Ungulates increase forest plant species richness to the benefit of non‐forest specialists

Large wild ungulates are a major biotic factor shaping plant communities. They influence species abundance and occurrence directly by herbivory and plant dispersal, or indirectly by modifying plant‐plant interactions and through soil disturbance. In forest ecosystems, researchers’ attention has been mainly focused on deer overabundance. Far less is known about the effects on understory plant dynamics and diversity of wild ungulates where their abundance is maintained at lower levels to mitigate impacts on tree regeneration. We used vegetation data collected over 10 years on 82 pairs of exclosure (excluding ungulates) and control plots located in a nation‐wide forest monitoring network (Renecofor). We report the effects of ungulate exclusion on (i) plant species richness and ecological characteristics, (ii) and cover percentage of herbaceous and shrub layers. We also analyzed the response of these variables along gradients of ungulate abundance, based on hunting statistics, for wild boar (Sus scrofa), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Outside the exclosures, forest ungulates maintained higher species richness in the herbaceous layer (+15%), while the shrub layer was 17% less rich, and the plant communities became more light‐demanding. Inside the exclosures, shrub cover increased, often to the benefit of bramble (Rubus fruticosus agg.). Ungulates tend to favour ruderal, hemerobic, epizoochorous and non‐forest species. Among plots, the magnitude of vegetation changes was proportional to deer abundance. We conclude that ungulates, through the control of the shrub layer, indirectly increase herbaceous plant species richness by increasing light reaching the ground. However, this increase is detrimental to the peculiarity of forest plant communities and contributes to a landscape‐level biotic homogenization. Even at population density levels considered to be harmless for overall plant species richness, ungulates remain a conservation issue for plant community composition.     

Ungulate browsers promote herbaceous layer diversity in logged temperate forests

Ungulates are leading drivers of plant communities worldwide, with impacts linked to animal density, disturbance and vegetation structure, and site productivity. Many ecosystems have more than one ungulate species; however, few studies have specifically examined the combined effects of two or more species on plant communities. We examined the extent to which two ungulate browsers (moose [Alces americanus]) and white‐tailed deer [Odocoileus virginianus]) have additive (compounding) or compensatory (opposing) effects on herbaceous layer composition and diversity, 5–6 years after timber harvest in Massachusetts, USA. We established three combinations of ungulates using two types of fenced exclosures – none (full exclosure), deer (partial exclosure), and deer + moose (control) in six replicated blocks. Species composition diverged among browser treatments, and changes were generally additive. Plant assemblages characteristic of closed canopy forests were less abundant and assemblages characteristic of open/disturbed habitats were more abundant in deer + moose plots compared with ungulate excluded areas. Browsing by deer + moose resulted in greater herbaceous species richness at the plot scale (169 m²) and greater woody species richness at the subplot scale (1 m²) than ungulate exclusion and deer alone. Browsing by deer + moose resulted in strong changes to the composition, structure, and diversity of forest herbaceous layers, relative to areas free of ungulates and areas browed by white‐tailed deer alone. Our results provide evidence that moderate browsing in forest openings can promote both herbaceous and woody plant diversity. These results are consistent with the classic grazing‐species richness curve, but have rarely been documented in forests.     

Deer Herbivory as an Ecological Constraint to Restoration of Degraded Riparian Corridors

Ungulate herbivory can impact riparian vegetation in several ways, such as by reducing vigor or reproductive output of mature plants, and through increased mortality of seedlings and saplings. Much work has focused on the effects of livestock grazing within riparian corridors, while few studies have addressed the influence of native ungulate herbivory on riparian vegetation. This study investigated the effect of deer herbivory on riparian regeneration along three streams with degraded riparian corridors in Mendocino County, California. We utilized existing stream restoration efforts by private landowners and natural resource agencies to compare six deer exclosures with six upstream control plots. Livestock were excluded from both exclosure and control plots. Three of the deer exclosures had been in place for 15 years, one for 6 years, and two for 4 years. The abundance and size distribution of woody riparian plant species such as Salix exigua, S. laevigata, S. lasiolepis, Alnus rhombifolia, and Fraxinus latifolia were quantified for each exclosure and control plot. The mean density of saplings in deer exclosures was 0.49 ± 0.15/m², while the mean density of saplings in control plots was 0.05 ± 0.02/m². Within exclosures, 35% of saplings were less than 1 m and 65% were greater than 1 m; within control plots, 97% of saplings were less than 1 m in height. The fact that little regeneration had occurred in control plots suggests that deer herbivory can substantially reduce the rate of recovery of woody riparian species within degraded riparian corridors. Exclusionary fencing has demonstrated promising results for riparian restoration in a region with intense deer herbivory.     

