Resilience of New?Zealand indigenous forest fragments to impacts of livestock and pest mammals

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.     

Vegetation recovery in rural kahikatea (

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.     

Effects of grazing and cultivation on forest plant communities in Mount Elgon National Park, Uganda

Plant communities in the montane forest of Mount Elgon National Park were studied in order to assess the impact of grazing and cultivation on species composition. Present and former land uses, tree, shrub and herb species, soil properties and the percentage cover and height of trees, shrubs and herbs were determined in 40 plots. An indirect ordination of these plots showed that species composition was primarily determined by successional stage and agricultural disturbance. In forest plots (ordinated separately) where the widest range of former and current grazing intensities had occurred, evidence of grazing history, soil phosphorus and vegetation height correlated negatively with the strongest ordination axis. Least grazed forest plots had fewer tree seedlings and saplings than more intensively grazed plots. This may be due to the increase in Mimulopsis alpina (Acanthaceae) in less grazed forest where tree regeneration might otherwise be more advanced. Tree seedlings and saplings were uncommon in the forest, rarely exceeding 30cm in height and there was no tree understorey. Although grazing is important for preserving species diversity in Mount Elgon National Park through the maintenance of species-rich grasslands, long-term effects on montane forest communities must be considered in future park management.     

Ground Beetles (Coleoptera, Carabidae) in Forest Fragments of the Manawatu, New Zealand: Collapsed Assemblages?

Botanically diverse and well-maintained, protected forest fragments in the Manawatu area of the North Island of New Zealand contained very species-poor carabid assemblages. In a nearby large forest tract, the potential source area, nine species were caught in pitfall traps, while the largest forest remnant had two species, and a well-managed suburban forest patch had three species but only one with a potentially reproducing population. Lack of grazing and high botanical diversity was insufficient to maintain the potential carabid assemblage in these fragments. Predation risk and a low dispersal power in endemic New Zealand ground beetles, combined with fragment size and degree of isolation could contribute to this collapse. Active management of ground-active invertebrate species seems necessary to protect them in isolated forest fragments in New Zealand.     

Effects of forest fragment management on vegetation condition and maintenance of canopy composition in a New Zealand pastoral landscape

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.     

Land rehabilitation and the conservation of birds in a degraded Afromontane landscape in northern Ethiopia

The few remaining Afromontane forest fragments in northern Ethiopia and the surrounding degraded, semiarid matrix form a habitat mosaic of varying suitability for forest birds. To evaluate the effect of recent land rehabilitation efforts on bird community composition and diversity, we studied bird species distributions in ten small forest fragments (0.40–20.95 ha), five grazing exclosures (10-year-old forest restoration areas without wood extraction and grazing livestock) and three grazed matrix sites during the rainy season (July–October 2004) using 277 one-hour species counts. Based on the distribution pattern of 146 bird species, sites were assigned to one of three bird communities (birds of moist forest, dry forest or degraded savanna), each occupying a well-defined position along an environmental gradient reflecting decreasing vegetation structure and density. All three communities were representative of the avifauna of Afrotropical Highland open forest and woodland with a high proportion of invasive and competitive generalist species (31%). Apart from these, exclosures shared more species with forest fragments (20%) than did the grazed matrix (5%), indicating local ecosystem recovery. By increasing habitat heterogeneity, exclosures have the potential to enhance landscape connectivity for forest birds and are, therefore, an effective instrument for conserving species in a fragmented landscape. However, 52 bird species (36%) occurred exclusively within forest patches and many forest birds that use exclosures are unlikely to maintain viable populations when forest fragments disappear, particularly as forest fragments may be a critical resource during the hot dry season. This highlights the high conservation value of small isolated forest fragments for less tolerant, forest-limited and/or biome-restricted species.     

