The Fractal Dimension as a Measure of the Quality of Habitats

Habitat fragmentation produces isolated patches characterized by increased edge effects from an originally continuous habitat. The shapes of these patches often show a high degree of irregularity: their shapes deviate significantly from regular geometrical shapes such as rectangular and elliptical ones. In fractal theory, the geometry of patches created by a common landscape transformation process should be statistically similar, i.e. their fractal dimensions and their form factors should be equal. In this paper, we analyze 49 woodlot fragments ( Pinus sylvestris L. ) in the Belgian Kempen region to study the direct relationship between a transformation process and the concomitant patch geometry. Although the fractal dimension of the woodlots is scattered (i.e. they are not statistically similar), the perimeter-area relation of the fragments is characterized by a single, 'dimension-like' exponent. This exponent suggests a certain shape homogeneity among the patches, which is confirmed by the absence of hierarchical levels associated with sharp increases of the fractal dimension at scale transitions. The interaction of different natural (soil factor, vegetation type) and anthropogenic (afforestation, urbanization) processes during patch development is assumed to have generated this feature. Comparison of the area and perimeter fractal dimension with an ecological index for habitat quality, the interior-to-edge ratio, shows that the fractal dimension is suitable for predicting interior habitat presence, which is more likely for patches with smooth perimeters and compact areas. The ratio of the area to the perimeter fractal dimension confirms this observation, with high values for high interior-to-edge ratios, characteristic for regularly shaped patches.     

About the Ranking of Isolated Habitats with Different Shapes: An Interior-to-Edge Ratio Study

Isolated habitats can be compared and ranked by comparing their interior-to-edge ratio (I/E). We would like to show here that results based on ranking by I/E ratio sometimes contradict Diamond's rule, which ranks the most rounded habitat (i.e. most compact) as the best one. The reason for this contradiction is the frequently overlooked size dependence of the I/E. Being the interior-to-edge ratio size dependent, from a given set of habitats of different sizes, compact shaped (rounded) habitats might have worse I/E ratios than elongated or irregular ones.     

上海环城林带景观美学评价及优化策略

选取上海环城林带7种植物群落,采用美景度评判法,从林内景观和林外景观2个空间层次和春、夏、秋、冬4个季节,应用数量化理论Ⅰ建立了美景度和各景观因子类目之间的景观评价与预测的多元回归模型,分析了群落的结构特征和季相特征对林内景观以及外貌特征对林外景观的影响,并提出相应的优化对策。结果表明:(1)群落结构特征对林内景观的影响主要因子为胸径(平均胸径和胸径变异系数)、郁闭度和疏透度。在春季,林内美景度随着树木胸径增大而增加;在夏季,郁闭度增大会提升林内美景度;在秋季,胸径变异小的群落具有更高的林内观赏性;在冬季,疏透度对林内景观美景度影响最大。(2)群落季相特征对林内景观的影响,在各季节表现亦不同。在春季,黄色、紫色等明度较高的色相和开花量适中的群落美景度最佳;在夏季,生长势好、林冠层变化小以及树干清晰度高的群落具较高的美景度,且观花可显著提高夏季林内美景度;在秋季,色彩越纯美景度越高;而在冬季,树皮颜色深的群落美景度高。(3)群落外貌特征对林外景观有显著影响,其中林冠线对林外景观美景度影响最大,其次为林缘线。具有起伏不大林冠线和自然流畅林缘线的植物群落美景度高。旨在通过对典型植被群落不同季相的美景度评价,对上海环城林带的群落景观进行定量的评价,进而为不同情景下的群落结构优化提出相应的对策,为城市森林的群落建构与管理提供科学依据。     

Habitat characterization of western hoolock gibbons Hoolock hoolock by examining home range microhabitat use

