Influence of light and soil moisture on Sierran mixed-conifer understory communities

Sierra Nevada forests have high understory species richness yet we do not know which site factors influence herb and shrub distribution or abundance. We examined the understory of an old-growth mixed-conifer Sierran forest and its distribution in relation to microsite conditions. The forest has high species richness (98 species sampled), most of which are herbs with sparse cover and relatively equal abundance. Shrub cover is highly concentrated in discrete patches. Using overstory tree cover and microsite environmental conditions, four habitats were identified; tree cluster, partial canopy, gap, and rock/shallow soil. Herb and shrub species were strongly linked with habitats. Soil moisture, litter depth and diffuse light were the most significant environmental gradients influencing understory plant distribution. Herb cover was most strongly influenced by soil moisture. Shrub cover is associated with more diffuse light, less direct light, and sites with lower soil moisture. Herb richness is most affected by conditions which influence soil moisture. Richness is positively correlated with litter depth, and negatively correlated with direct light and shrub cover. Disturbance or management practices which change forest floor conditions, shallow soil moisture and direct light are likely to have the strongest effect on Sierran understory abundance and richness.     

Pteridophyte diversity and species composition in four Amazonian rain forests

Abstract. Local variation in individual density, species composition, species richness and species diversity of terrestrial pteridophytes were studied at four sites in the tropical lowland rain forest of western Amazonia. 15 568 pteridophyte individuals representing 40 species were recorded in four plots. The variability among subplots within the same plot was considerable in all the characteristics measured (number of individuals, number of species, species diversity); the square 1‐ha plot was more homogeneous in these respects than any of the three 5 m by 1300 m transects. Species richness was affected by the density of individuals both within and among plots. Density of individuals was not affected by topographical position within any of the plots, whereas in some of the plots both species richness and species diversity were. Clustering and ordination analyses showed that floristically similar subplots could be found in different plots: although there was a tendency for subplots from the same plot to be floristically similar and therefore to group together, many recognized groups included subplots from two or more plots. Both within and among plots, the floristic differences corresponded to topographic position and were probably related to soil drainage. This was also evident in that the abundance patterns of many species followed the topography.     

How Does Restoration of Native Canopy Affect Understory Vegetation Composition? Evidence from Riparian Communities of the Hunter Valley Australia

Restoration of native vegetation often focuses on the canopy layer species, with the assumption that regeneration of the understory elements will occur as a consequence. The goal of this study was to assess the influence of canopy restoration on the composition and abundance of understory plant species assemblages along riparian margins in the Hunter Valley, NSW, Australia. We compared the floristic composition (richness, abundance, and diversity) of understory species between nonrevegetated (open) and canopy revegetated plots across five sites. A number of other factors that may also influence understory vegetation, including soil nutrients, proximity to main channel, and light availability, were also measured. We found that sites where the canopy had been restored had lower exotic species richness and abundance, as well as higher native species cover, but not native species richness, compared with open sites. Multivariate analysis of plots based on plant community composition showed that revegetated sites were associated with lower total species diversity, light availability, and exotic cover. This study has found that the restoration of the canopy layer does result in lower exotic species richness and cover, and higher native species cover and diversity in the understory, a desirable restoration outcome. Our results provide evidence that restoration of native canopy species may facilitate restoration of native understory species; however, other interventions to increase native species richness of the understory should also be considered as part of management practice.     

