Species-specific determinants of mortality and recruitment in the forest-steppe ecotone of northeast China

Tree mortality is a notable phenomenon in the forest-steppe ecotone of China. However, the association between mortality and factors such as a changing climate is uncertain. In the summer of 2014 tree mortality was investigated in 20 400 m(2) plots to determine the species-specific determinants of mortality and their influence on subsequent species recruitment. Nine soil physical-chemical properties were examined in addition to slope position, mean DBH and total number of trees. Generalized linear models analyzed relationships between these variables and mortality and recruitment. Mortality was positively associated with increasing average diameter and negatively to high soil pH and total nitrogen content. Recruitment models indicate that Populus davidiana recruitment was positively affected by available phosphorus and mortality, and negatively related to mean DBH. Slope position was the most important contributing variable to Betula platyphylla recruitment. With Quercus mongolica recruitment, soil variables played an important role. These results suggest that tree mortality is affected by soil properties, topography and tree size in China's forest-steppe ecotone, and may improve our understanding of species mortality and contribute to improved forest management.