Edge disturbance drives liana abundance increase and alteration of liana–host tree interactions in tropical forest fragments

Closed‐canopy forests are being rapidly fragmented across much of the tropical world. Determining the impacts of fragmentation on ecological processes enables better forest management and improves species‐conservation outcomes. Lianas are an integral part of tropical forests but can have detrimental and potentially complex interactions with their host trees. These effects can include reduced tree growth and fecundity, elevated tree mortality, alterations in tree‐species composition, degradation of forest succession, and a substantial decline in forest carbon storage. We examined the individual impacts of fragmentation and edge effects (0–100‐m transect from edge to forest interior) on the liana community and liana–host tree interactions in rainforests of the Atherton Tableland in north Queensland, Australia. We compared the liana and tree community, the traits of liana‐infested trees, and determinants of the rates of tree infestation within five forest fragments (23–58 ha in area) and five nearby intact‐forest sites. Fragmented forests experienced considerable disturbance‐induced degradation at their edges, resulting in a significant increase in liana abundance. This effect penetrated to significantly greater depths in forest fragments than in intact forests. The composition of the liana community in terms of climbing guilds was significantly different between fragmented and intact forests, likely because forest edges had more small‐sized trees favoring particular liana guilds which preferentially use these for climbing trellises. Sites that had higher liana abundances also exhibited higher infestation rates of trees, as did sites with the largest lianas. However, large lianas were associated with low‐disturbance forest sites. Our study shows that edge disturbance of forest fragments significantly altered the abundance and community composition of lianas and their ecological relationships with trees, with liana impacts on trees being elevated in fragments relative to intact forests. Consequently, effective control of lianas in forest fragments requires management practices which directly focus on minimizing forest edge disturbance.     

Leaf herbivory is more impacted by forest composition than by tree diversity or edge effects

Links between biodiversity and ecosystem functioning are well established. Beyond biodiversity per se, community composition can have strong effects on ecosystem functioning. Furthermore, spatial processes including edge effects, can impact the diversity-functioning relationship. These spatial processes are especially relevant within a food web context, such as the transfer of plant biomass across the food chain through herbivory. The relative importance of diversity, community composition and spatial context on herbivory pressure at the community and the species level is, however, poorly understood.To fill this gap in our understanding, we studied to what degree herbivory in temperate forest plots varies according to edge distance, tree diversity and forest composition. In contrast to the prevailing view of tree herbivory increasing at forest edges, we found that the effects of forest edge and tree diversity on leaf herbivory were masked by effects of forest composition, i.e. the specific contributions of the tree species. The strongest composition effect found was increased herbivory on Quercus robur in the presence of Fagus sylvatica.Our findings highlight that neither edge distance, tree diversity, nor the interaction affected one ecosystem function, namely herbivory, whilst tree community composition did. This warrants consideration of identity and composition effects in future studies if we are to deepen our understanding of the determinants of ecosystem functions across systems.     

Edge-related changes in tree communities in the understory of mesic temperate forest fragments of northern Japan

We have assessed the effects of habitat fragmentation on understory tree communities in mesic temperate forests of the Tokachi plain of northern Japan. Tree community composition was analyzed across 13 forest fragments of various sizes ranging from 0.30 to 8.51 ha. The community composition varied along the edge-to-interior gradient: there was a lower abundance of shade-tolerant shrubs in forest edges than in forest interiors, while saplings of dominant canopy trees and pioneer trees were more abundant near the edges. The edge influence extended approximately 56 m into the forest interiors. Even the interior area of small fragments were likely to be affected not only by the nearest edge but also by more distant edges. Consequently, most areas in fragments smaller than 2 ha were covered by these “edge-type” communities. These results indicate that it is of primary importance to conserve and restore forests with an area at least larger than several hectares to sustain forest-interior tree communities.     

