Non-linear effect of habitat fragmentation on plant diversity: Evidence from a sand dune field in a desertified grassland in northeastern China

Although a large number of empirical studies have documented the effect of habitat fragmentation on plant diversity, we are far from being able to draw effective conclusions due to a lack of a proper reference point and a large range of patch size. This study aims to test the hypothesis that the effect of habitat fragmentation on plant diversity is non-linear, i.e. there is a shift in the effect of habitat fragmentation on plant diversity from positive to negative (or from negative to positive) with intensifying fragmentation. A sand dune field in a desertified grassland in eastern Inner Mongolia, China, was used as the study site. Eighteen fragmented plots (inter-dune lowlands in the sand dune) and 14 continuous plots (different sizes of grassland) were selected. Plant diversity was estimated by species richness, functional groups and rare species. Logarithmic, power and exponential functions were used to analyze the relationship of species richness, frequency and abundance and plot area. There was a shift from positive to negative in the relationship between habitat fragmentation and species richness with the intensifying fragmentation. The number of plant functional groups increased due to habitat fragmentation, and different functional groups showed distinct responses to the degree of fragmentation. The effect of habitat fragmentation on rare species richness is non-linear, and the effect of habitat fragmentation on rare species population is negative. Our results indicate: (1) thresholds should be taken into consideration when drawing up plant diversity conservation plans; and (2) a single large reserve and several small reserves have different implications in plant diversity conservation.