Relationships between invasive alien grasses and native plants across different national nature reserves, Yunnan Province.
To examine the distribution of invasive alien grasses and the relationship between native and invasive alien grass richnesses, six national nature reserves located in Yunnan Province, one of biodiversity hotspots, were selected as study areas. Eighty-two subplots (1 m2) in 78 plots (100 m2) were investigated for the richness, abundance and cover of plant species in the six national nature reserves. The relationships between the richness and density of native and invasive alien grasses were compared among different nature reserves. The factors influencing the richness in different nature reserves were also analyzed. Twenty-two invasive alien grasses were found in the six national nature reserves, and 14 invasive alien species were distributed in the Nabanhe River Basin National Nature Reserve, but only two invasive alien species were distributed in the Jinping Watershed National Nature Reserve. At the one-square-meter scale, postive and negative relationships of the species richness and density between native and invasive alien grasses were found in the six national nature reserves. With increasing richness of native grass, the richness of invasive alien grass significantly decreased in Ailao Mountain National Nature Reserve, but no significant correlations trends were found in other nature reserves. The results of simple linear regressions showed that alien grass richness in different national natural reserves was negatively correlated with the native grass richness, cover of native grass and the species richness of native trees and shrubs. The results of multiple regression showed that the variance of invasive alien grass richness was mainly explained by the richness of native trees and shrubs, and the longitude and latitude.