Late spring-early summer drought and soil properties jointly modulate two pine species' decline and climatic sensitivity in temperate Northern China

Abstract

Increasing temperatures and severe droughts threaten forest vitality globally. Prediction of forest response to climate change requires knowledge of the spatiotemporal patterns of monthly or seasonal climatic impacts on the growth of tree species, likely driven by local climatic aridity, climate trends, edaphic conditions, and the climatic adaption of tree species. The ability of tree species to cope with changing climate and the effects of environmental variables on growth trends and growth-climate relationships across diverse bioclimatic regions are still poorly understood for many species. This study investigated radial growth trends, interannual growth variability, and growth-climate sensitivity of two dominant tree species, Pinus tabulaeformis (PT) and Pinus sylvestris var. mongolica (PS), across a broad climatic gradient with a variety of soil properties in temperate Northern China. Using a network of 83 tree ring chronologies (54 for PT and 29 for PS) from 1971 to 2010, we documented that both species maintained constant growth trends at wet sites, while both displayed rapid declines at dry sites. We reported the species-specific drivers of spatial heterogeneity in growth trends, interannual growth variability, and growth-climate relationships. Calculated climatic variables and soil properties were identified as the most critical factors affecting the growth trends and growth-climate relationships. However, climatic variables play more essential roles than soil properties in determining the spatial heterogeneity of the growth-climate relationship. Lower clay content and higher soil nutrient regimes can exacerbate the moisture-related susceptibility of tree growth. Our findings highlight that soil properties emerged as important modulating factors to predict the drought vulnerability of forests in addition to climatic variables. Considering the continued climate warming-drying trend in the future, both pines will face a more severe growth decline and increase in drought vulnerability at drier sites with lower clayed soil or higher nutrient regimes.