Red deer mediate spatial and temporal plant heterogeneity in boreal forests

Selective herbivory can influence both spatial and temporal vegetation heterogeneity. For example, many northern European populations of free-ranging ungulates have reached unprecedented levels, which can influence plant species turnover, long-term maintenance of biodiversity and the subsequent stability of boreal ecosystems. However, the mechanisms by which large herbivores affect spatial and temporal vegetation heterogeneity remain poorly understood. Here, we combined a 10-year exclusion experiment with a herbivore intensity gradient to investigate how red deer (Cervus elaphus) acts as a driver of temporal and spatial heterogeneity in the understory of a boreal forest. We measured the two dimensions of heterogeneity as temporal and spatial species turnover. We found that temporal heterogeneity was positively related to herbivory intensity, and we found a similar trend for spatial heterogeneity. Removing red deer (exclosure) from our study system caused a distinct shift in species composition, both spatially (slow response) and temporally (quick response). Vegetation from which red deer had been excluded for 10 years showed the highest spatial heterogeneity, suggesting that the most stable forest understory will occur where there are no large herbivores. However, excluding red deer resulted in lower species diversity and greater dominance by a low number of plant species. If both stable but species rich ecosystems are the management goal, these findings suggest that naturally fluctuating, but moderate red deer densities should be sustained.     

General and specific responses of understory vegetation to cervid herbivory across a range of boreal forests

Understanding the responses of ecological communities to perturbation is a key challenge within contemporary ecology research. In this study we seek to separate specific community responses from general community responses of plant communities to exclusion of large cervid herbivores. Cervid herbivory and forestry are the main drivers of vegetation structure and diversity in boreal forests. While many studies focus on the impact of cervids on trees, a high proportion of the biodiversity and ecosystem services in boreal forests is found in the field layer. However, experimental approaches investigating the influence of herbivory on understory vegetation are highly localised. In this study we use a regional‐scale design with 51 sites in four boreal forest regions of Norway, to investigate the influence of cervid herbivory on the physical and ecological structure of field layer vegetation. Our study sites cover a range of forest types differing in productivity, management and dominant cervid species, allowing us to identify generic responses and those that are specific to particular conditions. We found that the height of the field layer and the abundances of individual species were most susceptible to change following short‐term cervid exclusion across different forest types and cervid species. Total vegetation density and vascular plant diversity did not respond to cervid exclusion on the same time scale. We also found that the field‐layer vegetation in clear‐cut forests used by moose was more susceptible to change following cervid exclusion than mature forests used by red deer, but no strong evidence that the response of vegetation to herbivore exclusion varied with productivity. Our study suggests that the parameters that respond to cervid exclusion are consistent across forest types, but that the responsiveness of different forest types is idiosyncratic and hard to predict.     

Leaf herbivory is more impacted by forest composition than by tree diversity or edge effects

Links between biodiversity and ecosystem functioning are well established. Beyond biodiversity per se, community composition can have strong effects on ecosystem functioning. Furthermore, spatial processes including edge effects, can impact the diversity-functioning relationship. These spatial processes are especially relevant within a food web context, such as the transfer of plant biomass across the food chain through herbivory. The relative importance of diversity, community composition and spatial context on herbivory pressure at the community and the species level is, however, poorly understood.To fill this gap in our understanding, we studied to what degree herbivory in temperate forest plots varies according to edge distance, tree diversity and forest composition. In contrast to the prevailing view of tree herbivory increasing at forest edges, we found that the effects of forest edge and tree diversity on leaf herbivory were masked by effects of forest composition, i.e. the specific contributions of the tree species. The strongest composition effect found was increased herbivory on Quercus robur in the presence of Fagus sylvatica.Our findings highlight that neither edge distance, tree diversity, nor the interaction affected one ecosystem function, namely herbivory, whilst tree community composition did. This warrants consideration of identity and composition effects in future studies if we are to deepen our understanding of the determinants of ecosystem functions across systems.     