Species richness and soil properties in Pinus ponderosa forests: A structural equation modeling analysis

Question: How are the effects of mineral soil properties on understory plant species richness propagated through a network of processes involving the forest overstory, soil organic matter, soil nitrogen, and understory plant abundance? Location: North‐central Arizona, USA. Methods: We sampled 75 0.05‐ha plots across a broad soil gradient in a Pinus ponderosa (ponderosa pine) forest ecosystem. We evaluated multivariate models of plant species richness using structural equation modeling. Results: Richness was highest at intermediate levels of understory plant cover, suggesting that both colonization success and competitive exclusion can limit richness in this system. We did not detect a reciprocal positive effect of richness on plant cover. Richness was strongly related to soil nitrogen in the model, with evidence for both a direct negative effect and an indirect non‐linear relationship mediated through understory plant cover. Soil organic matter appeared to have a positive influence on understory richness that was independent of soil nitrogen. Richness was lowest where the forest overstory was densest, which can be explained through indirect effects on soil organic matter, soil nitrogen and understory cover. Finally, model results suggest a variety of direct and indirect processes whereby mineral soil properties can influence richness. Conclusions: Understory plant species richness and plant cover in P. ponderosa forests appear to be significantly influenced by soil organic matter and nitrogen, which are, in turn, related to overstory density and composition and mineral soil properties. Thus, soil properties can impose direct and indirect constraints on local species diversity in ponderosa pine forests.     

环境因子和干扰强度对高寒草甸植物多样性空间分异的影响

采用样带与样地结合的方法在三江源自然保护区的核心区沿海拔梯度在阴坡、阳坡分别进行草本植被调查,通过因子分析和偏相关分析研究丰富度指数、多样性指数与环境梯度（包括海拔梯度、裸斑面积、坡度、土壤总碳、总氮含量、土壤pH值、土壤总可溶性盐含量）和干扰强度（鼠类干扰强度、放牧强度）之间的关系。研究结果表明：杂类草丰富度指数（DMa杂）与总物种丰富度指数（DMa总）极显著相关（P<0.01）;阳坡DMa杂和DMa总均呈现“中海拔膨胀”现象,阴坡DMa杂和DMa总与海拔梯度呈正相关,莎草科和禾本科的丰富度指数（DMa莎和DMa禾）随海拔升高并无明显规律;通过主成分分析,及偏相关分析,第一主成分（裸斑面积、鼠类干扰和放牧强度）与除莎草科Margalef丰富度指数、禾本科Simpson指数和禾本科Pielou均匀度指数外的其他草地多样性指数均显著相关,是影响阳坡草地植物多样性的主要因子,土壤总碳、总氮含量对阳坡禾本科类群的多样性指数和均匀度指数有极显著影响,土壤pH值、TDS含量和坡度对阳坡莎草科类群的丰富度有显著影响;海拔梯度、土壤总碳、总氮以及pH值对阴坡草本植物群落的多样性影响较大。研究结论认为,植物群落生物多样性的空间分异特征是地理环境、土壤环境以及干扰强度等因素综合作用的结果。无干扰或干扰较弱时,物种多样性主要受土壤环境状况所影响;而在强干扰存在条件下,干扰强度对物种丰富度和多样性的影响比环境因子更显著;遏制高寒草甸植物多样性降低应首先控制放牧及鼠类等强干扰活动。     

基于冗余分析的城市森林林下层植物多样性预测

以4类多样性指数作为衡量城市森林林下层植物多样性差异的定量指标,并同时记录对应样方尺度的环境变量特征.以期应用冗余分析(RDA)手段提取城市森林林下层植物多样性的干扰控制因子,从而进一步揭示主要环境变量对城市森林林下层植物多样性变异的贡献率.RDA分析结果表明枯落物盖度、距林缘距离、小路面积和垃圾数4变量为能够显著解释林下叶层植物多样性变化的最小变量组合,解释信息量百分比达61%,10变量共同解释的信息量为72.1%.在RDA分析的基础上,对10环境变量组合与植物多样性特征进行双重筛选逐步回归,发现草本密度与海拔、坡度、距林缘距离、枯落物盖度呈极显著相关;草本层Pielou均匀度指数与海拔、坡度、郁闭度、枯落物盖度、岩石盖度呈极显著相关;草本层Simpson多样性指数与坡度、枯落物盖度、距林缘距离、岩石盖度、伐桩数呈极显著相关;灌木层Pielou均匀度指数则与海拔、郁闭度、小路面积、岩石盖度呈极显著相关.     

