Restoring biopedturbation in grasslands with anthropogenic focal disturbance

Grassland ecosystems evolved with natural disturbance events on multiple spatial scales in which focal, fine-scale soil disturbance by animals often was imbedded within large-scale grazing disturbance. The resulting plant communities adapted to both broad-scale and fine-scale disturbance that resulted in species-rich plant communities. These natural disturbance regimes have been largely replaced by anthropogenic disturbance. While we generally understand grassland response to modern grazing practices, we know much less about plant community response to soil disturbance imbedded within non-focal grazing. Therefore, we used a tracked vehicle to focally disturb soil in a North American mesic mixed prairie that was either undisturbed prairie or prairie with a recent history of disturbance from either grazing or haying. Successional trajectory and recovery time following focal soil disturbance was similar between grazed and hayed plant communities. Species composition did not differ (P < 0.05) between grazed or hayed prairie and the respective undisturbed prairie. Plant species richness and bare ground increased (P < 0.05) following focal soil disturbance in both grazed and hayed communities, but focal soil disturbance combined with either grazing or haying did not change either plant species richness or bare ground more than (P > 0.05) focal soil disturbance alone. Also, the effect of focal soil disturbance was shortlived with recovery in two growing seasons. Our results suggest that anthropogenic focal soil disturbance is a reasonable mechanism to restore soil disturbance to the grassland ecosystem.     

Vegetation recovery and plant facilitation in a human-disturbed lava field in a megacity: searching tools for ecosystem restoration

Unplanned urban development threatens natural ecosystems. Assessing ecosystem recovery after anthropogenic disturbances and identifying plant species that may facilitate vegetation regeneration are critical for the conservation of biodiversity and ecosystem services in urban areas. At the periphery of Mexico City, illegal human settlements produced different levels of disturbance on natural plant communities developed on a lava field near the Ajusco mountain range. We assessed natural regeneration of plant communities 20 years after the abandonment of the settlements, in sites that received low (manual harvesting of non-timber forest products), medium (removal of aboveground vegetation), and high (removal of substrate and whole vegetation) disturbance levels. We also tested the potential facilitative role played by dominant tree and shrub species. Plant diversity and vegetation biomass decreased as disturbance level increased. Sites with high disturbance level showed poor regeneration and the lowest species similarity compared to the least disturbed sites. Six dominant species (i.e., those with the highest abundance, frequency, and/or basal area) were common to all sites. Among them, three species (the tree Buddleja cordata, and two shrubs, Ageratina glabrata and Sedum oxypetalum) were identified as potential facilitators of community regeneration, because plant density and species richness were significantly higher under their canopies than at open sites. We propose that analyzing community structural traits of the successional vegetation (such as species diversity and biomass) and identifying potential facilitator species are useful steps in assessing the recovery ability of plant communities to anthropogenic disturbances, and in designing restoration strategies.     

Edge effects: impact of anthropogenic activities on vegetation structure and diversity in western Umfurudzi Park,Zimbabwe

Understanding the patterns and intensity of anthropogenic impacts on habitats is important in the conservation of tropical ecosystems. The aim of the study was to establish the associated edge effects of anthropogenic disturbances on vegetation in western Umfurudzi Park, Zimbabwe. Three study strata were established using distance from the boundary into the park. Vegetation attributes and anthropogenic disturbance levels data were collected in 2012. Significant differences (P < 0.05) were noted on tree and shrub density, woody plant height, woody plant diversity, grass height and grass sward width across the three strata. Land clearing, livestock grazing and firewood collection were the most frequent and pronounced disturbances occurring along the park boundary. These disturbances decreased in intensity as distance from the boundary increased. We recommend the following: (i) the need to revisit the buffer zone concept and policy measures associated with ecosystem services and goods provision for communities surrounding protected areas, (ii) engaging neighbouring communities on sustainable ways of deriving ecosystem goods and services from buffer zones and protected areas and (iii) further studies on the regeneration and recovery of cleared patches along the boundary and their use by wildlife species in the park.     

