Fragmented Subtropical Forest Research Articles

Soil fertility underlies the positive relationship between island area and litter decomposition in a fragmented subtropical forest landscape

Habitat fragmentation has transformed many once contiguous habitats into smaller patches varying in size, especially in forest ecosystems. However, while the consequences of habitat fragmentation for biodiversity and ecosystem functioning (e.g., productivity) have been widely documented, we know much less about how habitat fragmentation affects litter decomposition, a key component of biogeochemical cycling. Here we investigated the effect of forest fragment size on leaf litter decomposition by conducting a litterbag experiment on a group of land-bridge islands in the Thousand Island Lake in subtropical China. We also explored the mechanisms underlying litter decomposition-island area relationship by assessing the bottom-up (via soil nutrients) and top-down (via soil fauna) effects on litter decomposition. We found that the leaf litter of six common plant species with different litter quality, including Castanopsis sclerophylla, Dalbergia hupeana, Liquidambar formosana, Pinus massoniana, Quercus fabri, and Schima superba, consistently decomposed faster on larger islands, where greater soil fertility facilitated decomposition. Soil faunal diversity also enhanced litter decomposition, but its effect was mainly associated with litter quality and unaffected by island size. Our study demonstrates the deleterious effect of habitat fragmentation on litter decomposition, as well as the importance of bottom-up regulation by soil fertility in modulating habitat fragmentation effect on biogeochemical processes.

Edge effects and beta diversity in ground and canopy beetle communities of fragmented subtropical forest.

Clearing of dry forests globally creates edges between remnant forest and open anthropogenic habitats. We used flight intercept traps to evaluate how forest beetle communities are influenced by distance from such edges, together with vertical height, spatial location, and local vegetation structure, in an urbanising region (Brisbane, Australia). Species composition (but not total abundance or richness) differed greatly between ground and canopy. Species composition also varied strongly among sites at both ground and canopy levels, but almost all other significant effects occurred only at ground level, where: species richness declined from edge to interior; composition differed between positions near edges (<10 m) and interiors (> 50 m); high local canopy cover was associated with greater total abundance and richness and differing composition; and greater distances to the city centre were associated with increased total abundances and altered composition. Analyses of individual indicator species associated with this variation enabled further biological interpretations. A global literature synthesis showed that most spatially well-replicated studies of edge effects on ground-level beetles within forest fragments have likewise found that positions within tens of metres from edges with open anthropogenic habitats had increased species richness and different compositions from forest interior sites, with fewer effects on abundance. Accordingly, negative edge effects will not prevent relatively small compact fragments (if >10–20 ha) from supporting forest-like beetle communities, although indirect consequences of habitat degradation remain a threat. Retention of multiple spatially scattered forest areas will also be important in conserving forest-dependent beetles, given high levels of between-site diversity.

Influences of environmental and spatial factors on genetic and epigenetic variations in Rhododendron oldhamii (Ericaceae)

Test of the relationship of genetic and particularly epigenetic variation with geographic isolation and environment is important to reveal potential environmental drivers for selection. Rhododendron oldhamii is widespread but inhabits fragmented subtropical forest landscapes, and populations across its range may exhibit different levels of genetic and epigenetic structuring correlated to their environmental conditions. Here, we investigated the genetic and epigenetic variations and their ecological correlates in R. oldhamii. Genetic and epigenetic variations were surveyed using amplified fragment length polymorphism (AFLP) and methylation-sensitive amplification polymorphism (MSAP), respectively. Using variation partitioning by redundant analysis (RDA), we examined the pure and spatially structured environmental effects and pure spatial factors on genetic and epigenetic variations among individuals collected from 18 localities across R. oldhamii distribution range in Taiwan. We found that environments compared to geographic isolation among sites explained more genetic and epigenetic variations. Patchy distribution of the contemporary R. oldhamii populations was revealed by correlograms with patch size of approximately around 20–30 km based on the total genetic and epigenetic data. Spatial variables derived from the method of principal coordinates of neighbor matrices (PCNM), including PCNM3, PCNM5, PCNM7, and PCNM8 representing biotic processes, such as individual dispersal, were found to be important influencing potentially adaptive genetic and epigenetic variations. Annual mean temperature, annual precipitation, precipitation of the warmest quarter, aspect, slope, and soil moisture were the most important environmental variables influencing potentially adaptive genetic and epigenetic variations and could be particularly important for the evolution of local adaptation in R. oldhamii.