Viability of ecological processes in small Afromontane forest patches in South Africa

Abstract The conservation of biodiversity is dependent on protecting ecosystem‐level processes. We investigated the effects of fragment size and habitat edge on the relative functioning of three ecological processes – decomposition, predation and regeneration of trees – in small Afromontane forests in KwaZulu‐Natal, South Africa. Ten sampling stations were placed in each of four forest categories: the interior of three large indigenous forest fragments (100 m from the edge), the edges of these large fragments, 10 small indigenous fragments (<1 ha) and 10 small exotic woodlands (<0.5 ha). Fragment size and edge effects did not affect the abundance of the amphipod Talitriator africana, a litter decomposer, and overall dung beetle abundance and species richness significantly. Bird egg predation was marginally greater at large patch edges compared with the other forest categories, while seed predation did not differ among forest categories. Tree seedling assemblage composition did not differ significantly among large patch interiors and edges, and small indigenous fragments. Sapling and canopy assemblage composition each differed significantly among these three indigenous forest categories. Thus, while tree recruitment was not negatively affected by patch size or distance from the edge, conditions in small fragments and at edges appear to affect the composition of advanced tree regeneration. These ecological processes in Afromontane forests appear to be resilient to fragmentation effects. We speculate that this is because the organisms in these forests have evolved under fragmented conditions. Repeated extreme changes in climate and vegetation over the Pleistocene have acted as significant distribution and ecological extinction filters on these southern hemisphere forest biota, resulting in fauna and flora that are potentially resilient to contemporary fragmentation effects. We argue that because small patches and habitat edges appear to be ecologically viable they should be included in future conservation decisions.     

Microclimate and tree community linked to differences in lepidopteran larval communities between forest fragments and continuous forest

Aim  We aim to assess the impact of forest fragmentation on lepidopteran larval community and study the associations of microclimate and tree community with lepidopteran assemblage.
Location  Kibale National Park, Uganda.
Methods  We investigated the effects of forest fragmentation on leaf herbivory, density of lepidopteran caterpillars, species richness and diversity as well as the composition of herbivorous lepidopteran larval community. Microclimate, size of the fragment, distance to the continuous forest, and tree diversity were studied as possible explanatory factors. We sampled 10 Neoboutonia macrocalyx Pax. (Euphorbiaceae) trees in each fragment during dry and rainy season, total of four times, in a year to cover the seasonal variation.
Results  The rates of herbivory, total larval density and species richness were significantly lower in the forest fragments than in the continuous forest but species diversity expressed as Fisher's alpha did not differ. The dominance structure and community composition of the larval communities in the fragments was different from that of the continuous forest. None of the differences we observed were related to the fragment area or distance to the continuous forest. Instead, we found an indication of association between the herbivore and the tree communities. The fragments had significantly lower humidity during most of the day and higher temperature during the afternoons (14–17 h), which might partially explain the differences in lepidopteran larval communities.
Main conclusions  Decreased larval density and species richness as well as differences in the community composition and structure all highlight the importance of large continuous forest areas for maintaining larval biodiversity.     

Does plant diversity increase top–down control of herbivorous insects in tropical forest?

Higher trophic level interactions are key mediators of ecosystem functioning in tropical forests. A rich body of theory has been developed to predict the effects of plant diversity on communities at higher trophic levels and the mechanisms underlying such effects. The 'enemies hypothesis’ states that predators exert more effective top–down control of herbivorous insects with increasing plant diversity. Support for this hypothesis has been found in temperate forests and agroecosystems, but remains understudied in tropical forests. We compared incidence of attacks of different natural enemies using artificial caterpillars in a tropical forest landscape and investigated the role of plant community structure (i.e. species richness, composition and density), and the role of forest fragmentation (i.e. patch size, edge distance and canopy openness) on predation intensity. Plant community effects were tested with respect to three vegetation strata: trees, saplings and herbs. Observed predation was substantially due to ants. Predation rates increased with plant species richness for trees and herbs. Density of saplings, herb cover and herb species composition were important factors for predation. No significant patterns were found for fragmentation parameters, suggesting that forest fragmentation has not altered predation intensity. We conclude that in tropical forests, top–down control of herbivorous insects in the understory vegetation is affected by a combination of plant diversity, plant species composition and structural features of the plant community.     

