Environmental modulation of competition effects on intra-seasonal radial growth in planted larch forests of north China

Abstract

Competition and hydrothermal conditions jointly regulate tree growth, yet competitive effects are commonly assumed to be temporally constant and are usually assessed at annual scales. Such approaches may obscure periods within the growing season when competition becomes growth-limiting under specific environmental conditions. Using high-frequency dendrometer measurements, we examined whether competition effects on intra-seasonal radial growth depend on short-term hydrothermal variability in planted Larix principis-rupprechtii forests of northern China. Daily irreversible radial growth (GRO daily ) was extracted from 15-min stem radius series using the zero-growth concept. A distance-dependent competition index was incorporated into linear mixed-effects models with cluster-robust inference to quantify how competition interacted with standardized daily air temperature and soil moisture to influence GRO daily . Temperature and soil moisture were both negatively associated with daily irreversible radial growth at the intra-seasonal scale, whereas the main effect of competition was not statistically significant. However, a significant three-way interaction indicated that the magnitude of competition effects varied jointly with temperature and soil moisture. Conditional effect analyses showed that competition effects were strongest under cool and dry conditions and became weaker under relatively warm and dry conditions. Under relatively moist conditions, competition effects were comparatively weak. This pattern indicates that temperature further modulated the magnitude of competition effects under low soil moisture. The low-soil-moisture conditions in which competition effects were significantly negative accounted for approximately 55% of the growing-season days. These results demonstrate that competition-induced growth limitation exhibits pronounced intra-seasonal variability and is strongly modulated by short-term hydroclimatic variability, highlighting the need to explicitly represent environment-dependent competition in climate–growth assessments.