Effects of tree species composition on within‐forest distribution of understorey species

Question: Do tree species, with different litter qualities, affect the within‐forest distribution of forest understorey species on intermediate to base‐rich soils? Since habitat loss and fragmentation have caused ancient forest species to decline, those species are the main focus of this study. Location: Three ancient forests, along a soil gradient from acidification‐sensitive to base‐rich, were studied: Limbrichterbosch and Savelsbos in The Netherlands and Holtkrat in Denmark. Methods: Canopy and soil surveys along transects generated data for Redundancy Analysis on tree – humus relationships. We analysed the distribution of forest plant species with Canonical Correspondence Analysis. The explanatory factors were soil characteristics (pH, organic matter, loam content and thickness of the humus layers), external crown projection, ground water and canopy data. We further analysed the relationship between forest species and humus characteristics with Spearman correlations. Results: Tree species have a significant impact on humus characteristics through the nature of their litter. Humus characteristics significantly explain the distribution of forest understorey species. The pH of the first 25 cm mineral soil and the thickness of the F‐ (fermentation) layer are the primary factors affecting the distribution of ancient forest species. Conclusion: This study indicates that the species composition of the forest canopy affects the distribution of forest understorey species. Ancient forest species are more abundant and frequent underneath trees with base‐rich litter. On acidification‐sensitive soils these relationships were stronger than on more base‐rich, loamy soils.     

Species-specific characteristics of trees can determine the litter macroinvertebrate community and decomposition process below their canopies

This paper tests whether individual trees in a mature forest stand influence the process of litter decomposition and the macroinvertebrate communities in the soil underneath their canopies, as a result of species-specific characteristics. A field decomposition experiment was performed in a mature forest stand of tropical montane cloud forest in Mexico. The areas under the canopies of Quercus laurina Humbl. & Bompl., Oreopanax xalapensis (Kunth) Decne. & Planchon and Beilschmedia ovalis (Blake) C. K. Allen trees were used as experimental units. The natural soil and litter macroinvertebrate communities were monitored and compared to the community that invaded decomposition boxes with reciprocally transplanted leaf litter. The abundances of four macroinvertebrate taxa in natural litter differed among tree species independently of season. No differences were found in the soil community. The response to experimental litter by macroinvertebrate taxa suggests that the production of a specific quality of litter is an important mechanism by which a tree influences the litter macroinvertebrate community that develops under its canopy. However, not all differences in community composition naturally found between tree species can be explained by differences in litter quality during the first year of decomposition. Differences in nutrient release that occur after the first year, and physical properties of litter also probably play an important role. Independently of the canopy tree, the initial chemical quality (N, P, Ca, Mg and lignin) of experimental litter largely determined the decomposition rate and nutrient dynamics of decomposing leaves. However, it was found that under O. xalapensis trees the breakdown of lignin from the litter produced by the same species of tree was particularly effective. This suggests that a feedback has developed between this tree species and the decomposer community prevailing under its canopy.     

Litter Decomposition Within the Canopy and Forest Floor of Three Tree Species in a Tropical Lowland Rain forest,Costa Rica

The rain forest canopy hosts a large percentage of the world's plant biodiversity, which is maintained, in large part, by internal nutrient cycling. This is the first study to examine the effects of site (canopy, forest floor) and tree species (Dipteryx panamensis, Lecythis ampla, Hyeronima alchorneoides) on decay rates of a common substrate and in situ leaf litter in a tropical forest in Costa Rica. Decay rates were slower for both substrates within the canopy than on the forest floor. The slower rate of mass loss of the common substrate in the canopy was due to differences in microclimate between sites. Canopy litter decay rates were negatively correlated with litter lignin:P ratios, while forest floor decay rates were negatively correlated with lignin concentrations, indicating that the control of litter decay rates in the canopy is P availability while that of the forest floor is carbon quality. The slower cycling rates within the canopy are consistent with lower foliar nutrient concentrations of epiphytes compared with forest floor-rooted plants. Litter decay rates, but not common substrate decay rates, varied among tree species. The lack of variation in common substrate decay among tree species eliminated microclimatic variation as a possible cause for differences in litter decay and points to variation in litter quality, nutrient availability and decomposer community of tree species as the causal factors. The host tree contribution to canopy nutrient cycling via litter quality and inputs may influence the quality and quantity of canopy soil resources.     