Forest fragmentation and selective logging have inconsistent effects on multiple animal-mediated ecosystem processes in a tropical forest

Forest fragmentation and selective logging are two main drivers of global environmental change and modify biodiversity and environmental conditions in many tropical forests. The consequences of these changes for the functioning of tropical forest ecosystems have rarely been explored in a comprehensive approach. In a Kenyan rainforest, we studied six animal-mediated ecosystem processes and recorded species richness and community composition of all animal taxa involved in these processes. We used linear models and a formal meta-analysis to test whether forest fragmentation and selective logging affected ecosystem processes and biodiversity and used structural equation models to disentangle direct from biodiversity-related indirect effects of human disturbance on multiple ecosystem processes. Fragmentation increased decomposition and reduced antbird predation, while selective logging consistently increased pollination, seed dispersal and army-ant raiding. Fragmentation modified species richness or community composition of five taxa, whereas selective logging did not affect any component of biodiversity. Changes in the abundance of functionally important species were related to lower predation by antbirds and higher decomposition rates in small forest fragments. The positive effects of selective logging on bee pollination, bird seed dispersal and army-ant raiding were direct, i.e. not related to changes in biodiversity, and were probably due to behavioural changes of these highly mobile animal taxa. We conclude that animal-mediated ecosystem processes respond in distinct ways to different types of human disturbance in Kakamega Forest. Our findings suggest that forest fragmentation affects ecosystem processes indirectly by changes in biodiversity, whereas selective logging influences processes directly by modifying local environmental conditions and resource distributions. The positive to neutral effects of selective logging on ecosystem processes show that the functionality of tropical forests can be maintained in moderately disturbed forest fragments. Conservation concepts for tropical forests should thus include not only remaining pristine forests but also functionally viable forest remnants.     

Trophic structure stability and extinction dynamics of beetles (Coleoptera) in tropical forest fragments

A first analysis of the stability of trophic structure following tropical forest fragmentation was performed in an experimentally fragmented tropical forest landscape in Central Amazonia. A taxonomically and trophically diverse assemblage of 993 species of beetles was sampled from 920 m² of leaf litter at 46 sites varying in distance from forest edge and fragment area. Beetle density increased significantly towards the forest edge and showed non-linear changes with fragment area, due to the influx of numerous disturbed-area species into 10 ha and 1 ha fragments. There was a marked change in species composition with both decreasing distance from forest edge and decreasing fragment area, but surprisingly this change in composition was not accompanied by a change in species richness. Rarefied species richness did not vary significantly across any of the sites, indicating that local extinctions of deep forest species were balanced by equivalent colonization rates of disturbed-area species. The change in species composition with fragmentation was non-random across trophic groups. Proportions of predator species and xylophage species changed significantly with distance from forest edge, but no area-dependent changes in proportions of species in trophic groups were observed. Trophic structure was also analysed with respect to proportions of abundance in six trophic groups. Proportions of abundance of all trophic groups except xylomycetophages changed markedly with respect to both distance from forest edge and fragment area. Local extinction probabilities calculated for individual beetle species supported theoretical predictions of the differential susceptibility of higher trophic levels to extinction, and of changes in trophic structure following forest fragmentation. To reduce random effects due to sampling error, only abundant species (n = 46) were analysed for extinction probabilities, as defined by absence from samples. Of these common species, 27% had significantly higher probabilities of local extinction following fragmentation. The majority of these species were predators; 42% of all abundant predator species were significantly more likely to be absent from samples in forest fragments than in undisturbed forest. These figures are regarded as minimum estimates for the entire beetle assemblage because rarer species will inevitably have higher extinction probabilities. Absolute loss of biodiversity will affect ecosystem process rates, but the differential loss of species from trophic groups will have an even greater destabilizing effect on food web structure and ecosystem function.     