Conserving a species depends on an understanding of its habitat requirements. Primatologists often characterize the habitat requirements of primates using macroscale population-based approaches relying on correlations between habitat attributes and population abundances between sites with varying levels of disturbance. This approach only works for species spread between several populations. The populations of some primates do not fulfill these criteria, forcing researchers to rely on individual-based (microscale) rather than population-based approaches for habitat characterization. We examined the reliability of using micro-scale habitat characterizations by studying the microhabitat preferences of a group of wild western hoolock gibbons (Hoolock hoolock) in order to compare our results to the habitat preferences of western hoolock gibbons identified during a macroscale study of populations across Bangladesh. We used stepwise discriminant analysis to differentiate between the areas of low, medium, and high usage based on microhabitat characteristics (tree species availability, altitude, canopy connection, distance from forest edge, and levels of human disturbance). The gibbons used interior forest habitat with low food tree availability most frequently for sleeping and socializing, and used edge habitat containing high food tree availability for medium periods for feeding. These results indicate that the gibbons prefer interior forest but are frequently forced to visit the forest edge to feed. Therefore, the optimal habitat would be interior forest away from human disturbance with high sleeping-tree and feeding-tree availability. These habitat preferences are consistent with the habitat attributes of Bangladesh’s largest remaining western hoolock gibbon populations, which live in areas containing low agricultural encroachment and high food-tree availability. Microhabitat use studies can be used to characterize the habitat requirements of a species, but should include multiple scales of analysis wherever possible.     

Ant (Hymenoptera: Formicidae) diversity and community composition along sharp urban forest edges

The effects of forest edge on ant species richness and community composition were examined within an urbanized area of northeast Ohio. The ground-dwelling ant fauna was inventoried in three deciduous forest fragments that have resulted from human disturbance. We surveyed ants via leaf-litter extraction along 150 m transects positioned perpendicular to the forest edge. We collected 4,670 individuals from 14 genera and 29 species. Samples closest to the forest edge contained more species and accumulated species at a higher rate than did samples located in the forest interior. Our rarefied and expected richness estimates revealed a decline of species richness from edge to forest interior. The higher ant richness at the forest edge was due mostly to the presence of species characteristic of the neighboring open habitats. Although most of the typical forest ant species were represented equally at the edge and at the forest interior, a few responded to the presence of edges with changes in their relative abundance and frequency of occurrence. Forest edges had a higher proportion of opportunistic species and a lower proportion of cryptic ants, whereas interior locations exhibited a more even distribution among ant functional groups. In addition, we documented a community composition shift between the edge and the forest interior. Consistent with previous findings, we suggest that the edge effects are most pronounced within 25 m of the forest edge, which may have implications for the overall conservation of forest-dwelling fauna.     

Forest edge and diversity: carabids along forest-grassland transects

Diversity relationships of carabids in forest edges and the neighbouring forest interior and the surrounding grassland are studied. Samples were taken along three replicated forest-grassland transects using pitfall traps in the Aggtelek National Park in Hungary during 2 years. The study revealed significant edge effect on the carabids. The Shannon diversity of carabids were significantly higher in the forest edge and the grassland than in the forest interior. Carabids of the forest interior, forest edge and grassland can be separated from each other by ordinations, both on the species composition and abundance, suggesting that all three habitats have a distinct species assemblage. Moreover, indicator species analysis detected significant edge associated species; based on the specificity and fidelity of the carabids we have distinguished five groups of species: habitat generalists, grassland-associated species, forest generalists, forest specialists, and edge-associated species. Multiple linear regression analyses showed that relative air moisture, temperature of the ground and cover of the herbs are the most important factors determining the diversity of carabids along the transects. Our results show that the high diversity of carabids in forest edges is due to the edge-associated species and the presence of species characteristic to the adjacent habitats. The significance of forest edges in nature conservation, serving as a source habitat for dispersal processes, contributing to the recolonization of carabids after habitat destruction or other disturbance is emphasized.     