Bioconcentration of Cd and Zn in the soils of an uncontaminated forest in the Quebec Laurentians

Fine-scale trace element (TE) concentration patterns exist in soils that were never exposed to the direct deposition of TE in the past. We aimed to understand the role of vegetation, in particular trees, in defining these spatial patterns in the soil horizons of an uncontaminated forest ecosystem. Living tree leaves and surface soil samples (L, F, and B horizons) were collected from a ca. 1400 m² plot in the Hermine watershed where a strong gradient in the abundance of Yellow birches (Betula alleghaniensis—BA) exists. TE analysis showed that BA leaves had up to 13 times more Cd and Zn than the other tree species. Significantly similar spatial patterns were detected between the density of BA trunks, the abundance of BA leaves in the litter (L) layer, and Cd and Zn concentrations in the F horizon. The opposite trend was found in the upper B horizon, where Cd and Zn were depleted under a denser BA canopy. We submit that soil depletion could be associated with the preferential phytoextraction of Cd and Zn by BA over a period of several decades. Our study stresses the role of biological cycling by trees on the profile redistribution and the generation of patterns of soil TE in quasi-pristine forests.

     

Limit values for decomposition and convergence process of lignocellulose fraction in decomposing leaf litter of 14 tree species in a cool temperate forest

We examined limit values for decomposition and lignocellulose index (LCI, the ratio of acid-soluble holocellulose to acid-soluble holocellulose plus acid-insoluble lignin and lignin-like substances) in leaf litter decomposition of 14 tree species over 3 years. The study was carried out on upper (moder) and lower parts (mull) of a forest slope that showed different humus accumulation forms in a cool temperate forest in Japan. Limit values for accumulated mass loss of litter ranged from 46.8% to 94.1% and were not different between the sites. Limit values were positively correlated to initial LCI and lignin content. Final values of LCI of 14 litter types at the end of the study period showed a convergent trend among litter types at 0.25–0.26 as compared to their initial values (0.41 mean). The final LCI was not different between the sites. A review of limit values and initial and final values of LCI in leaf litter of temperate and boreal forests indicated that the limit values and final LCI in litter types in Japan were lower than those in Europe and North America, which can be primarily ascribed to lower initial LCI in Japan.     

The influence of tree species on canopy soil nutrient status in a tropical lowland wet forest in Costa Rica

The canopy is host to a large percentage of the flora and fauna in tropical wet forests and is distinct from the forest floor in plant richness, soil type and microclimate. In this study, we examined the influence of tree species and season on soil nutrient cycling processes in canopy soils of four tree species common to Costa Rican wet forests. We also compared the canopy soils to the associated forest floor mineral soils. Both tree species and season had strong effects on canopy soil nutrients and processes. Canopy soils from trees with high litter lignin concentrations had higher net N-mineralization rates and higher dissolved inorganic N concentrations than those with low lignin concentrations. During the dry season, net N-immobilization occurred and dissolved organic and inorganic N and available P concentrations were significantly higher than during the wet season. Overall, canopy soils had higher N levels and higher fungi + bacteria richness than forest floor mineral soils. The differences in canopy soil properties observed among tree species indicates that these species have distinct N cycles that reflect differences in both soil origin and biological controls.     

Links between environmental factors and hemiepiphytes along a slope of subtropical Atlantic forest