Resource availability and plant diversity explain patterns of invasion of an exotic grass

Aims In this study, we examine two common invasion biology hypotheses—biotic resistance and fluctuating resource availability—to explain the patterns of invasion of an invasive grass, Microstegium vimineum.Methods We used 13-year-old deer exclosures in Great Smoky Mountains National Park, USA, to examine how chronic disturbance by deer browsing affects available resources, plant diversity, and invasion in an understory plant community. Using two replicate 1 m 2 plots in each deer browsed and unbrowsed area, we recorded each plant species present, the abundance per species, and the fractional percent cover of vegetation by the cover classes: herbaceous, woody, and graminoid. For each sample plot, we also estimated overstory canopy cover, soil moisture, total soil carbon and nitrogen, and soil pH as a measure of abiotic differences between plots.Important findings We found that plant community composition between chronically browsed and unbrowsed plots differed markedly. Plant diversity was 40% lower in browsed than in unbrowsed plots. At our sites, diversity explained 48% and woody plant cover 35% of the variation in M. vimineum abundance. In addition, we found 3.3 times less M. vimineum in the unbrowsed plots due to higher woody plant cover and plant diversity than in the browsed plots. A parsimonious explanation of these results indicate that disturbances such as herbivory may elicit multiple conditions, namely releasing available resources such as open space, light, and decreasing plant diversity, which may facilitate the proliferation of an invasive species. Finally, by testing two different hypotheses, this study addresses more recent calls to incorporate multiple hypotheses into research attempting to explain plant invasion.     

Deer exclusion unveils abiotic filtering in forest understorey plant assemblages

Background and AimsThe role of deer (family Cervidae) in ecosystem functioning has traditionally been neglected by forest ecologists due to the animal’s scarcity in most parts of the northern hemisphere. However, the dramatic rebound in deer populations throughout the 20th century has brought deer browsing to the forefront of forest ecological questioning. Today there is ample evidence that deer affect tree regeneration, understorey plant and animal diversity, and even litter decomposition. However, the mechanisms underlying the effects of deer on forest ecosystems remain unclear. Among others, the relative role of abiotic factors versus biotic interactions (e.g. herbivory) in shaping plant assemblages remains largely unknown.MethodsWe used a large-scale experiment with exclosures distributed along abiotic gradients to understand the role of black-tailed deer (Odocoileus hemionus sitchensis) on the forest understorey on the Haida Gwaii archipelago (western Canada), a unique context where most of the key ecological effects of deer presence have already been intensively studied.Key ResultsOur results demonstrate that 20 years of deer exclusion resulted in a clear increase in vascular plant richness, diversity and cover, and caused a decline in bryophyte cover. Exclusion also unveiled abiotic (i.e. soil water availability and fertility) filtering of plant assemblages that would otherwise have been masked by the impact of abundant deer populations. However, deer exclusion did not lead to an increase in beta diversity, probably because some remnant species had a competitive advantage to regrow after decades of over browsing.ConclusionsWe demonstrated that long-term herbivory by deer can be a dominant factor structuring understorey plant communities that overwhelms abiotic factors. However, while exclosures prove useful to assess the overall effects of large herbivores, the results from our studies at broader scales on the Haida Gwaii archipelago suggest that exclosure experiments should be used cautiously when inferring the mechanisms at work.     

Ungulate herbivory reduces abundance and fluctuations of herbivorous insects in a boreal old-growth forest

