Individual Canopy‐tree Species Effects on Their Immediate Understory Microsite and Sapling Community Dynamics

Canopy trees are largely responsible for the environmental heterogeneity in the understory of tropical and subtropical species‐rich forests, which in turn may influence sapling community dynamics. We tested the effect of the specific identity of four cloud forest canopy trees on total solar radiation, canopy openness, soil moisture, litter depth, and soil temperature, as well as on the structure and dynamics of the sapling community growing beneath their canopies. We observed significant effects of the specific identity of canopy trees on most understory microenvironmental variables. Soil moisture was higher and canopy openness lower beneath Cornus disciflora. In turn, canopy openness and total solar radiation were higher beneath Oreopanax xalapensis, while the lowest soil moisture occurred beneath Quercus laurina. Moreover, Chiranthodendron pentadactylon was the only species having a positive effect on litter depth under its canopy. In spite of these between‐species environmental differences, only C. pentadactylon had significant, negative effects on sapling density and species richness, which may be associated to low seed germination and seedling establishment due to an increased litter depth in its vicinity. The relevance of the specific identity of canopy trees for natural regeneration processes and species richness maintenance depends on its potential to differentially affect sapling dynamics through species‐specific modifications of microenvironmental conditions.     

Community structures of Mesostigmata, Prostigmata and Oribatida in broad-leaved regeneration forests and conifer plantations of various ages

The community structures of Mesostigmata, Prostigmata, and Oribatida in the soil of broad-leaved regeneration forests and conifer plantations of various ages were assessed alongside soil and plant environmental variables using three response metrics (density, species richness, and species–abundance distribution). The density and species richness of mites recovered swiftly after clear-cutting or replanting. Oribatid mites dominated the soil mite communities in terms of densities and species richness for both forest types. Soil mite communities in broad-leaved forests was related to forest age, the crown tree communities index, and forest-floor litter weight. In contrast, soil mite communities in the conifer plantation sites were related to various indices of understory plants. The development of the understory plants was synchronized with the silvicultural schedules, including a closed canopy and thinning. Such a conifer plantation management may affect indirectly the community of mites.     

Scale-specific correlations between habitat heterogeneity and soil fauna diversity along a landscape structure gradient

Habitat heterogeneity contributes to the maintenance of diversity, but the extent that landscape-scale rather than local-scale heterogeneity influences the diversity of soil invertebrates—species with small range sizes—is less clear. Using a Scottish habitat heterogeneity gradient we correlated Collembola and lumbricid worm species richness and abundance with different elements (forest cover, habitat richness and patchiness) and qualities (plant species richness, soil variables) of habitat heterogeneity, at landscape (1 km²) and local (up to 200 m²) scales. Soil fauna assemblages showed considerable turnover in species composition along this habitat heterogeneity gradient. Soil fauna species richness and turnover was greatest in landscapes that were a mosaic of habitats. Soil fauna diversity was hump-shaped along a gradient of forest cover, peaking where there was a mixture of forest and open habitats in the landscape. Landscape-scale habitat richness was positively correlated with lumbricid diversity, while Collembola and lumbricid abundances were negatively and positively related to landscape spatial patchiness. Furthermore, soil fauna diversity was positively correlated with plant diversity, which in turn peaked in the sites that were a mosaic of forest and open habitat patches. There was less evidence that local-scale habitat variables (habitat richness, tree cover, plant species richness, litter cover, soil pH, depth of organic horizon) affected soil fauna diversity: Collembola diversity was independent of all these measures, while lumbricid diversity positively and negatively correlated with vascular plant species richness and tree canopy density. Landscape-scale habitat heterogeneity affects soil diversity regardless of taxon, while the influence of habitat heterogeneity at local scales is dependent on taxon identity, and hence ecological traits, e.g. body size. Landscape-scale habitat heterogeneity by providing different niches and refuges, together with passive dispersal and population patch dynamics, positively contributes to soil faunal diversity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seedling and Sapling Dynamics of Treefall Pits in Puerto Rico1

