Grazing Effects on Seedling Emergence in Contrasting Wet and Dry Year in a Semiarid Grassland

Abstract

Seedlings are a crucial part of the plant community and the basis of vegetation restoration and regeneration. Grazing and climate change are two main factors contributing to vegetation changes in semiarid grasslands. However, the effects of grazing on seedling emergence with rainfall variation are not clearly understood. This study aimed to address how seedling abundance and the emergence dynamics of annuals respond to grazing with rainfall changes in different years. We conducted a seedling investigation experiment in a grassland along a grazing intensity gradient (light grazing—LG; moderate grazing—MG; heavy grazing—HG) in contrasting wet and dry years. The results showed that MG increased the seedling richness of grasses and forbs in the wet year, but increasing grazing resulted in a decline in forb richness in the dry year. Seedling abundance of grasses was enhanced under MG, while seedling abundance of forbs was higher under HG. The monthly emergence dynamics were generally in a single peak pattern, but the peak time of seedling emergence for forbs advanced under HG. Seedling abundance of whole annuals increased with grazing in the wet year but was much higher under MG in the dry year. Our results suggest that more judicious grazing management based on rainfall variation and functional composition of the plant community should be undertaken to facilitate grassland restoration.