Contrasting growth responses in Himalayan trees to future climate

Rising temperatures and shifting regional precipitation patterns are exerting significant impact on tree growth in the Himalayan region. Despite growing concern about global warming, the regional- and species-specific growth responses to future climate scenarios remain poorly quantified across the two contrasting precipitation regimes (Eastern-monsoon vs Western-westerly) of the Himalaya. We analyzed 3370 time series of tree-ring width data of 14 dominant tree species in the Himalaya occurring between 1750 and 4100 m of elevation covering a large longitudinal monsoon-related environmental gradient. With Linear Mixed Models (LMMs), we predicted Basal Area Increment (BAI) trends for different temperature and precipitation changes under four representative concertation pathways (RCP 2.6, 4.5, 6.0 and 8.5). Results show contrasting patterns: in the Eastern region, species such as Cedrus deodara and Pinus roxburghii are projected to decline by 23-67 % in BAI by the end of the 21th century under all the climate scenarios due to warming-induced moisture stress. Conversely, in the Western region, species like Picea smithiana and Pinus wallichiana shows projected gain in BAI up 100 % likely due to enhanced winter and spring precipitation from westerlies. Likely increased forest carbon sequestration in selected species in the Western region highlights the importance of spatially targeted climate informed forest management. Our results evidence the need for conservation strategies in the Eastern region, while adaptive management should be considered in the Western region to maintain Himalayan forest resilience and sustainability in the face of future warming.