Seedling and sapling dynamics in a Puerto Rican rain forest were compared between forest understory and soil pits created by the uprooting of 27 trees during Hurricane Hugo. Soil N and P, organic matter, and soil moisture were lower and bulk densities were higher in the disturbed mineral soils of the pits than in undisturbed forest soils ten months after the hurricane. No differences in N and P levels were found in pit or forest soils under two trees with N–fixing symbionts (Inga laurina and Ormosia krugii) compared to soils under a tree species without N–fixing sym–bionts (Casearia arborea), but other soil variables (Al, Fe, K) did vary by tree species. Forest plots had greater species richness of seedlings (<10 cm tall) and saplings (10–100 cm tall) than plots in the soil pits (and greater sapling densities), but seedling densities were similar between plot types. Species richness and seedling densities did not vary among plots associated with the three tree species, but some saplings were more abundant under trees of the same species. Pit size did not affect species richness or seedling and sapling densities. Recruitment of young Cecropia schreberiana trees (>5 m tall) 45 months after the hurricane was entirely from the soil pits, with no tree recruitment from forest plots. Larger soil pits had more tree recruitment than smaller pits. Defoliation of the forest by the hurricane created a large but temporary increase in light availability. Recruitment of C. schreberiana to the canopy occurred in gaps created by the treefall pits that had lower soil nutrients but provided a longer–term increase in light availability. Treefall pits also significantly altered the recruitment and mortality of many understory species in the Puerto Rican rain forest but did not alter species richness.     

The effects of environmental variables and human disturbance on woody species richness and diversity in a bamboo–deciduous forest in northeastern Thailand

Variations in species richness and diversity at a local scale are affected by a number of complex and interacting variables, including both natural environmental factors and human-made changes to the local environment. Here we identified the most important determinants of woody species richness and diversity at different growth stages (i.e. adult, sapling and seedling) in a bamboo–deciduous forest in northeast Thailand. A total of 20 environmental and human disturbance variables were used to determine the variation in species richness and diversity. In total, we identified 125 adult, 111 sapling (within fifty 20 × 20-m plots) and 89 seedling species (within one hundred and twenty 1 × 1-m subplots). Overall results from stepwise multiple regression analyses showed that environmental variables were by far the most important in explaining the variation in species richness and diversity. Forest structure (i.e. number of bamboo clumps and canopy cover) was important in determining the adult species richness and diversity (R ² = 0.48, 0.30, respectively), while topography (i.e. elevation) and human disturbance (i.e. number of tree stumps) were important in determining the sapling species richness and diversity (R ² = 0.55, 0.39, respectively). Seedling species richness and diversity were negatively related to soil phosphorus. Based on our results, we suggest that the presence of bamboos should be incorporated in management strategies for maintaining woody species richness and diversity in these forest ecosystems. Specifically, if bamboos cover the forest floor at high densities, it may be necessary to actively control these species for successful tree establishment.     

Vegetation responses to burning in a rain forest in Borneo

During the 1997/98 ENSO (El Niño Southern Oscillation) event more than 5 million ha of East Kalimantan, Indonesia burned. Here we quantify the initial stages of regeneration (19982001), both in forest that burned and in unburned controls. Sapling and seedling density and species richness remained significantly lower in burned than in unburned forest and community composition remained substantially different between both forest types throughout the sampling period. The only pronounced edge effect was a significantly higher density of seedlings in the interior of unburned forest. Sapling density increased and seedling density declined in both unburned and burned forest during the four-year study period. In the unburned forest, sapling and seedling species richness remained stable, but sapling species richness declined significantly with time in the burned forest. The pioneer community in the burned forest was, furthermore, characterised by higher growth and recruitment than in the unburned forest but mortality did not differ between both forest types. Differences in environment (burned versus unburned: 2965% of variation explained) and the distance between sample sites (1323% of variation explained) explained substantial amounts of variation in sapling and seedling community similarity. Similarity was, however, only marginally (< 1% explained) related to the edge position and temporal variation (difference among sample events). Our results, four years after the initial burn, indicate that burned forest still differed greatly from unburned forest in terms of density, species richness and community composition. There was also no clear trend of a return to pre-disturbance conditions, which indicates that the burned forest may remain in a severely degraded state for a prolonged period of time.     

