Plant composition and diversity at edges in a semi-natural forest–grassland mosaic

Plant Ecology - As key components of landscapes, edges have received considerable scientific attention in anthropogenic ecosystems. However, edges in natural and semi-natural forest–grassland...     

Does fire increase the spatial heterogeneity of bird communities in Mediterranean landscapes?

The occurrence of large burnt areas has increased considerably in southern Europe in recent years. In order to design management plans to prevent large wildfires while preserving biodiversity, understanding of the ways in which birds respond to these fires is required. We investigated the spatial variability of both avifauna and habitat structure in three zones: unburnt, burnt in 1982, and burnt in 1994. The habitat structure of the unburnt zone was the most variable spatially. However, bird species composition between sampling points was very homogeneous in space. In contrast, the bird communities inhabiting burnt zones were more spatially heterogeneous. This pattern was caused by distinct specific responses to variations in habitat structure. Open-space species responded to small changes in habitat structure with large changes in local abundance, whereas the response of forest species to these structural variations was much less. We suggest that land managers should select specific zones with limited vegetation recovery within large burnt areas and maintain them as open space to keep combustibility low and provide an appropriate habitat for several open space species that are of conservation concern.     

Do riparian forest strips in modified forest landscapes aid in conserving bat diversity?

Agricultural practices lead to losses of natural resources and biodiversity. Maintaining forests alongside streams (riparian forest strips) has been used as a mechanism to minimize the impact of clearing for agriculture on biodiversity. To test the contribution of riparian forest strips to conserve biodiversity in production landscapes, we selected bats as a biodiversity model system and examined two dimensions of diversity: taxonomic and functional. We compared bat diversity and composition in forest, with and without stream habitat, and in narrow forest riparian strips surrounded by areas cleared for agriculture. We tested the hypothesis that riparian forest strips provide potential conservation value by providing habitat and serving as movement corridors for forest bat species. Riparian forest strips maintained 75% of the bat species registered in forested habitats. We found assemblage in sites with riparian forest strips were dominated by a few species with high abundance and included several species with low abundance. Bat species assemblage was more similar between sites with streams than between those sites to forests without stream habitat. These results highlight the importance of stream habitat in predicting presence of bat species. We registered similar number of guilds between forest sites and riparian forest strips sites. Relative to matrix habitats, stream and edge habitats in riparian forest strips sites were functionally more diverse, supporting our hypothesis about the potential conservation value of riparian forest strips. Results from this study suggest that maintaining riparian forest strips within cleared areas for agricultural areas helps conserve the taxonomic and functional diversity of bats. Also, it provides basic data to evaluate the efficacy of maintaining these landscape features for mitigating impacts of agricultural development on biodiversity. However, we caution that riparian forest strips alone are not sufficient for biodiversity maintenance; their value depends on maintenance of larger forest areas in their vicinity.     

Is there a trade-off between species diversity and genetic diversity in forest tree communities?

The two most important components of biodiversity, species diversity and genetic diversity, have generally been treated as separate topics, although a coordination between both components is believed to be critical for ecosystem stability and resilience. Based on a new trait concept that allows for the assessment of genetic diversity across species, the relationship between species diversity and genetic diversity was examined in eight forest tree communities composed of different tree genera including both climax and pioneer species. It was intended to check whether a trade-off exists between the two diversity components as was found in a few studies on animal species.Using several isozyme-gene systems as genetic markers, the genetic diversity across species within each of the tree communities was determined by two measures, the commonly used intraspecific genetic diversity averaged over species and the recently developed transspecific genetic diversity per species. Both data sets were compared with the corresponding community-specific species diversity resulting in a positive relationship between the two diversity components. A statistically significant positive correlation was established between the transspecific genetic diversity per species and the species diversity for three isozyme-gene systems. Beyond that, consistent results were obtained using different parameters of the diversity measure which characterize the total, the effective and the number of prevalent variants. The number of prevalent variants reflected most significantly the non-randomness of the observed diversity patterns.These findings can be explained by the observation that the pioneer tree species reveal a by far higher genetic diversity than the climax tree species, which means that an increase in species diversity, due to the addition of several pioneer species at the expense of one or two climax species, goes along with an increase in the level of genetic diversity. Forest tree communities with the highest degree of species diversity exhibit therefore the highest transspecific genetic diversity per species. This result was discussed with regard to the particular composition and stability of forest tree communities.     

