Satellite evidence of canopy-height dependence of forest drought resistance in southwestern China

Abstract

The frequency and intensity of drought events are increasing with warming climate, which has resulted in worldwide forest mortality. Previous studies have reached a general consensus on the size-dependency of forest resistance to drought, but further understanding at a local scale remains ambiguous with conflicting evidence. In this study, we assessed the impact of canopy height on forest drought resistance in the broadleaf deciduous forest of southwestern China for the 2010 extreme drought event using linear regression and a random forest (RF) model. Drought condition was quantified with standardized precipitation evapotranspiration index (SPEI) and drought resistance was measured with the ratio of normalized difference vegetation index during (i.e. 2010) and before (i.e. 2009) the drought. At the regional scale we found that (a) drought resistance of taller canopies (30 m and up) declined drastically more than that of canopies with lower height under extreme drought (SPEI < −2); (b) RF model showed that the importance of canopy height increased from 17.08% to 20.05% with the increase of drought intensities from no drought to extreme drought. Our results suggest that canopy structure plays a significant role in forest resistance to extreme drought, which has a broad range of implications in forest modeling and resource management.

Keywords

• forest resistance
• severe drought
• canopy height
• remote sensing
• SPEI
• NDVI