Ecological theory predicts the strongest ecosystem effects of herbivory when dominant and ecologically important species are consumed. Bilberry, Vaccinium myrtillus, is such a key plant species, attractive to many other species in the boreal forests, for example ungulate and invertebrate herbivores. Large herbivores may remove substantial biomass and alter plant quality and therefore affect abundance and populations of invertebrate animals sharing the same food plant. We combined experimental exclusion of ungulates with a browsing intensity gradient to investigate the 15-year effect of ungulate (Cervus elaphus and Ovis aries) browsing on bilberry plant size and on bilberry-feeding herbivorous larvae (Lepidoptera and Symphyta), in a Norwegian old growth boreal forest ecosystem. Bilberry ramets in exclosure plots had nearly nine times higher dry mass and three times higher abundance of invertebrates feeding on them than in ungulate-access plots. Sweep-netting data verified these findings as larval numbers were twice as high in exclosure plots. The pattern in the large herbivore effects on bilberry size and abundance of herbivorous larvae were identical along the browsing gradient. Differences in larval abundance between treatments, as indicated by leaf-chewing, increased during the 15-year study period, and the community fluctuations were larger when ungulate herbivores were excluded. The browsing effect was moderated by plant quality as larval densities were lowest on both heavily-browsed and non-browsed plants, and highest on ramets that had 50–74% of annual shoots browsed. Our study supports previous findings in that bilberry is relatively disturbance tolerant and may recover quickly, but that ungulates may compete with herbivorous larvae for food biomass. Additionally, our results strongly indicates that population insect community peaks and fluctuations are dampened by ungulate consumption. Our findings add to the understanding on how ungulates may structure forest ecosystems directly and indirectly.     

Herbivory and drought interact to enhance spatial patterning and diversity in a savanna understory

The combination of abiotic stress and consumer stress can have complex impacts on plant community structure. Effective conservation and management of semi-arid ecosystems requires an understanding of how different stresses interact to structure plant communities. We explored the separate and combined impacts of episodic drought, livestock grazing, and wild ungulate herbivory on species co-occurrence and diversity patterns in a relatively productive, semi-arid Acacia savanna. Specifically, we analyzed 9 years of biannual plant community data from the Kenya long-term exclosure experiment, a broad-scale manipulative experiment that has excluded different combinations of large mammalian herbivores from 18 4-ha plots since 1995. During droughts, we observed low species diversity and random species co-occurrence patterns. However, when rain followed a major drought, areas exposed to moderate cattle grazing displayed high species diversity and evidence of significant species aggregation. These patterns were not apparent in the absence of cattle, even if other large herbivores were present. To explore possible mechanisms, we examined patterns separately for common and rare species. We found that aggregation patterns were likely driven by rare species responding similarly to the availability of open micro-sites. Our results indicate that in a productive, fire-suppressed savanna, the combination of periodic drought and moderate cattle grazing can enhance plant biodiversity and fine-scale spatial heterogeneity by opening up space for species that are otherwise rare or cryptic. Our findings also emphasize that domestic herbivores can have significantly stronger impacts on plant community dynamics than wild herbivores, even in an ecosystem with a long history of grazing.     

Influence of a deer carcass on Coleopteran diversity in a Scandinavian boreal forest: a preliminary study

We tested the effect of a large ungulate carcass on boreal forest biodiversity by contrasting the local abundance and diversity of Coleoptera around a roe deer Capreolus capreolus carcass and in a control plot, between 8 August and 3 September 2003, in southern Norway. The two plots differed both in occurrence and richness of species, which were almost double at the carcass plot, although the diversity indices were similar. The higher evenness of the control plot compensated for its lower number of species, probably because the carcass plot was a disturbed area, colonized by many species, which were represented by few individuals. The number of beetles captured each day correlated positively with temperature at the control plot, but not at the carcass plot, indicating that the presence of an abundant and concentrated resource increased the local activity of Coleoptera. The carcass is likely to create a particular microclimate, which could partly buffer against extremes of air-temperature variation. These preliminary results indicate that ungulate carcasses have a significant ecological impact, which should be further investigated to improve the management and restoration of European boreal forest ecosystems.     