Trait‐mediated seed predation, dispersal and survival among frugivore‐dispersed plants in a fragmented subtropical forest, Southwest China

By tracking the fate of individual seeds from 6 frugivore-dispersed plants with contrasting seed traits in a fragmented subtropical forest in Southwest China, we explored how rodent seed predation and hoarding were influenced by seed traits such as seed size, seed coat hardness and seed profitability. Post-dispersal seed fates varied significantly among the 6 seed species and 3 patterns were witnessed: large-seeded species with a hard seed coat (i.e. Choerospoadias axillaries and Diospyros kaki var. silvestris) had more seeds removed, cached and then surviving at caches, and they also had fewer seeds predated but a higher proportion of seeds surviving at the source; medium-sized species with higher profitability and thinner seed coat (i.e. Phoebe zhennan and Padus braohypoda) were first harvested and had the lowest probability of seeds surviving either at the source or at caches due to higher predation before or after removal; and small-seeded species with lower profitability (i.e. Elaeocarpus japonicas and Cornus controversa) had the highest probability of seeds surviving at the source but the lowest probability of seeds surviving at caches due to lower predation at the source and lower hoarding at caches. Our study indicates that patterns of seed predation, dispersal and survival among frugivore-dispersed plants are highly determined by seed traits such as seed size, seed defense and seed profitability due to selective predation and hoarding by seed-eating rodents. Therefore, trait-mediated seed predation, dispersal and survival via seed-eating rodents can largely affect population and community dynamics of frugivore-dispersed plants in fragmented forests.

Long‐distance dispersal and habitat use of the butterfly Byasa impediens in a fragmented subtropical forest

Abstract. 1. Central and Southeast Asia currently faces rapid loss and degradation of tropical and subtropical forests with potentially severe effects on its biodiversity.2. We analysed population characteristics and dispersal of the butterfly Byasa impediens in eleven patches of a fragmented subtropical forest in Western China.3. In an area covering 30 km2, we found an unexpected high dispersal capacity of more than 5 km, and estimated a mean dispersal distance of 1 km according to the negative exponential function. However, the inverse power function gave a better fit and predicted a reasonably large fraction of long‐distance displacements: 4% of all movements were estimated to exceed 5 km.4. In spite of the high level of fragmentation and small sizes of some patches, we did not observe extinction or (re)colonisation events. Matching dispersal ability with the spatial grain of the resource patches in the landscape is seen as a major cause. In addition, persistence, emigration and immigration of individuals were exclusively affected by the amount of larval host plants, nectar plants and forest cover.5. Our study indicates the importance of long‐distance dispersal and shows that species with large dispersal abilities and a somewhat broader dietary niche, such as B. impediens, can sustain in fragmented areas if patch quality is sufficient.6. We suggest that conservation action may not only focus on particularly endangered species but also on relatively common, but often endemic, insect species. This is of particular concern given the global dominance of insects and their importance for ecosystem services, especially in an area of constantly increasing demands of agricultural products.

Remotely Sensed Percent Tree Cover Mapping Using Support Vector Machine Combined with Autonomous Endmember Extraction

Abstract Remotely sensed forest mapping has become an important way to meet the increasing needs for forest-cover-associated data. However, accuracy for such products varies with the condition of forest ecosystem. In this paper, a support vector machine (SVM) classifier combined with autonomous endmember extraction technique was performed to improve the performance of machine learning in satellite land cover classification and percent tree cover mapping. For the study area, Pingnan County, Guangxi Zhuang Autonomous Region, China, that featured as a complex and fragmented subtropical forest habitat, the TM imagery was first processed with SMACC endmember extraction to find spectral endmembers of expected land cover classes. Secondly, the refined endmembers were input into SVM instead of conventional visual selection of training ROIs. The percent tree cover for the county is 53.6%, underestimated by 1.3% when compared with the National Continuous Forest Inventory 2004 statistics, suggesting a fair agreement with ground truth. The approach also shows a robust performance with an overall RMSE of 10.1.