Change within and among forest communities: the influence of historic disturbance,environmental gradients,and community attributes

Understanding how ecological communities change over time is critical for biodiversity conservation, but few long‐term studies directly address decadal‐scale changes in both the within‐ and among‐community components of diversity. In this study, we use a network of permanent forest vegetation plots, established in Great Smoky Mountains National Park (USA) in 1978, to examine the factors that influence change in community composition within and among communities. In 2007, we resampled 15 plots that were logged in the late 1920s and 15 plots that had no documented history of intensive human disturbance. We found that understory species richness decreased by an average of 4.3 species over the 30‐yr study period in the logged plots, but remained relatively unchanged in the unlogged plots. In addition, tree density decreased by an average of 145 stems ha^?1 in the logged plots, but was relatively stable in the unlogged plots. However, we found that historic logging had no effect on within‐community understory or tree compositional turnover during this time period. Instead, sites at lower elevations and sites with lower understory biomass in 1978 had higher understory compositional turnover than did sites at higher elevations and sites with higher understory biomass. In addition, sites with lower soil cation exchange capacity (CEC) and with lower tree basal area in 1978 had higher tree compositional turnover than did sites with higher soil CEC and higher tree basal area. Among‐community similarity was unchanged from 1978 to 2007 for both the logged and unlogged plots. Overall, our results indicate that human disturbance can affect plant communities for decades, but the extent of temporal change in community composition may nevertheless depend more on environmental gradients and community attributes.     

The Influence of Soil Type on Rain Forest Insect Herbivore Communities

Insect herbivores were collected from five species of dipterocarp tree seedling within a large‐scale reciprocal transplant experiment in Sabah, Malaysia, on alluvial and sandstone soils in both gap and understory plots. The aim was to determine whether the location and ecological specialization of seedlings influenced the herbivore communities found on and around them. Three major groups of folivores were collected: Coleoptera, Orthoptera, and larval Lepidoptera. Herbivory of all species was confirmed through laboratory trials. Herbivore abundance in the understory plots was extremely low relative to the gaps. Rank‐abundance curves were similar on both soil types, differing only within the Lepidoptera. Coleoptera and Orthoptera communities were numerically dominated by a small suite of species capable of feeding on all dipterocarp species tested, whereas lepidopteran communities had both greater species richness and diversity. When corrected for leaf area surveyed, the abundance of Coleoptera was similar on both soil types, while larval Lepidoptera were more abundant in sandstone plots and Orthoptera were more abundant in alluvial plots. Estimated species richness of all three taxa was greater in alluvial forest, but there were contrasting patterns in Simpson diversity and evenness between groups. Species richness of Lepidoptera was greatest on seedlings when grown in their native soil type, providing partial evidence for possible escape effects, although this was not matched by differences in folivore abundance. The link between herbivore communities and herbivory rates on rain forest tree seedlings is complex and is unlikely to be detected through simplistic measures of abundance, species richness, or diversity.     

