Share the wealth: Trees with greater ectomycorrhizal species overlap share more carbon

The mutualistic symbiosis between forest trees and ectomycorrhizal fungi (EMF) is among the most ubiquitous and successful interactions in terrestrial ecosystems. Specific species of EMF are known to colonize specific tree species, benefitting from their carbon source, and in turn, improving their access to soil water and nutrients. EMF also form extensive mycelial networks that can link multiple root‐tips of different trees. Yet the number of tree species connected by such mycelial networks, and the traffic of material across them, are just now under study. Recently we reported substantial belowground carbon transfer between Picea, Pinus, Larix and Fagus trees in a mature forest. Here, we analyze the EMF community of these same individual trees and identify the most likely taxa responsible for the observed carbon transfer. Among the nearly 1,200 EMF root‐tips examined, 50%–70% belong to operational taxonomic units (OTUs) that were associated with three or four tree host species, and 90% of all OTUs were associated with at least two tree species. Sporocarp ¹³C signals indicated that carbon originating from labelled Picea trees was transferred among trees through EMF networks. Interestingly, phylogenetically more closely related tree species exhibited more similar EMF communities and exchanged more carbon. Our results show that belowground carbon transfer is well orchestrated by the evolution of EMFs and tree symbiosis.     

Detection of the horizontal spatial structure of soil fungal communities in a natural forest

Soil microbes are considered to be a key determinant of the aboveground plant community. They are not distributed uniformly in the environment, and their activity, abundance, and ecosystem functioning could vary across localities, characterized by high β-diversity. Investigating factors that contribute to high β-diversity can help infer the possible mechanisms of microbial community assembly, and predict the scale and extent of impacts that soil microbes have on the plant community. Because soil systems consist of multiple horizons (i.e., vertical stratification) associated with different soil properties, complete understanding of high β-diversity requires consideration of both horizontal and vertical spatial structures of soil microbial communities. We studied the community composition of soil fungi from the O- and A-horizons in a Castanopsis-dominated temperate forest, and compared horizontal spatial autocorrelation in species composition between the two soil horizons (O- versus A-horizons). Pyrosequencing analysis yielded 67,129 sequencing reads, summed across all the 48 forest soil samples. Clustering analysis resulted in 597 molecular operational taxonomic units (OTUs), 68 % of which were identified as fungi, represented by four phyla. The Mantel test revealed that the O-horizon communities are spatially clustered, and the observed high β-diversity was driven not only by changes in OTUs present, but also by high turnover in identities of OTUs in soil samples. Furthermore, Mantel correlogram analysis showed that the O-horizon communities resembled each other in composition within the range of 50 m, whereas the A-horizon communities lacked such horizontal autocorrelation. These differences in the scale patchiness could arise from two processes: (1) that environmental conditions could show higher heterogeneity in finer scale at the A-horizon than at the O-horizon; and/or (2) dispersal could be more frequent at the O-horizon than the A-horizon. The present study suggests that either environmental filtering (i.e., the niche-based process) or dispersal limitation (i.e., neutral process) could characterize the observed patterns of spatial clustering in the soil fungal community.     

Modularity Reveals the Tendency of Arbuscular Mycorrhizal Fungi To Interact Differently with Generalist and Specialist Plant Species in Gypsum Soils

Patterns in plant–soil biota interactions could be influenced by the spatial distribution of species due to soil conditions or by the functional traits of species. Gypsum environments usually constitute a mosaic of heterogeneous soils where gypsum and nongypsum soils are imbricated at a local scale. A case study of the interactions of plants with arbuscular mycorrhizal fungi (AMF) in gypsum environments can be illustrative of patterns in biotic interactions. We hypothesized that (i) soil characteristics might affect the AMF community and (ii) there are differences between the AMF communities (modules) associated with plants exclusive to gypsum soils (gypsophytes) and those associated with plants that show facultative behavior on gypsum and/or marly-limestone soils (gypsovags). We used indicator species and network analyses to test for differences between the AMF communities harbored in gypsophyte and gypsovag plants. We recorded 46 operational taxonomic units (OTUs) belonging to nine genera of Glomeromycota. The indicator species analysis showed two OTUs preferentially associating with gypsum soils and three OTUs preferentially associating with marly-limestone soils. Modularity analysis revealed that soil type can be a major factor shaping AMF communities, and some AMF groups showed a tendency to interact differently with plants that had distinct ecological strategies (gypsophytes and gypsovags). Characterization of ecological networks can be a valuable tool for ascertaining the potential influence of above- and below-ground biotic interactions (plant-AMF) on plant community composition.     