Frugivory and seed dispersal by a small carnivore, the Chinese ferret-badger, Melogale moschata, in a fragmented subtropical forest of central China

The capacity for the Chinese ferret-badger ( Melogale moschata), a small carnivorous mustelid mammal, as a frugivore and endozoochorous seed disperser was evaluated over the main fruiting period during 2 years of study in a fragmented subtropical forest of central China. Seeds of eight plant species were dispersed by M. moschata, based on the analysis of the 163 faecal samples. Three forest types were sampled; one subject to commercial clear-cut logging, the second a selectively logged site and the third a natural primary forest habitat. The proportion of seed-bearing faecal samples was greatest amongst those collected from the primary forest, with the selectively logged and clear-cut habitats having a lower frequency of seed-bearing faeces, respectively. Ferret-badgers mainly defecated in open habitats, however the proportion of seed-bearing faeces did not differ according to the type of cover present at the deposition sites. Ferret-badgers selected fleshy-fruited and seed-pulp rich species. Significantly, selection was found for the large-seeded species, Diospyros lotus, however, they chose to consume the smaller seeds from this plant. Seed passage time through the gut ranged between 0.8 and 5.9 h. No significant individual-specific differences were detected in the passage time for the different fleshy fruits. Five out of six dominant species had seeds germinate successfully from faecal samples. Only the germination of D. lotus seeds were lower than expected by comparison to the control seeds. By contrast, ingested seeds of Hovenia dulcis had higher germination rates than in control samples, but no statistical differences were detected. These findings indicated that ferret-badgers were legitimate (they defecated viable seeds), but inefficient dispersers (seeds in faeces were mainly deposited on open sites which were regarded as “unsafe microsites” for seed germination and seedling establishment). In order to fully understand the role of M. moschata in forest recruitment and regeneration, quantitative research on their efficiency as endozoochorous seed dispersers and the effects of their digging activities on the seed bank and seedling survival should be undertaken, focusing on sites degraded by forestry operations, especially in badly affected sites.

Characterizing termite assemblages in fragmented forests: A test case in the Argentinian Chaco

Abstract Termites are major decomposers in tropical ecosystems. To characterize their assemblages in terms of taxonomical and functional composition, Jones and Eggleton (2000, Journal of Applied Ecology 37, 191–203) recently proposed a standardized sampling protocol based on belt transects of 100 m × 2 m. We evaluated the representativeness of samples obtained by this protocol, and its suitability to calculate diversity statistics, by replicating it in an area of naturally fragmented subtropical forest. We sampled six 100 m transects in separate small forest islets, and one transect extended to 500 m in a large islet, recording presence/absence data (occurrences) of termite species in successive quadrats of 5 m × 2 m. In the large islet, strips of 100 m within the 500 m transect produced extremely variable species richness figures. This variability was primarily due to heterogeneity in the spatial distribution of soil‐dwelling termites. Combining non‐contiguous quadrats allowed us to span a broader diversity of microhabitats for an equal effort, providing less variable results and faster species accumulation. Individual transects of 100 m in small forest islets yielded too few samples to allow reliable estimations of total species richness, although these transects when pooled constituted a useful data set for comparison with other sites. In the focal habitat, a single 100 m transect appeared therefore inadequate to allow a reliable characterization of the termite assemblage, even at the level of a single forest islet. To improve the rate of species accumulation and to obtain diversity statistics allowing intersite comparisons, we suggest the use of smaller, non‐contiguous quadrats, and that sampling be continued until stable diversity estimates are obtained. In the habitat studied, such an alternative protocol could be adequately combined with a standardized protocol for collecting ground‐dwelling ants.