环境因子对桂西南蚬木林下植被物种多样性变异的解释

探索林下植被分布格局及其影响因素, 对于天然林保护和森林生物多样性维持机制研究具有重要意义。本文以桂西南喀斯特地区不同蚬木(Excentrodendron tonkinense)天然成熟林为研究对象, 采用植物群落样方调查、单因素方差分析、Pearson相关分析和冗余分析(RDA)等方法, 研究了8个县市蚬木天然成熟林林下植被物种多样性的变异及其对土壤、地形和光照等环境因子的响应。结果表明, 林下植被中灌木层优势种主要有越南槐(Sophora tonkinensis)、鹅掌柴(Schefflera heptaphylla)、毛果翼核果(Ventilago calyculata), 以及乔木层幼苗如蚬木、广西澄广花(Orophea anceps)、岩樟(Cinnamomum saxatile)、金丝李(Garcinia paucinervis)等, 主要来自豆科、五加科、鼠李科、椴树科、番荔枝科、樟科、藤黄科和大戟科等; 草本层优势种主要有肾蕨(Nephrolepis cordifolia)、石山棕(Guihaia argyrata)、崖姜(Pseudodrynaria coronans)、柔枝莠竹(Microstegium vimineum)、水蔗草(Apluda mutica)、沿阶草(Ophiopogon bodinieri)等, 主要来自肾蕨科、棕榈科、槲蕨科、禾本科、百合科、铁角蕨科和鳞毛蕨科等。土壤pH值、土壤含水量(SWC)、土壤全钾(TK)、土壤全磷(TP)和坡度(SLO)是林下植被物种多样性的主要影响因素, 它们分别解释了林下植被物种多样性32.3%、16.1%、9.7%、8.6%和8.6%的变异。灌木丰富度、灌木多样性指数与TK、SWC、土壤pH值和TP显著负相关, 而草本丰富度、草本多样性指数则与TK显著正相关; 灌木密度、灌木盖度与土壤pH值显著正相关, 草本密度与SWC和TK显著正相关, 草本盖度与TP、TK显著正相关, 与坡度显著负相关。土壤和地形因素是影响林下植被物种多样性变异的最主要因素, 而林分冠层结构的影响较小, 土壤各因素对林下植被物种多样性的影响高于地形因素。     

Plant succession in areas of scorched and blown-down forest after the 1980 eruption of Mount St. Helens,Washington

Abstract. Patterns of plant succession were studied in areas of scorched and blown-down forest resulting from the 1980 eruption of Mount St. Helens, Washington. Changes in species abundance were observed for 7 years in permanent sample plots representing four post-disturbance habitats, or site types. Total plant cover and species richness increased with time on all site types. In blown-down forests supporting snowpack at the time of eruption, understory recovery was dominated by the vegetative regeneration of species persisting through disturbance. In forests without snowpacks, plant survival was poorer. Increases in cover and diversity were dominated first by introduced grasses, then by colonizing forbs characteristic of early successional sites. Epilo-bium angustifolium and Anaphalis margaritacea showed widespread recruitment and clonal expansion throughout the devastated area. As a result, species composition on previously forested sites converged toward that on formerly clearcut sites, where early serai forbs resprouted vigorously from beneath the tephra. Total plant cover and species diversity were poorly correlated with post-disturbance habitat and general site characteristics (e.g. distance from the crater, elevation, slope, and aspect). However, distributions of several life-forms (e.g. low sub-shrubs and tall shrubs) were strongly correlated with depth of burial by tephra and with cover of tree rootwads. Thus, early community recovery may reflect microsite variation or chance survival and recruitment rather than broad-scale gradients in environment or disturbance. Recovery of pre-disturbance composition and structure will undoubtedly be much slower than after other types of catastrophic disturbance. The rate and direction of community recovery will largely depend on the degree to which original understory species survived the eruption.     

Plant richness and composition in hardwood forest understories vary along an acidic deposition and soil-chemical gradient in the northeastern United States

Aims

A century of atmospheric deposition of sulfur and nitrogen has acidified soils and undermined the health and recruitment of foundational tree species in the northeastern US. However, effects of acidic deposition on the forest understory plant communities of this region are poorly documented. We investigated how forest understory plant species composition and richness varied across gradients of acidic deposition and soil acidity in the Adirondack Mountains of New York State.

Methods

We surveyed understory vegetation and soils in hardwood forests on 20 small watersheds and built models of community composition and richness as functions of soil chemistry, nitrogen and sulfur deposition, and other environmental variables.

Results

Community composition varied significantly with gradients of acidic deposition, soil acidity, and base cation availability (63% variance explained). Several species increased with soil acidity while others decreased. Understory plant richness decreased significantly with increasing soil acidity (r?=?0.60). The best multivariate regression model to predict richness (p?<?0.001, adjusted-R²?=?0.60) reflected positive effects of pH and carbon-to-nitrogen ratio (C:N).