菌根真菌影响森林生态系统碳循环研究进展

森林生态系统在全球碳(C)储量中占据极为重要的地位。菌根真菌广泛存在于森林生态系统中,在森林生态系统C循环过程中发挥重要的作用。阐述了不同菌根类型真菌在森林生态系统C循环过程中的功能,对比了温带/北方森林与热带/亚热带森林中菌根真菌介导的C循环研究方面新近取得的研究结果。发现温带和北方森林的外生菌根(EcM)植物对地上生物量C的贡献相对较小,然而是地下C储量的主要贡献者;以丛枝菌根(AM)共生为主的热带/亚热带森林地表生物量占比较高,表明AM植被对热带/亚热带森林地上生物量C的贡献相对较大。我们还就全球变化背景下,菌根真菌及其介导的森林生态系统C汇功能,以及不同菌根类型树种影响C循环的机制等进行了总结。菌根真菌通过影响凋落物分解、土壤有机质形成及地下根系生物量,进而影响整个森林生态系统的C循环功能。菌根介导的森林C循环过程很大程度上取决于(优势)树木的菌根类型和森林土壤中菌根真菌的群落结构。最后指出了当前研究存在的主要问题以及未来研究展望。本文旨在明确菌根真菌在森林生态系统C循环转化过程中的重要生态功能,有助于准确地评估森林生态系统C汇现状,为应对全球变化等提供重要的依据。     

Biodiversity of leaf-litter ants in fragmented tropical rainforests of Borneo: the value of publically and privately managed forest fragments

In view of the rapid rate of expansion of agriculture in tropical regions, attention has focused on the potential for privately-managed rainforest patches within agricultural land to contribute to biodiversity conservation. However, these sites generally differ in their history of forest disturbance and management compared with other forest fragments, and more information is required on the biodiversity value of these privately-managed sites, particularly in oil-palm dominated landscapes of SE Asia. Here we address this issue, using tropical leaf-litter ants in rainforest fragments surrounded by mature oil palm plantations in Sabah, Borneo as a model system. We compare the species richness and composition of ant assemblages in privately-managed forest fragments (‘high conservation value’ fragments; HCVs) with those in publically-managed fragments of forest (virgin jungle reserves; VJRs) and control sites in extensive tracts of primary forest. In this way, we test the hypothesis that privately-managed and publically-managed forest fragments differ in their species richness and composition as a result of differences in history and management and hence in habitat quality. In support of this hypothesis, we found that HCVs had much poorer habitat quality than VJRs, including lower sizes and densities of trees, less canopy cover, fewer dipterocarp trees and shallower leaf litter. Consequently, HCVs supported only half the species richness of ants in VJRs, which in turn supported 70 % of the species richness of control sites, with vegetation structure and composition explaining 77 % of the variation among forest fragments in ant species richness. HCVs were also much smaller than VJRs but there was only a weak relationship between fragment size and habitat quality, and species richness was not related to fragment size. VJRs supported 78 % of the 156 species found in extensive tracts of forest whereas HCVs supported only 22 %, which was only slightly higher than the proportion previously recorded in oil palm (19 %). These data support previous findings that publically-managed VJR fragments can make an important contribution to biodiversity conservation within agricultural landscapes. However, we suggest that for these HCVs to be effective as reservoirs of biodiversity, management is required to restore vegetation structure and habitat quality, for instance through enrichment planting with native tree species.     

Impacts of forest fragmentation on species composition and forest structure in the temperate landscape of southern Chile

Aim Few studies have explicitly examined the influence of spatial attributes of forest fragments when examining the impacts of fragmentation on woody species. The aim of this study was to assess the diverse impacts of fragmentation on forest habitats by integrating landscape‐level and species‐level approaches. Location The investigation was undertaken in temperate rain forests located in southern Chile. This ecosystem is characterized by high endemism and by intensive recent changes in land use. Method Measures of diversity, richness, species composition, forest structure and anthropogenic disturbances were related to spatial attributes of the landscape (size, shape, connectivity, isolation and interior forest area) of forest fragments using generalized linear models. A total of 63 sampling plots distributed in 51 forest fragments with different spatial attributes were sampled. Results Patch size was the most important attribute influencing different measures of species composition, stand structure and anthropogenic disturbances. The abundance of tree and shrub species associated with interior and edge habitats was significantly related to variation in patch size. Basal area, a measure of forest structure, significantly declined with decreasing patch size, suggesting that fragmentation is affecting successional processes in the remaining forests. Small patches also displayed a greater number of stumps, animal trails and cow pats, and lower values of canopy cover as a result of selective logging and livestock grazing in relatively accessible fragments. However, tree richness and β‐diversity of tree species were not significantly related to fragmentation. Main conclusions This study demonstrates that progressive fragmentation by logging and clearance is associated with dramatic changes in the structure and composition of the temperate forests in southern Chile. If this fragmentation process continues, the ability of the remnant forests to maintain their original biodiversity and ecological processes will be significantly reduced.     