水淹干扰下水库水滨带植物群落谱系结构与物种多样性格局

群落谱系结构将物种系统发育信息整合到群落中,给生物多样性研究提供了全新视角。为探讨水淹干扰下水库水滨带植物群落物种多样性维持机制,以丹江口水库水滨带为研究区域,以南水北调中线一期工程运行前的原有水滨带植被为研究对象,分析不同水淹干扰强度下群落谱系结构和物种多样性及其与环境因素的关系。结果表明：(1)随着水淹干扰强度增加,群落物种丰富度、物种多样性和谱系多样性显著降低。谱系结构指数虽无显著差异,但随着水淹干扰强度增加呈现由发散到聚集的变化趋势。表明水滨带植物群落物种多样性维持机制是生境过滤和生态位分化共同驱动的结果,并且随着水淹干扰强度增加呈现生境过滤作用增加、物种间竞争排斥作用减弱的生态过程影响规律。(2)坡度、土壤质地、速效氮和全氮含量对整个水滨带植物群落物种丰富度、物种多样性和谱系多样性影响显著。此外,土层厚度和速效磷对物种丰富度和土层厚度对谱系多样性也影响显著。而仅有速效氮含量对谱系结构指数影响显著;轻度水淹干扰下坡向、速效磷含量与多样性指数显著相关;中度水淹干扰下坡度、土层厚度、土壤质地、土壤总氮含量与多样性指数显著相关,土壤pH、全氮和全磷含量与谱系结构指数显著相关;重度水淹...     

Importance of molehill disturbances for invasion by Bunias orientalis in meadows and pastures

Small-scale soil disturbances by fossorial animals can change physical and biotic conditions in disturbed patches and influence spatial and temporal dynamics, and the composition of plant communities. They create regeneration niches and colonization openings for native plants and, according to the intermediate disturbance hypothesis, they are expected to increase plant community diversity. However, it also has been reported that increased disturbance resource availability and decreased competition with native species may result in the invasion of communities by alien plant species, as predicted by the fluctuating resources theory of invasibility. In this study, we investigated the importance of European mole disturbances for the invasion of semi-natural fresh meadows and pastures by the alien plant, Bunias orientalis, which has mainly spread throughout Central Europe on anthropogenically disturbed sites. We hypothesized that the invader, being particularly well adapted to anthropogenic disturbances, enters into dense vegetation of meadows and pastures mainly on mole mounds. To assess the seedling recruitment of B. orientalis in relation to disturbance, we counted the number of seedlings that emerged on molehills and control plots in meadows and pastures. The establishment of juvenile (0–1 year) rosette plants on and off molehills was surveyed on 5 × 5 m plots. In accordance with our hypothesis, mole disturbances were found to serve as a gateway for B. orientalis by which the invader may colonize semi-natural grasslands. The seedlings of the species emerged almost solely on molehills and the young rosettes were established predominantly on mole mounds. Although the seedling density did not differ significantly between the meadows and pastures, the number of established plants in the pastures was considerably higher. We suggest that the invasion by B. orientalis in pastures may be facilitated by vegetative regeneration following root fragmentation by sheep pasturing.     

Impacts of water stress removal and disturbance regimes on Mediterranean dry grasslands diversity and succession

Our goal was to disentangle the effects of stress removal and disturbance on plant communities of a Mediterranean rangeland, La Crau (southeastern France). We compared undisturbed reference steppe vegetation with vegetation impacted by changes in land use such as earlier phases of cultivation (dating back 20 years) and/or current water infiltrations (revealed by the presence of Brachypodium ph?nicoïdes), since the establishment of adjacent hay meadows. We considered plots with and without brambles (Rubus ulmifolius), an indigenous shrub species that had colonized the area after the land-use changes. We monitored the composition and measured the taxonomic richness and richness of functional groups, evenness and similarities of plant communities. The species richness of the undisturbed community was significantly higher than that of all disturbed plant communities. Although cultivation led to the dominance of ruderal species, the removal of water stress had a stronger negative impact, enabling the establishment of herbaceous competitor species such as B. ph?nicoïdes. The dominance of this species resulted in a significant decline in species richness and evenness after water stress removal. The presence of brambles correlating with former cultivation and/or current water infiltration did not have a significant impact on plant species richness in the vicinity of bramble bushes, although it significantly modified the composition of the adjacent herbaceous vegetation. Our study highlights again the low resilience of Mediterranean dry grasslands after disturbance. While both the disturbance and the water stress removal resulted in changes within the plant community, our findings reveal a stronger impact of the water stress removal. Water infiltration led to decreased plant species richness and evenness because the greater availability of water favored competitor species over the stress-tolerant xeric species. Therefore, for restoring the original steppe species richness, the priority will be to control water infiltrations, even before any scrub-clearing is undertaken to control bramble colonization.     