Beetle assemblages of kahikatea forest fragments in a pasture- dominated landscape

Fragments of kahikatea (Dacrycarpus dacrydioides) forest provide a major opportunity for conservation of indigenous biodiversity in the heavily deforested landscape of the Waikato Basin, New Zealand. However, there is little documented information on what indigenous fauna survives in these fragments. Using Malaise traps set 20 m and 50 m into fragments and 20 m and 50 m into the adjacent pasture, we analysed the beetle (Coleoptera) assemblages associated with two such kahikatea forest fragments in the south Waikato Basin in order to determine the scope of biotic invasion by adventive species and use of the surrounding pasture by indigenous species. A total of 3706 beetles were caught, encompassing 37 families and 206 recognisable taxonomic units. The forest fragments had a sharply defined edge, and were dominated by indigenous beetle species, with only a few adventive species present. Beetle assemblages sampled in the surrounding pasture were numerically dominated by adventive species. Despite no indigenous plant species being present in the pastures, 55 indigenous beetles species (61% of total species sampled in the pasture) were recorded in this habitat. Traps in the pasture of greatest floral diversity caught the most indigenous beetle species. Beetles of the detritivore guild dominated the samples from forest, but in samples from pasture, detritovores and predatores were co-dominant. Indigenous herbivore species were poorly represented in samples from pasture compared to other guilds. The kahikatea fragments have a rich indigenous beetle fauna and represent important refuges in the pastoral landscape of the Waikato. Many indigenous species are utilising the pasture to some degree, although their abundance and species richness declines with distance from the forest edge. This may have implications for successful dispersal to new patches. Species that could potentially be used as indicators of kahikatea forest fragment community structure and its resistance to invasion are suggested.     

Options for enhancing forest biodiversity across New Zealand's managed landscapes based on ecosystem modelling and spatial design

In most regions of the world removal of environmental stress facilitates regeneration of native plants and habitats. However, in many of New Zealands modified landscapes, exotic species are likely to respond first to any reduction in stress because these fast-growing species are prevalent in local vegetation and dominate seed banks. Given the trend in agriculture towards intensive management on larger units, the indigenous character in New Zealand landscapes is being marginalised and there is the risk that further reduction in visibility of native vegetation may be perpetuated by a growing familiarity and identification with ubiquitous exotic species. Alternative landscapes, based on an understanding of ecosystem processes, need to be explored if biodiversity goals set by international convention and national resource management law are to be achieved. This study provides a set of predictions and pathways, backed by field observations, to underpin a restoration strategy at patch to landscape scales. A forest model, LINKNZ, is employed to simulate species succession under New Zealand conditions. The incorporation of disturbance regimes and species dispersal processes in the model permits a wide range of scenarios to be investigated encompassing indigenous forest development, exotic species interactions with indigenous forest ecosystems, management of mixed introduced-indigenous forests, and landscape dynamics. The results illustrate an approach that identifies potential biosecurity threats and provides additional options for integrating nature and production in New Zealands rural and urban landscapes.     

Comparison of biodiversity and ground cover between a commercial rotationally grazed property and an adjacent nature reserve in semi‐arid rangeland

Continuous livestock grazing can have negative effects on biodiversity and landscape function in arid and semi‐arid rangelands. Alternative grazing management practices, such as rotational grazing, may be a viable option for broad‐scale biodiversity conservation and sustainable pastoral management. This study compared ground cover, plant species composition and floristic and functional diversity along gradients of grazing intensity between a pastoral property rotationally grazed by goats and an adjacent nature reserve (ungrazed by commercial livestock) in semi‐arid south‐eastern Australia. Understorey plant species composition differed significantly between the rotationally grazed property and the nature reserve, with a greater proportion and frequency of palatable species recorded in the nature reserve. Understorey plant species richness, diversity, functional biodiversity measures and ground cover declined with increasing grazing pressure close to water points under commercial rotational grazing management. However, at a whole‐paddock scale, there were few differences in plant biodiversity and ground cover between the rotationally grazed property and the nature reserve, despite differences in overall plant species composition. Flexible, adaptive, rotational grazing should be investigated further for its potential to achieve both socio‐economic and biodiversity conservation outcomes in semi‐arid rangelands to complement existing conservation reserves.     

