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.     

片段化森林群落构建的生态过程及其检验方法

鉴于全球森林均呈现片段化(破碎化)的分布状态, 理解片段化森林群落构建的过程很有必要。该文通过综述群落构建的主要生态过程如生态漂变、扩散、选择和物种形成等在片段化森林群落构建中的相对作用, 发现因片段化森林形成方式的不同, 重构群落(片段化生境中通过次生演替重新形成的森林群落)和解构群落(原有森林被片段化后形成的森林群落)在不同演替阶段所受到的主要生态过程的相对作用有所不同。虽然利用基于群落内物种分布格局推测构建过程(如物种多度分布、零模型结合β多样性的方法、功能特征的收敛和发散等)、人工控制实验、群落结构动态分析等方法对片段化森林中群落构建的过程进行了有效的检验, 但是针对片段化森林群落构建过程的实验性研究仍然不足。未来有待在理论模型、群落构建过程的检验以及理论与物种保护相结合等方面继续开展深入的研究。     

Edge effects and tropical forest canopy invertebrates

The term edge effect can be used to encompass a wide range of both biotic and abiotic trends associated with boundaries between adjacent habitat types, whether these be natural or anthropogenic. Edge effects have been shown to represent significant forces affecting both faunal and floral assemblages in fragmented ecosystems. Specific studies of faunal assemblages associated with habitat edges have revealed trends at all levels of biological organisation from individuals to communities.Studies of edge effects on invertebrates in tropical forests have been relatively scarce. In this paper we review the nature and organisation of edge effects, focusing upon the processes which may lead to detrimental consequences for both forest canopy invertebrates and the forests themselves. We present as a case study data illustrating the very large amount of variance (over 50%) in community structure that is predicted simply by abiotic (microclimatic) variables in both a tropical and a temperate forest edge. We summarise major features of edge effects amongst forest invertebrates, stress the inter-relatedness of edge and canopy biology, and present an agenda for study of the canopy as an edge.     

Strong but taxon‐specific responses of termites and wood‐nesting ants to forest regeneration in Borneo

Land use change is accelerating globally at the expense of biodiversity and ecosystem functioning. Invertebrates are numerically dominant and functionally important in old growth tropical rain forests but highly susceptible to the adverse effects of forest degradation and fragmentation. Ants (Formicidae) and termites (Blattodea: Termitoidae) perform crucial ecosystem services. Here, the potential effects of anthropogenic disturbance on ant and termite communities in dead wood are investigated. Community composition, generic richness, and occupancy rates of ants and termites were compared among two old growth sites (Danum Valley and Maliau Basin) and one twice‐logged site (the Stability of Altered Forest Ecosystems’ (SAFE) Project), in Sabah, Malaysian Borneo. Occupancy was measured as the number of ant or termite encounters (1) per deadwood items, and (2) per deadwood volume, and acts as surrogates for relative abundance (or generic richness). Termites had a lower wood‐occupancy per volume in logged forest. In contrast, there were more ant encounters, and more ant genera, in logged sites and there was a community shift (especially, there were more Crematogaster encounters). The disruption of soil and canopy structure in logged forest may reduce both termite and fungal decay rates, inducing increased deadwood residence times and therefore favoring ants that nest in dead wood. There is an anthropogenic‐induced shift of dead wood in ants and termites in response to disturbance in tropical rain forests and the nature of that shift is taxon‐specific.     

NEECF: a project of nutrient enrichment experiments in China's forests

Anthropogenic nitrogen (N) emissions to atmosphere have increased dramatically in China since 1980s, and this increase has aroused great concerns on its ecological impacts on terrestrial ecosystems. Previous studies have showed that terrestrial ecosystems in China are acting as a large carbon (C) sink, but its potential in the future remains largely uncertain. So far little work on the impacts of the N deposition on C sequestration in China's terrestrial ecosystems has been assessed at a national scale. Aiming to assess and predict how ecological processes especially the C cycling respond to the increasing N deposition in China's forests, recently researchers from Peking University and their partners have established a manipulation experimental network on the ecological effects of the N deposition: Nutrient Enrichment Experiments in China's Forests Project (NEECF). The NEECF comprises 10 experiments at 7 sites located from north to south China, covering major zonal forest vegetation in eastern China from boreal forest in Greater Khingan Mountains to tropical forests in Hainan Island. This paper introduces the framework of the NEECF project and its potential policy implications.     