Several basic ecological aspects of hemiepiphytes, such as abundance, diversity and distribution, are still scarcely addressed in scientific papers and thus remain poorly documented. The main aim of this study was to analyse the relative importance of different environmental factors on the abundance and richness of primary hemiepiphytes, secondary hemiepiphytes and root‐climbing lianas, at three altitudinal levels in one slope of the south Brazilian Atlantic forest. Fifteen 400‐m² square sample plots within the altitudinal levels at the slope of Serra Geral in northeastern Rio Grande do Sul were defined. Abundance of species, the percentage of host trees colonized by each life form, canopy openness, soil composition and tree density were recorded for each sample plot, besides climatic variables for each altitudinal level. We sampled a total of 1994 occurrences belonging to 16 species. The three life forms showed different compositions in the three altitudinal levels and presented different intensities in their response to the analysed variables. The abundance of secondary hemiepiphytes increased up to four times from the lower to upper altitudinal levels, while root‐climbing lianas increased almost twice in the same direction, following an increase in precipitation. The species richness decreased toward the upper level for the three life forms. Our study also identifies, for the first time, significant correlations between abundance of secondary hemiepiphytes and soil composition, and also with support availability (tree density).     

Leaf litter inputs reinforce islands of nitrogen fertility in a lowland tropical forest

The role of lowland tropical forest tree communities in shaping soil nutrient cycling has been challenging to elucidate in the face of high species diversity. Previously, we showed that differences in tree species composition and canopy foliar nitrogen (N) concentrations correlated with differences in soil N availability in a mature Costa Rican rainforest. Here, we investigate potential mechanisms explaining this correlation. We used imaging spectroscopy to identify study plots containing 10–20 canopy trees with either high or low mean canopy N relative to the landscape mean. Plots were restricted to an uplifted terrace with relatively uniform parent material and climate. In order to assess whether canopy and soil N could be linked by litterfall inputs, we tracked litter production in the plots and measured rates of litter decay and the carbon and N content of leaf litter and leaf litter leachate. We also compared the abundance of putative N fixing trees and rates of free-living N fixation as well as soil pH, texture, cation exchange capacity, and topographic curvature to assess whether biological N fixation and/or soil properties could account for differences in soil N that were, in turn, imprinted on the canopy. We found no evidence of differences in legume communities, free-living N fixation, or abiotic properties. However, soils beneath high canopy N assemblages received ~ 60% more N via leaf litterfall due to variability in litter N content between plot types. The correlation of N in canopy leaves, leaf litter, and soil suggests that, under similar abiotic conditions, litterfall-mediated feedbacks can help maintain soil N differences among tropical tree assemblages in this diverse tropical forest.

     

长白山阔叶红松林演替序列植物-凋落物-土壤碳同位素特征

稳定碳同位素组成能精确指示生态系统碳循环过程,可以为深入研究森林演替进程对碳循环过程和固碳潜力的影响提供关键信息.利用稳定碳同位素技术对长白山阔叶红松林演替序列3种林分——中龄杨桦次生林、成熟杨桦次生林、阔叶红松林的叶片、树干、根系、凋落物和土壤δ¹³C值及碳、氮元素含量进行测定.结果表明: 各演替序列优势树种叶片δ¹³C从冠上到冠下均呈降低趋势;树干δ¹³C表现为树皮小于木质部;根系δ¹³C表现为细根小于粗根.阔叶红松林未分解凋落物δ¹³C小于半分解及全分解凋落物,次生林相反;土壤δ¹³C沿深度逐渐增加.总体上,δ¹³C值叶片<凋落物<根系<树干<土壤,说明植物各器官之间有明显的碳同位素分馏效应,且相同器官不同部位之间也存在差异;植物δ¹³C沿演替方向先减小后增加,土壤δ¹³C沿演替方向不断增加,且变化规律可以通过氮元素含量与碳同位素分馏效应的关系解释,说明长白山阔叶红松林演替过程优势树种和碳周转速率的变化影响了碳同位素分馏.     