Secondary succession and summer herbivory in a subarctic grassland: community structure and diversity

A field experiment was established in a subarctic grassland in the Finnish Lapland to study the role of summer herbivory in plant community succession Perennial vegetation and moss cover were removed in an area of 324 m² The site was divided into four blocks, of which two were fenced to prevent herbivory by large mammals (reindeer, hare)
Early successional changes in the vegetation were assessed Mean species richness per 3 × 3 m plot was consistently higher in the fenced area, indicating that herbivory can suppress small-scale diversity Herbivory affected the height of several plant species However, there was no correlation between frequency and height of individual species There was a weak indication that taller species were more successful m early succession when grazed Light competition is apparently not a key process determining successional change Thus, in early stage of succession, summer herbivory has little effect on diversity by limiting light competition, and most species are equally successful in grazed and ungrazed plots There was some indirect evidence about competitive interactions in the developing community However, unlike temperate grasslands, large mammal herbivory and competition for light seem not to be important determinants of community change in this subarctic grassland (at least what concernes early successional stages) This may be explained by the harshness of local climate, and abundance of light due to the polar day     

Understory Plant Community Composition Is Associated with Fine-Scale Above- and Below-Ground Resource Heterogeneity in Mature Lodgepole Pine (Pinus contorta) Forests

Understory plant communities play critical ecological roles in forest ecosystems. Both above- and below-ground ecosystem properties and processes influence these communities but relatively little is known about such effects at fine (i.e., one to several meters within-stand) scales, particularly for forests in which the canopy is dominated by a single species. An improved understanding of these effects is critical for understanding how understory biodiversity is regulated in such forests and for anticipating impacts of changing disturbance regimes. Our primary objective was to examine the patterns of fine-scale variation in understory plant communities and their relationships to above- and below-ground resource and environmental heterogeneity within mature lodgepole pine forests. We assessed composition and diversity of understory vegetation in relation to heterogeneity of both the above-ground (canopy tree density, canopy and tall shrub basal area and cover, downed wood biomass, litter cover) and below-ground (soil nutrient availability, decomposition, forest floor thickness, pH, and phospholipid fatty acids (PLFAs) and multiple carbon-source substrate-induced respiration (MSIR) of the forest floor microbial community) environment. There was notable variation in fine-scale plant community composition; cluster and indicator species analyses of the 24 most commonly occurring understory species distinguished four assemblages, one for which a pioneer forb species had the highest cover levels, and three others that were characterized by different bryophyte species having the highest cover. Constrained ordination (distance-based redundancy analysis) showed that two above-ground (mean tree diameter, litter cover) and eight below-ground (forest floor pH, plant available boron, microbial community composition and function as indicated by MSIR and PLFAs) properties were associated with variation in understory plant community composition. These results provide novel insights into the important ecological associations between understory plant community composition and heterogeneity in ecosystem properties and processes within forests dominated by a single canopy species.     

Long-Term Effects of White-Tailed Deer Exclusion on the Invasion of Exotic Plants: A Case Study in a Mid-Atlantic Temperate Forest

Exotic plant invasions and chronic high levels of herbivory are two of the major biotic stressors impacting temperate forest ecosystems in eastern North America, and the two problems are often linked. We used a 4-ha deer exclosure maintained since 1991 to examine the influence of a generalist herbivore, white-tailed deer (Odocoileus virginianus), on the abundance of four exotic invasive (Rosa multiflora, Berberis thunbergii, Rubus phoenicolasius and Microstegium vimineum) and one native (Cynoglossum virginianum) plant species, within a 25.6-ha mature temperate forest dynamics plot in Virginia, USA. We identified significant predictors of the abundance of each focal species using generalized linear models incorporating 10 environmental and landscape variables. After controlling for those predictors, we applied our models to a 4-ha deer exclusion site and a 4-ha reference site, both embedded within the larger plot, to test the role of deer on the abundance of the focal species. Slope, edge effects and soil pH were the most frequent predictors of the abundance of the focal species on the larger plot. The abundance of C. virginianum, known to be deer-dispersed, was significantly lower in the exclosure. Similar patterns were detected for B. thunbergii, R. phoenicolasius and M. vimineum, whereas R. multiflora was more abundant within the exclosure. Our results indicate that chronic high deer density facilitates increased abundances of several exotic invasive plant species, with the notable exception of R. multiflora. We infer that the invasion of many exotic plant species that are browse-tolerant to white-tailed deer could be limited by reducing deer populations.     

