适宜空间日趋缩小下的森林服务功能变化

本文是中德“森林多功能性”研讨会的成果之一。在研讨了森林与人类相互关系的基础上,来自德国和中国林业和木材领域的20名科学家和“利益相关者”阐述了森林多功能性的内涵:(1)森林多功能性是现代森林经营的要求;(2)森林的整体功能优先;(3)森林生物多样性的维持;(4)可持续经营与生态文明的融合;(5)经济学与生态学知识的结合;(6)通过培训提高经营者素质;(7)林业必须在生态、经济和文化三个方面找到平衡点;(8)应对气候的变化;(9)面对未来的需求和挑战;(10)实现多功能是一个过程。结论认为“多功能”和“可持续性”实际上是一枚硬币的两个面。

Micro-site Conditions of Epiphytic Orchids in a Human Impact Gradient in Kathmandu Valley, Nepal

We studied distribution and site conditions of epiphytic orchids in a gradient of human interference in Kathmandu valley, central Nepal. The aim was to understand the recent distribution pattern of epiphytic orchids, with respect to (i) the micro-site conditions and (ii) the type and intensity of land use. The occurrence of epiphytic orchids was recorded for a grid with 1.5 km cell size. The cells represent different types and intensities of human impact. Site factors such as bark rugosity, bark pH, diameter at breast height (dbh; 1.3 m) of host trees, exposure to wind and sunlight intensity were recorded. With regard to the species richness and abundance of epiphytic orchids, we compared different human impact categories from very strong human impact (settlement area) to very low human impact (national park). Remote sensing was used for a supervised classification of land cover. Ficus religiosa turned out to be the most important host species for orchids in urban areas, while Schima wallichii and Alnus nepalensis significantly host orchids in the other categories. Both species richness and abundance of epiphytic orchids were significantly higher under very low human impact (forest in national park) and also some remaining patches of primary forest than the other regions. Micro-climate is crucial for orchid populations. Host bark pH, bark rugosity, sunlight intensity and host exposure were significantly different for all human impact categories in order to harbour epiphytic orchid species. Habitats with a mixture of mature trees are suitable and essential for the conservation of viable populations of epiphytic orchids in settled areas. The study reveals that to improve the population size of orchids it is essential for future urban forestry to: (i) Protect old trees as carriers of existing epiphytic orchid diversity, (ii) protect medium old trees to ensure that they may become old trees, (iii) plant new host trees for the future, (iv) plant in groups instead of single isolate trees. Trees should especially be planted in areas where orchids still exist to provide more trees for orchid population enlargement (e.g. along riparian system). Native species should be favoured; the pool of such native host species is wide.

Diversity, composition and host-species relationships of epiphytic orchids and ferns in two forests in Nepal

Epiphytic plant species are an important part of biological diversity. It is therefore essential to understand the distribution pattern and the factors influencing such patterns. The present study is aimed at observing the patterns of species richness, abundances and species composition of epiphytic orchids and ferns in two subtropical forests in Nepal. We also studied the relationship of host plants(Schima wallichii and Quercus lanata) and epiphyte species. Data were collected in Naudhara community forest(CF) and the national forest(NF) in Shivapuri Nagarjun National Park. The data were analyzed using univariate and multivariate tests. In total, we recorded 41 species of epiphytes(33 orchid and 8 fern species). Orchid species abundance is significantlyhigher in CF compared to NF. Orchid species richness and abundance increased with increasing southern aspect whereas it decreased with increasing canopy cover, and fern species richness increased with host bark roughness. Orchid abundance was positively correlated with increasing bark p H, stem size, tree age and tree height and negatively correlated with increasing steepness of the area. Likewise, fern abundances were high in places with high canopy cover, trees that were tall and big, but decreased with increasing altitude and southern aspect. The composition of the orchid and fern species was affected by altitude, aspect, canopy cover, DBH, number of forks and forest management types. We showed that the diversity of orchid and fern epiphytes is influenced by host characteristics as well as host types. The most important pre-requisite for a high epiphyte biodiversity is the presence of oldrespectively tall trees, independent of the recent protection status. This means:(i) for protection, e.g.in the frame of the national park declaration, such areas should be used which host such old tall trees;and(ii) also in managed forests and even in intensively used landscapes epiphytes can be protected by letting a certain number of trees be and by giving them space to grow old and tall.

Soil conditions and phylogenetic relatedness influence total community trait space during early plant succession

Aims the total space of traits covered by the members of plant com-munities is an important parameter of ecosystem functioning and complexity.We trace the variability of trait space during early plant succession and ask how trait space co-varies with phylogenetic community structure and soil conditions.Particularly,we are inter-ested in the small-scale variability in trait space and the influence of biotic and abiotic filters.Methods We use data on species richness and soil conditions from the first 7 years of initial succession of an artificial catchment in north-east-ern germany.total functional attribute diversity serves as a proxy to total trait space.Important Findingstotal trait space steadily increased during succession.We observed high small-scale variability in total trait space that was positively correlated with species richness and phylogenetic segregation and negatively correlated with total plant cover.trait space increased with soil carbonate content,while pH and the fraction of sandy material behaved indifferently.our results indicate that during early succession,habitat filtering processes gain importance leading to a lesser increase in trait space than expected from the increase in species richness alone.

Directional changes of species spatial dispersion and realized environmental niches drive plant community assembly during early plant succession

Aims Probabilistic models of species co-occurrences predict aggre-gated intraspecific spatial distributions that might decrease the degree of joint species occurrences and increase community rich-ness.Yet,little is known about the influence of intraspecific aggre-gation on the co-occurrence of species in natural,species-rich communities.Here,we focus on early plant succession and ask how changes in intraspecific aggregation of colonizing plant spe-cies influence the pattern of species co-existence,richness and turnover.Methods We studied the early vegetation succession in a six ha constructed catchment within the abandoned part of a lignite mine in NE Germany.At two spatial scales(1-and 25-m2 plots),we compared for each pair of species the intraspecific degree of aggregation and the pattern of co-occurrence and compared observed rela-tionships with temporal changes in important species functional traits.Important Findings The majority of species occurred in an aggregated manner,particu-larly in the first 2 years of succession.In pairwise comparisons,we found an excess of segregated species occurrences leading to a posi-tive link between intraspecific aggregation and pairwise species seg-regation as predicted by the aggregation hypothesis,particularly at the lower spatial resolution.The degree of intraspecific aggregation was negatively correlated with the community-wide level of species spatial turnover and with plot species richness.Our results are the first direct confirmation that increasing intraspecific aggregation and interspecific competitive interactions counteract in shaping plant community structure during succession.The respective effects of aggregation were strongest at intermediate states of early succession.