Climate-induced tree-mortality pulses are obscured by broad-scale and long-term greening

Yuchao Yan; Shilong Piao; William M Hammond; Anping Chen; Songbai Hong; Hao Xu; Seth M Munson; Ranga B Myneni; Craig D Allen

doi:10.1038/s41559-024-02372-1

Climate-induced tree-mortality pulses are obscured by broad-scale and long-term greening

Nat Ecol Evol. 2024 Mar 11. doi: 10.1038/s41559-024-02372-1. Online ahead of print.

Authors

Yuchao Yan¹, Shilong Piao^{2

3}, William M Hammond⁴, Anping Chen⁵, Songbai Hong¹, Hao Xu¹, Seth M Munson⁶, Ranga B Myneni⁷, Craig D Allen⁸

Affiliations

¹ Institute of Carbon Neutrality, Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing, China.
² Institute of Carbon Neutrality, Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing, China. slpiao@pku.edu.cn.
³ State Key Laboratory of Tibetan Plateau Earth System, Resources and Environment, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China. slpiao@pku.edu.cn.
⁴ Institute of Food and Agricultural Sciences, Agronomy Department, University of Florida, Gainesville, FL, USA.
⁵ Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, USA. anping.chen@colostate.edu.
⁶ U.S. Geological Survey, Southwest Biological Science Center, Flagstaff, AZ, USA.
⁷ Department of Earth and Environment, Boston University, Boston, MA, USA.
⁸ Department of Geography and Environmental Studies, University of New Mexico, Albuquerque, NM, USA.

PMID: 38467712
DOI: 10.1038/s41559-024-02372-1

Abstract

Vegetation greening has been suggested to be a dominant trend over recent decades, but severe pulses of tree mortality in forests after droughts and heatwaves have also been extensively reported. These observations raise the question of to what extent the observed severe pulses of tree mortality induced by climate could affect overall vegetation greenness across spatial grains and temporal extents. To address this issue, here we analyse three satellite-based datasets of detrended growing-season normalized difference vegetation index (NDVI_GS) with spatial resolutions ranging from 30 m to 8 km for 1,303 field-documented sites experiencing severe drought- or heat-induced tree-mortality events around the globe. We find that severe tree-mortality events have distinctive but localized imprints on vegetation greenness over annual timescales, which are obscured by broad-scale and long-term greening. Specifically, although anomalies in NDVI_GS (ΔNDVI) are negative during tree-mortality years, this reduction diminishes at coarser spatial resolutions (that is, 250 m and 8 km). Notably, tree-mortality-induced reductions in NDVI_GS (|ΔNDVI|) at 30-m resolution are negatively related to native plant species richness and forest height, whereas topographic heterogeneity is the major factor affecting ΔNDVI differences across various spatial grain sizes. Over time periods of a decade or longer, greening consistently dominates all spatial resolutions. The findings underscore the fundamental importance of spatio-temporal scales for cohesively understanding the effects of climate change on forest productivity and tree mortality under both gradual and abrupt changes.