No abstract

Based on the data from China's second national soil survey and field observations in northwest China, we estimated soil organic carbon (SOC) storage in China and investigated its spatial and vertical distribution. China's SOC storage in a depth of 1 meter was estimated as 69.1 Pg (10 15 g), with an average density of 7.8 kg m -2 . About 48% of the storage was concentrated in the top 30 cm. The SOC density decreased from the southeast to the northwest, and increased from arid to semi-humid zone in northern China and from tropical to cold-temperate zone in the eastern part of the country. The vertical distribution of SOC differed in various climatic zones and biomes; SOC distributed deeper in arid climate and water-limited biomes than in humid climate. An analysis of general linear model suggested that climate, vegetation, and soil texture significantly influenced spatial pattern of SOC, explaining 78.2% of the total variance, and that climate and vegetation interpreted 78.9% of the total variance in the vertical SOC distribution.

Most of the world's terrestrial biome types can be found in China. To systematically investigate species composition and structure of China's forest communities, we launched a long-term project consisting forest vegetation surveys across China's mountains in the mid 1990s. Over the study period, we have conducted vegetation surveys for 65 mountains and collected vegetation data from about 1500 forest plots, using consistent sampling protocols. In this paper we first introduce the aims, protocols, and major research themes of the project, and then describe the major characteristics of forest communities and their geographic patterns and climatic controls. As latitude increased, diameter at breast height (DBH) and height of trees increased, while individual density of trees and woody species richness decreased. Total basal area (TBA) of trees and species richness of herbs did not vary with latitude. Contemporary climate seems to drive these patterns: temperature was the leading factor for DBH, precipitation was most important for tree height and individual density, actual evapotranspiration (a surrogate of productivity) determined woody (trees and shrubs) species richness, and rainfall was the major controller of the herb species richness. The species-abundance relationship showed that species dominance (measured by the number of individuals per species) declined significantly from boreal forests to evergreen broadleaf forests from north to south. Our results are in line with the idea that productivity drives woody species richness. Similarly, we find that biomass (measured as TBA) is invariant along the environmental gradients. However, individual density varies dramatically, in contrast to the assumptions underlying the metabolic theory of ecology.

Biodiversity patterns and their underlying mechanisms have long been focal topics of study for ecologists and biogeographers. However, compared with spatial variation in species richness (a-and g-diversity), b-diversity, or the dissimilarity of species composition between two or more sites has until recently received limited attention. In this study, we explored the large-scale patterns of altitudinal turnover (b-diversity) of plants in montane forests of China, based on systematic inventories of 1153 plots from 46 mountains distributed over ~ 30 degrees of latitude (21.9-51.7°N) and ~ 4100 m of altitude (160-4250 m). The b-diversity of trees and shrubs declined significantly with increasing latitude. Along the altitudinal gradient, b-diversity of both trees and shrubs showed non-significant trends in most mountains. Differences in climate explained ~ 30.0% of the variation in tree b-diversity (27.7, 36.5, and 26.2% for the Jaccard's, b j , Sorenson's, b s , and Simpson's dissimilarity, b sim , respectively), with mean annual temperature being most important, and  10.0% of that in shrub b-diversity (10.0, 8.2, and 7.0% for b j , b s , and b sim , respectively), with annual actual evapotranspiration and annual precipitation as the main predictors. However, climatic controls of b-diversity varied dramatically in different biogeograpical regions. The b-diversity of trees exhibited stronger, whereas that of shrubs showed weaker, climatic patterns in temperate and arid than subtropical regions. These results suggest that mechanisms causing patterns of b-diversity may differ between latitudinal and altitudinal gradients, and among biogeographical regions; as a result, caution should be exercised in drawing close parallels between patterns and causes of b-diversity along latitudinal and altitudinal gradients and among regions.

As one of the most important hypotheses on biogeographical distribution, Rapoport's rule has attracted attention around the world. However, it is unclear whether the applicability of the elevational Rapoport's Rule differs between organisms from different biogeographical regions. We used Stevens’ method, which uses species diversity and the averaged range sizes of all species within each (100 m) elevational band to explore diversity‐elevation, range‐elevation, and diversity‐range relationships. We compared support for the elevational Rapoport's rule between tropical and temperate species of seed plants in Nepal. Neither tropical nor temperate species supported the predictions of the elevational Rapoport's rule along the elevation gradient of 100–6,000 m a.s.l. for any of the studied relationships. However, along the smaller 1,000–5,000 m a.s.l. gradient (4,300 m a.s.l. for range‐elevation relationships) which is thought to be less influenced by boundary effects, we observed consistent support for the rule by tropical species, although temperate species did not show consistent support. The degree of support for the elevational Rapoport's rule may not only be influenced by hard boundary effects, but also by the biogeographical affinities of the focal taxa. With ongoing global warming and increasing variability of temperature in high‐elevation regions, tropical taxa may shift upward into higher elevations and expand their elevational ranges, causing the loss of temperate taxa diversity. Relevant studies on the elevational Rapoport's rule with regard to biogeographical affinities may be a promising avenue to further our understanding of this rule.