Mapping a forest mosaic – A comparison of vegetation and bird distributions using geographic boundary analysis

Many areas of ecological inquiry require the ability to detect and characterize change in ecological variables across both space and time. The purpose of this study was to investigate ways in which geographic boundary analysis techniques could be used to characterize the pattern of change over space in plant distributions in a forested wetland mosaic. With vegetation maps created using spatially constrained clustering and difference boundary delineation, we examined similarities between the identified boundaries in plant distributions and the occurrence of six species of songbirds. We found that vegetation boundaries were significantly cohesive, suggesting one or more crisp vegetation transition zones exist in the study site. Smaller, less cohesive boundary areas also provided important information about patterns of treefall gaps and dense patches of understory within the study area. Boundaries for songbird abundance were not cohesive, and bird and vegetation difference boundaries did not show significant overlap. However, bird boundaries did overlap significantly with vegetation cluster boundaries. Vegetation clusters delineated using constrained clustering techniques have the potential to be very useful for stratifying bird abundance data collected in different sections of the study site, which could be used to improve the efficiency of monitoring efforts for rare bird species.     

Long‐term dynamics of bird diversity in forest and suburb: decay,turnover or homogenization?

Aim Urbanization and deforestation are important drivers of biodiversity change. However, long‐term changes in faunal communities within urbanizing regions are poorly understood. We investigated how well observed community changes in both space and time agree with expectations based on current paradigms in urban ecology. Location Greater Brisbane region, Australia. Methods We compared bird assemblages in two time‐periods 15 years apart, at multiple sites in remnant forest and residential suburbs across an urbanizing landscape. Differences in assemblage composition, species abundances and functional groupings were assessed within and between habitats. Results Compared with forest, suburbs in both time‐periods had over twice the total bird abundance, a different species composition, greater between‐site community similarity, a greater proportion of non‐native species and greater dominance by large‐bodied species. These differences corresponded with changes in sites whose habitat was converted from forest to suburb. Between time‐periods, abundances of 58% of suburban species changed significantly compared with those of 11% in forest. Increaser species outnumbered decreasers in suburbs, with the reverse in forest. Abundance of small‐bodied birds decreased 70% in suburbs and 20% in forest. Broad‐spectrum competitors and nest predators were common among suburban increasers. Among invasive species, the number of increasers was counterbalanced by decreasers. Both site‐scale species richness and between‐site community similarity increased to a small extent in both habitats. Main conclusions Species composition and ecological function of suburban bird communities were very dynamic. Suburban assemblages were neither a subset of forest species nor an increasingly non‐native compilation. Communities in large forest patches were comparatively stable. The notion of habitat‐specific species turnover better characterizes the nature of most changes than either species decline or homogenization, even though both of these were evident. There is considerable scope for careful urban planning, focused on both among‐ and within‐habitat variety, to sustain bird diversity in urbanizing landscapes.     

Testing heterogeneity–diversity relationships in tropical forest restoration

Restoring small-scale habitat heterogeneity in highly diverse systems, like tropical forests, is a conservation challenge and offers an excellent opportunity to test factors affecting community assembly. We investigated whether (1) the applied nucleation restoration strategy (planting tree islands) resulted in higher habitat heterogeneity than more homogeneous forest restoration approaches, (2) increased heterogeneity resulted in more diverse tree recruitment, and (3) the mean or coefficient of variation of habitat variables best explained tree recruitment. We measured soil nutrients, overstory and understory vegetation structure, and tree recruitment at six sites with three 5- to 7-year-old restoration treatments: control (no planting), planted tree islands, and conventional, mixed-species tree plantations. Canopy openness and soil base saturation were more variable in island treatments than in controls and plantations, whereas most soil nutrients had similar coefficients of variation across treatments, and bare ground was more variable in control plots. Seedling and sapling species density were equivalent in plantations and islands, and were substantially higher than in controls. Species spatial turnover, diversity, and richness were similar in island and plantation treatments. Mean canopy openness, rather than heterogeneity, explained the largest proportion of variance in species density. Our results show that, whereas canopy openness and soil base saturation are more heterogeneous with the applied nucleation restoration strategy, this pattern does not translate into greater tree diversity. The lack of a heterogeneity–diversity relationship is likely due to the fact that recruits respond more strongly to mean resource gradients than variability at this early stage in succession, and that seed dispersal limitation likely reduces the available species pool. Results show that planting tree islands facilitates tree recruitment to a similar degree as intensive plantation-style restoration strategies.     