哀牢山两类山地森林林冠及林下腐殖质微生物群落比较

中山湿性常绿阔叶林、山顶苔藓矮林是云南哀牢山高海拔山地主要的原生森林植被类型.本文对哀牢山徐家坝地区两类森林林冠及各自林下地表腐殖质的理化特性、微生物组成、数量、生化活性、代谢活性及其季节动态,以及两类森林不同优势树种林冠腐殖质微生物数量及代谢活性进行了研究.结果表明： 两类森林林冠腐殖质的真菌、放线菌的数量、微生物生物量C、N、固氮作用和纤维素分解作用的强度均显著高于林下地表腐殖质;中山湿性常绿阔叶林林冠腐殖质的纤维素分解菌、纤维素分解强度、微生物生物量C、N、有机碳、土壤呼吸强度等指标均显著高于苔藓矮林.在季节变化方面,湿季林冠腐殖质中真菌、细菌及好氧性固氮菌的数量以及呼吸强度均高于干季,放线菌则相反,纤维素分解菌干湿季间差异不显著.两类森林林冠腐殖质微生物数量及生化活性的季节变化幅度均大于林下地表腐殖质.不同树种之间冠层腐殖质的微生物数量差异显著,其中湿季的差异比干季更为明显.林冠层腐殖质的微生物在维系林冠附生植物多样性以及为林冠繁茂的附生植物生长发育提供所需的养分等方面具有重要的生态功能.     

Influence of the phenolic compound bearing species Ledum palustre on soil N cycling in a boreal hardwood forest

The effects of the understory shrub Ledum palustre on soil N cycling were studied in a hardwood forest of Interior Alaska. This species releases high concentrations of phenolic compounds from green leaves and decomposing litter by rainfall. Organic and mineral soils sampled underneath L. palustre and at nearby non-Ledum sites were amended with L. palustre litter leachates and incubated at controlled conditions. We aimed to know (i) whether L. palustre presence and litter leachate addition changed net N cycling rates in organic and mineral soils, and (ii) what N cycling processes, including gross N mineralization, N immobilization and gross N nitrification, were affected in association with L. palustre. Our results indicate that N transformation rates in the surface organic horizon were not affected by L. palustre presence or leachate addition. However, mineral soils underneath L. palustre as well as soils amended with leachates had significantly higher C/N ratios and microbial respiration rates, and lower net N mineralization and N-to-C mineralization compared to no Ledum and no leachates soils. No nitrification was detected. Plant presence and leachate addition also tended to increase both gross N mineralization and immobilization. These results suggest that soluble C compounds present in L. palustre increased N immobilization in mineral soils when soil biota used them as a C source. Increases in gross N mineralization may have been caused by an enhanced microbial biomass due to C addition. Since both plant presence and leachate addition decreased soil C/N ratio and had similar effects on N transformation rates, our results suggest that litter leachates could be partially responsible for plant presence effects. The lower N availability under L. palustre canopy could exert negative interactions on the establishment and growth of other plant species.     

Spatial pattern of soil nitrogen availability and its relationship to stand structure in a coniferous-broadleaved mixed forest with a dense dwarf bamboo understory in northern Japan

Natural disturbances create spatial patterns of the ecosystem processes and functions in natural forests. However, how dynamics and the spatial structure of forests relate to soil nitrogen dynamics is not well understood. We examined the spatial relationship between the distributions of canopy and understory species, and soil nitrogen dynamics in a natural coniferous-broadleaved mixed forest with a dense understory of Sasa dwarf bamboo in northern Japan. The O horizon was thick where coniferous litter predominated, and it was thin where broadleaved litter predominated. The soil water content was low in areas with a thick O horizon and a high abundance of coniferous trees. The soil nitrate content was low where the soil water content was low, and the soil nitrate content increased linearly with increasing net nitrification potential. These results suggest that the soil nitrate content under the coniferous canopy was lower because of the low nitrification potential of soil microbes in soils with low water contents. The soil nitrate content and nitrification potential were higher in the canopy gap than under the canopy. Our results suggest that forest structure, specifically the thickness of the forest floor, significantly affects the spatial pattern of the soil water content, thereby creating a spatial pattern of soil nitrogen availability at a relatively small scale with flat topography. The higher nitrification potential under the canopy gap could pose a long-term risk of nitrate leaching because of the suppression of the natural regeneration of canopy species by dense Sasa dwarf bamboo in this forest ecosystem.     