The diversity of beetle assemblages in different habitat types in Sabah, Malaysia

The diversity of beetle assemblages in different habitat types (primary forest, logged forest, acacia plantation and oil palm plantation) in Sabah, Malaysia was investigated using three different methods based on habitat levels (Winkler sampling, flight-interception-trapping and mist-blowing). The overall diversity was extremely high, with 1711 species recorded from only 8028 individuals and 81 families (115 family and subfamily groups). Different degrees of environmental changes had varying effects on the beetle species richness and abundance, with oil palm plantation assemblage being most severely affected, followed by acacia plantation and then logged forest. A few species became numerically dominant in the oil palm plantation. In terms of beetle species composition, the acacia fauna showed much similarity with the logged forest fauna, and the oil palm fauna was very different from the rest. The effects of environmental variables (number of plant species, sapling and tree densities, amount of leaf litter, ground cover, canopy cover, soil pH and compaction) on the beetle assemblage were also investigated. Leaf litter correlated with species richness, abundance and composition of subterranean beetles. Plant species richness, tree and sapling densities correlated with species richness, abundance and composition of understorey beetles while ground cover correlated only with the species richness and abundance of these beetles. Canopy cover correlated only with arboreal beetles. In trophic structure, predators represented more than 40% of the species and individuals. Environmental changes affected the trophic structure with proportionally more herbivores (abundance) but fewer predators (species richness and abundance) in the oil palm plantation. Biodiversity, conservation and practical aspects of pest management were also highlighted in this study.     

北京松山自然保护区森林群落物种多样性及其神经网络预测

物种多样性是群落结构和功能复杂性的一种度量,物种多样性的空间分布格局受许多环境因子的影响.运用多样性指数,多层感知器网络,分析了松山保护区森林群落物种多样性与群落类型、结构和生境之间的关系.结果表明:(1)大果榆+山杨混交林、油松+青杨混交林物种丰富度、多样性和均匀度均较高,而大果榆林、华北落叶松林的各项指数值均较低.Patrick指数和Shannon-Weiner指数在森林群落中均表现为草本层＞灌木层＞乔木层;Pielou指数在榆林中表现为草本层＞乔木层＞灌木层,而在其他森林群落中表现为灌木层＞草本层＞乔木层.(2)功能层物种多样性在海拔梯度上的变化趋势不同,在乔木层,丰富度、多样性和均匀度随海拔的升高逐渐降低;在灌木层,丰富度、多样性和均匀度均呈比较明显的单峰曲线变化趋势;在草本层,丰富度和多样性随海拔的升高都呈下降趋势,而在草本层,均匀度变化不大.(3)用多层感知器网络预测功能层多样性效果很好,结果发现坡向对乔木层和灌木层物种多样性的影响最大,而海拔高度对草本层物种多样性的影响最大.     

Homegardens on Amazonian Dark Earths,Non-anthropogenic Upland,and Floodplain Soils along the Brazilian Middle Madeira River Exhibit Diverging Agrobiodiversity<Superscript>1</Superscript>