Geostatistical analysis of soil properties in a secondary tropical dry forest,St. Lucia,West Indies

Spatial variability of soil properties directly influences forest growth. However, spatial variation in soil properties has not been studied within tropical dry forests. As such, it is unclear whether soil properties, like moisture and N availability, display spatial variation at scales similar to that of other ecosystems. To gain insight into this variation, we established a 56 × 56 m sampling grid in tropical dry forest on the Caribbean island of St. Lucia. Samples collected at 4-m intervals were analyzed for forest floor mass, soil texture, pH, organic C, net N mineralization, net nitrification and available P. Geostatistical procedures were used to determine spatial autocorrelation of the aforementioned properties and processes. Semivariogram parameters were used in a block kriging procedure to produce spatial maps of soil properties. At the scale of our study, most soil properties exhibited spatial autocorrelation at distances of 24 m or less. Varying degrees of similarity were found between patterns of forest floor mass, organic C, net N mineralization, net nitrification and available P. No similarity was found between soil texture or pH and other properties. Fine-scale spatial patterns of net N mineralization and net nitrification are likely driven by overstory litter inputs, rather than variation in soil texture and water availability.     

The importance of small-scale heterogeneity in boreal forests: variation in diversity in forest-floor invertebrates across the succession gradient

Heterogeneity in species assemblages of forest-floor arthropods — carabid beetles, ants and spiders — within and between different forest age classes was studied in the southern Finnish taiga. The importance of processes operating on the local scale (within the movement radius of the species) vs on the regional scale (among forest stands) in determining the observed variation was assessed. Four data sets with different spatial resolutions in mesic forests in the same general study area were used. The material consists of 18 283 carabids of 51 species, 48 769 spiders of 212 species, and 126 718 worker ants of 23 species. Analyses of abundance variation and species complementarity among successional stages revealed that in all the three taxa species occurring in the mature forest were prevalent in the younger successional stages as well, constituting more than half of the catch in any age class. A great majority of carabid and spider species were widely distributed across the forest age classes, whereas ants include a higher proportion of species with a narrower amplitude across the succession gradient. Comparisons of similarity between samples at increasing distance from one another on the local scale within forest stands (a few tens of meters to a few hundreds of meters) showed a quite consistent pattern in carabids and spiders: there was more variation between sampling sites in young successional forests than in the mature forest. Furthermore, only in the mature forest a slight, albeit statistically not significant, negative relationship between similarity of samples and distance between sampling sites was detected. In carabids and spiders, comparisons between samples located at a distance of 10–15 m from each other showed considerable heterogeneity, the mean percentage similarity being c. 0.6 (in ants c. 0.8). On the regional scale, systematic variation between young and mature forest stands is a major element increasing the total diversity (species turnover c. 50% in carabids and spiders; compositional similarity c. 0.3–0.4 in carabids, 0.2–0.3 in spiders), but variation within forest stands on a spatial scale of 10–15 meters is another important component in the total heterogeneity. The results suggest that regional abundance variation is a primary factor influencing the composition of local assemblages; a set of hypotheses elaborating this conclusion is formulated. The result implies that maintenance of habitat heterogeneity on a small scale (10–15 m) is needed to preserve biodiversity in managed forests.     

