Nested plant and fungal communities; the importance of area and habitat quality in maximizing species capture in boreal old-growth forests

Knowledge of the distribution of rare species is crucial for species conservation in fragmented habitats. Species communities often exhibit nestedness, i.e. species in species-poor sites comprise a subset of richer ones. Thus, rare species are confined to species-rich sites. We evaluate whether plant and fungal communities in 46 old-growth spruce forest patches (0.17-12 ha) exhibit nestedness. The question whether a single large patch or several small patches capture most species (i.e. the SLOSS-issue) is evaluated in combination with species saturation analyses. All species groups exhibited significant nestedness. Area was generally related to nestedness, i.e. rare species were over-represented in the largest patches. Species saturation analysis indicated that large patches accumulated more Red-list species in patch interiors than small patches. Thus, rare and Red-list species were best captured in large patches. However, nestedness also emerged in equal sized sample plots, i.e. rare species were over-represented in high quality habitats. Thus, small habitats of high quality should not be neglected in a conservation perspective.     

Oribatid mite community structure and tree species diversity: A link?

Differences in tree species may lead to contrasting soil environments via differences in litter chemical quality and physical environmental factors, such as soil type and soil moisture. However, separating the effects of litter quality and physical environment is difficult under field conditions. Both litter quality and soil environment affect the species composition of the soil animal community. A diversity gradient of canopy tree species (11–25 species) located on homogeneous soil substrate at Tomakomai Experimental Forest of Hokkaido University was used to analyse the relationship between tree species diversity and oribatid mite community structure. Soil samples were collected from three levels of tree species richness (high, intermediate and low) with three replicates each, in July 2000. Leaf area index (LAI) was positively correlated with tree species diversity suggesting higher litter input into the soils with increasing tree diversity. However, the tree species diversity gradient affected neither accumulation of litter on the forest floor nor abundance and species richness of oribatid mites. Canopy and understory plant species richness, LAI, total soil carbon and biomass of epigeic and endogeic earthworms did not significantly affect mite community structure as indicated by redundancy analysis (RDA). The results suggest that oribatid mite community structure is minimally affected by tree species diversity and associated changes in litter diversity.     

Effect of tree species on methane and ammonium oxidation capacity in forest soils

High and low affinity methane oxidation potentials were measured for soils under five fully replicated land-use treatments over an entire calendar year. Simultaneous measurements of soil nitrification potential in replicate soil samples were also made. Both high and low affinity CH₄ oxidation were significantly reduced in the nitrate-rich soils under alder, compared to the other four vegetation treatments (oak, Norway spruce, Scots pine and grass). However, the effect of land-use was less for high affinity methanotrophy than for low affinity CH₄ oxidation. Nitrification rates were highest in alder soils, with the greatest potential for oxidation occurring in the top 5 cm of the soil. No significant relationship between potential nitrification rate and low affinity CH₄ oxidation was seen. However, a significant negative relationship between nitrification and high affinity CH₄ oxidation was identified. We found vegetation type to be a key determinant of soil-mediated CH₄ and oxidation, but found no evidence for significant CH₄ oxidation by nitrifying bacteria.     

Lichen species diversity and substrate amounts in young planted boreal forests: A comparison between slash and stumps of Picea abies

The increasing demand for biofuel may decrease the dead wood supply in managed forests, and hence the amount of substrate available for dead wood dependent species. Slash is already being harvested for biofuel purposes, and stumps are an even bigger potential source of wood fuel. Both substrates constitute a major component of dead wood in managed forests, but have been poorly studied in terms of lichen diversity. We compared lichen species diversity between the lateral surface of slash and the cut surface of stumps of Norway spruce in planted boreonemoral Swedish forests of four age classes; 4-5, 8-9, 12-13, and 16-18 years. We also estimated the amounts of the two substrates, and discriminated between slash with bark and decorticated slash. There were no differences in species number per surface area, but slash had more species when equal volumes were compared. We found compositional differences between slash and stumps throughout the decay process. The majority of species found on both substrates were more frequent on stumps, which also had a higher number of unique species and species in the literature indicated as nationally rare or uncommon. The volume per hectare of stumps was ten times greater than that of slash but conversely, the lateral surface area of slash was five times greater than the cut surface area of stumps. Few dead wood specialist lichen species were, however, strictly associated with slash, whereas stumps offer a more heterogeneous environment and may provide important habitats for rare lichens in the managed forest landscape.     