Conclusions

The relationship we found between understory plant communities and a soil-chemical gradient, suggests that soil acidification can reduce diversity and alter the composition of these communities in northern hardwood forests exposed to acidic deposition.

     

Simulated N and S deposition affected soil chemistry and understory plant communities in a boreal forest in western Canada

Aims We conducted a simulated nitrogen (N) and sulfur (S) deposition experiment from 2006 to 2012 to answer the following questions: (i) does chronic N and S deposition decrease cation concentrations in the soil and foliage of understory plant species, and (ii) does chronic N and S deposition decrease plant diversity and alter species composition of the understory plant community in a boreal forest in western Canada where intensifying industrial activities are increasing N and S deposition. Methods Our field site was a mixedwood boreal forest stand located ~100 km southeast of Fort McMurray, Alberta, Canada. The experiment involved a 2 × 2 factorial design, with two levels each of N (0 and 30 kg N ha^-1 yr^-1; applied as NH₄NO₃) and S addition (0 and 30 kg S ha^-1 yr^-1; applied as Na₂SO₄). Four blocks were established in July 2006, each with four plots of 20 × 20 m randomly assigned to the treatments. Soil and understory vegetation were sampled and cover (%) of individual species of herb (height ≤ 0.5 m) and shrub (height 0.5–1 m) layers was determined in August 2012. Important findings Seven years after the treatments began, N addition increased dissolved organic carbon and N in the mineral soil (P < 0.05), whereas S addition decreased exchangeable cations (P < 0.05) in the forest floor. In the shrub layer, species evenness, and overall diversity were decreased by N addition (P < 0.05) due to increases in abundance of nitrophilous species and S addition (P < 0.01) due to decreased cation concentrations in soils. Total shrub cover decreased with S addition (P < 0.10). Nitrogen and S addition affected neither species richness nor evenness in the herb layer. However, permutational multivariate analysis of variance and non-metric multidimensional scaling analyses (based on plant cover) indicated that the effect of N and S addition on understory plant species composition in the both shrub and herb layers was species-specific. Addition of N decreased foliar phosphorus and potassium concentrations in some species, suggesting potential risk of N-meditated nutrient imbalance in those species. Our results indicate that long-term elevated levels of N and S deposition can negatively impact plant nutrition and decrease the diversity of the understory plant community in boreal forests in northern Alberta, Canada. However, considering that the current N and S deposition rates in northern Alberta are much lower than the rates used in this study, N and S deposition should not negatively affect plant diversity in the near future.     

Density of herbaceous plants and distribution of western gorillas in different habitat types in south‐east Cameroon

The study of forest herb availability improves knowledge of ecology and conservation of gorillas that depend on such herbs. Density patterns of herbs and location of western gorilla nest sites were studied in different habitat types at a site in south‐east Cameroon to assess their relationship. Herb stems of the families Marantaceae and Zingiberaceae were identified and counted in 10,713 1‐m² plots distributed within six habitat types. Stem density correlated with light availability and ranged from 2.38 stems m^?² in near primary forest to 4.66 stems m^?² in light gaps. Gorillas showed marked preferences for habitats with high herb densities such as light gaps, swamps and young secondary forest. However, no clear relationship exists between terrestrial herbaceous vegetation and gorilla densities across Central Africa. It is suggested that differences in ecological factors and land use history within and between sites may explain differences in herb density and diversity which partly account for variations in the historical and present population distribution and density of western gorillas. Formerly logged and swamp forests, which are characterized by an abundance of herbs, may prove to be of great value in the conservation of western gorillas given appropriate forest management practices, adequate protection from poaching and limited human encroachment.     

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.     