Structure and function in two tropical gallery forest communities: implications for forest conservation in fragmented systems

1. Composition, growth and turnover of trees in two species-rich tropical gallery forests were examined to evaluate what community reorganization may be needed to transform recently created tropical forest fragments into stable refugia for regional forest biotas.
2. Rates of tree growth and turnover over a 5-year interval were comparable to those recorded in continuous forests and in both communities there had been some tree species turnover in the measured stem size classes during the 5-year interval.
3. The more abundant tree species in both communities formed three functional groups along gradients between streams and forest edges: edge-concentrators, core-concentrators and generalists.
4. Soil fertility showed no consistent increase close to streams and neither tree growth nor recruitment rates were increased in this zone. In contrast, forest edge zones exhibited increased rates of tree growth and recruitment indicating that growth processes in these forests are light-limited rather than soil-limited, and that forest edge zones are generally favourable habitats for tree populations.
5. Both communities showed signs of past fire incursions, and the tendency of a subset of tree species to concentrate in the more growth-limited core habitats is attributed to their fire sensitivity.
6. Rapid development of an edge zone of fire-insensitive tree species is considered to be essential to the survival of forest community fragments in the fire-prone landscapes of the tropics, and the edges of gallery forests are recommended as potential sources of species with which to fashion these protective ecotones.
7. Preservation of a diverse forest biota in the fire-protected interiors of fragments will require natural or artificially enhanced immigration rates that are sufficient to offset local extinctions.     

Long‐term recovery of the functional community assembly and carbon pools in an African tropical forest succession

On the African continent, the population is expected to expand fourfold in the next century, which will increasingly impact the global carbon cycle and biodiversity conservation. Therefore, it is of vital importance to understand how carbon stocks and community assembly recover after slash‐and‐burn events in tropical second growth forests. We inventoried a chronosequence of 15 1‐ha plots in lowland tropical forest of the central Congo Basin and evaluated changes in aboveground and soil organic carbon stocks and in tree species diversity, functional composition, and community‐weighted functional traits with succession. We aimed to track long‐term recovery trajectories of species and carbon stocks in secondary forests, comparing 5 to 200 + year old secondary forest with reference primary forest. Along the successional gradient, the functional composition followed a trajectory from resource acquisition to resource conservation, except for nitrogen‐related leaf traits. Despite a fast, initial recovery of species diversity and functional composition, there were still important structural and carbon stock differences between old growth secondary and pristine forest, which suggests that a full recovery of secondary forests might take much longer than currently shown. As such, the aboveground carbon stocks of 200 + year old forest were only 57% of those in the pristine reference forest, which suggests a slow recovery of aboveground carbon stocks, although more research is needed to confirm this observation. The results of this study highlight the need for more in‐depth studies on forest recovery in Central Africa, to gain insight into the processes that control biodiversity and carbon stock recovery.     

Response of wood-inhabiting fungal community to fragmentation in a beech forest landscape

Fragmentation of natural habitats has become one of the main causes of the loss of biodiversity. To assess the effects of forest fragmentation on wood-inhabiting fungal community in a beech-dominated landscape, 15 differently shaped beech forest fragments were examined in northern Spain. This work covers all the wood-inhabiting macromycetes, including Basidiomycota and Ascomycota. A modelling approach was used to examine the predictability of the fungal community in a fragmented beech forest landscape. In the beech forest patches, a large proportion of edge, low tree densities and low levels of variety of woody debris caused a decrease of wood-inhabiting fungal richness. The fungal community composition proved complex to model due to its specific traits: it is made up of many species, most of which are rare, and each fungal group responds differently to environmental variables. Nevertheless, the dead wood availability and the exposure to light significantly affected the fungal community composition.     