What shapes cerambycid beetle communities in a tropical forest mosaic? Assessing the effects of host tree identity,forest structure,and vertical stratification

Due to anthropogenic activities, tropical rain forests face many challenges in sustaining biodiversity and maintaining global climates. This study explores how forest successional stage, tree composition, and stratum affect communities of saproxylic cerambycid beetles—concealed feeders that play important roles in forest nutrient cycling. Forty trees in five families (Fabaceae, Lecythidaceae, Malvaceae, Moraceae, and Sapotaceae) were sampled in a mosaic of old‐growth and secondary forest on the Osa Peninsula, Costa Rica. Bait branches yielded 3549 cerambycid individuals in 49 species. Species richness was almost identical in old‐growth and secondary forest, and both yielded specialists, but abundance was higher in old‐growth forest. Overall community structure was most strongly influenced by host plant species; within most plant families it was also impacted by forest successional status. Moraceae was the exception, presumably because the focal tree species was abundant in both old‐growth and secondary forest. Several host and old‐growth specialist species reached high densities within patches of old‐growth forest, but seldom colonized apparently suitable trees within secondary forest. This suggests that even small areas of old‐growth forest can act as refuges, but that secondary forest may act as a barrier to dispersal. The vulnerability of specialized saproxylic insects to land use change will be linked to the ability of their preferred hosts to disperse to and persist in successional habitats; rearing studies may provide the most accurate method to monitor community changes over time.     

Breeding bird communities of second‐rotation plantations at different stages of the forest cycle

Capsule Early stages of the plantation forest cycle have distinct bird communities and bird density was significantly higher in the second rotation than in the first for a given age class.

Aims To characterize the bird communities in Irish second-rotation plantations and to compare them with those of first-rotation plantations.

Methods Point counts were used to survey 20 plantation forests in four age classes (Pre-thicket; Thicket; Mid‐rotation; and Mature) in the breeding season of 2007. distance software was used to generate bird densities. Ordination, indicator species analysis, and glm were used to analyse the bird communities.

Results Bird communities of Pre‐thicket and, to a lesser extent, Thicket age classes were distinct from those of more mature forests. Bird communities of Mid‐rotation and Mature age classes were indistinguishable from each other and were therefore combined into a single age class (Closed canopy). Pre‐thicket held significantly lower total bird density, but significantly higher migrant bird density, than this Closed canopy age class. Bird density was significantly higher in the second rotation in all age classes except for Pre‐thicket, but migrant density was significantly higher in Pre‐thicket in the second rotation. There was no difference in species richness between the first and second rotation.

Conclusions Differences between rotations are probably due to changes in vegetation structure, and the increase in second‐rotation forests in Ireland is likely to be a positive development for bird communities. Especially encouraging is the higher migrant bird density in second‐rotation Pre‐thicket, as some of these species are in decline throughout Europe. However, the largest differences in population density between rotations were exhibited by common species and such species will likely benefit most from future increases in the area of second‐rotation plantation forests.     

Intra- and interspecific tree diversity promotes multitrophic plant–Hemiptera–ant interactions in a forest diversity experiment

Interactions between species of different trophic levels have long been recognized as fundamental processes in ecology. Although mounting evidence indicates that plant species diversity (PSD) or plant genetic diversity (PGD) can influence the plant-associated arthropod community, these two fundamental levels of biodiversity are not often manipulated simultaneously to assess their effects on species interactions. We used a large tree diversity experiment (BEF-China), which manipulates PSD and PGD in a crossed design to test individual and combined effects of PSD and PGD on multitrophic interaction networks and interaction partner species richness and occurrence. We focused on two tree species, on which sap-sucking Hemiptera and interacting ant species commonly occur. This tri-trophic interaction can be divided into the antagonistic plant–Hemiptera interaction and the mutualistic Hemiptera–ant interaction, known as trophobioses. Qualitative evaluation of tri-trophic interaction networks at different PSD and PGD combinations showed increased interaction partner redundancy at high PSD and PGD. This was supported by increased Hemiptera species richness at high PSD and PGD. Furthermore, the data indicate higher occurrence of Hemiptera and trophobioses and higher trophobiotic ant species richness with increasing PSD and PGD. As no plant diversity component alone caused an effect we conclude that the combined effect of high PGD and high PSD might be additive. In summary, as plant genetic diversity, especially at low species richness, seems to increase the interaction partner redundancy in interaction networks and the diversity of interacting communities, we suggest that genetic diversity should be considered in forest conservation and restoration programs.     