Composition of grazed and cleared temperate grassy woodlands in eastern Australia: patterns in space and inferences in time

Abstract. A regional vegetation survey of the temperate grassy woodlands (temperate savanna) in Australia was designed to assess the effects of clearing and grazing on the composition of vegetation remnants and the adjacent pasture matrix. Vegetation was sampled across a range of habitats using 77 0.1024‐ha quadrats; the relative abundance of species was recorded. Classification analysis clustered the sites into three main groups that corresponded to intensity of grazing/clearing followed by groups based on underlying lithology (basalt, metasediment, granites). Using Canonical Correspondence Analysis, exogenous disturbance and environmental variables were related to the relative abundance of species; grazing intensity had the highest eigenvalue (0.27) followed by tree canopy cover (0.25), lithology (0.18), altitude (0.17) and slope (0.10). Based on two‐dimensional ordination scores, six species response groups were defined relating to intensity of pastoralism and nutrient status of the landscape. Abundance and dominance of native shrubs, sub‐shrubs, twiners and geophytes were strongly associated with areas of less‐intense pastoralism on low‐nutrient soils. The strongest effects on species richness were grazing followed by canopy cover. Continuously grazed sites had lower native species richness across all growth forms except native grasses. There was no indication that intermediate grazing intensities enhanced forb richness as a result of competitive release. Species richness for all native plants was lowest where trees were absent especially under grazed conditions. Canopy cover in ungrazed sites appeared to promote the co‐existence of shrubs with the herbaceous layer. Predicted declines in forb richness in treeless, ungrazed, sites were not detected. The lack of a disturbance‐mediated enhancement of the herbaceous layer was attributed to habitat heterogeneity at 0.1 ha sampling scale.     

Microclimate and tree community linked to differences in lepidopteran larval communities between forest fragments and continuous forest

Aim  We aim to assess the impact of forest fragmentation on lepidopteran larval community and study the associations of microclimate and tree community with lepidopteran assemblage.
Location  Kibale National Park, Uganda.
Methods  We investigated the effects of forest fragmentation on leaf herbivory, density of lepidopteran caterpillars, species richness and diversity as well as the composition of herbivorous lepidopteran larval community. Microclimate, size of the fragment, distance to the continuous forest, and tree diversity were studied as possible explanatory factors. We sampled 10 Neoboutonia macrocalyx Pax. (Euphorbiaceae) trees in each fragment during dry and rainy season, total of four times, in a year to cover the seasonal variation.
Results  The rates of herbivory, total larval density and species richness were significantly lower in the forest fragments than in the continuous forest but species diversity expressed as Fisher's alpha did not differ. The dominance structure and community composition of the larval communities in the fragments was different from that of the continuous forest. None of the differences we observed were related to the fragment area or distance to the continuous forest. Instead, we found an indication of association between the herbivore and the tree communities. The fragments had significantly lower humidity during most of the day and higher temperature during the afternoons (14–17 h), which might partially explain the differences in lepidopteran larval communities.
Main conclusions  Decreased larval density and species richness as well as differences in the community composition and structure all highlight the importance of large continuous forest areas for maintaining larval biodiversity.     

Importance of riparian remnants for frog species diversity in a highly fragmented rainforest

Tropical forests undergo continuous transformation to other land uses, resulting in landscapes typified by forest fragments surrounded by anthropogenic habitats. Small forest fragments, specifically strip-shaped remnants flanking streams (referred to as riparian remnants), can be particularly important for the maintenance and conservation of biodiversity within highly fragmented forests. We compared frog species diversity between riparian remnants, other forest fragments and cattle pastures in a tropical landscape in Los Tuxtlas, Mexico. We found similar species richness in the three habitats studied and a similar assemblage structure between riparian remnants and forest fragments, although species composition differed by 50 per cent. Frog abundance was halved in riparian remnants compared with forest fragments, but was twice that found in pastures. Our results suggest that riparian remnants play an important role in maintaining a portion of frog species diversity in a highly fragmented forest, particularly during environmentally stressful (hot and dry) periods. In this regard, however, the role of riparian remnants is complementary, rather than substitutive, with respect to the function of other forest fragments within the fragmented forest.     