Edge effects on palm diversity in rain forest fragments in western Ecuador

At the edges of tropical rain forest fragments, altered abiotic and biotic conditions influence the structure and dynamics of plant communities. In Neotropical rain forests, palms (Arecaceae) are important floristic and ecological elements. Palms’ responses to edge effects appear to be idiosyncratic and to depend on the level of disturbance at edges. This paper explores how variation in forest structure at the edges of two old-growth forest fragments in a tropical rain forest in western Ecuador affects palms of different species, life-forms, and size classes. We investigate (1) how edge effects influence the relative proportion of palm adults and juveniles, (2) how distance from the forest edge affects palm density and species richness, (3) how altered forest structure along edges affects palm density. We found that at edges (1) palm communities had a lower proportion of adults relative to juvenile individuals compared to continuous forests, (2) the density of two species of palms and the overall species richness of the palm community tended to decrease toward the edges within forest fragments, and, (3) altered forest structure decreased the density of adult palms. Hence, edge effects on palms were controlled by the degree of modification of the forest structure, and by species responses to edge-related disturbance.     

Depth-dependent effects of ericoid mycorrhizal shrubs on soil carbon and nitrogen pools are accentuated under arbuscular mycorrhizal trees

Plant mycorrhizal associations influence the accumulation and persistence of soil organic matter and could therefore shape ecosystem biogeochemical responses to global changes that are altering forest composition. For instance, arbuscular mycorrhizal (AM) tree dominance is increasing in temperate forests, and ericoid mycorrhizal (ErM) shrubs can respond positively to canopy disturbances. Yet how shifts in the co-occurrence of trees and shrubs with different mycorrhizal associations will affect soil organic matter pools remains largely unknown. We examine the effects of ErM shrubs on soil carbon and nitrogen stocks and indicators of microbial activity at different depths across gradients of AM versus ectomycorrhizal (EcM) tree dominance in three temperate forest sites. We find that ErM shrubs strongly modulate tree mycorrhizal dominance effects. In surface soils, ErM shrubs increase particulate organic matter accumulation and weaken the positive relationship between soil organic matter stocks and indicators of microbial activity. These effects are strongest under AM trees that lack fungal symbionts that can degrade organic matter. In subsurface soil organic matter pools, by contrast, tree mycorrhizal dominance effects are stronger than those of ErM shrubs. Ectomycorrhizal tree dominance has a negative influence on particulate and mineral-associated soil organic matter pools, and these effects are stronger for nitrogen than for carbon stocks. Our findings suggest that increasing co-occurrence of ErM shrubs and AM trees will enhance particulate organic matter accumulation in surface soils by suppressing microbial activity while having little influence on mineral-associated organic matter in subsurface soils. Our study highlights the importance of considering interactions between co-occurring plant mycorrhizal types, as well as their depth-dependent effects, for projecting changes in soil carbon and nitrogen stocks in response to compositional shifts in temperate forests driven by disturbances and global change.     

Disturbance-Mediated Drift in Tree Functional Groups in Amazonian Forest Fragments

The interactive effects of forest disturbance and fragmentation on tropical tree assemblages remain poorly understood. We examined the effects of forest patch and landscape metrics, and levels of forest disturbance on the patterns of floristic composition and abundance of tree functional groups within 21 forest fragments and two continuous forest sites in southern Brazilian Amazonia. Trees were sampled within 60 (10 × 250 m) plots placed in the core areas of the fragments. Tree assemblage composition and abundance were summarized using nonmetric multidimensional scaling (NMDS). Forest patch size explained 36.2 percent and 30 percent of the variance in the proportion of small-seeded softwood and hardwood stems in the 21 forest patches, respectively. Large fragments retained a higher abundance of hardwood tree species whereas small-seeded softwood trees appear to proliferate rapidly in small disturbed fragments. Generalized linear mixed models showed that time since fragmentation had both positive and negative effects on the density of different functional groups of trees and on the ordination axes describing tree abundance. The composition and abundance of different tree genera were also related to time since fragmentation, distance to the nearest edge, and fire severity, despite the recent post-isolation history of the forest patches surveyed. Both the proliferation of fast-growing pioneer trees and the decline of hardwood trees found in our forest plots have profound consequences on the floristic composition, forest dynamics, carbon storage, and nutrient cycling in Amazonian forest fragments.     