黔中地区火灾对马尾松外生菌根真菌群落的影响

林火会对森林植被及其相关联的微生物群落产生重要影响。为揭示火灾对马尾松外生菌根真菌(ectomycorrhizal fungi,EMF)群落的影响,本研究以火灾马尾松林为研究对象,以周边立地条件相对一致、未火灾马尾松林为对照,采用形态鉴定与分子生物学技术相结合的研究方法,分析火灾对马尾松EMF群落的影响。共鉴定出马尾松EMF OTUs 69个,隶属于2门7纲15目18科23属,且担子菌门丰富度明显高于子囊菌门。火灾显著改变了马尾松EMF群落的组成和结构,其中火灾马尾松林中EMF群落的优势属主要为蜡蘑属Laccaria、红菇属Russula和棉革菌属Tomentella,未火灾马尾松林中EMF群落的优势属主要为乳菇属Lactarius、棉革菌属Tomentella和土生空团菌属Cenococcum。火灾样地马尾松的EMF群落相对于对照样地在组成与结构上存在明显差异,表现出特有OTUs高于共有OTUs。相对于未火灾马尾松林,火灾马尾松EMF群落的多样性指数和丰富度指数呈下降趋势(P>0.05)。RDA分析表明,pH和TP是影响马尾松EMF群落的重要环境因子。综上所述,火灾干扰是影响黔中地区马尾松EMF群落的重要生态因素之一。     

Controls of Soil Spatial Variability in a Dry Tropical Forest

We examined the roles of lithology, topography, vegetation and fire in generating local-scale (<1 km²) soil spatial variability in a seasonally dry tropical forest (SDTF) in southern India. For this, we mapped soil (available nutrients, Al, total C, pH, moisture and texture in the top 10cm), rock outcrops, topography, all native woody plants ≥1 cm diameter at breast height (DBH), and spatial variation in fire frequency (times burnt during the 17 years preceding soil sampling) in a permanent 50-ha plot. Unlike classic catenas, lower elevation soils had lesser moisture, plant-available Ca, Cu, Mn, Mg, Zn, B, clay and total C. The distribution of plant-available Ca, Cu, Mn and Mg appeared to largely be determined by the whole-rock chemical composition differences between amphibolites and hornblende-biotite gneisses. Amphibolites were associated with summit positions, while gneisses dominated lower elevations, an observation that concurs with other studies in the region which suggest that hillslope-scale topography has been shaped by differential weathering of lithologies. Neither NO₃⁻-N nor NH₄⁺-N was explained by the basal area of trees belonging to Fabaceae, a family associated with N-fixing species, and no long-term effects of fire on soil parameters were detected. Local-scale lithological variation is an important first-order control over soil variability at the hillslope scale in this SDTF, by both direct influence on nutrient stocks and indirect influence via control of local relief.     

插值方法与样点数对县域土壤有效磷空间变异特征评价的影响

与欧美大规模农场经营不同,土地分散经营使我国县域土壤养分空间变异特征评价更加困难.本研究以安徽芜湖土壤有效磷为例,系统地评价插值方法与样点数对县域土壤养分空间变异特征评价准确性的影响.结果表明：局部多项式、普通克里格、简单克里格和析取克里格插值方法的评价效果优于反距离加权法、全局多项式、径向基插值和泛克里格等插值方法,考虑到实际操作简单,推荐用普通克里格方法进行县域土壤有效磷空间变异特征评价.随着参与空间插值样点数的增加,县域土壤有效磷空间变异特征预测的准确性增加,充分考虑评价的准确性和田间取样费用,建议县域土壤有效磷空间变异特征评价的适宜样点数应介于500～1000个.     