Relationships between the density of two potential restoration tree species and plant species abundance and richness in a degraded Afromontane forest of Kenya

In recent years, there have been considerable efforts to restore degraded tropical montane forests through active restoration using indigenous tree species. However, little is known about how these species used for restoration influence other species. In this study, two potential restoration species, Albizia gummifera and Neoboutonia macrocalyx, are investigated with regard to the relationship between their density and the abundance and richness of other plant species. The study was conducted in a degraded forest consisting of disturbed transition zones and secondary forest. Our results show positive relationships between the density of A. gummifera and the abundance of tree seedling and sapling richness in the transition zones and in the secondary forest. Shrub richness was negatively related to the density of A. gummifera. Abundance and richness of tree saplings and shrubs were positively related to N. macrocalyx density both in the transition zones and in the secondary forest. Herb species richness declined with N. macrocalyx density in the transition zones but increased with N. macrocalyx density in the secondary forest. The positive relationships between the density of the two tree species and species richness of other woody species suggest that both A. gummifera and N. macrocalyx can be suitable for active restoration of degraded mountain forests within their natural range.     

Species richness effects on grassland recovery from drought depend on community productivity in a multisite experiment

Biodiversity can buffer ecosystem functioning against extreme climatic events, but few experiments have explicitly tested this. Here, we present the first multisite biodiversity × drought manipulation experiment to examine drought resistance and recovery at five temperate and Mediterranean grassland sites. Aboveground biomass production declined by 30% due to experimental drought (standardised local extremity by rainfall exclusion for 72–98 consecutive days). Species richness did not affect resistance but promoted recovery. Recovery was only positively affected by species richness in low‐productive communities, with most diverse communities even showing overcompensation. This positive diversity effect could be linked to asynchrony of species responses. Our results suggest that a more context‐dependent view considering the nature of the climatic disturbance as well as the productivity of the studied system will help identify under which circumstances biodiversity promotes drought resistance or recovery. Stability of biomass production can generally be expected to decrease with biodiversity loss and climate change.     

人为干扰下雅安市雨城区青衣江河岸带草本植物群落物种多样性及生态位的研究

以雅安市雨城区段青衣江河岸带的草本植被为研究对象,采用典型样地法选取沿岸受3种不同强度人为干扰的样地(轻度干扰的河滩地、中度干扰的割草地和重度干扰的弃耕地),探究不同人为干扰强度对青衣江沿岸的草本植物群落物种多样性和生态位的影响。结果表明:在3种类型的样地中共观测到64个物种,隶属于26科53属,物种数随着干扰强度的增加而降低;分析重要值发现,不同干扰强度下群落的主体均为菊科(Compositae)、禾本科(Gramineae)、蓼科(Polygonaceae)和豆科(Leguminosae)的种类,各物种重要值的差异不大,优势种不明显,种间竞争激烈;受不同干扰强度群落的生境存在差异,轻度干扰、中度干扰和重度干扰群落的生态位重叠值在0.5以上的物种数比率分别为95.0%、85.4%、74.2%,受不同强度干扰群落之间的物种相似程度不同,轻度干扰与中度干扰、中度干扰与重度干扰、轻度干扰与重度干扰的群落相似性系数分别为0.733、0.719、0.625;受不同强度人为干扰的群落中物种丰富度指数D值和Shannon-Wiener多样性指数H值的大小排序为轻度干扰中度干扰重度干扰,但Simpson指数H'值和Pielou均匀度指数Jsw值在样地之间的差异不显著。     