Litter N-content influences soil millipede abundance,species richness and feeding preferences in a semi-evergreen dry forest of Guadeloupe (Lesser Antilles)

Despite the impact of soil millipedes on litter fragmentation in tropical forests, there have been few studies dealing with factors determining their habitat preference in these ecosystems. In a natural secondary dry forest of Guadeloupe on Leptosol, two complementary studies were carried out in order to test the hypothesis that litter N-content strongly influences millipede distribution. Millipede abundance and species richness were described in the field under two tree species, Bursera simaruba and Pisonia subcordata, and were related to the chemical characteristics of their foliage. In addition, a laboratory experiment was done in order to assess millipede feeding preferences regarding the chemical characteristics of leaves from various species. Millipede abundance and species richness were significantly higher under P. subcordata than under B. simaruba, probably due to the higher N content of P. subcordata leaves. Moreover, millipedes fed preferentially on N-rich leaves. The present study confirms that there was a close correlation between the preferred food, its chemical composition and the local distribution of millipede populations.     

Collembola species composition and diversity effects on ecosystem functioning vary with plant functional group identity

The relationship between decomposer diversity and ecosystem functioning is little understood although soils accommodate a significant proportion of worldwide biodiversity. Collembola are among the most abundant and diverse decomposers and are known to modify plant growth. We examined the effects of Collembola species diversity (one, two and three species belonging to different life history groups) and composition on litter decomposition and the performance of plant communities (above- and belowground productivity) of different functional groups (grasses, forbs and legumes). Collembola densities did not increase with diversity indicating niche overlap. Generally, Collembola species composition was a better predictor for ecosystem functioning than Collembola species number with the impacts of Collembola diversity and composition on ecosystem functioning strongly depending on plant functional group identity. Non-linear effects of Collembola diversity on litter decomposition and plant productivity suggest pronounced and context dependent species interactions and feeding habits. Net surface litter decomposition was decreased by Collembola, whereas root litter decomposition was at maximum in the highest Collembola diversity treatment. Forbs benefitted most from the presence of three Collembola species. Similarly, Collembola diversity influenced root depth distribution in a plant functional group specific way: while grass root biomass decreased with increasing Collembola diversity in the upper and lower soil layer, legume root biomass increased particularly in the lower soil layer. Idiosyncratic and context dependent effects of Collembola diversity and composition even in rather simple assemblages of one to three species suggest that changes in Collembola diversity may have unpredictable consequences for ecosystem functioning. The finding that changes in Collembola performance did not directly translate to alterations in ecosystem functioning indicates that response traits do not necessarily conform to effect traits. Distinct plant functional group specific impacts of Collembola diversity on root depth distribution are likely to modify plant competition in complex plant communities and add a novel mechanism how decomposers may affect plant community assembly.     

Spatial patterns, density changes and implications on biodiversity for old trees in the boreal landscape of northern Sweden

Logging and modern forest management reduced the frequency of key features of old-growth forest, especially old, dying and dead trees in the Scandinavian boreal forest during the 20th century. To quantify the decline and spatial differences, we have analysed density changes of old trees between 1926 and 1996 on a regional scale (approximately 50,000 km²) in boreal Sweden. The occurrence of old-conifer trees (+159 years) has dramatically decreased in the studied area and today only one third as many old Scots pines (Pinus sylvestris L.) and Norway spruces (Picea abies (L.) Karst.) can be found as in the 1920s. However, the density of old deciduous trees (+99 years) has not decreased since the early 20th century. Historical baseline data such as these are needed for modern forest management, conservation programmes and ecological restoration projects. Existing old trees are very important for biodiversity, and may also preserve elements of cultural heritage from pre-industrial times.     