Forest and Landscape Structure as Predictors of Capercaillie Occurrence

ABSTRACT Capercaillie (Tetrao urogallus) is a large, endangered forest grouse species with narrow habitat preferences and large spatial requirements that make it susceptible to habitat changes at different spatial scales. Our aim was to evaluate the relative power of variables relating to forest versus landscape structure in predicting capercaillie occurrence at different spatial scales. We investigated capercaillie-habitat relationships at the scales of forest stand and forest-stand mosaic in 2 Swiss regions. We assessed forest structure from aerial photographs in 52 study plots each 5 km². We classified plots into one of 3 categories denoting the observed local population trend (stable, declining, extinct), and we compared forest structure between categories. At the stand scale, we used presence-absence data for grid cells within the plots to build predictive habitat models based on logistic regression. At this scale, habitat models that included only variables relating to forest structure explained the occurrence of capercaillie only in part, whereas variables selected by the models differed between regions. Including variables relating to landscape features improved the models significantly. At the scale of stand mosaic, variables describing forest structure (e.g., mean canopy cover, proportion of open forest, and proportion of multistoried forest) differed between plot categories. We conclude that small-scale forest structure has limited power to predict capercaillie occurrence at the stand scale, but that it explains well at the scale of the stand mosaic. Including variables for landscape structure improves predictions at the forest-stand scale. Habitat models built with data from one region cannot be expected to predict the species occurrence in other regions well. Thus, multiscale approaches are necessary to better understand species-habitat relationships. Our results can help regional authorities and forest-management planners to identify areas where suitable habitat for capercaillie is not available in the required proportion and, thus, where management actions are needed to improve habitat suitability.     

Arbuscular mycorrhizal fungal communities are phylogenetically clustered at small scales

Next-generation sequencing technologies with markers covering the full Glomeromycota phylum were used to uncover phylogenetic community structure of arbuscular mycorrhizal fungi (AMF) associated with Festuca brevipila. The study system was a semi-arid grassland with high plant diversity and a steep environmental gradient in pH, C, N, P and soil water content. The AMF community in roots and rhizosphere soil were analyzed separately and consisted of 74 distinct operational taxonomic units (OTUs) in total. Community-level variance partitioning showed that the role of environmental factors in determining AM species composition was marginal when controlling for spatial autocorrelation at multiple scales. Instead, phylogenetic distance and spatial distance were major correlates of AMF communities: OTUs that were more closely related (and which therefore may have similar traits) were more likely to co-occur. This pattern was insensitive to phylogenetic sampling breadth. Given the minor effects of the environment, we propose that at small scales closely related AMF positively associate through biotic factors such as plant-AMF filtering and interactions within the soil biota.     

Variation in soil seed bank species composition of a dry coniferous forest: spatial scale and sampling considerations

In order to assess the effects of disturbance on soil seed bank spatial structure, variation in seed bank species composition was analyzed at two spatial scales in mature (undisturbed) and recently disturbed stands of Interior Douglas-fir forest in south-central British Columbia. Coarse-scale analysis among stands 10–100 km apart using Multi-Response Permutation Procedures showed that individual mature stands were mainly characterized by unique seed bank species compositions. Disturbance had an homogenizing effect on seed bank species composition at the coarse scale––there was less variability among stands following disturbance by both low and high severity fires, and by non-salvage logging. In contrast, finer scale analysis among sampling units c. 10 m apart showed that heterogeneity in seed bank species composition was greater on severely burned and logged sites, commensurate with greater levels of soil disturbance, than on lightly burned and undisturbed sites. Despite the high intensity of seed bank sampling (sixty 25 cm² soil samples from each of 16 sites), species-area curves leveled off only when infrequent species were removed from the dataset. The number of seed bank samples required to account for the common species ranged from 84 on severely burned sites, to 196 on undisturbed sites; more than the 240 samples collected per disturbance class in this study would have been required to account for the remaining infrequent species. Overall, this study highlights the importance of sampling intensively within multiple stands to capture the variation in species composition inherent to these dry coniferous forest soil seed banks.     

