Impact of climate on individual tree radial growth based on generalized additive model

The generalized additive model (GAM) was used to investigate the effects of climate on individual tree radial growth and tree species' responses to climate. The data was collected from long-term permanent plots of larch-spruce-fir forests repeatedly measured for 25 years in Wangqing Forestry Bureau, Jilin Province of northeastern China. Our results showed that accumulated temperature in growing season, mean minimum temperature during growing season, annual total precipitation, mean temperature difference between the coldest and warmest months and the ratio of annual temperature and annual total precipitation significantly explained the variation in radial growth, but varied in the response variables and magnitude of different tree species (larch, spruce, fir, Korean pine and two hardwood groups). The full model, reduced model 1 (stand variables) and 2 (climate variables) could explain 50.8%, 45.7% and 29.5% of the variation in radial growth, respectively. It is concluded that climate has limited capacity in explaining the variation in radial growth, while the size, competition among individuals and stand density are the main drivers to radial growth on the local scale.