Disentangling effects of habitat diversity and area on orthopteran species with contrasting mobility

Loss of semi-natural grasslands and reduction of habitat diversity are considered major potential threats to arthropod diversity in agricultural landscapes. The main aim of this study was to investigate how area and habitat diversity, mediated by shrub encroachment after grassland abandonment, affect species richness of orthopterans in island-like grasslands, and how contrasting mobility might alter species richness response to both factors. We selected 35 isolated patches in landscapes dominated by arable land (durum wheat) in order to obtain two statistically uncorrelated gradients: (i) one in habitat area ranging from 0.2 to 55 ha and (ii) one in habitat diversity ranging from patches dominated by one habitat (either open grasslands or shrublands) to patches with a mosaic of different habitats. Habitat loss due to land-use conversion into arable fields was associated with a substantial loss of species with a positive species-area relationship (SAR), with sedentary species having a steeper and stronger SAR than mobile species. Halting habitat loss is, therefore, needed to avoid further species extinctions. Shrub encroachment, triggered by abandonment, presented a hump-shaped relationship with habitat diversity. An increase in habitat diversity enhanced species richness irrespective of patch area and mobility. Maintaining or enhancing habitat diversity, by cutting or burning small sectors and by reintroducing extensive sheep grazing into abandoned grassland, are suggested as complementary strategies to mitigate further decline of orthopteran diversity in the remnant patches. This would be equally important in both small and large patches.     

Soil fauna abundance and diversity in a secondary semi-evergreen forest in Guadeloupe (Lesser Antilles): influence of soil type and dominant tree species

The importance of secondary tropical forests regarding the maintenance of soil fauna abundance and diversity is poorly known. The aims of this study were (1) to describe soil fauna abundance and diversity and (2) to assess the determinants of soil fauna abundance and diversity in two stands of a tropical semi-evergreen secondary forest. Soil macrofauna and microarthropod abundance and soil macrofauna diversity were described at two sites developed on different soils and with different site histories: (1) a natural secondary stand (natural forest) under two dominant tree species, Pisonia subcordata and Bursera simaruba, and (2) a planted secondary forest (planted forest) under three tree species, B. simaruba, Swietenia macrophylla, and Tabebuia heterophylla. The effects of both soil and main tree species’ litter quality were assessed to explain soil fauna abundance and diversity. The abundance of soil macrofauna was significantly higher in the soil under the planted forest, and soil fauna communities were contrasted between the two sites. In the planted forest, a soil-dwelling macrofauna community developed (mainly consisting of the anecic earthworm Polypheretima elongata). In the natural forest, soil macrofauna and microarthropod communities were located at the soil surface. The effect of plant litter quality varied according to each dominant tree species and was superimposed to soil effect. The lowest macrofauna abundance was associated with B. simaruba in the natural forest. T. heterophylla supported a much greater macrofauna community than the two other tree species studied at the same soil, and it appears likely that this is due to the palatability of its leaves compared with the other trees (low lignin, tannins, soluble phenols).     

中亚热带常绿阔叶林林隙与物种多样性的关系研究

对万木林中亚热带常绿阔叶林非林隙与林隙内物种多样性及物种多样性随林隙大小的变化规律研究结果表明 ,万木林常绿阔叶林林隙内物种多样性高于非林隙内 ,乔木树种物种多样性随林隙大小的变化呈双峰曲线 ,其物种多样性为 2 0 0～ 30 0m2 面积林隙内达最大值 ;而灌木树种多样性随林隙大小的变化呈单峰曲线 ,其物种多样性为 4 0 0～ 5 0 0m2 面积林隙内达最大值。     

Effects of habitat degradation on the abundance, richness and diversity of raptors across Neotropical biomes

Population growth and human development result in biodiversity loss and biological homogenization not only in developed countries, but increasingly in the less developed countries as well. In those countries, where urbanization and agricultural intensification occur at a faster rate than in developed countries, habitat degradation appears to be the leading cause of wildlife loss. During the breeding seasons of 2002–2005 we conducted road surveys across five biomes of Argentina to detect variations in raptor community attributes as potential indicators of broad scale habitat degradation. Abundance of individuals, richness and diversity of species were calculated to assess the effects of habitat transformation and patch size on these community attributes. Raptor communities strongly varied in relation to habitat transformations, with lower abundance of individuals, richness and diversity of species in more transformed landscapes. Small patches of natural vegetation and locations in which natural and cultivated lands where interspersed showed lower richness and diversity of raptors than large patches. Fragmentation was the main cause of reductions in abundance of individuals. Although the relative contribution of our two estimates of habitat degradation to abundance, richness and diversity of raptors varied among biomes, these community attributes proved useful as predictors of habitat degradation. This was especially true in habitats where raptor communities are more complex although overall patterns remained constant across biomes, from forests to deserts. Taking into account current trends of habitat transformation (drastic increments in monocultures, urban areas, and habitat patchiness), the conservation of raptor communities in these biomes could be seriously compromised. In terms of species-specific responses of raptors to habitat degradation, a rapid process of homogenization can be expected, resulting in only a few winner species within a general scenario of losers.     