Homegardens on Amazonian Dark Earths, Non-anthropogenic Upland, and Floodplain Soils along the Brazilian Middle Madeira River Exhibit Diverging Agrobiodiversity. We test the hypothesis that the agrobiodiversity associated with homegardens on three different soils—upland Amazonian Dark Earths (ADE) and Oxisols (OX), and Fluvent Entisols (FL)—commonly found along the middle Madeira River in the municipality of Manicoré, Amazonas State, Brazil, is different due to the contrasting biotic, abiotic, and cultural settings specific to each of these soils. Using data from interviews with 63 farmers about food and utility species, we compare structural and floristic characteristics of homegarden agrobiodiversity. The density of individuals is higher on ADE than on the other soils (mean ± standard deviation: 715 ± 363 on ADE, 474 ± 283 on OX, 642 ± 399 on FL). ADE and OX have higher species richness (28.2 ± 5.6 on ADE, 25 ± 3.7on OX, 23.6 ± 5 on FL), while ADE and FL have a greater degree of domestication (2 ± 0.6 on ADE, 1.3 ± 0.5 on OX, 2.3 ± 0.6 on FL). ADE and OX have greater proportions of richness, density, and coverage composed of South American species, while FL has greater proportions of richness and density composed of Old World species. ADE has higher proportions of density and coverage of Mesoamerican species. Floristic composition is also different between soils: ADE occupies an intermediate position, composed of species associated with each of the other soil types and species that are most common on ADE. These differences in agrobiodiversity emerge through the interaction of human agency, plant responses, and the unique properties of soils in relation to socioeconomic and historical trajectories over time.     

Ground beetle diversity in ancient woodland remnants in north-western Germany (Coleoptera, Carabidae)

We investigated ground beetle communities (Coleoptera, Carabidae) in ancient woodland remnants in north-western Lower Saxony, Germany. A total of 90 pitfall traps was exposed in a stratified design in 10 stands of mature oak–beech and oak–hornbeam forests in the year 2003. Overall, 47 species (10,676 individuals) were recorded. Among these were the two relict species Carabus glabratus and Abax parallelus, and 14 further eurytopic forest species. Eleven species exhibited a high frequency and were found in all of the ten stands. Multiple linear regressions showed several significant relationships at two scales for species richness of different groups of carabids and for several of the measured environmental factors. Forest area, litter depth, amount of dead wood, distance to forest edge, and soil moisture were found to be key factors determining species richness. Furthermore, recent disturbance by logging reduced the number of forest species. According to direct gradient analyses soil moisture and litter depth have greatest influence on species communities of both, forest species and widespread species. Habitat suitability models for the two recorded relict species, A. paralellus and C. glabratus, were developed using logistic regression. The presence of A. parallelus in the mature ancient woodland remnants depends mainly on higher values of soil moisture, whereas for C. glabratus none of the measured environmental variables appeared to be key factors. Implications for the conservation of carabid assemblages in mature ancient woodlands include the advice to spread out logging over long periods of time and over various woodlands in order to keep the stand disturbance at a long-term low level. Variation in logging practices may help to conserve diverse structures. Afforestation with non-native tree species should be avoided in the managed ancient woodlands. Finally, especially the preservation of a high soil moisture seems to be important to conserve typical carabid communities.     

三种温带森林大型土壤动物群落结构的时空动态

对帽儿山3种典型森林群落大型土壤动物进行了连续6个月的野外调查研究。通过系统分析,共获得大型土壤动物3604只,隶属于3门6纲17目50科。其中正蚓科(Lumbricidae)、线蚓科(Enchytraeidae)和石蜈蚣目(Lithobiomorpha)为优势类群,常见类群11类。结果表明:(1)水平分布上,密度和生物量红松人工林最高,其次为硬阔叶林,蒙古栎林最少;类群数硬阔叶林最多,蒙古栎林最少;香农指数和丰富度指数均为蒙古栎林最高,红松人工林最低;优势度指数与两者相反;均匀度指数蒙古栎林最高,硬阔叶林最低;(2)垂直分布上,个体密度、类群数及生物量均差异显著(P < 0.001)。3个样地大型土壤动物个体密度表聚性明显;类群数红松人工林自凋落物层向下减少,硬阔叶林和蒙古栎林0-10 cm最多;生物量在0-10 cm土层最大;香农指数随深度增加而减小,优势度指数则相反;(3)在时间变化上,5月和10月个体密度和类群数较多,9月生物量最大;香农指数和优势度指数差异显著(P < 0.01),其他指数各月间无明显差异;(4)与土壤环境因子关系上,总有机碳含量与类群数、个体密度及生物量显著正相关,容重与香农指数显著负相关;典型对应分析结果表明,不同类群大型土壤动物与环境相关性不同。     