Predictors of forest fragmentation sensitivity in Neotropical vertebrates: a quantitative review

Species' responses to tropical forest fragmentation are variable and not well understood. Species' functional traits might help to reveal patterns of fragmentation sensitivity and provide valuable guidance to conservation practice. On the basis of 30 reviewed studies published between 1997 and 2008, we present a quantitative analysis of 730 responses of Neotropical vertebrates to forest fragmentation and habitat loss in terms of Species' presence, abundance or fitness. Our intention was to identify possible ecological predictors of sensitivity to fragmentation, such as vertebrate group, feeding guild, forest dependency, and body size. We also controlled for methodology and study site characteristics, i.e. parameters studied, study design, study ID, and site ID. These ecological and methodological variables are frequently hypothesized to have an influence on reported fragmentation sensitivity. We conducted Linear Mixed Model analyses in order to relate the potential predictor variables to reported fragmentation effects. Model performance was assessed on the basis of AIC values. The best models included feeding guild, feeding guild+study design and feeding guild+forest dependency, respectively. We found that study ID and site ID significantly improved the models. Post‐hoc tests revealed that nectarivores, possibly herbivores, and species able to use open habitats were affected significantly less by forest fragmentation than others. We therefore conclude that Neotropical nectarivores that are able to use open habitats are less negatively affected by forest fragmentation. Furthermore, a study site's characteristics will always be crucial in explaining observed fragmentation effects.     

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.     

Increased isolation of two Biosphere Reserves and surrounding protected areas (WAP ecological complex, West Africa)

Protected areas such as nature reserves have been found to be effective in preventing habitat destruction and protecting ecosystems within their borders. Recent studies however found extensive loss of tropical forest habitat around protected areas, vastly contributing to increase the levels of ecological isolation. Using high-resolution satellite data we investigated the isolation trend occurring in the W-Arly-Pendjari (WAP) ecological complex in West Africa. A land-cover change analysis was performed for the period 1984–2002: savanna vegetation extension and loss were derived within the complex and in a 30 km peripheral buffer. Sample regions in the buffer were also analysed using selected spatial indicators to quantify temporal trends in habitat fragmentation. Implications for change in relative capacity to conserve biodiversity were discussed through the calculation of the species richness capacity (SRC). More than 14.5% of savanna habitat was lost in the WAP peripheral areas, while 0.3% was converted inside the complex. The degree of fragmentation of remnant savanna habitat has also drastically increased. Despite the effectiveness of the park conservation programme, we found through the SRC approach that the WAP complex is decreasing its potential capacity to conserve species richness. This process is mainly due to the rapid and extended agricultural expansion taking place around the complex. A better understanding of the ecological dynamics occurring in the peripheral regions of reserves and the consideration of development needs are key variables to achieve conservation goals in protected areas.     

Hyperdynamism in fragmented habitats

Abstract. Are the dynamics of most ecological processes fundamentally increased in frequency or magnitude in fragmented habitats? Hyperdynamism could alter a wide range of population, community, and landscape phenomena, and appears to be evident in fragmented tropical, temperate, and boreal communities. I suggest some potential causes and consequences of hyperdynamism, and argue that the responses of many species and ecological processes to habitat fragmentation can be understood in this context.     

Effects of Edge Habitat and Nest Characteristics on Depredation of Artificial Nests in Fragmented Australian Tropical Rainforest