内蒙半干旱低山区不同纯林土壤腐殖质分异特征及其与其他生物化学性质的关系

纯林土壤腐殖质含量及其构成是否会因枯落叶组成的单一性和单优群落环境的特殊性而发生分异变化是关系到森林可持续经营的关键问题.本文以内蒙半干旱低山区的6种典型纯林为研究对象,研究了不同树种纯林土壤腐殖质分异特征及其与其他生物化学性质的关系.结果表明：云杉和白桦林地土壤的腐殖质含量、缩合程度和稳定性均较高,其次为小叶杨和落叶松林地,再次为白榆林地,而油松林地土壤的腐殖质含量和缩合程度均最低、稳定性最差.土壤微生物生物量和磷酸酶活性与腐殖质各组分的积累及其稳定性存在相互促进作用;过氧化氢酶和脱氢酶活性则与土壤腐殖质存在相互抑制作用,且脱氢酶活性的提高可能破坏腐殖质的稳定性.速效N含量与腐殖质积累及其稳定性呈正相关,而全量Cu、Fe、Zn含量与腐殖质呈负相关,全Cu、Fe的增加可能会破坏腐殖质的稳定性.纯林环境及其枯落叶性质的特殊性是造成腐殖质分异的重要原因,混交改造或增加林下植被是改善土壤腐殖质构成的根本措施.     

Regeneration niche of three epiphytic species of Gesneriaceae from Chilean rainforests: implications for the evolution of growth habits in Coronanthereae

Ecological and evolutionary studies of the epiphytic growth habit in angiosperms are limited. In this article, we assess the relationship between growth habit and regeneration niche in Coronanthereae (Gesneriaceae) and discuss its implications for the evolution of epiphytism in this lineage. In the temperate rainforest of southern Chile, we quantified the vertical distribution and experimentally examined the regeneration niche of three endemic species of Coronanthereae. One species was a holoepiphyte, which was more frequent in the upper canopy, and two species were secondary hemiepiphytes, which decreased in abundance with tree height. Seed germination of the holoepiphyte was higher on tree bark substrates and under open canopy than on forest soil and in the shade. In contrast, seed germination of both secondary hemiepiphytes did not differ between substrates (bark vs. soil) or light conditions (light vs. shade). Seedling survival percentage of secondary hemiepiphytes was higher on forest soil and under a closed canopy, thus behaving as shade‐tolerant species. In turn, the holoepiphyte behaved as a shade‐intolerant species. The reconstruction of the ancestral growth habits and regeneration niches on the inferred phylogenetic tree of Coronanthereae revealed that the specialized regeneration niche of Sarmienta repens, characterized by requirements of shade intolerance and germination on tree bark, was coupled with the evolution of the holoepiphytic growth habit. We conclude that differentiation in the regeneration niche is a key process in the evolution of epiphytic growth habits in Coronanthereae. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 79–92.     

Multivariate path analysis of the relationships between seedling regeneration and environmental factors beneath a dwarf bamboo understory

Seedling emergence and establishment are fragile processes that determine the direction and structure of forest succession and regeneration. However, seedling emergence and establishment are easily affected by biotic and abiotic (environmental) factors. A dense and expanding understory of dwarf bamboo is one such important factor that can seriously hinder the seedling regeneration. We conducted a field experiment to investigate the emergence and establishment of canopy tree seedlings under artificially controlled densities of dwarf bamboo. We found that understory dwarf bamboo obstructed seedling emergence but reduced the death of seedlings. Although understory dwarf bamboo reduced the median retention time of seedlings, dense bamboo increased the mean survival time of seedlings. Our results suggest that understory dwarf bamboo has multiple selectivities for tree seedling emergence and establishment: high‐density dwarf bamboo was beneficial to evergreen species but lower‐density of bamboo was conducive to the survival of deciduous species, it means the dwarf bamboo potentially alters successional trajectories of forest communities. Path analysis revealed that the most important factors affecting tree seedling emergence and death were the abundance of seeds in the seed bank and the density of emerged seedlings, and that the soil temperature promoted seedling emergence but increased seedling death, the thickness of litter limited seedling emergence, and the leaf area index of the bamboo canopy limited seedling death. The present study suggests that dwarf bamboo can directly alter the microenvironment, significantly reducing light levels and soil temperature but increasing the thickness of litter and soil humus, thereby indirectly impacting the regeneration of tree seedlings. Our results indicate that various factors affected seedling emergence, and there were complex indirect relationships among these factors. In general, biological factors had a stronger influence on tree seedling regeneration than environmental factors.     

