Junmeng Lu

Beta diversity determinants in Badagongshan, a subtropical forest in central China

Niche and neutral theories emphasize different processes contributing to the maintenance of species diversity. In this study, we calculated the local contribution to beta diversity (LCBD) of every cell, using variation partitioning in combination with spatial distance and environmental variables of the 25-ha Badagongshan plot (BDGS), to determine the contribution of environmentally-related variation versus pure spatial variation. We used topography and soil characteristics as environmental variables, distance-based Moran’s eigenvectors maps (dbMEM) to describe spatial relationships among cells and redundancy analysis (RDA) to apportion the variation in beta diversity into three components: pure environmental, spatially-structured environmental, and pure spatial. Results showed LCBD values were negatively related to number of common species and positively related to number of rare species. Environment and space jointly explained ~60% of the variation in species composition; soil variables alone explained 21.6%, slightly more than the topographic variables that explained 15.7%; topography and soil together explained 27%, slightly inferior to spatial variables that explained 34%. The BDGS forest was controlled both by the spatial and environmental variables, and the results were consistent across different life forms and life stages.

Species associations in a species-rich subtropical forest were not well-explained by stochastic geometry of biodiversity.

The stochastic dilution hypothesis has been proposed to explain species coexistence in species-rich communities. The relative importance of the stochastic dilution effects with respect to other effects such as competition and habitat filtering required to be tested. In this study, using data from a 25-ha species-rich subtropical forest plot with a strong topographic structure at Badagongshan in central China, we analyzed overall species associations and fine-scale species interactions between 2,550 species pairs. The result showed that: (1) the proportion of segregation in overall species association analysis at 2 m neighborhood in this plot followed the prediction of the stochastic dilution hypothesis that segregations should decrease with species richness but that at 10 m neighborhood was higher than the prediction. (2) The proportion of no association type was lower than the expectation of stochastic dilution hypothesis. (3) Fine-scale species interaction analyses using Heterogeneous Poisson processes as null models revealed a high proportion (47%) of significant species effects. However, the assumption of separation of scale of this method was not fully met in this plot with a strong fine-scale topographic structure. We also found that for species within the same families, fine-scale positive species interactions occurred more frequently and negative ones occurred less frequently than expected by chance. These results suggested effects of environmental filtering other than species interaction in this forest. (4) We also found that arbor species showed a much higher proportion of significant fine-scale species interactions (66%) than shrub species (18%). We concluded that the stochastic dilution hypothesis only be partly supported and environmental filtering left discernible spatial signals in the spatial associations between species in this species-rich subtropical forest with a strong topographic structure.

Original component of grain size index in core sediment from southwestern slope of the South China Sea and its paleoenvironmental implication

A new approach to the basic composition character of deep sea sediment is discussed in this paper for indicating its paleoenvironment meaning. For this purpose high precision grain size character of sediments from core NS93-5 was analysed by using the Laser Diffraction Particle Size Analyzer, combining with results of micropalaeontologic counting and trace element and calcium carbonate testing, to illustrate some main grain size indexes and their relationship with micropalaeontologic makeup and terrigenous input. It was showed that the grain sizes of deep sea sediment may reflect materials properties and their buildup framework. There are obvious relations between indexes of grain size ranges and abundances of different micropalaeontologic groups and terrigenous matters, in which grain size of <2 μm represents terrigenous composition, that of >5 μm is mainly made up of various microfossil shells, except for containing volcanic dust layers, and median diameter (MD) of grain size may be taken as proxy of paleoproductivity or paleoecological dynamic. These index and proxy were consistent with micropaleontologic records for well indicating important features of paleoceanographic ecology, showing that the micropalaeontologic growth in the southwestern slope area of the South China Sea (SCS) was negatively correlated to terrigenous input since late Pleistocene and corresponded to glacial-interglacial global climatic changes incompletely, but had a regional particularity in this sea area.

Root-sprouting ability in an evergreen and deciduous broad-leaved mixed forest

As an important way for forest regeneration, root-sprouting plays an important role in maintaining population and species diversity. Using the initial census data of Badagongshan 25-hm2 forest plot, we analyzed the relationship between root-sprouting ability and topographic factors, and tested the phylogenetic signal of root-sprouting ability. We found that there are 33039 individuals with root-sprouts which account for 17.70% of all the individuals and the total number of root-sprouts was 54184. Results of Spearmans correlation analyses with torus-translation tests showed that the root-sprouting ability significantly negatively correlated with elevation, convex, and vertical distance from channel network. However it significantly positively correlated with topographic wetness index. These may be due to that the low valley areas were disturbed by the stream flow, thus accelerating the root-sprouting ability. The root-sprouting ability of 126 common species showed significant phylogenetic signal. It showed significant phylogenetic signal for shrub species and deciduous species but not for canopy species, sub-canopy species and evergreen species in different life forms. These suggested that root-sprouting ability was a very unstable functional trait in the evolutionary history. In conclusion, the root-sprouting ability of ligneous plants at Badagongshan plot was influenced by topographic factors and phylogenetic history.