Variation in nest predation levels associated with rainforest fragmentation (edge effects) was assessed in Australia's Wet Tropics bioregion. Artificial nests were placed in the forest understorey at seven edge sites where continuous forest adjoined pasture, seven interiors (about 1 km from the edge), and six linear riparian forest remnants (50–100 m wide) that were connected to continuous forest. Four nest types were also compared, representing different combinations of two factors; height (ground, shrub) and shape (open, domed). At each site, four nests of each type, containing one quail egg and two model plasticine eggs, were interspersed about 15 m apart within a 160 m transect during September–October 2001. Predators were identified from marks on the plasticine eggs. The overall depredation rate was 66.5% of 320 nests' contents damaged over a three-day period. Large rodents, especially the rat Uromys caudimaculatus, and birds, especially the spotted catbird Ailuroedus melanotis, were the main predators. Mammals comprised 56.5% and birds 31.0% of predators, with 12.5% of unknown identity. The depredation rate did not vary among site-types, or between open and domed nests, and there were no statistically significant interactions. Nest height strongly affected depredation rates by particular types of predator; depredation rates by mammals were highest at ground nests, whereas attacks by birds were most frequent at shrub nests. These effects counterbalanced so that overall there was little net effect of nest height. Mammals accounted for 78.4% of depredated ground nests and birds for at least 47.4% of shrub nests (and possibly up to 70.1%). The main predators were species characteristic of rainforest, rather than habitat generalists, open-country or edge specialists. For birds that nest in the tropical rainforest understorey of the study region, it is unlikely that edges and linear remnants presently function as ecological population sinks due to mortality associated with increased nest predation.     

The role of patch area and habitat diversity in explaining native plant species richness in disturbed suburban forest patches in northern Belgium

Relatively easy measurable patch characteristics (especially habitat diversity measures) have proven to be valuable indicators of forest plant species richness in forest fragments of relatively undisturbed areas. Urban and suburban forest patches, however, are characterized by a specific landscape ecological context implying that specific processes may influence ecosystem functioning and hence that other abiotic indicators for plant diversity are more appropriate. We studied the relation between functional ecological plant species groups and suburban forest patch characteristics such as patch area, habitat diversity and isolation. Some components of species richness were related to the isolation of the patches. In contrast to previous similar large-scale fragmentation studies in more rural areas, further results stressed the overwhelming importance of patch area relative to habitat variables in determining species richness. This suggests (1) the occurrence of density-dependent species extinction processes in small forest patches; or (2) the existence of external deterministic factors which put a major constraint on species richness in small patches. We tend to support the latter hypothesis and propose forest disturbance and associated black cherry (Prunus serotina Ehrh.) invasion as such a possible external factor. Small forest patches may be more sensitive to disturbance and biological invasion due to various reasons. Hence large forest patches are to be preferred for plant conservation in the suburban area.     

Relationships between spatial configuration of tropical forest patches and woody plant diversity in northeastern Puerto Rico

The destruction and fragmentation of tropical forests are major sources of global biodiversity loss. A better understanding of anthropogenically altered landscapes and their relationships with species diversity and composition is needed in order to protect biodiversity in these environments. The spatial patterns of a landscape may control the ecological processes that shape species diversity and composition. However, there is little information about how plant diversity varies with the spatial configuration of forest patches especially in fragmented tropical habitats. The northeastern part of Puerto Rico provides the opportunity to study the relationships between species richness and composition of woody plants (shrubs and trees) and spatial variables [i.e., patch area and shape, patch isolation, connectivity, and distance to the Luquillo Experimental Forest (LEF)] in tropical forest patches that have regenerated from pasturelands. The spatial data were obtained from aerial color photographs from year 2000. Each photo interpretation was digitized into a GIS package, and 12 forest patches (24–34 years old) were selected within a study area of 28 km². The woody plant species composition of the patches was determined by a systematic floristic survey. The species diversity (Shannon index) and species richness of woody plants correlated positively with the area and the shape of the forest patch. Larger patches, and patches with more habitat edge or convolution, provided conditions for a higher diversity of woody plants. Moreover, the distance of the forest patches to the LEF, which is a source of propagules, correlated negatively with species richness. Plant species composition was also related to patch size and shape and distance to the LEF. These results indicate that there is a link between landscape structure and species diversity and composition and that patches that have similar area, shape, and distance to the LEF provide similar conditions for the existence of a particular plant community. In addition, forest patches that were closer together had more similarity in woody plant species composition than patches that were farther apart, suggesting that seed dispersal for some species is limited at the scale of 10 km.     