Complex vegetation responses to soil disturbances in mountain grassland

We studied vegetation responses to disturbances originated by ants and voles in subalpine grasslands in the Eastern Pyrenees. We compared the effects of these small-scale disturbances with those of a large-scale disturbance caused by ploughing. We wanted to know if these soil disturbances promoted species richness through the existence of a specific guild of plants colonizing these areas, and if this guild was the same for all soil disturbances, independently of their extent. In general, grassland vegetation seemed to recover relatively quickly from soil-displacement disturbances, and the effects could be scaled up in time and space in terms of species richness and composition. Vole mound composition was similar to that in the surrounding grassland, suggesting that mounds were rapidly colonized by the neighbouring vegetation. Vegetation composition differed between the grassland and the ant mounds. Grasses and erect dicots coped well with repeated disturbance, while rosette-forming species and sedges were very sensitive to it. Landscape processes could be important to understanding recolonization. Species from xeric grasslands were found in mesic grasslands when disturbed by ploughing and on the tops of active ant mounds. Furrows in mesic grasslands recovered well, but decades after disturbance showed long persistence of some xeric species and increased species richness compared to terraces, while xeric grasslands showed decreased richness. This suggests that, because of those disturbances, within-habitat diversity was increased, although landscape diversity was not. However, specific disturbances showed idiosyncratic effects, which could enhance the species richness globally. In ant-affected areas, the grassland itself showed the highest plant species richness, partially associated to the presence of some species with elaiosomes not, or only rarely, found in adjacent grasslands without ant mounds. Therefore, soil disturbances occurring at different spatial scales contributed to complexity in vegetation patterns in addition to abiotic factors and grazing. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Nomenclature of the species follows Tutin et al. (1964–1980) and Bolòs et al. (1993).     

Encroachment of upland Mediterranean plant species in riparian ecosystems of southern Portugal

Riparian ecosystems have unique biodiversity, are highly sensitive to disturbance and anthropogenic influence. As world water resources become scarcer, scientists predict greater competition among species for water resources. Indeed, increased encroachment of upland plants into the riparian zone is already occurring, irreversibly changing riparian plant communities. Since semi-arid regions such as Mediterranean-type ecosystems are likely to follow this same trajectory, assessing the contributions of riparian versus upland (sclerophyllous) plants to community composition is important. A survey of seventy 2 km-long riparian transects on the Sado and Guadiana watersheds in southern Portugal assessed (1) the woody riparian plant community composition, (2) how much richness is due to strictly riparian plants versus sclerophyllous upland plants, and (3) which combinations of biotic and abiotic factors allow higher species richness in the strictly riparian, sclerophyllous, and overall plant communities. The survey detected 53 different woody plant species (28 endemic) across all communities. Riparian community richness was on average 16 species, seven of which were strictly riparian and the remainder being sclerophyllous, exotic species or fruit trees. Sclerophyllous plant species occurred consistently across sampling units (90% of transects). On average, 46% of the total woody plant community richness was due to strictly riparian plants and 28% was due to sclerophyllous plants. Community richness was positively affected by the area of shrubs in the riparian zone and by the absence of human activities and goats. Surrounding landscape pattern only affected the strictly riparian plant richness. These results suggest that natural and human-mediated disturbances in riparian ecosystems create gaps and clearings for which riparian and sclerophyllous plants compete. Establishment success seems to be related to the propagule pressure of the neighbouring landscape, its diversity and density, as well as the presence of herbivores. Preserving strictly riparian plants, removing exotic species, preventing grazing, and promoting riparian values (recreation, aesthetics and the provision of ecosystem services) will aid the future conservation of the unique biodiversity of riparian ecosystems.     

