Effects of biotic and abiotic drivers on the growth rates of individual trees in temperate natural forests

Understanding the driving factors for individual tree growth is of great significance to devise effective forest management strategies. Such information can be used to select appropriate tree harvesting times, and to provide valuable guidance for creating suitable local environmental conditions during the period of tree growth. However, currently it remains unclear how biotic and abiotic factors affect individual tree growth on large geographical scales. In the present study, based on a dataset from 457 field plots and the growth records of 7,560 individual trees in natural forests in northeastern China, the effects of tree size, local environmental conditions, and regional climate characteristics on the 5-year basal area increment (BAI) of the three dominant species (Quercus mongolica, Betula platyphylla, and Larix gmelinii) were investigated using nonlinear mixed-effects models. Although the magnitude and direction of the drivers’ effects on the BAI differed among the three species, the following variables explained major proportions of the variation (conditional R2 ranging from 0.57 to 0.66) in the BAI: 1) Diameter at breast height; 2) Mean temperature and precipitation during the growing seasons; and 3) Species mingling and the basal areas of larger trees. In addition, an interactive effect between temperature and precipitation was significant for Q. mongolica. On the basis of our results, we identified the most important variables among multiple drivers affecting the growth of individual trees, and developed individual tree growth models for the three species. Our results provide an initial basis for the future scientific management of some of the most important natural forest regions in the world.