Does climate play a more important role than competition in modeling height to crown base of Larix principis-rupprechtii in northern China?

Abstract

Competition is the major factor influencing crown recession rates and therefore plays an important role in height to crown base (HCB) modeling. However, few studies have directly investigated the effects of climate on HCB modeling. In this study, a climate-sensitive individual tree HCB model was developed using measurements from a total of 9902 Rupprecht larch (Larix principis-rupprechtii Mayr) trees on 156 sample plots located in northern China. The impacts of tree height, inter-tree competition, site condition, and climate on HCB modeling were assessed using the mixed-effects modeling approach. Results showed that HCB increased with tree height and competition intensity. The inclusion of climate variables significantly improved model performance. HCB was negatively associated with mean temperature of the coldest month and positively associated with autumn precipitation averaged over the previous five years. According to hierarchical partitioning analysis, tree height is the most important factor affecting HCB (relative contribution 50.03%), followed by climate (22.51%), inter-tree competition (20.17%), and site condition (6.06%). Our findings highlighted the importance of considering regional climate differences in improving HCB predictions at a large spatial scale. Disentangling different sources of variations in HCB will help advance our understanding of the factors driving crown recession and reduce uncertainty in predicting crown characteristics under changing climates.