Altitude effects on spatial components of vascular plant diversity in a subarctic mountain tundra

Environmental gradients are caused by gradual changes in abiotic factors, which affect species abundances and distributions, and are important for the spatial distribution of biodiversity. One prominent environmental gradient is the altitude gradient. Understanding ecological processes associated with altitude gradients may help us to understand the possible effects climate change could have on species communities. We quantified vegetation cover, species richness, species evenness, beta diversity, and spatial patterns of community structure of vascular plants along altitude gradients in a subarctic mountain tundra in northern Sweden. Vascular plant cover and plant species richness showed unimodal relationships with altitude. However, species evenness did not change with altitude, suggesting that no individual species became dominant when species richness declined. Beta diversity also showed a unimodal relationship with altitude, but only for an intermediate spatial scale of 1 km. A lack of relationships with altitude for either patch or landscape scales suggests that any altitude effects on plant spatial heterogeneity occurred on scales larger than individual patches but were not effective across the whole landscape. We observed both nested and modular patterns of community structures, but only the modular patterns corresponded with altitude. Our observations point to biotic regulations of plant communities at high altitudes, but we found both scale dependencies and inconsistent magnitude of the effects of altitude on different diversity components. We urge for further studies evaluating how different factors influence plant communities in high altitude and high latitude environments, as well as studies identifying scale and context dependencies in any such influences.     

抚育间伐对人工林土壤肥力的影响

研究了杉木、马尾松、建柏、柳杉和木荷人工林的抚育间伐对林分土壤肥力的影响.结果表明,杉木、马尾松、建柏、柳杉、木荷间伐后降低了林分的郁闭度.改变了林内的生境条件,促进了林下乡土植被的生长和繁衍,林下植被覆盖度、植被生物量和物种丰富度有了较大幅度的增加,间伐的强度越大.增加的幅度也越大.与不间伐林分相比,各间伐林分两年后土壤微生物数量增加、酶活性增强、土壤容重降低、总孔隙度和速效养分提高,土壤肥力得到了改善和提高.间伐后林分土壤肥力得到提高的实质在于:间伐后林下植被生物多样性的提高诱发了土壤微生物多样性和数量的提高,并由此而增强了土壤的生物活性,加速了土壤养分的循环.     

Forest plant community as a driver of soil biodiversity: experimental evidence from collembolan assemblages through large‐scale and long‐term removal of oak canopy trees Quercus petraea

Plant–soil interactions are increasingly recognized to play a major role in terrestrial ecosystems functioning. However, few studies to date have focused on slow dynamic ecosystems such as forests. As they are vertically stratified by multiple vegetation strata, canopy tree removal by thinning operations could alter forest plant community through tree canopy opening. Very little is known about cascading effects on soil biodiversity. We conducted a large‐scale, multi‐site assessment of collembolan assemblage response to long‐term canopy tree removal in sessile oak Quercus petraea temperate forests. A total of 33 experimental plots were studied covering a large gradient of canopy tree basal area, stand age and local abiotic contexts. Collembolan abundance strongly declined with canopy tree removal in early forest successional stage and this was mediated by negative effect of understory plant community composition changes, i.e. shift from moss and forb to tree seedling, fern, shrub and grass species. Negative effect of this composition shift on collembolan species richness was largely offset by positive effect of the increase in understory plant species richness. This gives support to both the plant mass‐ratio and functional diversity hypotheses. Collembolan functional groups had contrasting response patterns, which were mediated by different ecological factors. Epedaphic (r‐strategist) abundance and species richness increased with canopy tree removal in relation with the increase in understory plant species richness. In contrast, euedaphic (K‐strategist) abundance and species richness declined with canopy tree removal in early forest successional stage in relation with changes in understory plant community composition and species richness, as well as microclimatic conditions. Overall, our study provides experimental evidence that forest plant community can be a strong driver of collembolan assemblages. It also emphasizes the role of trees as foundation species of forest ecosystems that can shape soil biodiversity through their regulation of understory plant community and ecosystem abiotic conditions.     