The ectomycorrhizal flora of primary and secondary stands of Pinus sylvestris in relation to soil conditions and ectomycorrhizal succession

Abstract. Ectomycorrhizal species composition and sporocarp abundance in two 15–20-yr old primary stands of Pinus sylvestris in the central part of the Netherlands was compared with those in two 16- and 27-yr old secondary stands of P. sylvestris in the Northeast of the country. The trees of the primary stands were spontaneously seeded in a drifting sand area. Only thin litter and humus layers were present. The trees of the 16-yr old secondary stand were planted on podzolic sandy soil and those of the 27-yr old stand on non-podzolic sandy soil. In both secondary stands thick litter and humus layers had developed. The litter and humus partly originated from former stands at the same sites and partly from the present stands. In the secondary stands the thick litter and humus layers and herb vegetation were removed (‘sod-cutting’) in order to simulate the thin litter and humus layers in the primary stands. Control treatments were present. Surveys in 1991, 1992 and 1993 showed that sod-cutting enhanced both abundance and diversity of ectomycorrhizal fungi. However, species richness and diversity were higher in the primary stands than in the secondary ones, also even in the sod-cut plots. High species richness and diversity were associated with low concentrations of nitrogen and relatively high pH in the litter and humus layers, and in the mineral soil.     

湖南栎类天然次生林幼树更新特征及影响因子

以湖南典型栎类天然次生林为研究对象,基于51块样地的调查数据,采用k-means聚类分析划分林分类型,研究湖南不同栎类天然次生林幼树更新特征,分析了湖南不同栎类天然次生林幼树更新指标(幼树密度、幼树平均地径、平均高以及平均冠幅)与环境因子、林分因子的相关性,旨在阐明环境因子、林分因子对幼树更新的影响,以期为湖南不同栎类天然次生林的恢复与经营管理提供理论依据。结果表明:(1)利用聚类分析可将研究区内栎类天然次生林划分为5个类型,包括甜槠锥栗混交林(CC)、亮叶水青冈多脉青冈混交林(FC)、石栎樟树混交林(LC)、枹栎甜槠混交林(QC)、青冈栎混交林(CG)。(2)不同类型栎类天然次生林更新幼树优势种分化明显,物种丰富度差异显著(P0.05)。5种不同栎类次生林幼树密度均未超过500株/hm~2,更新情况较差;幼树数量差异显著(P0.05),为亮叶水青冈多脉青冈混交林石栎樟树混交林青冈栎混交林枹栎甜槠混交林甜槠锥栗混交林;生长情况差异显著(P0.05),为青冈栎混交林亮叶水青冈多脉青冈混交林枹栎甜槠混交林甜槠锥栗混交林石栎樟树混交林。(3)相关分析结果显示,不同类型次生林幼树更新的主要影响因子存在差异。甜槠锥栗混交林中幼树密度与腐殖质厚度呈显著负相关(P0.05);幼树平均高与灌木盖度呈显著正相关(P0.05);幼树平均地径与草本盖度、灌木盖度呈显著正相关(P0.05)。亮叶水青冈多脉青冈混交林中幼树密度与海拔、腐殖质厚度、枯落物厚度呈显著正相关(P0.05),与草本盖度呈极显著正相关(P0.01);幼树平均地径与郁闭度呈显著负相关(P0.05);幼树平均高、幼树平均冠幅与坡位呈显著正相关(P0.05)。石栎樟树混交林中幼树密度与坡向、土壤厚度呈显著正相关(P0.05),其余因子对幼树生长无显著影响。枹栎甜槠混交林中幼树密度与郁闭度、乔木密度呈极显著正相关(P0.01),与坡位呈显著负相关(P0.05);幼树平均冠幅与坡度呈显著负相关(P0.05)。青冈栎混交林中幼树平均地径与土壤厚度呈显著正相关(P0.05),与乔木密度呈极显著正相关(P0.01);幼树平均冠幅与灌木盖度呈显著正相关(P0.05)。     

Spatial Patchiness of Litter, Nutrients and Macroinvertebrates during Secondary Succession in a Tropical Montane Cloud Forest in Mexico