Small-scale spatial heterogeneity of arbuscular mycorrhizal fungal abundance and community composition in a wetland plant community

Although it has become increasingly clear that arbuscular mycorrhizal fungi (AMF) play important roles in population, community, and ecosystem ecology, there is limited information on the spatial structure of the community composition of AMF in the field. We assessed small-scale spatial variation in the abundance and molecular diversity of AMF in a calcareous fen, where strong underlying environmental gradients such as depth to water table may influence AMF. Throughout an intensively sampled 2 × 2 m plot, we assessed AMF inoculum potential at a depth of 0–6 and 6–12 cm and molecular diversity of the AMF community using terminal restriction fragment length polymorphism of 18S rDNA. Inoculum potential was only significantly spatially autocorrelated at a depth of 6–12 cm and was significantly positively correlated with depth to water table at both depths. Molecular diversity of the AMF community was highly variable within the plot, ranging from 2–14 terminal restriction fragments (T-RFs) per core, but the number of T-RFs did not relate to water table or plant species richness. Plant community composition was spatially autocorrelated at small scales, but AMF community composition showed no significant spatial autocorrelation. Saturated soils of calcareous fens contain many infective AMF propagules and the abundance and diversity of AMF inoculum is patchy over small spatial scales. An erratum to this article can be found at     

The combined role of topography and overstorey tree composition in promoting edaphic and floristic variation in a Mediterranean forest

This study aimed to address which factors, other than topography, contribute to the floristic variation of forested slopes. The natural forest studied is located in the Sudoeste Alentejano e Costa Vicentina Nature Park (southwestern Portugal). We sampled topographic, edaphic, floristic and community structure variables along three bottom–top hillside transects. Multivariate analyses of soil variables (by PCA), and of woody species composition and floristic–environmental relationships (by CCA and pCCA) were performed. Environmental–floristic trends strongly associated with the elevation gradient were identified. At lower altitudes, the lowest species richness, the highest soil fertility, and the tallest and most dense (least available light) canopy occurred. The spatial variation in woody species composition and abundance was closely associated with Zn availability in the soil and litter groundcover, but these varibles had significant spatial structure in the studied forest. The non-spatially structured species variance was better predicted by soil NO₃^– and NH₄⁺. The spatial variation of species data not shared with environmental variables was also calculated. We suggest that the influence of topographic gradient on the variation of edaphic variables and on the distribution and abundance of woody species was mediated by overstorey tree composition. Locally dominant tree species, in particular Quercus faginea and Quercus suber, may function as ecosystem engineers promoting environmental changes (i.e., Zn availability in soil, litter accumulation and light availability) that influence overall floristic variation.     

Partitioning the impact of abiotic factors and spatial patterns on species richness and community structure of ground ant assemblages in four Bornean rainforests

Contrasting theories have been proposed to explain the structure of ecological communities. Here, we studied the impact of environmental factors and spatial patterns on ground‐foraging ant communities in four different forest types of Gunung Mulu National Park in Sarawak, Borneo, Malaysia. Forest types differed in their environmental parameters and were inhabited by distinct ant communities, with various indicator species characteristic for single forest types. Three environmental parameters, soil volume, number of trees and amount of leaf litter, had the most influence on ant communities. Spatial patterns were correlated with environmental parameters and also influenced ant communities. Environmental parameters influenced community composition only moderately (r²=0.14), but had a high impact on species richness (r²=0.44). Spatial patterns explained only a small fraction of the total variance in species patterns, while much of the residual space in the ordination space of ant community patterns remained unexplained. We conclude that environmental parameters shape the number of niches within a tropical soil habitat, but identities of species that occupy those niches are accounted for by other factors like competition, traits and neutral processes that may further reduce unexplained variance in species ordination.     