The effect of habitat fragmentation on the bee visitor assemblages of three Australian tropical rainforest tree species

Tropical forest loss and fragmentation can change bee community dynamics and potentially interrupt plant–pollinator relationships. While bee community responses to forest fragmentation have been investigated in a number of tropical regions, no studies have focused on this topic in Australia. In this study, we examine taxonomic and functional diversity of bees visiting flowers of three tree species across small and large rainforest fragments in Australian tropical landscapes. We found lower taxonomic diversity of bees visiting flowers of trees in small rainforest fragments compared with large forest fragments and show that bee species in small fragments were subsets of species in larger fragments. Bees visiting trees in small fragments also had higher mean body sizes than those in larger fragments, suggesting that small‐sized bees may be less likely to persist in small fragments. Lastly, we found reductions in the abundance of eusocial stingless bees visiting flowers in small fragments compared to large fragments. These results suggest that pollinator visits to native trees living in small tropical forest remnants may be reduced, which may in turn impact on a range of processes, potentially including forest regeneration and diversity maintenance in small forest remnants in Australian tropical countryside landscapes.     

Local vs regional factors as determinants of the invasibility of indigenous forest fragments by alien plant species

Both local and regional filters can determine the invasion of alien species into native plant communities. However, their relative importance is essentially unknown. We used plot data from fragments of indigenous forests in southeastern New Zealand to infer which factors are important in explaining invasibility, measured as alien species richness. Twenty-eight predictor variables comprising both local factors (stand structure and soil) and regional ones (climate and land cover) were assessed. Reduction or increase in deviance in linear models was assessed, both individually and with a forward and backward stepwise variable selection procedure using the Akaike information criterion (AIC).
We found that higher alien species richness was mainly associated with forest fragments of small area in warm and dry climates and where there were only small areas of surrounding indigenous forest. Local soil and stand structure variables had considerably smaller effects on alien species richness than the regional land cover and climate variables. Alien species richness showed no relationship with native species richness. We conclude that in the forest fragments investigated here, of the variables included in the analyses, regional land cover and climate variables are potentially important drivers for alien species richness at plot level. This has implications for projections of alien species spread in the future under different climate change and land use scenarios.     

Impact of an exotic vine Clematis vitalba (F. Ranunculaceae) and of control measures on plant biodiversity in indigenous forest,Taihape, New Zealand

The exotic vine, Clematis vitalba L. (F. Ranunculaceae), has been in forest reserves around Taihape in the Rangitikei Ecological Region of the central North Island, New Zealand, for about 70 years. Before this weed was abundant, Taihape forests were rich in species of indigenous vascular plants, especially woody species. Clematis vitalba and its control are contributing to a loss of forest structure and of indigenous biodiversity at the ecosystem and species levels, to a lack of recruitment of indigenous species, to an influx of other weeds and to changes in growth forms of indigenous shrubs. Species that have disappeared or become uncommon in forest with C. vitalba tend to be those that are nationally threatened or uncommon, have restricted distributions or are biogeographically significant. Current control of C. vitalba in the Taihape forest is piecemeal and long-term. It is based on mechanical and chemical methods, followed by grazing with sheep to prevent regeneration. Recommendations are made for rapid removal of C. vitalba from all untreated parts of the reserve, followed by manual control or spot- spraying, permanent removal of sheep, control of other serious weeds and implementation of a restoration programme.     

Re-examination of recent loss of indigenous cover in New Zealand and the relative contributions of different land uses

Loss of indigenous habitat is a key factor in the decline of New Zealand?s biodiversity. A recent contribution by Walker et al. (2006, New Zealand Journal of Ecology 30: 169?177) described losses of indigenous vegetation between 1996/97 and 2001/02 (some 17 000 ha) based on an analysis of changes in the Land Cover Database, LCDB1 and LCDB2, respectively. We agree that the general approach of using these and other spatial datasets appears to be appropriate to investigate changes in land cover and the types of land uses that are responsible, but we would like to offer some comments to aid with the interpretation of this and other studies that use LCDB comparisons and similar techniques. Using aerial photography, satellite imagery, site visits, and other methods, we evaluated a stratified sample of 67 of the 449 polygons that were indicated to have changed from the most affected indigenous classes (?Tall Tussock Grassland?, ?Manuka and/or Kanuka?, and ?Broadleaved Indigenous Hardwoods?) to the exotic forest classes ?Afforestation (not imaged)? and ?Afforestation (imaged, post LCDB1)?. Our assessment of the entire area of each of these polygons covered 56.6% of the total area that was identified to have changed, and this revealed an error rate of c. 70% for this particular comparison of LCDB1 and LCDB2 data. This indicates the accuracy of such analyses may be too low to be meaningful and requires verification of the data that are primarily based on remote sensing, even when the overall aggregate accuracy is very high. In addition, we comment on the relative merits of different land uses in relation to the conservation of indigenous biodiversity, particularly the contributions of low-producing exotic grassland and exotic plantation forests. This is important because much indigenous biodiversity remains in exotic forests and embedded indigenous remnants, and the current clearing of potentially over 100 000 ha of such land for exotic pasture will cause significant losses of indigenous biodiversity.     

