The influence of environmental factors on species composition and distribution in a community forest in Northern Thailand

Understanding the environmental factors that influence tree species composition is essential for successful management of biodiversity and sustainable use of community forest resources.This study aims to assess tree species composition and distribution in the deciduous Ban Mae Chiang Rai Lum Community Forest in Northern Thailand and to analyze the influence of environmental factors on tree biodiversity in the forest.We conducted a stratified systematic sampling of the forest’s total area of 3925 ha,and twenty-five 0.16 ha survey plots were established in three different stands of the deciduous forests to estimate and characterize the difference in biological diversity among the stands.Canonical correspondence analysis(CCA)was used to investigate the environment factors affecting such differences in biodiversity of the stands.The results showed a high diversity of trees in the forest as 197 species,144 genera,and 62 plant families were recorded.The CCA ordination identified the environmental factors—the most important of which were elevation,distance to streams,soil moisture,organic matter,and distance to communities—that signifi-cantly influenced the diversity and distribution of tree species(p<0.05)in the community forest.Our findings indicate that the implementation of drought reduction measures such as building check dams,fire protection,and monitoring community forest-product usage would be recommended to further biodiversity conservation and the sustainable use of community forest resources.

Spatial variation of plant species richness in a sand dune field of northeastern Inner Mongolia, China

Species richness is an important indicator of species diversity. Different sampling intensities will very likely produce different species richness values. Substantial efforts have already been made to explicitly quantify the spatial variability of soil properties in different ecosystems. However, concerns still remain on how to characterize the effect of different sampling intensities on plant species richness within a given region. This study characterized the spatial variability of plant species richness and the species distribution pattern in a 25-hm2 sand dune plot in northeastern Inner Mongolia, China by using an intense sampling method（n=10,000）. We also evaluated the overall effect of information loss associated with the spatial variability and distribution patterns of species richness under various scenarios of sampling intensities（n=10,000 to 289）. Our results showed that semi-variograms of species richness were best described by the spherical and exponential models. As indicated by the nugget/sill ratio, species richness was different in terms of the strength of the spatial relationship. The different spatial metrics of species richness with increasing sampling intensities can represent different responses of the spatial patterns when compared with the reference set（n=10,000）. This study indicated that an appropriate sampling intensity should be taken into account in field samplings for evaluating species biodiversity properly. A sampling intensity of n＆gt;2,500 for species richness yielded satisfactory results to resemble the spatial pattern of the above-quantified reference set（n=10,000） in this sand dune region of China.

Effects of grassland management on the community structure, aboveground biomass and stability of a temperate steppe in Inner Mongolia, China

Plant community structure responds strongly to anthropogenic disturbances, which greatly influence community stability. The changes in community structure, aboveground biomass（AGB）, biodiversity and community stability associated with different management practices were studied with a three-year field investigation in a temperate steppe of Inner Mongolia, China. The species richness, Shannon-Wiener index, evenness, plant functional type abundance, AGB, temporal community stability, summed covariance, scaling coefficient and dominant species stability were compared among areas subjected to long-term reservation（R）, long-term grazing（G）, mowing since enclosure in 2008（M） and grazing enclosure since 2008（E）. Site R had higher perennial grass abundance and lower species richness than sites G, M and E, although the AGB was not significantly different among the four sites. The species structure varied from a single dominant species at site R to multiple dominant species at sites G, M and E. The long-term reservation grassland had lower biodiversity but higher stability, whereas the enclosed grassland with/without mowing had higher biodiversity but lower stability. Different stability mechanisms, such as the compensatory dynamics, mean-variance scaling and dominant species stability were examined. Results showed that community stability was most closely related to the relative stability of the dominant species, which supports the biomass ratio hypothesis proposed by Grime.