Structural–functional approach to identify post-disturbance recovery indicators in forests from northwestern Patagonia: A tool to prevent state transitions

The disruption of the natural post-disturbance recovery process, either by changes in disturbance regime or by another disturbance, can trigger transitions to alternative degraded states. In a scenario of high disturbance pressure on ecological systems, it is essential to detect recovery indicators to define the period when the system needs more protection as well as the period when the system supports certain use pressure without affecting its resilience. Recovery indicators can be identified by non-linear changes in structural and functional variables. Fire largely modulates the dynamic and stability of plant communities worldwide, and is this the case in northwestern (NW) Patagonia. The ultimate goal of this study is to propose a structural–functional approach based on a reference system (i.e. chronosequence) as a tool to detect post-disturbance recovery indicators in forests from NW Patagonia. In NW Patagonia (40–42°S), we sampled 25 Austrocedrus chilensis and Nothofagus spp. communities differing in post-fire age (0.3–180 years). In each community we recorded structural (woody species cover and height, solar radiation, air temperature, relative humidity) and functional (annual recruitment of woody and tree species) attributes. We modeled these attributes in function of post-fire age and analized the relationship between a functional attribute and a Structural Recovery Index (SRI). Communities varying in time-since-last-fire were structurally and functionally different. Moreover, response variables showed non-linear changes along the chronosequence, allowing the selection of recovery indicators. We suggest to use vegetation variables instead of environmental variables as structural recovery indicators. Horizontal and Vertical Vegetation Heterogeneity indices provided the information necessary to describe vegetation spatial reorganization after fire. Tree species annual recruitment was a good indicator of the functional recovery of forest communities. The relationship between a functional attribute and SRI allowed us to detect phases with high- and low-risk of degradation during post-fire succession. High-risk phases (<36 years old) had the highest horizontal vegetation heterogeneity and scarce tree seedling density (<7000 seedlings ha⁻¹ year⁻¹). Whereas, low-risk phases (>36 years old) had the highest vertical vegetation heterogeneity and tree species seedling density (>10,000 seedlings ha⁻¹ year⁻¹). Due to the low structural–functional levels, communities at high-risk phases would be more vulnerable to antropic pressure (e.g. livestock raising, logging) than communities at low-risk phases. The proposed approach contributes to the sustainable management of forest communities because it allows to estimate the minimum structural–functional levels from which forest communities could be harvested.     

Butterfly Community Composition Across a Successional Gradient in a Human‐disturbed Afro‐tropical Rain Forest

Knowledge of the recovery of insect communities after forest disturbance in tropical Africa is very limited. Here, fruit‐feeding butterflies in a tropical rain forest at Kibale National Park, Uganda, were used as a model system to uncover how, and how fast, insect communities recover after forest disturbance. We trapped butterflies monthly along a successional gradient for one year. Traps were placed in intact primary forest compartments, heavily logged forest compartments with and without arboricide treatment approximately 43 years ago, and in conifer‐clearcut compartments, ranging from 9 to 19 years of age. The species richness, total abundance, diversity, dominance, and similarity of the community composition of butterflies in the eight compartments were compared with uni‐ and multivariate statistics. A total of 16,728 individuals representing 88 species were trapped during the study. Butterfly species richness, abundance, and diversity did not show an increasing trend along the successional gradient but species richness and abundance peaked at intermediate stages. There was monthly variation in species richness, abundance, diversity and composition. Butterfly community structure differed significantly among the eight successional stages and only a marginal directional change along the successional gradient emerged. The greatest number of indicator species and intact forest interior specialists were found in one of the primary forests. Our results show that forest disturbance has a long‐term impact on the recovery of butterfly species composition, emphasizing the value of intact primary forests for butterfly conservation.     