Can forest management have season-dependent effects on bird diversity?

Forest management modified the original structure of most European forests, and in the most extreme cases, genuinely natural and semi-natural forests were turned into plantations through clear felling and replanting, often using non-native species. We compared the bird community structure of native oak woods of northern Italy with that of their anthropogenic counter-parts: black locust and sweet chestnut woods. The three stand types were compared in terms of vegetation structure, bird species richness, diversity and abundance of foraging guilds. We analysed both the overwintering and the breeding community, to assess whether management had specific seasonal effects on bird diversity. Forestry-imposed disturbances affected bird diversity more consistently in winter than in breeding time: bird species richness and diversity were significantly greater in oak and chestnut stands, which were the preferred habitat for bark foragers and foliage gleaners. In the breeding period, bird diversity of black locust woodlands increased, and inter-stand differences were not significant. At this time of year, understorey gleaners were more abundant in black locust stands (where shrubs were denser). In winter, species richness, diversity and the abundance of several guilds were positively correlated with stand age, whereas in the breeding period canopy gleaners preferred younger woodlots. Despite the lack of inter-stand differences in breeding bird diversity, young-managed woods benefited generalist birds that need no particular conservation efforts. Conversely, priority species for forest conservation such as specialised bark foragers positively selected native and mature stands throughout the year. We suggest that detailed year-round studies on diversity and community composition could sharpen the precision with which it is possible to prescribe conservation measures in forested areas.     

The energy–diversity relationship of complex bacterial communities in Arctic deep-sea sediments

The availability of nutrients and energy is a main driver of biodiversity for plant and animal communities in terrestrial and marine ecosystems, but we are only beginning to understand whether and how energy–diversity relationships may be extended to complex natural bacterial communities. Here, we analyzed the link between phytodetritus input, diversity and activity of bacterial communities of the Siberian continental margin (37–3427 m water depth). Community structure and functions, such as enzymatic activity, oxygen consumption and carbon remineralization rates, were highly related to each other, and with energy availability. Bacterial richness substantially increased with increasing sediment pigment content, suggesting a positive energy–diversity relationship in oligotrophic regions. Richness leveled off, forming a plateau, when mesotrophic sites were included, suggesting that bacterial communities and other benthic fauna may be structured by similar mechanisms. Dominant bacterial taxa showed strong positive or negative relationships with phytodetritus input and allowed us to identify candidate bioindicator taxa. Contrasting responses of individual taxa to changes in phytodetritus input also suggest varying ecological strategies among bacterial groups along the energy gradient. Our results imply that environmental changes affecting primary productivity and particle export from the surface ocean will not only affect bacterial community structure but also bacterial functions in Arctic deep-sea sediment, and that sediment bacterial communities can record shifts in the whole ocean ecosystem functioning.     

Characteristics and diversity of microbial communities in lead–zinc tailings under heavy metal stress in north-west China

High-throughput 16S rRNA and 18S rRNA sequencing were performed to study the changes of soil microbial diversity and community structure under different heavy metal pollution levels in Chengxian lead–zinc mining area, Gansu Province. In this study, we characterized the main physicochemical properties, multiple heavy metal pollution, and microbial community structure of the soil in the tailings. The results show that the soil near the tailings pond was alkaline, barren and the heavy metals were seriously polluted. The microbial diversity and richness of S1 and S2 sites were significantly lower than that of CK2 site (P < 0·05), indicating that the heavy metal pollution could change the physicochemical properties and microbial community structure in soil. Among 97 identified core operating taxa of fungal communities, Ascomycota, Teguta and Basidiomycota were dominant at the phylum level, while among 1523 identified core operating taxa of bacterial communities, Actinomycota was dominant at the phylum level. In addition, the redundancy analysis and Spearman correlation analysis showed that the physicochemical properties and the heavy metal concentration had significant effects on the composition and distribution of soil microbial community. The basic characteristics of soil physicochemical properties, multiple heavy metal pollution and microbial community structure in the tailings were revealed, hoping to provide a basis for ecological rehabilitation of tailings by revealing the variance rule of microbial community diversity in the future.