Abstract:In order to understand the changes in species relationship of dominant species with sample scale, a typical wetland in the Poyang Lake region, the Nanji Wetland National Nature Reserve was selected as the study area, three belt transects with spacing interval 100 m were surveyed, which consisting of 2-3 sample plots (8 m×8 m in size) with sample spacing interval 80 m for each transect, eight sample plots in total. Each sample plot was divided into three sample unit scales with spatial sizes of 1 m×1 m, 2 m×2 m and 4 m×4 m. The methods of variance ratio test, χ2 test, Jaccard index were used to measure the change tendency of overall interspecies association and pair interspecies association for the community dominant plants with expansion of the sample unit scales. The results showed that Carex cinerascens, Cardamine lyrata, Artemisia selengensis, Mazus japonicus, Potentilla tanacetifolia, Triarrhena lutarioriparia, and Poa annua were dominant species according impotance value. With increase of sample unit scale, the changes in importance value of dominant species were not significant except of Carex cinerascens, which increased at first and then decreased. According to variance ratio test, there were no significant difference in overall interspecies association for the 21 species pairs from the seven dominant species, and which changed from negative association to positive association with the increment of the sample unit scale. From χ2 test, there was no significant difference in species-species association for most of the 21 species pairs at the three sample unit scales. With enlargement of sample unit sizes, the number of species pairs with significant association dropped down and that with positive association stepped up gradually. According to Jaccard index, the degree of species pair association enhanced continuously with increment of sample unit scales. Therefore, it was caused that there were many plant species with low occurrence frequency, the resources distribution variation within plant communities at different sample scales and the competition/cooperation relations between plant species in the study area.