Effects of road age and distance on plant biodiversity: a case study in the Yellow River Delta of China

A majority of ecological studies of roads have usually focused on their deleterious effect, and these preconceptions have hampered a full evaluation of ecological functions of roads. We examined the effect of road disturbance on plant communities by investigating roadside vegetation in the protogenic road ecosystem of the Yellow River Delta (YRD), China. Specifically, we examined the effect of distance from the road verge and road age on the pattern of plant species richness, diversity, and composition at 17 sites. The results revealed that roads retained higher species richness adjacent to the road verge than far away from the road verge (>200 m). Additionally, species richness and diversity of roadside plants significantly decreased as the distance from the road verge increased. Plant species richness and diversity increased with road age in majority of prescribed distances, while species richness at the road verge significantly increased with road age and peaked at a road age of 20 years, after which species richness plateaued. A correspondence analysis illuminated that the roadside vegetation primarily consists of non-halophytic native species. The percentage of halophytes increased with the distance from the road verge and decreased with road age. Additionally, different performances of alien and native species in response to road disturbance were observed. Furthermore, it is worth noting that roadside environments provide survival habitats for some threatened species, such as wild soybean. In the present study, both positive and negative effects of roads on the plant community were observed from road construction to the long-term operational phases.     

Long‐term Changes in Bird Communities after Wildfires in the Central Brazilian Amazon

We examined long‐term responses of an Amazonian bird assemblage to wildfire disturbance, investigating how understory birds reacted to forest regeneration 1, 3, and 10 years after a widespread fire event. The bird community was sampled along the Arapiuns and Maró river catchments in central Brazilian Amazonia. Sampling took place in 1998, 2000, and 2008 using mist‐nets in eight plots (four burned, four unburned sites). Species richness did not change significantly in unburned sites. In burned sites, however, we found significantly lower richness in 1998, higher richness in 2000, and similar richness in 2008. Multi‐dimensional scaling ordination showed consistent differences in bird communities both within burned sites sampled in different sampling years, and between burned and unburned sites in all years. Of the 30 most abundant species, 12 had not recovered 10 years after the fires, including habitat specialists such as mixed flocks specialists and ant‐followers. Fire‐disturbance favored three species (two hummingbirds and a manakin) in the short term only. All other species were either favored throughout the study (seven species of omnivores and small insectivores) or did not show a clear response (eight species). In burned sites, we also found significantly lower abundance of species sensitive to disturbances and habitat specialists over the entire study period. Although the bird community seems to be recovering in terms of richness, the overall community composition and abundance of some species in post‐burned and unburned sites remain very different, and have not recovered after 10 years of forest regeneration.     

Effects of anthropogenic disturbance on tree population structure and diversity of a rain forest biosphere reserve in Ghana,West Africa

We evaluated the impacts of anthropogenic disturbance on community structure and diversity along three management zones of the Bia biosphere reserve in Ghana. Sixty sample plots were distributed among the core, buffer and transition zones. We estimated the degree of disturbances from discernible indicators on the field and satellite images. All tree species ≥10 cm dbh (diameter at breast height) were identified and enumerated. Inventory data were compared across the zones and related to intensity of disturbances. A total of 1176 individual trees from 108 species and 33 families were encountered. Number of species varied from 27 in the highly disturbed (HD) to 61 in the least disturbed (LD) zone. Mean basal area (BA) varied from 11.71 in the HD to 28.26 in the LD. Both Margalef's species richness and Shannon‐Weiner's α‐diversity were highest in the moderately disturbed (MD) than either the least and most disturbed zones. Our study revealed significant differences in tree abundance, stem density, BA and species diversity, attributable to differences in degree of anthropogenic disturbances among zones. Given the different levels of anthropogenic disturbance and corresponding impacts across the reserve, we recommend an integrated management strategy for the conservation of biodiversity in the Bia biosphere reserve.     

Rapid biodiversity declines in both ungrazed and intensely grazed exotic grasslands