Effects of tree species and topography on soil chemistry, litter quality, and decomposition in Northeast Turkey

Leaf litters from beech (Fagus orientalis Lipsky.) and oak (Quercus robur L.), and needle litters from fir (Abies nordmanniana Spach.) and pine (Pinus sylvestris L.) trees were collected from north-facing site and south-facing site and at three slope positions (top, middle and bottom) on each aspect that varied in soil chemical characteristics (soil pH, cation exchange capacity and base saturation). The litters were analysed for initial total carbon, nitrogen, acid detergent fibre, lignin and cellulose concentrations. Nitrogen, acid detergent fibre and lignin concentrations and carbon:nitrogen and lignin:nitrogen ratios varied significantly within and between species according to soil chemical characteristics on aspects and slope positions. Litter decomposition was studied in the field using the litterbag technique. The litters were placed on two aspects and at three slopes on each aspect in October 2001, and were sampled every 6-month for 2 years. The main effects of aspect, species and slope position on decomposition rates were all statistically significant. Oak leaf litter showed highest decomposition rates, followed by pine, fir and beech litter, and the litters placed on north-facing site decomposed faster than those on the south-facing site. The litters placed at the top slope position decomposed slower than at those at either the bottom or middle positions. Initial lignin concentrations explained most of the variation in decomposition rates between species, and within species for the aspects and the slope positions, but the explained variance showed differences between aspects and slope positions. This result illustrates the important point that litter quality may define the potential rates of microbial decomposition but these are significantly influenced by the biotic and abiotic environment in which decomposition takes place.     

Effects of habitat fragmentation on pollen flow and genetic diversity of the endangered tropical tree Swietenia humilis (Meliaceae)

Fragmentation of tropical forest represents a major threat to some tree populations by reducing local population size and gene flow from other populations. Both processes can decrease outcrossing rates and genetic variation in remnant stands. Despite these risks, some tree species have pollen vectors that mitigate these negative consequences for fragmented populations. In this paper, we assess both pollen flow and diversity of pollen sources in continuous forest and isolated stands of Swietenia humilis, a tropical tree species pollinated by small insects. Using seven nuclear microsatellite markers, we test the hypothesis that genetic diversity and the number of pollen donors are lower in remnant populations. Results show that allelic richness of seeds is lower in isolated populations (6.1 vs. 8.3 alleles per locus), even though adult populations do not show this difference.Pollen pool structure is greater in isolated patches (Φ_Iso = 0.26) than in continuous forest (Φ_For = 0.14), which yields estimates of the average effective number of pollen donors (N_ep) of 1.9 and 3.6 respectively. In addition, estimates of number of sires per mother indicate that isolated trees have half the number of pollen sources (4.98) than trees in the forest (9.8). Although extensive pollen movement (>2000 m) was recorded on both habitat conditions, indicating that fragmented patches are not isolated from pollen-mediated gene flow, this extensive pollen flow among trees in fragmented landscapes may not serve to counteract deleterious reproductive and genetic consequences of habitat fragmentation.     

Linkages between below and aboveground communities: Decomposer responses to simulated tree species loss are largely additive