Spatial patterns of hypolithic cyanobacterial diversity in Northern Australia

Photosynthetic microbial communities under translucent rocks (hypolithic) are found in many arid regions. At the global scale, there has been little intercontinental gene flow, and at a local scale, microbial composition is related to fine‐scale features of the rocks and their environment. Few studies have investigated patterns of hypolithic community composition at intermediate distances. We examined hypolithic cyanobacterial diversity in semi‐arid Australia along a 10‐km transect by sampling six rocks from four adjacent 1 m² quadrats (“distance zero”) and from additional quadrats at 10, 100, 1,000, and 10,000 m to test the hypothesis that diversity would increase with the number of rocks sampled and distance. A total of 3,108 cyanobacterial operational taxonomic units (OTUs) were detected. Most were neither widespread nor abundant. The few that were widespread tended to be abundant. There was no difference in the community composition between the four sites at distance zero, but the samples 10 m away were significantly different, as were those at all other distances compared to distance zero. Many additional OTUs were recorded with increasing distance up to 100 m. These patterns of distribution are consistent with a colonization model involving dispersal from rock to rock. Our results indicate that distance was a significant factor that can be confounded by interrock differences. Most diversity was represented in the first 100 m of the transect, with an additional 1.5% of the total diversity added by the sample at 1 km, but only 0.2% added with the addition of the 10‐km site.     

宝天曼落叶阔叶林土壤细菌多样性

土壤微生物在森林生态系统中起着重要作用。高通量测序方法的出现为进一步认识土壤微生物提供了契机。本文利用Illumina Miseq高通量测序技术对宝天曼森林土壤的细菌多样性进行了初步研究。结果显示: 在31个采样点内, 随着采样点增加, 检测出不同分类水平的土壤细菌类群也在增多, 当采样点达到31个时, 检测出的土壤细菌类群达到45门163纲319目495科785属和42,632个OTU; 31个土壤样品中所检测出的细菌类群平均有34.2门114.7纲215.2目323.7科446.6属5,924.7个OTU, 其中门、纲、目分类水平上的优势类群(所占比例)分别为变形菌门(Proteobacteria)(38.30%)、α-变形菌纲(α-Proteobacteria)(18.08%)、根瘤菌目(Rhizobiales)(10.62%)。这些初步研究结果表明在一定程度上宝天曼森林土壤有较高的细菌多样性水平, 为进一步认识森林土壤细菌多样性与植物多样性关系等奠定了基础。     

Relative importance of climate vs local factors in shaping the regional patterns of forest plant richness across northeast China

Northeast (NE) China covers three climatic zones and contains all the major forest types of NE Asia. We sampled 108 forest plots in six nature reserves across NE China to examine the influence of climate and local factors (canopy seasonality, successional stage, topography and forest structure) on geographic patterns of plant richness. We analyzed the relative effects of different factors at two spatial scales: the regional scale (across both latitude and altitude) and the local scale (along the altitudinal gradient within site). Our results showed that the relative importance of climate vs local factors differed remarkably depending on scale and functional group. While total and tree species richness were mainly limited by climate, herb and shrub richness was more related to local factors (especially at the local scale). In the climatic factors, heat sum was the major correlate of tree, shrub and total species richness, while herb richness was more associated with winter coldness. Precipitation was not a limiting factor for forest plant richness in NE China. Climate accounted for 34–76% of variation in richness at the regional scale, but explained only 0–44% at the local scale. Among the local factors, shrub species richness was sensitive to seasonal canopy openness, with higher richness in deciduous forests than in the evergreen needle-leaf forest. On the other hand, herb richness was sensitive to forest successional stage, with higher richness in middle- successional forests than in the early and late-sucessional forests. Local topography (aspect and position on slope) and forest structure (tree density) also showed remarkable influence on species richness. Our results suggest the importance of including local factors when examining large scale diversity gradient (especially for understory species), and the necessity of comparing diversity patterns among functional groups at different spatial scales.     

Determinants of the distribution of nitrogen-cycling microbial communities at the landscape scale

Little information is available regarding the landscape-scale distribution of microbial communities and its environmental determinants. However, a landscape perspective is needed to understand the relative importance of local and regional factors and land management for the microbial communities and the ecosystem services they provide. In the most comprehensive analysis of spatial patterns of microbial communities to date, we investigated the distribution of functional microbial communities involved in N-cycling and of the total bacterial and crenarchaeal communities over 107 sites in Burgundy, a 31 500 km² region of France, using a 16 × 16 km² sampling grid. At each sampling site, the abundance of total bacteria, crenarchaea, nitrate reducers, denitrifiers- and ammonia oxidizers were estimated by quantitative PCR and 42 soil physico-chemical properties were measured. The relative contributions of land use, spatial distance, climatic conditions, time, and soil physico-chemical properties to the spatial distribution of the different communities were analyzed by canonical variation partitioning. Our results indicate that 43–85% of the spatial variation in community abundances could be explained by the measured environmental parameters, with soil chemical properties (mostly pH) being the main driver. We found spatial autocorrelation up to 739 km and used geostatistical modelling to generate predictive maps of the distribution of microbial communities at the landscape scale. The present study highlights the potential of a spatially explicit approach for microbial ecology to identify the overarching factors driving the spatial heterogeneity of microbial communities even at the landscape scale.     