Deer herbivory as an important driver of divergence of ground vegetation communities in temperate forests

Ungulate herbivory can fundamentally affect terrestrial vegetation at the landscape and regional levels, but its impact has never been analyzed from meta‐community perspectives. Here, we study a meta‐community of forest ground‐layer plants in a warm‐temperate region along a clear gradient of deer density interplaying with gradients of other environmental factors (forest type, sky openness and topographic wetness). Canonical corresponding analysis showed that deer density was the most important determinant of species distributions. These distributions conformed to a two‐directional filtering model, which selects for competitive species at low deer density but favours herbivory‐tolerant plants at high deer density, with these two directions counterbalancing each other when herbivory is intermediary. This resulted in a bi‐directionally nested meta‐community, in which local species richness was highest at intermediate levels of deer density, conforming also to the intermediate disturbance hypothesis. Our results suggest that herbivory can be the most important driver of meta‐community structure in mesic systems; this contrasts with the results of earlier studies conducted in harsh environments, where species sorting by abiotic factors at early life stages reduced the role of biotic interactions, including herbivory.     

Dispersal process driving subtropical forest reassembly: evidence from functional and phylogenetic analysis

Understanding the mechanisms of secondary succession related to forest management practices is receiving increasing attention in community ecology and biodiversity conservation. Abiotic and biotic filtering are deterministic processes driving community reassembly. A functional trait or phylogeny-based approach predicts that environmental filtering induced by clearcut-logging results in functional/phylogenetic clustering in younger forests, while biotic filtering (competitive exclusion) promotes functional/phylogenetic overdispersion in old-growth forests. From this perspective, we examined the patterns of functional/phylogenetic structures using tree community data (147 species × 170 plots). These data were chronosequenced from clearcut secondary forests to old-growth subtropical forests in the Ryukyu Archipelago, with species’ trait data (leaf and stem) and species level phylogeny. To detect clustering or overdispersion in the functional and phylogenetic structures, we calculated the standardized effect size of mean nearest trait distance and mean nearest phylogenetic distance within the plots. Functional or phylogenetic clustering was relatively weak in secondary forests, and their directional change with increasing forest age was not generally detected. Mean nearest trait/phylogenetic distance for most plots fell within the range of random expectation. The results suggest that abiotic/biotic filtering related to functional traits or phylogenetic relatedness plays a diminished role in shaping species assembly during secondary succession in the subtropical forest. Our findings of functional and phylogenetic properties might shed light on the importance of dispersal (stochastic) processes in the regional species pool during community reassembly after anthropogenic disturbance. It will also contribute to the development of coordinated schemes that maintain potential species assembly processes in the subtropical forest.     

Deer density affects ground-layer vegetation differently in conifer plantations and hardwood forests on the Boso Peninsula, Japan

Deer overabundance reduces forest ground-layer vegetation and can cause cascading impacts on a forest ecosystem. To predict these effects, we must elucidate the relationship between deer density and the status of ground-layer vegetation. This relationship was studied in the Boso Peninsula, where the deer population density exhibits a clear geographical gradient. We examined species richness and cover of ground-layer vegetation at several cedar plantations and hardwood forests in the Boso Peninsula. We also examined whether deer impacts were altered by light condition, soil water content and forest type (cedar and hardwood). Species richness of ground-layer vegetation was maximized at an intermediate level of deer density, suggesting an intermediate disturbance effect. This phenomenon was compatible with the observation that evergreen species, which were competitive dominants, decreased with increasing deer density, whereas less competitive deciduous species increased until herbivory was intermediate. As deer density increased, cover of ground-layer vegetation gradually decreased, but species unpalatable to deer increased in abundance, suggesting indirect positive effects of deer for unpalatable species. Cedar plantations tended to have greater species richness and ground-layer cover than hardwood forests with similar deer levels. Canopy openness, an indicator of light conditions, increased species richness of hardwood forests and ground-layer cover of cedar plantations, even under deer herbivory. Topographic wetness index, an indicator of soil water content, significantly increased the ground-layer cover of cedar plantations under deer herbivory. These results emphasize the importance of environmental productivity and forest type in the management of ground-layer vegetation experiencing deer overabundance.     