Lowland boreal forests characterization in Algonquin Provincial Park relative to beaver (Castor canadensis) foraging and edaphic factors

Beaver (Caster canadensis) foraging and edaphic conditions can modify the vegetational characteristics of woody plant community in lowland boreal forests. Effective management of these areas requires an understanding of the relative contribution of these factors in shaping the woody plant community structure. Our objective was to quantify the effects of herbivory by beavers and edaphic conditions on woody plant community organization of lowland boreal forests surrounding beaver ponds. Woody vegetation and soils were sampled at 15 ponds occupied by beavers and one other pond abandoned by them in southern Algonquin Park, Ontario. We measured spatial variation in plant diversity, foraging rates and sapling recruitment of trees and shrubs along gradients of beaver foraging intensity and soil moisture, P, K, Mg, and pH. Beavers fed preferentially on a small number of deciduous species and the number of cut stems declined sharply with increasing distance from ponds. Conifers increased in relative dominance to deciduous species in the presence of beavers. Plant species richness and stem and basal area diversity peaked at intermediate distances (about 25 m) from ponds. Sapling recruitment by non-preferred species was positively related to foraging intensity. Total stem abundance and basal area and sapling recruitment by four preferred species (Populus tremuloides, Acer rubrum, Acer saccharum and Corylus cornuta) were negatively related to foraging intensity. However, by including Alnus rugosa and Salix bebbiana (also preferred by beavers) these patterns changed, becoming positively related to foraging intensity. There was also a pronounced gradient in soil moisture, which also decreased with distance from ponds. The other measured edaphic variables did not vary consistently with distance from ponds. Sapling recruitment in mesic versus xeric species varied consistently with hydrid conditions along the moisture gradient, such that variation in moisture also could produce the observed pattern of plant diversity. Diversity patterns changed three years after beaver abandonment of a pond, though sapling recruitment patterns in preferred and non-preferred species around the abandoned pond were similar to the occupied ponds. These observations suggest spatial variation in woody plant richness and diversity could be determined by combined effects of both herbivory (disturbance by beavers) and variable responses of different species to edaphic conditions.     

热带森林不同演替阶段蚂蚁巢穴的分布特征及其影响因素

为探明热带森林蚂蚁巢穴的分布特征及其影响因素, 采用样方法研究了西双版纳不同演替阶段热带森林定居巢穴蚂蚁的种类及其巢穴的密度、盖度和空间分布特征, 并分析了土壤理化环境与蚂蚁种类总数、巢穴密度及盖度的相关性。结果表明, 不同演替阶段热带森林蚂蚁种类总数、巢穴的密度及盖度大小顺序为: 小果野芭蕉 (Musa acuminata)群落>白背桐(Mallotus paniculatus)群落>思茅崖豆(Mellettia leptobotrya)群落, 并且热带森林的演替类型显著影响蚂蚁种类总数及巢穴密度, 而对巢穴盖度的影响未达到显著水平; 蚂蚁种类总数、巢穴密度与土壤总有机碳和水解氮显著正相关, 与土壤容重和土壤含水率显著负相关, 但所选择的土壤理化指标与巢穴盖度的相关性均未达到显著水平; 蚂蚁巢穴的空间分布呈随机分布格局。我们的数据表明, 不同演替阶段热带森林所形成的植被类型及土壤环境状况共同影响定居的蚂蚁种类总数与筑巢密度。     

Effects of environmental factors on the ant fauna of restinga community in Rio de Janeiro, Brazil

The effects of environmental factors on the richness, diversity and abundance of ants were studied in the Restinga da Marambaia, south coast of Rio de Janeiro State, Brazil. The samples were taken using pitfall traps in August/2004 (winter) and March/2005 (summer) in three different vegetation types: (1) herbaceous ridge palmoid (homogeneous habitat); (2) shrub dune thicket and (3) ridge forest (heterogeneous habitats). At each habitat a range of environmental attributes was recorded: soil temperature and humidity, percentage of soil covering by litter and litter depth. Ninety-two ant species belonging to 36 genera and eight subfamilies were recorded. Density of ant species and abundance varied significantly between habitats and seasons; ant diversity varied only between habitats. Homogeneous habitat had lower ant species density, abundance and diversity than heterogeneous habitats. The two first variables were positively correlated with litter depth and both were higher in summer than in winter samples. There were more species of Ponerinae and Ectatomminae in heterogeneous than in the homogeneous habitat, whereas the Formicinae species were more abundant in the later.     