集水区尺度下东北东部森林土壤呼吸的模拟

IBIS模型是陆地碳循环模拟的有利工具,土壤呼吸是陆地碳循环的关键生态学过程,利用IBIS模型模拟估算土壤呼吸对陆地碳循环和全球变化研究具有重要意义.在地形数据、植被参数、土壤质地参数和气象数据支持下,利用改造后的IBIS模型模拟2004年张家沟集水区5种森林类型的土壤呼吸,以实测数据对模拟结果进行验证,并分析土壤呼吸时空格局及其与土壤温湿度的关系.结果表明:(1)改造后的IBIS模型模拟的土壤呼吸值与实测值相关性显著,可较好地用于集水区尺度的森林土壤呼吸模拟估算.(2)土壤呼吸年均值为571 gCm-2 a-1,年土壤呼吸空间格局与生长季土壤呼吸空间格局相似,均表现为高值区主要分布在北部、西南和东南区域,低值区主要分布在沟谷附近,该格局与集水区的地形、植被及其组合等因素有关.(3)生长季内,5种森林类型土壤呼吸的季节性变化均呈单峰曲线形式,土壤呼吸峰值均出现在7月,其中落叶松林峰值最低,为85.5gC/m2,杂木林峰值最高,为146.3 gC/m2.(4)5种森林类型的土壤呼吸值与5 cm深土壤温度存在极显著的指数关系,与土壤湿度的相关性较低,土壤温度的变化可以解释土壤呼吸约70％的季节变化.     

Soil aggregates in a tropical deciduous forest: effects on C and N dynamics, and microbial communities as determined by t-RFLPs

The aim of this study was to analyze C and N dynamics, as well as, soil bacterial community structure within soil micro- and macro-aggregates in a tropical deciduous forest in México. We measured, for three landscape positions and three seasons of the year: total, microbial and available forms of C and N; potential C and N mineralization; and soil bacterial communities by using t-RFLPs. The highest total C concentrations were found in the north-slopes and in the dry season (DS) samples. In general, micro-aggregates had higher concentrations than macro-aggregates of available C and N forms, and microbial C. Similarly, micro-aggregates had the highest potential C mineralization and net N mineralization. We detected 149 different OTUs (operational taxonomic units) from which 50% was shared by the two aggregate size fractions, 25% was exclusive to micro-aggregates and the 25% left was found only in macro-aggregates. Top-hills were richer in OTUs than north and south-slopes. The Unweighted Pair Group Method with Arithmetic mean (UPGMA) analysis indicated clear differences in community composition between the two aggregate size-fractions in relation to the presence of OTUs. These results suggest that the main difference between micro- and macro-aggregates is due to the community structure within each soil fraction and this difference could affect soil nutrients dynamics.     

