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2 Polish Journal of Ecology

2 2009

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Lu T., Ma K., Zhang Y., Ni H., Fu B.

Polish Journal of Ecology

2009

Vol. 57, nr 4

647-657

Disturbance is considered to be one of the main factors influencing variations in species diversity. While many experimental and observational studies provide a good understanding of how disturbance maintains the [alfa]-diversity, we know little about how disturbance influences [beta]-diversity, and the effects of disturbance intensity on spatial species turnover are lacking. The aim of this paper is to evaluate the effects of disturbance on patterns of species similarity in wetland communities, and to identify how disturbance intensity affects the species similarity - distance relationship. In our study, four isolated wetland remnants under different agricultural drainage ditch densities were surveyed in Sanjiang Plain, Northeast China. Wetland disturbance was assessed by agricultural ditch densities, and species similarity was quantified by the Jaccard index. A simple measure of environmental distance was obtained by using water level and five soil variables, and a corresponding measure of geographical distance was made between pairs of plots from each site. Based on these data, we estimated rates of distance decay through regression of log-transformed compositional similarity against both environmental and geographical distance for pair-wise comparisons of wetland plots from each site. One key finding of our research is that disturbance intensity does influence the species similarity - distance relationship. At each site, species similarity decreased significantly with distance, and both effects of geographical and environmental distance were statistically significant. The results indicate that with disturbance intensity increasing, the distance decay rate decreases.

Diversity and composition of wetland communities along an agricultural drainage ditch density gradient

Lu T., Ma K., Fu B., Zhang J., LU Q., Hudson S.

Polish Journal of Ecology

2009

Vol. 57, nr 1

113-123

Agricultural drainage ditches are a reflection of the disturbance caused by agriculture and other human perturbations associated with agricultural activities, and the density of them can be seen as an important gradient reflecting local disturbance. However, no studies to date have examined the changes in wetland communities in relation to drainage ditch densities, yet such information is urgently needed for the conservation of wetland ecosystems facing intensive cultivation. In this paper, we inventoried 67 plots at four wetland mosaics with the ditch density values ranged 0-3.6 km km[^-2] in the Sanjiang Plain, and the species richness, composition and diversity were compared among those four sites. Linear regression was used to explore relationships between wetland community pattern and agricultural ditch density, and the results show that there is significant relationship (r[^2] = 0.56, P <0.001). The diversity comparisons show that there exist a clear negative relationship between ditch density and species diversity indices, and the species diversity did not differ greatly among sites, but species composition varied considerably. With increasing ditch density, an increasing loss of indigenous wetland species paralleled with an increasing incursion of upland species. Management implication from the drainage ditches is that the density of 1.2 km km[^-2] be the maximum value suitable for the protection of native wetlands in Sanjiang plain.