Edge-mediated effects on stand dynamic processes in forest interiors: a coupled field and simulation approach

Researchers studying forest edge effects in fragmented landscapes have begun to move beyond merely documenting changes along the edge itself to examining the dynamic influences that edges may have on processes in adjacent areas. One such "edge-mediated effect" is the influence that edges may have on canopy gap replacement processes within the forest interior by acting as seed sources for shade-intolerant plant species. In this paper, we coupled analyses of woody species composition in gap and non-gap areas within the interior of an Ohio hardwood forest with a simple cellular automata model of forest dynamics. Non-gap composition was primarily correlated with disturbance history and site conditions (topographic position and slope) while a comparable analysis using a 24-year time series of composition in gaps showed that gap composition was related most strongly to the proximity of edge communities for the first 10–15 years. However, after 15–20 years of gap succession, composition was correlated with essentially the same variables and to the same degree as non-gap vegetation, suggesting that the influence of edge proximity on interior stand dynamic processes was transient. These results were used to develop a simple mathematical model of stand dynamics that showed that losses of interior forest area may be much greater than typically predicted by core-area models, which do not consider dynamic, edge-mediated effects. Further, our findings suggest the importance of considering disturbance interval in mediating edge-interior relationships, particularly as it may interact with forest size and shape.     

Life on the edge: gastrointestinal parasites from the forest edge and interior primate groups

Humans are responsible for massive changes to primate habitats, and one unanticipated consequence of these alterations may be changes in host-parasite interactions. Edges are a ubiquitous aspect of human disturbance to forest landscapes. Here we examine how changes associated with the creation of edges in Kibale National Park, Uganda, alter the parasite community that is supported by two species of African colobines: the endangered red colobus (Piliocolobus tephrosceles) and the black-and-white colobus (Colobus guereza). An analysis of 822 fecal samples from edge and forest interior groups revealed no difference in the richness of parasite communities (i.e., the number of parasite species recovered from the host's fecal sample). However, for both species the proportion of individuals with multiple infections was greater in edge than forest interior groups. The prevalence of specific parasites also varied between edge and forest interior groups. Oesophagostomum sp., a potentially deleterious parasite, was 7.4 times more prevalent in red colobus on the edge than in those in the forest interior, and Entamoeba coli was four times more prevalent in red colobus on the edge than in animals from the forest interior. Environmental contamination with parasites (measured as parasite eggs/gm feces) by red colobus from the edge and forest interior differed in a similar fashion to prevalence for red colobus, but it did not differ for black-and-white colobus. For example, egg counts of Oesophagostomum sp. were 10 times higher in red colobus from the edge than in those from the interior. The less severe infections in the black-and-white colobus relative to the red colobus may reflect the fact that black-and-white colobus raid agricultural crops while red colobus do not. This nutritional gain may facilitate a more effective immune response to parasites by the black-and-white colobus. The fact that animals on the edge are likely not nutritionally stressed raises an intriguing question as to what facilitates the elevated infections in edge animals. We speculate that interactions with humans may be linked to the observed patterns of infections, and hence that understanding the ecology of infectious diseases in nonhuman primates is of paramount importance for conservation and potentially for human-health planning.     

Plant–frugivore networks are less specialized and more robust at forest–farmland edges than in the interior of a tropical forest

Forest fragmentation and local disturbance are prevailing threats to tropical forest ecosystems and affect frugivore communities and animal seed dispersal in different ways. However, very little is known about the effects of anthropogenic forest edges and of local disturbance on the structure and robustness of plant–frugivore networks. We carried out focal tree observations to record the frugivore species feeding on eight canopy tree species in the forest interior and at forest–farmland edges in a little and a highly disturbed part of a Kenyan rain forest. For each frugivore species, we recorded its body mass and its forest dependence. We examined how forest edge and local disturbance affected the abundance, the richness and the composition of the frugivore community and tested whether forest edge and local disturbance affected plant frugivore networks. Abundance and species richness of frugivores were higher at edges than in the forest interior. Forest visitors and small‐bodied frugivores increased, while forest specialists decreased in abundance at forest edges. The changes in frugivore community composition resulted in plant–frugivore networks that were more connected, more nested and more robust against species extinctions at forest–farmland edges than in the forest interior. Network specialization was lower at forest edges than in the forest interior because at the edges plant specialization on frugivores was very low in small‐fruited species. In contrast, small‐fruited plants were more specialized than large‐fruited plants in the forest interior. Our findings suggest that forest‐visiting birds may stabilize seed‐dispersal services for small‐fruited plant species at rain forest margins, while seed‐dispersal services for large‐fruited plant species may be disrupted at forest edges due to the decrease of large‐bodied frugviores. To assess the ultimate consequences of bird movements from farmland to forest edges for ecosystem functioning, future studies are required to investigate the seed‐dispersal qualities provided by forest‐visiting bird species in the tropics.     