Inputs of aboveground plant litter influence the abundance and activities of belowground decomposer biota. Litter-mixing studies have examined whether the diversity and heterogeneity of litter inputs affect decomposer communities in ways that can be predicted from monocultures. They have mainly attempted to detect non-additive effects of litter mixing, although individual species effects (additivity) as well as species interactions (non-additivity) may alter decomposition rates. To determine potential impacts of plant species loss on aboveground-decomposer linkages, we assessed both additive and non-additive effects of litter mixing on decomposer communities. A full-factorial litterbag experiment with leaves from four deciduous tree species was conducted, to assess responses of bacteria, fungi, nematodes, and microarthropods. Data were analyzed using a statistical method that first looked for additive effects based on the presence or absence of species and then any significant species interactions. We observed almost exclusively additive effects of all four litter species on decomposer biota, with each species exerting effects on different aspects of the community. These results imply that the consequences of species loss for the decomposer community will be largely predictable from knowledge of single species litter dynamics. The two species at opposite ends of the quality spectrum exerted the most effects. High-quality Liriodendron tulipifera supported a more diverse arthropod community and drove bottom-up effects on the decomposer food web. Low-quality Rhododendron maximum had negative effects on most groups of biota. Litter of mid-quality species exerted fewer effects. The influence of litter species richness on the Tylenchidae (nematodes) was the only non-additive effect of litter mixing. Together, these data demonstrate an effect of plant community composition on decomposer biomass, abundance, and diversity, confirming a link between above and belowground communities. We were able to identify the species to which the decomposer community is most sensitive, aiding predictions of the consequences of the loss of these dominant species on the decomposer community, with potential feedbacks for organic matter and nutrient turnover.     

Nematodes and their relationship to forest dynamics: I. Species and trophic groups

Nematode populations were studied in parallel with successional stages of forest dynamics (clearing, growth, mature and senescence phases) in a nature reserve within the state forest of Fontainebleau (La Tillaie, France). Soil conditions were identical in all habitats (acid mull). A heterogeneous nematode fauna was found, resulting from the natural forest dynamics: vertical distribution of animals, horizontal distribution according to the nature and density of the plant cover, and different trophic groups. We also demonstrated the characteristics of the disruption zone of the ecosystem (clearing) and the subsequent succession, depending on where the clearing occurred. Similarly, changes in trophic group emphasized the continuity in time from clearing to the senescence phase.     

Litterfall, litter decomposition and nutrient release patterns in four native tree species raised on coal mine spoil at Singrauli, India

 Litterfall, leaf litter decomposition and N and P release were studied in four tree species (Dalbergia sissoo, Azadirachta indica, Pongamia pinnata and Shorea robusta) planted on a mine spoil habitat. Annual litterfall varied from 1220 kg ha^–1 in the S. robusta stand to 3620 kg ha^–1 in the A. indica stand. The fast-growing species A. indica and D. sissoo exhibited higher litter production in comparison to the other two slow-growing species. The total N returned to the soil through litterfall ranged from 8.6 kg ha^–1 year^–1 in the S. robusta stand to 36.5 kg ha^–1 year^–1 in the D. sissoo stand. The annual percent leaf litter mass loss was distinctly greater in A. indica (73%) and D. sissoo (69%) in comparison to P. pinatta (59%) and S. robusta (47%). The mean relative decomposition rates of leaf litter material were maximum in the rainy season and minimum in summer. Rainfall and its associated variables exhibited greater control over litter docomposition than temperature. Lignin and water-soluble compounds were better predictors of annual mass loss rates accounting for 90% variability. Mass loss was positively correlated with N and P mineralization rates. Lignin was the best predictor of annual N and P mineralization rates. Nutrient release pattern differed; constant release occurred in A. indica, initial release followed by delayed immobilization and release occurred in D. sissoo and P. pinnata, and initial immobilization followed by gradual release was noticed in S. robusta. A. indica and D. sissoo, showing high litterfall and rapid litter decomposition rate, hold promise for the rehabilitation of nutrient-poor coal mine spoils. On the other hand, S. robusta with less litterfall and a slow decomposition rate may prove disadvantageous. Received: 10 March 1998     

The influence of field shape, area and surrounding landscape on plant species richness in grazed ex-fields

Over the past 100 years species-rich semi-natural grasslands have decreased dramatically in Western Europe, where former arable fields (ex-fields) are used instead as pasture. The disappearance of semi-natural grasslands has caused a threat to the biodiversity in agricultural landscapes. Many typical grassland plants are dispersal limited, thus grazed ex-fields can be used to investigate if species spontaneously colonise these new grassland habitats. We examined the relationship between surrounding landscape, field area, shape, distance between edge and centre, and plant species diversity in ex-fields that had been grazed for 15-18 years. The results showed that there were 35% more plant species in fields surrounded by commercial forestry production compared to those surrounded by open agricultural landscape. Area and shape did not influence species richness, although there was increasing number of species in the centre with decreasing distance from the edge. Twenty-five percent of the species where typical grassland species, and ex-fields surrounded by forest had 91% more grassland species compared to those in the open landscape. It is possible to increase grassland plant occurrences by grazing ex-fields surrounded by forest or other grassland remnant habitats, particularly in landscapes where grazed semi-natural grasslands are scarce.     

