High water demand limits carbon sink and transpiration in tall forests during extreme drought in Southwest China

Drought-related forest mortality or dieback is increasing with climate warming. Previous studies have showed canopy height was one of the most important factors that related to forest survival and growth under drought, but the mechanism of this canopy height-dependency is still unclear. Based on standardized precipitation evapotranspiration index (SPEI) data, gross primary productivity (GPP) data and vegetation transpiration data, we use linear regression (LR) and random forest (RF) model to explored the impact of canopy height on forest carbon and water cycle in southwestern China for the 2010 extreme drought. Regardless of forest types, the results showed that the decline of GPP and transpiration were not only related to drought intensity but also depend on canopy height. Tall forest (> 30 m) would lose more GPP and transpiration than short forest (< 20 m), and the increasing drought intensities would improve this canopy height-dependency, especially under extreme drought condition (SPEI < −2). Regarding how canopy height affects forest water cycle, the canopy height has correlation with both SPEI and transpiration (p < 0.001) which mean tall forest needs more water to maintain growth. These results explore the reason why forest drought resistance distinguishing by canopy height, which may have a broad range implication in forest dynamics research and management.