We test the hypothesis that secondary succession in Tropical Montane Cloud Forest (TMCF) in Mexico is accompanied by an increase in the spatial structuring of litter resources, soil nutrient concentrations and the soil macroinvertebrate community at a within-plot scale (5–25 m). This increased spatial structuring is expected because secondary succession in these forests is associated with an increase in the diversity of trees that dominate the canopy. If each tree species generates a particular soil environment under its canopy, then under a diverse tree community, soil properties will be spatially very heterogeneous. Tree censuses and grid sampling were performed in four successional stages of a secondary chronosequence of TMCF. Variography was used to analyse spatial patterns in continuous variables such as nutrient concentrations, while Spatial Analysis by Distance Indices (SADIE) was applied to determine patchiness in the distribution of soil macroinvertebrate taxa. Secondary succession was found to be accompanied by the predicted increase in the spatial structuring of litter resources and the macroinvertebrate community at the within-plot scale. Spatial patterns in the macroinvertebrate community only became evident for all taxa in the oldest forest (100 years old). Patches with low Ca and Mg concentrations in early successional soils were associated with patches where pine litter was most abundant while those with low P concentrations in late successional stages were associated with patches where oak litter was most abundant. Results suggest that anthropogenic disturbance aboveground promotes a more homogeneous resource environment in the surface soil, which compared to older forests, sustains a less diverse and less spatially structured macroinvertebrate community.     

Tropical tree species composition affects the oxidation of dissolved organic matter from litter

Plant species effects on soil nutrient availability are relatively well documented, but the effects of species differences in litter chemistry on soil carbon cycling are less well understood, especially in the species-rich tropics. In many wet tropical forest ecosystems, leaching of dissolved organic matter (DOM) from the litter layer accounts for a significant proportion of litter mass loss during decomposition. Here we investigated how tree species differences in soluble dissolved organic C (DOC) and nutrients affected soil CO₂ fluxes in laboratory incubations. We leached DOM from freshly fallen litter of six canopy tree species collected from a tropical rain forest in Costa Rica and measured C-mineralization. We found significant differences in litter solubility and nutrient availability. Following DOM additions to soil, rates of heterotrophic respiration varied by as much as an order of magnitude between species, and overall differences in total soil CO₂ efflux varied by more than four-fold. Variation in the carbon: phosphorus ratio accounted for 51% of the variation in total CO₂ flux between species. These results suggest that tropical tree species composition may influence soil C storage and mineralization via inter-specific variation in plant litter chemistry.     

Tree species distribution in canopy gaps and mature forest in an area of cloud forest of the Ibitipoca Range,south-eastern Brazil

The tree community of both canopy gaps and mature forest was surveyed in a 5 ha plot of cloud forest in the Ibitipoca Range, south-eastern Brazil, aiming at: (a) comparing the tree community structure of canopy gaps with that of three strata of the mature forest, and (b) relating the tree community structure of canopy gaps with environmental and biotic variables. All saplings of canopy trees with 1–5 m of height established in 31 canopy gaps found within the plot were identified and measured. Mature forest trees with dbh 3 cm were sampled in four 40×40 quadrats laid on the four soil sites recognised in the local soil catena. All surveyed trees were identified, measured and distributed into three forest strata: understorey (<5 m of height), sub-canopy (5.1–15 m) and canopy (15.1–30 m). The following variables were obtained for each gap: mode of formation, age, soil site, slope grade, size, canopy openness and abundance of bamboos and lianas. A detrended correspondence analysis indicated that the tree community structure of gaps in all soil sites was more similar to that of the mature forest understorey, suggesting that the bank of immatures plays an important role in rebuilding the forest canopy and that gap phases may be important for understorey shade-tolerant species. There was evidence of gap-dependence for establishment for only one canopy tree species. Both canonical correspondence analysis and correlation analysis demonstrated for a number of tree species that the distribution of their saplings in canopy gaps was significantly correlated with two variables: soil site and canopy openness. The future forest structure at each gap is probably highly influenced by both the present structure of the adjacent mature forest and the gap creation event.