基于植被和环境因子的亚高山森林土壤水源涵养功能空间尺度上推模型构建——以岷江上游杂谷脑流域为例

土壤层水源涵养功能是森林水源涵养功能的主体。目前关于森林土壤水源涵养功能的研究主要集中在林地或坡面尺度上。由于流域尺度,尤其是环境空间异质性强的西南亚高山区流域,如何将林地尺度实测结果上推至流域或更大空间尺度仍是生态水文领域面临的巨大挑战之一。以川西岷江上游杂谷脑流域为研究对象,融合多种森林类型样地实测与流域尺度多源遥感数据,构建了基于植被和环境因子的林地-流域森林土壤水源涵养功能尺度转换模型,实现了流域尺度土壤水源涵养功能快速评价及其空间分布预测。样地尺度研究结果表明各类型森林的土壤水文特性各异,总体表现为天然林优于人工林,混交林优于单纯林。林地土壤持水能力受到区域气候、植被、土壤及地形等因子的共同影响,其中风速、NDVI及林龄与土壤最大持水量、毛管持水量及非毛管持水量均呈极显著正相关（P<0.01）。基于关键植被和环境因子构建的林地-流域土壤水源涵养功能尺度上推模型精度较高,土壤最大持水量、土壤毛管持水量和土壤非毛管持水量模型拟合优度R²分别为0.700、0.720和0.908;土壤最大持水量、土壤毛管持水量和土壤非毛管持水量的模型预测值与野外实测值的相关系数介于0.69-0.79之间,平均误差均低于20%,表明模型预测结果可靠。利用构建的土壤水源涵养功能尺度上推模型,估算得出流域尺度森林土壤持水量的空间分布,其结果表明杂谷脑流域森林土壤持水量空间分异明显,海拔较高区域森林土壤持水量最高,其次为距道路和河流有一定距离的缓坡地带,下游干旱河谷地区土壤持水量最低。本研究为亚高山森林生态功能的恢复和提升提供了科学依据和评价工具。     

Changes in plant species density in an experimentally fragmented forest landscape: Are the effects scale‐dependent?

The establishment of commercial tree plantations is a common cause of habitat fragmentation globally, yet the influence of this land use on plant species density in fragmented native forests requires further understanding. Theory predicts species density will be highest in large areas of habitat, and should decline as area is reduced, but whether these effects are scale‐dependent is largely unknown. We assessed plant species density (total, common and uncommon species) in experimentally fragmented eucalypt forest remnants (0.25, 0.88, 3.06 ha) surrounded by a pine plantation, at three spatial scales using nested quadrats. Specifically, we consider how plant species density varies across three different sized fragments, and whether the response of species density is magnified in common or uncommon species. Species density in small fragments was higher than continuous forest for all species groupings at the smallest spatial scale (1 m²), and for total and common species at the next smallest spatial scale (16 m²). No species groupings responded to reductions in habitat area at the largest spatial scale (144 m²). We suggest that pine plantations may cause higher species density in small fragments via two mechanisms, either by allowing species to infill unoccupied areas within small fragments, or by buffering small fragments from species losses during a severe and prolonged drought. In both cases we suspect reduced moisture stress (e.g. increased soil moisture, higher shading and reduced temperature) in small fragments has led to the observed changes in species density.     

Frequency and distribution patterns of zoosporic fungi from moss-covered and exposed forest soils

Uniflagellate zoosporic "fungi" (=Chytridiomycota and the zoosporic protista Hyphochytriomycota) are common inhabitants of soil. However, at what scale differences in their spatial distribution can be detected is poorly known. The first objective of this study was to assess the association of organismal distribution and frequency with two microhabitats: moss-covered and exposed forest soils, at four macroscopically similar but spatially separate sites in the Blue Ridge and Allegheny Mountains of Virginia. The second objective was to provide statistically either acceptance or denial of inferences derived from sampling regimes involving a more limited number of samples. To evaluate the scale where distributional differences may occur within a site, protocols involved four collection regimes and random point and linear transect sampling. Chytrid frequency on thalli of two moss genera was greatest in the soil surrounding and under the moss rhizoids. Random point sampling methods suggested differences in zoosporic fungal frequency between moss-covered soil and the exposed soil adjacent to mosses, as well as between two moss taxa. Linear transect sampling methods also suggested differences in zoosporic fungal frequencies between moss-covered soil and soil proximal to mosses. However, statistical analysis of random point samples using a goodness-of-fit test demonstrated that there was no significant difference in frequency of zoosporic fungi from moss-covered soil and exposed soil proximal to mosses. More importantly, there was a significant difference in the frequency of ubiquitous and common zoosporic fungal species between different moss/soil complexes. This study demonstrates that differences in chytrid distribution can be detected at a microscale while at a larger scale, similarity in frequency and distribution was found.