Native plantations as an important element for biodiversity in vanishing forested landscapes: A study of the near threatened araucaria tit spinetail (Leptasthenura setaria,Furnariidae)

Although forest loss is still a problem worldwide, estimated rates of deforestation have declined in the last decade, primarily because of an increase in the area of tree plantations. This leads to the central question of how suitable plantations are for indigenous species. Native plantations are thought to have higher value for biodiversity than plantations of non‐native trees; however, not all studies support this view. We assessed occupancy and density of the araucaria tit spinetail (Leptasthenura setaria, Furnariidae), a near threatened species, in the highly endangered araucaria forests of north‐eastern Argentina and in araucaria plantations, which comprise 90% of the remaining habitat for this species. All natural forest remnants were occupied by araucaria tit spinetails. Only 85% of the plantations were occupied; however, density was almost threefold higher in plantations compared with natural forests. Our models indicated that stand age was the most important factor in determining occupancy and density of this bird species in plantations. Plantations <10 years old exhibited lower densities than older plantations. This species does not occur in plantations of non‐native trees, but our results indicate that native plantations may provide important habitat for the araucaria tit spinetail, particularly given that most native forest has been removed. Restoration of natural remnants and conservation of old, connected plantations may assure the protection of significant populations of spinetails. The role of native araucaria plantations as habitat for other species merits further examination.     

Reintroduction of large herbivores restored plant species richness in abandoned dry temperate grassland

Naturalistic grazing by large herbivores is an increasingly practiced way of managing habitats with conservational value. It has the potential to restore and enhance biodiversity, creating self-sustainable environments vital for organisms requiring regular disturbances to moderate and/or reverse successional changes. European bison, Exmoor pony, and Tauros cattle were introduced in 2015 to a former military training area in Milovice, Czech Republic. The prevailing vegetation type is a forest-steppe savanna with Bromus erectus-dominated xeric grasslands mixed with deciduous shrubs and trees. After the cessation of military use, the area was abandoned which led to successional changes, including the dominance of tall grasses, litter accumulation, and bush encroachment. In 2017–2021, we monitored grassland vegetation in 30 grazed permanent plots (2?×?2 m) and 5 control plots representative of ungrazed, abandoned vegetation adjacent to the grazed areas. Naturalistic grazing increased species richness and the cover of forbs, while the cover of grasses and legumes was minimally affected. Grazing increased functional diversity of plant community, promoted a compositional change to small statured species and an increased incidence of red-list species. Seven years of continuous grazing increased the conservation value of this forest-steppe vegetation, a habitat type rapidly declining in Europe.

     

Seed bed treatment effects on vegetation and seedling establishment in a New Zealand pasture one year after seeding with native woody species

Summary Efforts to re‐establish indigenous forests in pastoral New Zealand have increased as the value of native biodiversity has been realized. Direct seeding of woody species is preferable to transplanting, as labour and material costs are less. However, the success rate of direct seeding in pasture has been variable due to intense competition from adventive species. We initiated an experiment in pasture plots adjacent to a forest fragment where seed bed treatments (increasing in degree of disturbance from herbicide application to turf removal and topsoil removal) in combination with mulch treatments (wood chip shavings with and without forest floor organic material) were seeded with a mixture of New Zealand lowland forest species. The objective of the study was to determine if early successional plant communities, and ultimately seedling establishment, differed as a result of seed bed preparation after 1 year. Coprosma robusta (Karamu) and Kunzea ericoides (Kanuka) seedlings established on plots in significant numbers: both species were most abundant on topsoil‐removed plots where bare substrate was greatest and plant cover least. Both seed bed treatments and mulching treatments led to measurable differences in overall composition of early successional plant communities. However, absence of plant cover and low soil fertility (both associated with the topsoil‐removed treatment) were the most important factors in seedling success.