Core and Satellite Species in Degraded Habitats: an Analysis Using Malagasy Tree Communities

Core-satellite theory predicts that, via the “rescue effect”, widespread, abundant species should have reduced risk of local extinctions. We test this hypothesis in southeastern Malagasy littoral forest using data on distribution and abundance of trees and woody understory vegetation in tropical forest fragments along a disturbance gradient. We partition the mortality risk into two kinds of extinction factors, separately operating at demographic (local) and landscape (regional) scales, contrary to core-satellite predictions, for both trees and woody understory vegetation, that the relative number of core (abundant) species declined significantly with increasing disturbance. In the least-degraded forest fragments there was a strong mode of core species, while in the moderately- and severely-degraded fragments the species distributions were essentially log-normal, lacking a substantial core mode. While the rescue effect mitigates one kind of extinction risk, namely local environmental and demographic stochasticity, it may not counterbalance widespread pervasive sources of mortality. The amount of internal forest fragmentation appears to have a much greater effect on species richness and diversity than either fragment size or shape.     

Comparing bird assemblages in large and small fragments of the Atlantic Forest hotspots

The Atlantic Forest (AF) is one of the five most threatened and megadiverse world hotspots. It is arguably the most devastated and highly threatened ecosystem on the planet. The vast scope of habitat loss and extreme fragmentation in the AF hotspots has left intact very few extensive and continuous forested fragments. We compared bird assemblages between small (<100 ha) and large (>6,000 ha) forest remnants, in one of the largest AF remnants in Argentina. We performed 84 point-counts of birds in four large fragments (LF) and 67 points in 25 small fragments (SF). We recorded 4,527 bird individuals belonging to 173 species; 2,632 belonging to 153 species in LF and 1,897 in 124 species in SF. Small fragments suffered a significant loss of bird richness, mainly forest dependent species, but the birds abundance did not decrease, due to an increase in abundance of forest independent and semi-dependent bird species (edge and non forest species) that benefit from forest fragmentation. The bird guilds of frugivores, undestory, terrestrial and midstory insectivores, nectarivores and raptors, and the endemic species of AF were area sensitive, decreasing significantly in richness and abundance in the SF. Terrestrial granivores were the only guild positively affected by forest fragmentation, containing mainly edge species, which forage in open areas or borders including crops. Our first observations on fragmentation effects on bird assemblages in the southernmost Argentinean Atlantic Forests did not validate the hypothesis on pre-adaptation to human disturbances in the bird communities of AF. On the contrary, we observed that forest dependent, endemic and several sensitive bird guilds were strongly affected by fragmentation, putting in evidence the vulnerability to the fragmentation process and the necessity to conserve large remnants to avoid reduction of the high biodiversity of AF birds.     

Frugivorous butterfly species in tropical forest fragments: correlates of vulnerability to extinction

Insects exhibit a variety of population-level responses to forest fragmentation, ranging from population increase to extinction. However, the biological attributes that underlie differences in extinction vulnerability among insects have been little-studied. Using the frugivorous butterfly community of tropical dry forest in Venezuela, we studied body size, population density and colonization ability as attributes that might underlie the range of responses of insects to forest fragmentation. The study was carried out in a set of forest fragments in the reservoir Lago Guri, formed by the damming of the Caroni River in eastern Venezuela. Results show that larger butterfly species were more vulnerable to extinction from habitat fragments than smaller ones. Rarer species were not more vulnerable to extinction, showing that rarity may not be an important correlate of vulnerability to extinction amongst insects. Contrary to expectation, faster-flying species were more and not less vulnerable to extinction from small habitat fragments. We speculate on the possible reasons for the observed patterns in extinction vulnerability using additional observations on behavioural patterns and larval host plant distributions of some of the butterfly species.     

Connecting soundscape to landscape: Which acoustic index best describes landscape configuration?

Soundscape assessment has been proposed as a remote ecological monitoring tool for measuring biodiversity, but few studies have examined how soundscape patterns vary with landscape configuration and condition. The goal of our study was to examine a suite of published acoustic indices to determine whether they provide comparable results relative to varying levels of landscape fragmentation and ecological condition in nineteen forest sites in eastern Australia. Our comparison of six acoustic indices according to time of day revealed that two indices, the acoustic complexity and the bioacoustic index, presented a similar pattern that was linked to avian song intensity, but was not related to landscape and biodiversity attributes. The diversity indices, acoustic entropy and acoustic diversity, and the normalized difference soundscape index revealed high nighttime sound, as well as a dawn and dusk chorus. These indices appear to be sensitive to nocturnal biodiversity which is abundant at night in warm, subtropical environments. We argue that there is need to better understand temporal partitioning of the soundscape by specific taxonomic groups, and this should involve integrated research on amphibians, insects and birds during a 24 h cycle. The three indices that best connected the soundscape with landscape characteristics, ecological condition and bird species richness were acoustic entropy, acoustic evenness and the normalized difference soundscape index. This study has demonstrated that remote soundscape assessment can be implemented as an ecological monitoring tool in fragmented Australian forest landscapes. However, further investigation should be dedicated to refining and/or combining existing acoustic indices and also to determine if these indices are appropriate in other landscapes and for other survey purposes.     