有机肥和植被去除管理对人工林土壤节肢动物多样性的影响

施用有机肥和林下抚育（植被去除）是人工林重要的管理措施;土壤节肢动物物种丰富,是土壤生态系统的重要组成成分,对环境变化敏感,可以作为森林管理的指示生物。人工林植被去除和施肥管理影响土壤性质、资源输入量及微生物多样性,从而影响土壤节肢动物多样性,但是相关研究还十分缺乏。以沿海地区杨树人工林为对象,研究了施用有机肥和林下植被去除对土壤节肢动物的数量和多样性的影响。结果表明,有机肥和植被去除管理对不同土壤层土壤节肢动物的数量和多样性指标影响不一致。有机肥增加0-10 cm深度土壤节肢动物总数量、蜱螨目数量,降低土壤节肢动物群落物种丰富度、均匀度和Shannon多样性指数;植被去除减少0-10 cm深度土壤节肢动物总数量和弹尾目数量,降低均匀度指数。两种处理对10-20 cm深度土壤节肢动物群落的数量和各多样性指标影响不显著。总体来说（0-20 cm）,有机肥处理土壤节肢动物的数量显著增加,优势类群前气门亚目（Prostigmata）的数量增长为对照的4倍,但是土壤节肢动物群落的均匀度和Shannon多样性指数显著降低,这可能是土壤节肢动物优势类群前气门亚目密度急剧增加,而物种丰富度没有变化所导致;此外,施用有机肥增加了土壤有机质、总氮、有效磷的含量,降低土壤pH值,并且与前气门亚目密度显著相关。林下植被去除没有影响0-20 cm深度土壤节肢动物的数量和各多样性指标。     

Patterns of Rodent Species Diversity and Abundance in a Kenyan Relict Tropical Rainforest

Patterns of rodent species abundance and diversity were examined over a 5 months period in two areas of a Kenyan relict tropical rainforest. The two areas are subjected to different administrations which lead to various levels of anthropogenic disturbance: one can be considered relatively disturbed and one relatively undisturbed. Anthropogenic disturbance causes a reduction in woody stem density between 0 and 1.5 m and reduced understory tree canopy cover. Rodent abundance was estimated using the program CAPTURE and compared with the number of individuals actually captured. Density was estimated with three different methods, two of these utilised a boundary strip to estimate effective size of the area trapped. Density resulted in being relatively high in both areas, so population might have been at a peak. Species richness was higher in the disturbed forest, while species diversity and evenness was higher in the undisturbed forest. We suggest that in the disturbed forest the increase in number of species might be due to sporadical entrance in the forest by non-forest species, while the decrease in diversity might be due to the decrease of lower strata vegetation that occurs in the disturbed forest, hence this factor might affect species equitability. Bibliographic data supports this hypothesis as rodent species diversity and ground vegetation cover have been found to be correlated.     

坡度对农田土壤动物群落结构及多样性的影响

为了研究坡度对土壤动物群落的影响,于2010年3月和9月分别对川中丘陵区坡度为5°、15°、25°的3种农田土壤动物进行了调查。共采集土壤动物11657只,隶属4门11纲21目,弹尾目、蜱螨目、颤蚓目和线虫为优势类群。土壤动物群落的类群数在3月随坡度增加无显著变化(P>0.05),9月则呈波动性上升(P<0.01)。群落密度在3月随坡度增加而显著下降(P<0.01),9月的变化趋势则相反(P<0.05)。群落多样性指数在3、9两月均随坡度增加呈显著波动性变化(P<0.05)。坡度对弹尾目、蜱螨目和线虫等主要类群的密度影响显著(P<0.05),并具季节差异。主成分分析(PCA)结果表明坡度对农田土壤动物的群落结构有明显影响,Sorenson和Morisita-Horn相似性系数进一步表明坡度在3月份主要影响土壤动物群落的类群组成,在9月主要影响优势类群的密度。研究结果表明坡度对土壤动物的群落结构、多样性及主要类群的密度有显著影响,并存在季节差异。