Species-area relationship within and across functional groups at alpine grasslands on the northern Tibetan Plateau, China

The species-area relationship (SAR) is one of the most fundamental concepts in community ecology and is helpful for biodiversity conservation. However, few studies have systematically addressed this topic for different alpine grassland types on the Tibetan Plateau, China. We explored whether the plant composition of different functional groups affects the manner in which species richness increases with increasing area at scales ≤ 1.0 m2. We also compared species richness (S) within and across forbs, legumes, sedges and grasses, with sampling subplot area (A) increasing from 0.0625 m2 to 1.0 m2 between alpine meadow and steppe communities. We applied a logarithmic function (S = b0 + b1 ln A) to determine the slope and intercept of SAR curves within and across functional groups. The results showed that the logarithmic relationship holds true between species richness and sampling area at these small scales. Both the intercept and slope of the logarithmic forbs-area curves are significantly higher than those for the three other functional groups (P < 0.05). Forb accounts for about 91.9 % of the variation in the intercept and 75.0% of the variation in the slope of the SAR curve when all functional groups’ data were pooled together. Our results indicated that the different SAR patterns should be linked with species dispersal capabilities, environmental filtering, and life form composition within alpine grassland communities. Further studies on the relationship between species diversity and ecosystem functions should specify the differential responses of different functional groups to variations in climate and anthropogenic disturbances.