The Glocal Forest

Spatial ecological patterns reflect the underlying processes that shape the structure of species and communities. Mechanisms like intra- and inter-specific competition, dispersal and host-pathogen interactions can act over a wide range of scales. Yet, the inference of such processes from patterns is a challenging task. Here we call attention to a quite unexpected phenomenon in the extensively studied tropical forest at the Barro-Colorado Island (BCI): the spatial deployment of (almost) all tree species is statistically equivalent, once distances are normalized by ℓ₀, the typical distance between neighboring conspecific trees. Correlation function, cluster statistics and nearest-neighbor distance distribution become species-independent after this rescaling. Global observables (species frequencies) and local spatial structure appear to be interrelated. This "glocality" suggests a radical interpretation of recent experiments that show a correlation between species'' abundance and the negative feedback among conspecifics. For the forest to be glocal, the negative feedback must govern spatial patterns over all scales.     

Elevation‐dependent effects of forest fragmentation on plant–bird interaction networks in the tropical Andes

Tropical forests harbor diverse ecological communities of plants and animals that are organized in complex interaction networks. The diversity and structure of plant–animal interaction networks may change along elevational gradients and in response to human‐induced habitat fragmentation. While previous studies have analyzed the effects of elevation and forest fragmentation on species interaction networks in isolation, to our knowledge no study has investigated whether the effects of forest fragmentation on species interactions may differ along elevational gradients. In this study, we analyzed main and interaction effects of elevation and forest fragmentation on plant–frugivore interaction networks at plant and bird species level. Over a period spanning two years, we recorded plant–frugivore interactions at three elevations (1000, 2000 and 3000 m a.s.l.) and in two habitat types (continuous and fragmented forest) in tropical montane forests in southern Ecuador. We found a consistent effect of elevation on the structure of plant–frugivore networks. We observed a decrease in the number of effective bird partners of plants and, thus, a decline in the redundancy of bird species with increasing elevation. Furthermore, bird specialization on specific plant partners increased towards high elevations. Fragmentation had a relatively weak effect on the interaction networks for both plant and bird species, but resulted in a significant increase in bird specialization in fragmented forests at high elevations. Our results indicate that forest fragmentation may have stronger effects on plant–frugivore interaction networks at high compared to low elevations because bird species richness declined more steeply towards high elevations than plant species richness. We conclude that conservation efforts should prioritize the maintenance of consumer diversity, for instance by maintaining stretches of continuous forest. This applies in particular to species‐poor communities, such as those at high elevations, as the ecological processes in these communities seem most sensitive towards forest fragmentation.     

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.     

叶附生苔植物物种多样性分布格局及生态成因

叶附生苔植物(以下简称叶附生苔)是一类附生在维管植物叶片表面的、一般只出现在热带雨林和常绿阔叶林中的苔类植物。它们具有重要的生态功能, 如影响碳、氮、水循环, 对气候变化和森林破碎化反应敏感, 可用作环境变化的指示植物。该文对叶附生苔的形态特性、物种多样性的研究历史和进展、地理分布格局, 以及对环境的要求(附主和生境的特性)等进行了综述, 探讨了叶附生苔多样性分布格局形成的可能原因, 即环境(空气湿度高、林冠层发育好、干扰少)和适应特征(无性繁殖、形体微小)的选择。根据全球叶附生苔研究进展状况及所存在的问题提出未来可开展的研究方向, 如叶附生苔的形成原因、与附主间的物质交换和能量流动机制、在森林生态系统中的生态功能、气候变化指示作用研究等, 大尺度上的研究也值得关注。