Diverse responses of forest growth to drought time-scales in the Northern Hemisphere

Abstract

Aim: To identify the main spatiotemporal patterns of tree growth responses to different time-scales of drought at a hemispheric scale using a climate drought index and tree-ring records, and to determine whether those patterns are driven by different climate and forest features. Location: Northern Hemisphere. Methods: We used a large-scale dendrochronological data set of tree-ring width series from 1657 sites and a time-dependent drought index which incorporates information on precipitation and temperature variability (standardized precipitation-evapotranspiration index, SPEI). Correlation analysis was used to quantify how tree growth responds to different drought time-scales. Variation in the correlations was summarized using principal components analysis (PCA) and the contribution of the various environmental factors was estimated using predictive discriminant analysis (PDA). Results: The period between the water shortage and the impact on tree growth differs noticeably among forest types and tree families. There is a gradient in the response of growth to drought including: (1) forests that do not respond to drought, such as those located in cold and very humid areas; (2) forests located in semi-arid areas characterized by responses to long-term droughts; (3) forests that respond to medium- to long-term droughts subjected to subhumid conditions; and (4) forests that dominate humid sites and respond to short-term droughts. Main conclusion: Forests that experience semi-arid and subhumid conditions tend to respond over longer time-scales than those located in more humid areas. The characteristic time-scale at which forest growth mainly responds to drought is a proxy for drought vulnerability, reflecting the trees' ability to cope with water deficits of different durations and severities. © 2014 John Wiley & Sons Ltd.