犬尾田鼠在斑块生境中更喜好内部区域

我们在斑块化的景观中实验测定了犬尾田鼠(Microtus canicaudus)的生境喜好,验证下列假说:在一斑块生境中,与边缘区域相比,雌性田鼠喜好内部区域.在低密度和高密度时成年雌性的巢区在生境内部区域分别占100% 和76%.高密度时在边缘区域雌性的捕获率较低,这种差异在低密度时更突出.在高密度时通过选择性去除生境内部和边缘区域的一些雌体,边缘区域13只雌体中8只(占62%)的巢区发生从边缘到内部区域的转移,内部区域20只雌体中只有3只(占15%)的巢区向边缘区域转移.动物的繁殖率、生存和体重在两个区域之间没有差异.但是,边缘区域个体的巢区比内部区域的要小.这些结果支持一些关于其他啮齿动物的研究观察结果(如鼠平类和田鼠类),但与草原田鼠不同.因此在一斑块生境中,与边缘区域相比,长尾田鼠更喜好内部区域,边缘区域与内部区域的比率可潜在影响动物的生境选择,也可能会影响斑块化生境中的种群统计学特征.     

The effects of city–suburb–exurb landscape context and distance to the edge on plant diversity of forests in Wuhan,China

Abstract

We analysed the relative role of landscape context (city, suburb and exurb) and distance to the edge (from forest edge to 45 m in interior) on plant diversity of natural forests in Wuhan city. The results indicated that landscape context had significant effects on plant diversity, and both landscape context and distance to the edge affect vegetation and disturbance characteristics. Landscape context was the main factor affecting richness of woods, herbs, indigenous species, forest generalists and insect or wind pollination species. These species tended to be higher in exurban forests while non-indigenous species were higher in the urban forests. The number of non-indigenous species, forest specialists, herbs and insect pollination species also depended on distance to the edge or on both interactions. Richness of non-indigenous species decreased with increasing distance to the edge in urban forest. Vegetation characteristics that shrub cover was lower and disturbance characteristics that disturbed cover and human activity were higher in the urban edge than in the suburb and exurb edge, which decreased from the edge to the interior. Therefore, we should prioritize the preservation of less disturbed and frequented forests (suburban and exurban) to buffer the invasion of non-indigenous species, and to reserve more indigenous species.     

Anthropogenic edges impact howler monkey (Alouatta palliata) feeding behaviour in a Costa Rican rainforest

Anthropogenic forest fragmentation impacts many aspects of animal behaviour, including feeding ecology. With forests increasingly fragmented in tropical regions due to human development, the proportion of forest edge (≤?100 m from clear-cut regions) is higher relative to forest interior. Forest edges differ in vegetation from interior, making it important to better understand how anthropogenic edges impact the feeding behaviour of primates such as mantled howler monkeys (Alouatta palliata). We predicted that howler monkeys would feed on higher-quality plant resources, from a larger number of tree families, and from larger trees in forest interior compared to anthropogenic forest edge. We surveyed howler monkey feeding behaviour across forest zones in a fragmented rainforest in Costa Rica, La Suerte Biological Research Station. We observed individual monkeys for 30-minute periods, collecting data on their feeding behaviour and tree use at 2-minute intervals. We measured feeding trees and recorded the plant parts and taxonomy of resources consumed. Monkeys consumed more leaves and fewer stems and fed from a smaller number of tree families in the forest interior, while they consumed fewer leaves and more stems and fed from a larger number of tree families in the forest edge. Monkeys also fed from larger, taller trees in the forest interior than the edge. The differences in howler monkey feeding behaviour between forest zones attest to the impact of human disturbance on howler monkey feeding ecology.