Endemic species: Contribution to community uniqueness, effect of habitat alteration, and conservation priorities

The biodiversity crisis, particularly dramatic in freshwaters, has prompted further setting of global and regional conservation priorities. Species rarity and endemism are among the most fundamental criteria for establishing these priorities. We studied the patterns of rarity and the role of rare species in community uniqueness using data on freshwater bivalve molluscs (family Unionidae) in Texas. Due to the large size and gradients in landscape and climate, Texas has diverse and distinct unionid communities, including numerous regional and state endemic species. Analysis of the state-wide distribution and abundance of Unionidae allowed us to develop a non-arbitrary method to classify species rarity based on their range size and relative density. Of the 46 Unionidae species currently present in Texas, 65% were classified as rare and very rare, including all state and regional endemics. We found that endemic species were a critical component in defining the uniqueness of unionid communities. Almost all endemics were found exclusively in streams and rivers, where diversity was almost double that of lentic waters. Man’s ongoing alteration of lotic with lentic waterbodies favors common species, and dramatically reduces habitat for endemics, contributing to homogenization of unionid fauna. We identified hotspots of endemism, prioritized species in need of protection, estimated their population size, and recommended changes to their current conservation status.     

Impact of season, stem diameter and intensity of debarking on survival and bark re-growth pattern of medicinal tree species, Benin, West Africa

Bark is a greatly coveted non-timber forest product (NTFP). Its overexploitation from medicinal tree species threatens an essential source of medication for rural populations. Despite the relevance of bark, not much information is available on the ecological impact of bark harvesting. In Benin, West Africa, we investigated how various harvesting techniques affect the bark re-growth of 12 tree species and the survival of debarked trees. Trees were debarked following a combination of three factors: (i) season of bark harvesting (dry or rainy season), (ii) size class of the tree (three stem diameter classes) and (iii) intensity of debarking (seven different percentages of trunk circumference debarked). Measurements of edge growth and survival were taken every 6 months during 2 years. Ring-barking (100% of trunk circumference debarked) did not allow the sustainable exploitation of any species, while all trees with 75% of debarked circumference remained alive and produced edge growth. Whatever the bark harvesting technique, 5 out of the 12 species had a bark recovery rate below 1 cm/year, rendering the wound closure very unlikely. On the other hand, five species showed good to very good bark recovery rates (>7 cm/year) and for these species the combination of debarking factors (season, dbh and intensity) allowing the highest edge growth was determined. This experimental bark stripping revealed the complexities involved in decision-making for sustainable tree management. Studying the patterns of bark recovery rates provides a relevant tool to assess for each species the delay for achieving closure of a specific wound area.     

Spring bryophytes in forested landscapes: Land use effects on bryophyte species richness, community structure and persistence

Many freshwater ecosystems face severe threats from anthropogenic disturbances, yet little is known about the degree to which their biotic communities have been degraded by human activities. We analysed temporal changes and persistence of bryophyte communities in 40 springs in eastern Finland by comparing field surveys conducted in 1986 and 2000. During that period, some springs had remained in a near-pristine state, while others had undergone varying degrees of disturbance from forest management, drainage, and water abstraction. Several spring bryophytes (e.g., Philonotis fontana) declined between the study years, whereas Sphagnum mosses (e.g., Sphagnum warnstorfii) increased in abundance. Species richness of spring bryophytes declined significantly from 1986 to 2000, irrespective of bryophyte group (spring vs. other bryophytes) and spring condition (severely disturbed vs. unaltered springs). Bryophyte cover also decreased dramatically from 1986 to 2000, but this effect was related to both spring condition and bryophyte type. Spring bryophytes lost much of their cover in severely altered springs, while in unaltered springs they remained relatively stable through time. No such trend was observed for other, habitat generalist bryophytes. Persistence and stability of bryophyte communities showed significant, albeit rather weak, relationships with spring condition, with communities in unaltered springs being more persistent than those in altered springs. Given the importance of springs to boreal forest and aquatic biodiversity, restoration of degraded springs is a major challenge to maintaining and conserving biodiversity of boreal landscapes.