from continuous forest to forest fragments. Corners of 100‐ha fragments had lower densities of seedlings than plots in centers and edges. In both 100‐ and 10‐ha fragments, edge seedling density increased toward forest interior, but the increment was significant for only one site. Edge effects were more important than area effects per se in affecting seedling abundance. Overall, the centers of larger fragments (100 ha) did not have significantly higher densities of tree seedlings than smaller ones (10 and 1 ha). I suggest that a decrease in seed rain produced by increased tree mortality, reduced seed output and dispersal, high seed predation, and lower seedling establishment might explain the lower seedling numbers observed in forest fragments and fragment edges. These results suggest that forest fragmentation at Manaus may affect the regenerative potential of the forest.
Impacto de la Fragmentación Forestal en la Abundancia de Plántulas en un Bosque Tropical Lluvioso
Para evaluar el impacto de la fragmentación sobre la regeneración de la selva, utilizé la abundancia de plántulas (individuos entre 5 y 100 cm de altura) de árboles tolerantes a la sombra o de bosque maduro, como indicador de la alteración. Censé la abundancia de plántulas en sistemas no fragmentados y fragmentados en tres sitios (A, B, y C) al norte de Manaus, Brasil. Los hábitats estudiados fueron: (1) selva virgen (control, n = 5); (2) fragmentos de 100 ha (n = 2); (3) fragmentos de 10 ha (n = 4); y (4) fragmentos de 1 ha (n = 5). Para los fragmentos de 100 y de 10 ha la densidad de plántulas se midió en el centro, el borde y en la esquina de los fragmentos y también, a intervalos de 20 m, hasta 100 m del borde. La densidad de plántulas (número de plántulas/m ² ) decreció significativamente de la selva virgen a los fragmentos de diferentes tamaños. Las esquinas de los fragmentos de 100 ha tuvieron menor número de plántulas que los centros y los bordes. En los fragmentos de 100 y 10 ha, la densidad de plántulas aumentó del borde hacia el interior del fragmento, pero éste incremento fue significativo únicamente para el Sitio B. Los efectos de borde parecen tener un impacto mayor sobre la abundancia de plántulas que el tamaño del fragmento. Los centros de los fragmentos de mayor tamaño (100 ha) tuvieron una densidad de plántulas similar a los menores (10 y 1 ha). La información existente y los resultados obtenidos en este trabajo, sugieren que una disminución en la lluvia de semillas, producida por un incremento en la mortalidad de árboles, una dispersión reducida, alta predación, y un pobre desempeño de las plántulas pueden explicar la disminución en el número de plántulas en los fragmentos y en los bordes de los fragmentos. Todo parece indicar que la fragmentación, en este sitio, puede afectar el potencial regenerativo de la selva.
Indigenous forest fragments in rural New Zealand are increasingly valued as reservoirs of native biodiversity. Most forest species are adapted to soils of low phosphorus (P) availability, but fragments are often intermingled with managed pastures and subjected to unintended P inputs from aerial topdressing, which may compromise their long-term sustainability. Phosphorus availability and other nutrients in forest fragments were compared with adjacent fertilised pasture and reference forest areas not receiving fertiliser additions. Inorganic (H2SO4 soluble) P and available (Olsen) P were approximately ten times greater in fragment forest soils than reference forest soils, while total P was two times greater. The strong linear relationship between total P and cadmium, an element contained in rock phosphate fertilisers, suggested that the increased Plevels in fragment forests could be attributed to P from aerial topdressing. Comparison of foliar N:P ratios show that P is being conserved in reference forests but not in fragment forest. A 5-fold increase in Pmineralisation rate in forest fragments high in available P and a significant relationship between total P in forests and soil respiration suggests Pavailability may be limiting microbial activity in these forest systems. Forest Fragments also had base saturation and Ca, Mg, and K levels twice that of reference forests. Increased nutrient levels have been shown to alter plant successional dynamics and community composition, and raise concerns over future successional patterns and long-term stability of these forest fragments.
Microclimate (photosynthetically active radiation; air temperature; vapour pressure deficit) and vegetation edge effects were investigated in five podocarp-broadleaf forest fragments in the North Island of New Zealand. Distinct forest edge microclimate regimes were found to exist for part of the year and these were associated with differences in vegetation composition and structure between the forest edge and interior. Some species-specific edge/interior differences could be related to timing of critical life history stages (e.g. germination and early establishment) relative to the temporal stability of edge microclimate regimes. Penetration of gross microclimatic edge effects was approximately 50 m regardless of fragment size. These results suggest that regularly shaped forest fragments <9·10 ha are dominated by edge patterns and processes and that below 1·0 ha fragments do not support forest interior conditions or vegetation associations.