     

How patch configuration affects the impact of disturbances on metapopulation persistence

Disturbances affect metapopulations directly through reductions in population size and indirectly through habitat modification. We consider how metapopulation persistence is affected by different disturbance regimes and the way in which disturbances spread, when metapopulations are compact or elongated, using a stochastic spatially explicit model which includes metapopulation and habitat dynamics. We discover that the risk of population extinction is larger for spatially aggregated disturbances than for spatially random disturbances. By changing the spatial configuration of the patches in the system--leading to different proportions of edge and interior patches--we demonstrate that the probability of metapopulation extinction is smaller when the metapopulation is more compact. Both of these results become more pronounced when colonization connectivity decreases. Our results have important management implication as edge patches, which are invariably considered to be less important, may play an important role as disturbance refugia.     

Edge disturbance shapes liana diversity and abundance but not liana‐tree interaction network patterns in moist semi‐deciduous forests,Ghana

Edge disturbance can drive liana community changes and alter liana‐tree interaction networks, with ramifications for forest functioning. Understanding edge effects on liana community structure and liana‐tree interactions is therefore essential for forest management and conservation. We evaluated the response patterns of liana community structure and liana‐tree interaction structure to forest edge in two moist semi‐deciduous forests in Ghana (Asenanyo and Suhuma Forest Reserves: AFR and SFR, respectively). Liana community structure and liana‐tree interactions were assessed in 24 50 × 50 m randomly located plots in three forest sites (edge, interior and deep‐interior) established at 0–50 m, 200 m and 400 m from edge. Edge effects positively and negatively influenced liana diversity in forest edges of AFR and SFR, respectively. There was a positive influence of edge disturbance on liana abundance in both forests. We observed anti‐nested structure in all the liana‐tree networks in AFR, while no nestedness was observed in the networks in SFR. The networks in both forests were less connected, and thus more modular and specialised than their null models. Many liana and tree species were specialised, with specialisation tending to be symmetrical. The plant species played different roles in relation to modularity. Most of the species acted as peripherals (specialists), with only a few species having structural importance to the networks. The latter species group consisted of connectors (generalists) and hubs (highly connected generalists). Some of the species showed consistency in their roles across the sites, while the roles of other species changed. Generally, liana species co‐occurred randomly on tree species in all the forest sites, except edge site in AFR where lianas showed positive co‐occurrence. Our findings deepen our understanding of the response of liana communities and liana‐tree interactions to forest edge disturbance, which are useful for managing forest edge.     

Forest–farm edge effects on communities of ground beetles (Coleoptera: Carabidae) under different landscape structures

In fragmented landscapes, ecological processes may be significantly influenced by edge effects, but few data are available for edge effects across forest–farmland edges. We investigated patterns of species richness, abundance, and species composition in ground beetles across forest–farm edges in two different agro-forest landscapes in Korea. Nine and five sites were selected from Hwaseong, a fragmented landscape, in 2011 and 2012, respectively, while eight sites were selected from Hoengseong, a relatively well-protected landscape, in 2012. Ground beetles were collected by pitfall trapping. Species richness was higher in the surrounding habitat than in the forest interior or edge in both Hwaseong and Hoengseong. However, in Hwaseong, species richness of the forest edge was similar to that of the forest interior, while in Hoengseong forest edge species richness was intermediate between that of the forest interior and surrounding areas. In addition, non-metric multidimensional scaling based on the combined data of both locations showed that the species composition of ground beetles in the forest edge was more similar to that of the forest interior than the surrounding areas, although some open-habitat species occurred at the forest edges. Three characteristic groups (forest specialists, edge-associated species, and open-habitat species) of ground beetle species were detected by indicator value analysis. In our study, ground beetle assemblages differed in the forest edges of two agro-forest landscapes, suggesting that the edge effect on biota can be influenced by landscape structure.     

