Pre-monsoon precipitation dominates the tree radial growth of Picea smithiana in the western Nepal Himalayas

Abstract

High mountain forest ecosystems provide valuable insights into the impacts of climate and atmospheric changes on tree growth, forest dynamics, ecosystem functioning, species composition, carbon cycling, and hydrological processes, as these regions are experiencing higher rates of warming and are particularly sensitive to climatic variations. The diverse bioclimatic environments and elevation-driven gradients in temperature and precipitation in these ecosystems make them ideal natural laboratories for studying how trees respond to a changing climate. The present study analyzed the growth-climate variability of Picea smithiana along an elevation (2800–3200 m) and two aspects (north and south) in Rara National Park (RNP), western, Nepal. Altogether, four chronologies of high-elevation P. smithiana were developed, with the oldest chronology spanning 148 years from 1873 to 2021 AD. Tree-growth at both higher and lower elevations on south and north aspects showed a significant negative correlation (p < 0.05) with maximum temperature (Tmax) in March and April while a significant positive correlation (p < 0.05) was found with precipitation of same month. Tree-growth at the lower elevation of south-east aspects (SE 3000 m) exhibited significant negative relationships with Tmax in previous year August (pAug) (r = − 0.31, p < 0.05), November (pNov) (r = − 0.37, p < 0.05), and December (pDec) (r = − 0.40, p < 0.05). Tree-growth of P. smithiana showed positive associations with scPDSI, with variation along elevation and aspect gradients. The strength of scPDSI effects were more pronounced at lower elevations and on south-east aspects compared to higher elevations and north-east aspects, highlighting the critical role of soil moisture availability for radial growth during the growing season. Seasonal and moving correlation analyses of growth-climate relationships also revealed a persistent response of tree-growth to spring (March) temperatures, points towards variations in tree growth with reduced or slow growth rates. The results offer a better understanding of the impacts of climatic change on species distribution ranges, which is essential for formulating effective forest management and conservation strategies against the adverse effects of climate change. The observed elevation and aspect-specific growth responses further indicate that continued warming and moisture stress may substantially alter the distribution patterns and growth dynamics of P. smithiana in the future.