不同干扰对黄土区典型草原物种多样性和生物量的影响

对黄土区典型草原进行封育+施肥(EF)、封育+火烧(EB)、封育(E)和放牧(G)处理,实地调查分析群落盖度、高度、密度、地上现存量和物种多样性,以研究不同干扰对黄土区典型草原群落物种多样性和生物量的影响.结果表明:在4种干扰类型中,施肥+封育草地群落盖度和地上生物量最高,且优势度指数最高,这与禾本科草占优势地位有关,群落均匀度指数和多样性指数最低,符合“生态位理论”;放牧地群落高度、盖度、密度和地上现存量最低,群落丰富度指数和多样性指数最高,支持“中度干扰理论”;封育地密度和均匀度指数最高;具体表现为:4种干扰类型地上生物量的变化趋势为封育+施肥＞封育+火烧＞封育＞放牧;说明长时间的封育对草地是一种严重干扰.群落丰富度指数(R和Ma)的排列顺序为放牧＞封育+施肥＞封育+火烧＞封育,群落物种多样性指数(H'和D)的排列顺序为放牧＞封育＞封育+火烧＞封育+施肥,优势度指数与多样性指数相反,群落均匀度指数(Jsw和Ea)的排列顺序为封育＞放牧＞封育+火烧＞封育+施肥.不同干扰样地群落生产力与Shannon-Wiener和Simpson 多样性指数间呈负相关关系,这个结论可以用地上/地下竞争的相互作用来解释.     

Plant diversity induces shifts in the functional structure and diversity across trophic levels

Changes to primary producer diversity can cascade up to consumers and affect ecosystem processes. Although the effect of producer diversity on higher trophic groups have been studied, these studies often quantify taxonomy‐based measures of biodiversity, like species richness, which do not necessarily reflect the functioning of these communities. In this study, we assess how plant species richness affects the functional composition and diversity of higher trophic levels and discuss how this might affect ecosystem processes, such as herbivory, predation and decomposition. Based on six different consumer traits, we examined the functional composition of arthropod communities sampled in experimental plots that differed in plant species richness. The two components we focused on were functional variation in the consumer community structure (functional structure) and functional diversity, expressed as functional richness, evenness and divergence. We found a consistent positive effect of plant species richness on the functional richness of herbivores, carnivores, and omnivores, but not decomposers, and contrasting patterns for functional evenness and divergence. Increasing plant species richness shifted the omnivore community to more predatory and less mobile species, and the herbivore community to more specialized and smaller species. This was accompanied by a shift towards more species occurring in the vegetation than in the ground layer. Our study shows that plant species richness strongly affects the functional structure and diversity of aboveground arthropod communities. The observed shifts in body size (herbivores), specialization (herbivores), and feeding mode (omnivores) together with changes in the functional diversity may underlie previously observed increases in herbivory and predation in plant communities of higher diversity.     

The impact of ecological differentiation and dispersal limitation on species turnover and phylogenetic structure of inselberg's plant communities

Phylogenetic structure analysis is a novel way to address the relative importance of stochastic and deterministic processes governing species assemblages. Here we investigate the phylogenetic structure of the vegetation of inselbergs located in the African rain forest. Inselbergs combine strong ecological gradients at the local scale due to soil depth variation and insular properties at the regional scale. They are therefore ideal models to assess the influence of ecological sorting and dispersal limitation on the phylogenetic structure of plant communities. On 21 inselbergs separated by up to 200 km where five microhabitat-types were recognized, 311 vegetation plots were inventoried. We found that floristic similarity between plots depended on both microhabitat differentiation and spatial distance, while phylogenetic clustering (i.e. excess of phylogenetic similarity between species from a same plot) only appeared between plots from differentiated microhabitats and increased with ecological distance. Within a microhabitat-type, the absence of phylogenetic structure between inselbergs indicates that species turnover is probably due to dispersal limitation rather than to regional-scale variations in environmental factors. Hence, phylogenetic structure analysis can help disentangle the effects of ecological sorting and dispersal limitation on species assemblages. To estimate the time-scale of the processes generating the phylogenetic structure, we investigated how lineage similarity changes with increasing age in the phylogenetic tree. High lineage similarity levels between ecologically very differentiated plots were only reached at the proximity of the root of the phylogenetic tree. This was observed even when considering only plots sharing no species and indicates that phylogenetic niche conservatism has been important for generating the observed phylogenetic structure. Hence, ancient diversification exerts an impact on the assembly of current plant communities.