Wild pigs (Sus scrofa) mediate large-scale edge effects in a lowland tropical rainforest in Peninsular Malaysia

Edge-effects greatly extend the area of tropical forests degraded through human activities. At Pasoh, Peninsular Malaysia, it has been suggested that soil disturbance by highly abundant wild pigs (Sus scrofa), which feed in adjacent Oil Palm plantations, may have mediated the invasion of Clidemia hirta (Melastomataceae) into the diverse tropical lowland rain forest. To investigate this hypothesis, we established three 1 km transects from the forest/Oil Palm plantation boundary into the forest interior. We recorded the distribution of soil disturbance by wild pigs, C. hirta abundance, and environmental variables. These data were analyzed using a hierarchical Bayesian model that incorporated spatial auto-correlation in the environmental variables. As predicted, soil disturbance by wild pigs declined with distance from forest edge and C. hirta abundance was correlated with the level of soil disturbance. Importantly there was no effect of distance on C. hirta abundance, after controlling for the effect of soil disturbance. Clidemia hirta abundance was also correlated with the presence of canopy openings, but there was no significant association between the occurrence of canopy openings and distance from the edge. Increased levels of soil disturbance and C. hirta abundance were still detectable approximately 1 km from the edge, demonstrating the potential for exceptionally large-scale animal mediated edge effects.     

Response of a raptor community to shrinking area and degradation of tropical rain forest in the south western Ghâts (India)

The influence of irregular or incomplete fragmentation and increasing degradation of natural rain forest on diurnal raptor community was studied in the northern part of the western Ghâts in southwestern India A census of mainly territorial breeding pairs on 400 ha sample quadrats was associated with a measure of the percent cover of the main habitat types and a degree of forest fragmentation including irregular patch shape and habitat heterogeneity
Four groups of 3-4 species were defined according to their decreasing tolerance to forest fragmentation and disturbance, from mostly open grassland species to interior forest specialists Habitat selection, density and sensitivity to landscape structure were investigated The community composition and dynamic of each habitat were the sum of these specific reactions The distribution of species along the succession of increasing fragmentation and forest degradation was thus found to be non random, but did not follow a nested subset pattern The density of forest species declined with forest patch size possibly because of the irregular patch shape, the increased edge effects and the consequent increase of linear distance for a bird to cover within its territory However, sensitivity to habitat structure and disturbance was found to be even higher than sensitivity to area per se The need to conserve the largest patches of little disturbed forest is emphasized, as well as the conservation value of woodlots-open habitat mosaics that are suitable for a different set of species     

Distribution of ground-dwelling beetles （Coleoptera） across a forest-clearcut ecotone in Wolong Natural Reserve, southwestern China

Abstract The influence of edge effect on ground-dwelling beetles (Coleoptera) across a forest-clearcut ecotone was studied in Wolong Natural Reserve, southwestern China. During the field research, a total of 30 739 beetles were collected with pitfall traps along transects, which extending 100 m from the edge into the forest interior and 100 m into the clearcut. Of the collection, Carabidae comprised 92%, Staphylinidae 3%, Curculionidae 2%, and Tenebrionidae 2%, and these four families can be considered as abundant groups. Family richness, Shannon diversity and equitability display a significant decrease from forest interior, edge to clearcut. Based on the family composition and abundance, ground-dwelling beetles of the forest interior can be separated from those in the clearcut by Principal coordinate analysis ordination, and beetle assemblages in the forest edge were more similar to forest assemblages than to those found in the clearcut by cluster analysis. Seasonal dynamics of family richness showed a monotone peak in the middle season, with a highest value in the forest interior and a lowest value in the clearcut. Family abundance showed two peaks in the middle season, always with more individuals in the clearcut than in the forest interior or in the edge. Multiple linear regression analyses showed that the cover of shrub and litter were the two most important factors in determining family richness, Shannon diversity, equitability and abundance. Our results show that the forest edge and clearcut have obviously different composition and diversity of ground-dwelling beetles from forest interior at the family level. However, more edges have been formed due to increasing forest fragmentation (clearcutting or logging), so it is necessary to preserve large and intact forest to protect the diversity of ground-dwelling beetles in Wolong Natural Reserve.