In the fragmented Maulino forest (in Central Chile), differences in the relative frequencies of species between seedlings and mature trees are strong indicators of a changing replacement dynamics in the community. Stationary Markov chain models predict that the future tree composition such Maulino forest fragments will differ from that of continuous, intact forest. We found that the persistence probability was highest for Aristotelia chilensis and lowest for Nothofagus glauca. These two tree species are the most affected by fragmentation, and changes in their abundances appear to be the main drivers of the long-term change in stand composition. The aim of our study was to test if the management of just these two species would be sufficient to avoid long-term changes in the composition of forest fragments or would recover their composition toward a state more similar to the continuous forest. For this purpose, we constructed a Markov matrix model from published information, and calculated the future stable stand composition under different management simulations: (1) reduction of A. chilensis recruitment, (2) increased recruitment of N. glauca, and (3) a combined treatment. To evaluate the effectiveness of management treatments, the future composition of fragments was compared with the composition expected for continuous (i.e., undisturbed) Maulino forest. We performed a sensitivity analysis of the stable composition in order to assess the intensity of changes in the future composition driven by the treatments, and to determine to what extend the recruitment of other coexisting species contributes to changes in relative frequencies of A. chilensis and N. glauca.
All specimens of 19 tree and 11 shrub species greater than 10 cm dbh (more than 3000 stems of trees and tree ferns) were labeled, measured, and mapped in 2.25 ha of lowland forest near Wellington, New Zealand. Their fate, growth, and additional recruitment were monitored in three surveys over 16 yr, from 1969 to 1985. During the vegetation study, movements, diet, density, and breeding success of the introduced Australian brushtail possum (Trichosurus vulpecula) were studied in the same area of forest. In the study plot the number of stems and their total basal area increased between 1969 and 1985. However, several species that are eaten by possums have suffered substantial losses of both stems and total basal area. These include Beilschmiedia tawa, Weinmannia racemosa, Metrosideros robusta, and the tree fern Cyathea medullaris. Species not eaten by possums have increased in both numbers and basal area. These include Hedycarya arborea, Cyathea smithii, Cyathea dealbata, and Laurelia novaezelandiae. During the study there has been a decline in basal area of emergent trees, an increase in basal area of canopy trees (but little increase in their numbers), and an increase in numbers and basal area of minor species and dead trees. If present trends in structure and composition of this lowland forest continue, the future forest will have a greater proportion of tree ferns and more short-lived, small-diameter species. Canopy height and species diversity are also likely to decrease.
Habitat loss has pervasive and disruptive impacts on biodiversity in habitat remnants. The magnitude of the ecological impacts of habitat loss can be exacerbated by the spatial arrangement – or fragmentation – of remaining habitat. Fragmentation per se is a landscape-level phenomenon in which species that survive in habitat remnants are confronted with a modified environment of reduced area, increased isolation and novel ecological boundaries. The implications of this for individual organisms are many and varied, because species with differing life history strategies are differentially affected by habitat fragmentation. Here, we review the extensive literature on species responses to habitat fragmentation, and detail the numerous ways in which confounding factors have either masked the detection, or prevented the manifestation, of predicted fragmentation effects.
Methods for the chemical analysis of soils Department of Scientific and Industrial Research, Lower Hutt, New Zealand. Brockie W. (1992) A Living New Zealand Forest Conifers and cows: forest survival in a New Zealand dairy landscape
- L C Blakemore
- P L Searle
- B K Daly
- B R Burns
- G Barker
- R J Harris
Blakemore L. C., Searle P. L. & Daly B. K. (1987) Methods for the chemical analysis of soils. New Zealand Soil Bureau Scientific Report 80. Department of Scientific and Industrial Research, Lower Hutt, New Zealand. Brockie W. (1992) A Living New Zealand Forest. David Bateman, Auckland. Burns B. R., Barker G., Harris R. J. et al. (2000) Conifers and cows: forest survival in a New Zealand dairy landscape. In: Nature Conservation 5: Nature Conservation in Production Environments: Managing the Matrix (eds J. L. Craig, N. D.