Spatial structure of litter-dwelling ant distribution in a subtropical dry forest

Understanding the spatial patterns of species distribution is essential to characterize the structure of communities, to optimize species inventories and to evaluate the impact of biotic and abiotic variables. Here we describe the spatial structure of the distribution of leaf litter ant species, and of biotic factors that could explain it, in a subtropical semi-deciduous forest of the Argentinian Chaco, characterized by a dense understorey of shrubs and terrestrial bromeliads. Environmental variables (leaf litter quantity and ground bromeliad density) were measured and ants were collected in 1 m² quadrats distributed along two 200 m transects at intervals of 1.25 m. Overall 87 species were collected. Sixteen positive associations and a single negative association were observed between the 11 most frequent species taken pair-wise. Our results suggest that the spatial distribution of leaf litter ants was determined at two different scales. At a small scale (period below 10 m) a periodic spatial structure, likely due to intraspecific competition, produced a succession of peaks of abundance separated by gaps. At a larger scale (period around 50 m), periodically distributed environmental factors induced aggregates of colonies of species responding positively to these factors. A high quantity of leaf litter and, to a lesser extent, a high density of ground bromeliads promoted a high density and a high species richness of ants. Numerically dominant ants being generally positively associated, interspecific competition was apparently weak. All ant species whose abundance was correlated with an environmental factor were not completely spatially structured by it. This suggests that some other factors, such as intraspecific competition, may have counter-effects. Received 14 March 2005; revised 26 April 2005; accepted 10 May 2005.     

The role of water depth and soil temperature in determining initial composition of prairie wetland coenoclines

In this study, we examined the effects of water depth and temperature on seedling recruitment from a prairie wetland seed bank. We collected seed-bank samples from natural and restored prairie pothole wetlands in northwestern Iowa and combined them into a single sample. We examined seedling recruitment from this seed-bank sample in an experimental study using a factorial design of 4 temperature treatments (5° night and 15° day to 20° night and 30° day) and 3 water-depth treatments (0, 2, and 7 cm).Principal Components Analysis showed that both water depth and temperature had significant effects on the composition of the seedling community as measured by changes in relative stem density and biomass. Water depth had its strongest effects on stem density while temperature had its strongest effects on biomass.For the 22 most common species, stem density varied with water depth for 95% of the species and with temperature for 50% of the species. Most species with water depth responses had lower stem counts as water depth increased, and for the majority of species with temperature responses stem density increased with temperature.Total, annual, and perennial species richness was negatively correlated with water depth. Total and annual species richness was positively correlated to temperature, while perennial species richness was unresponsive to temperature. In addition, species found at low elevations as adults emerged at higher rates in the deep water treatments while species that occurred at higher elevations as adults had their highest emergence rates in the low water treatments.Our results suggest that differences in environmental conditions along coenoclines can affect the initial distribution of species emerging from the soil seed bank. Water depth sorted seedlings according to their adult water-depth tolerances, and temperature determined the proportion of annuals in the seedling community.     

长春市不同土地利用生境土壤弹尾虫群落结构特征

对长春市郊区天然次生林、农田、防护林和市区公园绿地等典型土地利用生境进行土壤弹尾虫调查,研究土地利用差异对土壤弹尾虫群落结构的影响.结果表明,长春市土地利用差异对弹尾虫群落结构特征影响明显,地表凋落物移除和耕作活动是影响弹尾虫群落结构特征的主要因素,地表凋落物移除显著减少弹尾虫的个体数量和群落多样性,耕作活动影响弹尾虫个体数量在土体中的垂直分布;地表植物群落类型对土壤弹尾虫群落结构特征也有一定影响.