Exotic-dominated ecosystems with low diversity are becoming increasingly common. It remains unclear, though, whether differences between native and exotic species (driver model), or changes in disturbances or resources (passenger model), allow exotics to become competitive dominants. In our field experiment, plant species origin (native or exotic), cattle grazing (ungrazed or intensely grazed once), and species composition treatments were fully crossed and randomly assigned to four-species mixtures and monocultures of grassland plants. We found that biodiversity declined more rapidly in exotic than in native species mixtures, regardless of our grazing disturbance treatment. Early declines in species evenness (i.e., increases in dominance) led to subsequent declines in species richness (i.e., local extinctions) in exotic mixtures. Specifically, Simpson’s diversity was 29% lower after 1 year, and species richness was 15% lower after 3 years, in exotic than in native mixtures. These rapid biodiversity declines in exotic mixtures were partly explained by decreased complementarity (i.e., niche partitioning and facilitation), presumably because exotic species lack the coevolutionary history that can lead to complementarity and coexistence in native communities. Thus, our results suggest that exotic species can drive biodiversity declines in the presence or absence of a grazing disturbance, partly because exotic species interactions differ from native species interactions. This implies that restoring plant biodiversity in grasslands may require removal of exotic species, in addition to disturbance management.     

Combined disturbances and the role of their spatial and temporal properties in shaping community structure

Disturbances are characteristic for many ecosystems. However, we still lack generalizations concerning their role in shaping communities, particularly when disturbances co-occur. To study such effects, we used a novel modeling approach that is unrestricted by a priori tradeoffs among specific plant traits, except for those generated by allocation principles. Thus, trait combinations were emergent properties associated with biotic and abiotic constraints. Specifically, we asked which traits dominate under specific disturbance regimes, whether single and combined disturbance regimes promote similar trait tradeoffs and how complex disturbance regimes affect species richness and functional diversity. Overall, disturbances’ temporal properties governed the outcome of combined disturbances and were a stronger assortative force than spatial disturbance properties: low temporal predictability decreased seed-dispersability and dormancy, but increased competitive ability and disturbance tolerance. Evidence for tradeoffs between different colonization modes and between dormancy and disturbance tolerance were found, while surprisingly, the widely accepted colonization–competition tradeoff was not generated. Diversity was highest at intermediate disturbance intensity, but decreased monotonically with increasing unpredictability. In accordance with our results, future models should avoid restrictive assumptions about tradeoffs to generate robust and more general predictions about the role of disturbances for community dynamics.     

人为干扰对闽北森林群落物种多样性的影响

本文从群落及其组成结构等方面分析了闽北长期封禁保护的森林（ｃｏｎｓｅｒｖｅｄｆｏｒｅｓｔ,ＣＦ）和人为干扰后的退化森林（ｄｅｇｒａｄｅｄｆｏｒｅｓｔ,ＤＦ）群落物种多样性,结果认为,ＤＦ群落的植物物种丰富度和ＳｈａｎｎｏｎＷｉｅｎｅｒ指数与ＣＦ群落相近或略高,但ＤＦ群落植物种类组成和层次结构的物种多样性发生明显变化,群落物种种群基础已改变,稀有种和渐危种缺乏,这正是ＤＦ与ＣＦ群落物种多样性的本质差异。     

Disturbance and diversity at two spatial scales

The spatial scale of disturbance is a factor potentially influencing the relationship between disturbance and diversity. There has been discussion on whether disturbances that affect local communities and create a mosaic of patches in different successional stages have the same effect on diversity as regional disturbances that affect the whole landscape. In a microcosm experiment with metacommunities of aquatic protists, we compared the effect of local and regional disturbances on the disturbance–diversity relationship. Local disturbances destroyed entire local communities of the metacommunity and required reimmigration from neighboring communities, while regional disturbances affected the whole metacommunity but left part of each local community intact. Both disturbance types led to a negative relationship between disturbance intensity and Shannon diversity. With strong local disturbance, this decrease in diversity was due to species loss, while strong regional disturbance had no effect on species richness but reduced the evenness of the community. Growth rate appeared to be the most important trait for survival after strong local disturbance and dominance after strong regional disturbance. The pattern of the disturbance–diversity relationship was similar for both local and regional diversity. Although local disturbances at least temporally increased beta diversity by creating a mosaic of differently disturbed patches, this high dissimilarity did not result in regional diversity being increased relative to local diversity. The disturbance–diversity relationship was negative for both scales of diversity. The flat competitive hierarchy and absence of a trade-off between competition and colonization ability are a likely explanation for this pattern.