Fine-scale distribution of aboveground biomass of herbaceous vegetation and soil nutrients on an oceanic island after goat eradication are correlated with grazing damage and seabird nesting.

Abstract

We tested whether vegetation recovery on an oceanic island after the eradication of feral goats is related to disturbances by goats and recovery of seabird nesting in an island. To test, we investigated relationships among the aboveground biomass of herbaceous vegetation, nutrient concentrations in the soil after goat eradication, and vegetation degradation before goat eradication and seabird nesting after the eradication. The investigation was conducted on the island of Nakoudojima, a subtropical island situated in the northwestern Pacific Ocean with consideration of fine-scale variation of topography and structure of current vegetation. The aboveground biomass of herbaceous vegetation was correlated with the presence of vegetation degradation before goat eradication but not with seabird nesting after eradication. Concentrations of carbon and nitrogen in the soil were correlated with both the presence of vegetation degradation and seabird nesting. The concentration of available phosphorus in the soil was correlated with nesting seabirds but not with vegetation degradation. The presence of nesting seabirds was correlated with differences in dominant species in the vegetation after goat eradication and with topography. Our results suggested that fine-scale heterogeneities of the aboveground biomass of herbaceous vegetation and the concentrations of nutrients in the soil after goat eradication in an island could be related to vegetation degradation and subsequent erosion of surface soil caused by goats and seabird nesting after the goat eradication.