Edge influence on herbaceous plant species,diversity and soil properties in sparse oak forest fragments in Iran

伊朗稀疏橡木林片段对草本植物物种多样性和土壤特性的边缘影响 温带和热带森林中的森林边缘现象已经得到了很好的研究,但在稀疏的橡木林片段中的相关研究却较为缺乏。本文研究了稀疏橡木林片段对植物物种多样性和土壤特性的边缘影响。本研究沿着伊朗克尔曼沙赫省3个小型(<10 ha)和3个大型(>10 ha)橡木林片段的3个横断面收集了从边缘到内部的相 关数据,测量了0(森林边缘)、25、50、100和150 m处的草本植物(高度<0.5 m)和土壤特性。使用香农指数量化了物种多样性,使用稀疏标准化方法比较了两个大小不同片段中的物种丰富度,并应用了非度量多维测度排序研究了物种组成的变化。通过随机化测试估算了边缘影响的距离,并利用Tukey HSD事后检验法的广义线性混合模型评估了距边缘距离和片段大小对多样性和土壤特性的影响。研究结果表明,大小片段边缘具有较高的物种丰富度、多样性和均匀度,而大片段边缘的土壤氮和有机碳含量则较内部更低(边缘50 m范围内的变化最大)。大小片段的物种组成、土壤有机碳和氮总量都存在显 著差异。本研究关于这些稀疏森林对草本植物和土壤特性产生显著边缘影响的发现,对于边缘研究,尤其是边缘和草本植物的相关研究具有重大贡献。     

Chaco forest fragmentation effects on leaf litter decomposition are not explained by changes in litter fauna

Forest fragmentation is a component of global change, with substantial impact on biodiversity and ecosystem functioning. Despite extensive evidence of forest fragmentation effects on above‐ground ecological processes, little is understood about its below‐ground effects. Abundance and richness of leaf litter fauna can be affected by forest fragmentation, and this can have cascading effects on the decomposition process. Here, we examine how fragmentation of a subtropical dry forest affects aspects of ecosystem structure and functioning, by unravel area and edge effects on leaf litter fauna and decomposition rates and testing whether changes in abundance or richness of litter fauna mediated fragment area and edge effects on litter decomposition. We incubated litterbags filled with a common substrate, at the edge and interior of 12 fragments of Chaco Serrano forest in Central Argentina, for 180 days. We found that invertebrate abundance was higher at the forest edge but independent of fragment area, whereas decomposition declined with fragment size independently of edge or interior location. According to our results, the effect of forest size on decomposition was not mediated by changes in abundance or richness of leaf litter fauna, suggesting independent changes in ecosystem structure and functioning.     

Leaf litter arthropod responses to tropical forest restoration

Soil and litter arthropods represent a large proportion of tropical biodiversity and perform important ecosystem functions, but little is known about the efficacy of different tropical forest restoration strategies in facilitating their recovery in degraded habitats. We sampled arthropods in four 7‐ to 8‐year‐old restoration treatments and in nearby reference forests. Sampling was conducted during the wet and dry seasons using extractions from litter and pitfall samples. Restoration treatments were replicated in 50 × 50‐m plots in four former pasture sites in southern Costa Rica: plantation – trees planted throughout the plot; applied nucleation/islands – trees planted in patches of different sizes; and natural regeneration – no tree planting. Arthropod abundance, measures of richness and diversity, and a number of functional groups were greater in the island treatment than in natural regeneration or plantation treatments and, in many cases, were similar to reference forest. Litter and pitfall morphospecies and functional group composition in all three restoration treatments were significantly different than reference sites, but island and plantation treatments showed more recovery than natural regeneration. Abundance and functional group diversity showed a much greater degree of recovery than community composition. Synthesis and applications: The less resource‐intensive restoration strategy of planting tree islands was more effective than tree plantations in restoring arthropod abundance, richness, and functional diversity. None of the restoration strategies, however, resulted in similar community composition as reference forest after 8 years of recovery, highlighting the slow rate of recovery of arthropod communities after disturbance, and underscoring the importance of conservation of remnant forests in fragmented landscapes.