An international study jointly led by researchers from the Department of Geography and the Institute for Climate and Carbon Neutrality at the Faculty of Social Sciences, The University of Hong Kong (HKU), has revealed that vegetation resilience across Northern Hemisphere permafrost regions underwent a widespread reversal around 2008, declining broadly despite continued greening. The findings, published in the prestigious international academic journal Nature Plants, highlight emerging vulnerabilities in high-latitude ecosystems driven by atmospheric drying and climate extremes.
Permafrost regions - often termed the "frozen heartlands" of our planet - are warming rapidly, triggering profound ecological and biogeochemical shifts. Previous satellite observations have documented widespread "greening" across the Arctic and boreal ecosystems. However, whether this greening translates to greater ecosystem stability - specifically the capacity to withstand and recover from environmental disturbances (resilience) - has remained unclear.
To address this critical knowledge gap, the research team led by Professor Yuyu Zhou of HKU, with first author Dr. Zhengfei Guo and co-corresponding author Dr. Jian Wang of the Chinese Academy of Sciences, analysed MODIS satellite observations from 2000 to 2023. Using a trend-, seasonality- and climate-adjusted analytical framework, the team assessed vegetation resilience through the temporal autocorrelation (TAC) of a satellite-derived vegetation index (kNDVI). They also employed interpretable artificial intelligence-based machine learning methods to identify environmental factors associated with resilience changes.
Key findings of the study include:
Widespread Reversal in Vegetation Resilience: Permafrost vegetation resilience (where higher TAC indicates slower recovery and lower resilience) showed a significant strengthening trend prior to 2008, followed by a widespread and pronounced reversal and decline thereafter. This shift was consistent across diverse vegetation types (needleleaf forests, shrublands, grasslands, etc.) and permafrost categories (continuous, discontinuous, sporadic, and isolated patches).
Greening Does Not Equal Greater Stability: Despite continued greening trends in leaf area index and vegetation indices, ecosystem resilience declined post-2008. This destabilisation was accompanied by a synchronised surge in the interannual variability of vegetation carbon uptake (gross primary productivity, GPP), indicating that permafrost ecosystems are losing their buffering capacity against environmental fluctuations.
Atmospheric Drying as a Key Associated Factor: Using interpretable machine learning (XGBoost combined with SHAP attribution analysis), the researchers identified climate variables as the dominant drivers of resilience variability. Vapour pressure deficit (VPD) - an indicator of atmospheric dryness - emerged as the strongest predictor associated with the post-2008 resilience decline. Analyses of moisture transport and ocean evaporation suggest that changes in oceanic moisture supply and atmospheric circulation contributed to the timing of this high-latitude drying.
Wildfire Amplification and Model Deficiencies: Acute disturbances such as wildfires substantially compounded resilience losses, with recurrent burns trapping ecosystems in arrested successional states. Crucially, an evaluation of 15 dynamic global vegetation models (DGVMs from the TRENDY v7 ensemble) revealed a major model-data discrepancy: most models failed to capture the observed resilience reversal, pointing to a critical underestimation of climate risks to northern carbon sinks in current Earth system projections.
"Our findings challenge the assumption that continued vegetation greening necessarily indicates healthier and more stable ecosystems," said Professor Yuyu Zhou. "Even as northern permafrost vegetation becomes greener, indicators of its ability to recover from environmental disturbances are declining. This widespread reversal is closely associated with intensifying atmospheric dryness, highlighting an emerging vulnerability of high-latitude ecosystems to climate change."
The study "Widespread reversal of vegetation resilience in permafrost ecosystems" was published in the leading journal Nature Plants.
Link to the paper: https://www.nature.com/articles/s41477-026-02462-x
About the research team:
This research was led by Professor Yuyu Zhou. Professor Yuyu Zhou: AAAS Fellow, Professor of the Department of Geography and the Institute for Climate and Carbon Neutrality, HKU, Director of Sustainable Cities Lab (SCL). The collaborative team includes Dr Zhengfei Guo, Postdoctoral Researcher, Department of Geography, HKU; Dr Jian Wang, the Chinese Academy of Sciences; Professor Taylor Smith, University of Potsdam; Dr Wenyu Li, University of Toronto; Professor Kun Zhang, Sun Yat-sen University; Professor Jin Wu, School of Biological Sciences, HKU; Professor Peng Gong, Chair Professor of Global Sustainability & Vice-President and Pro-Vice-Chancellor (Academic Development), HKU.
This study is supported by Research Grants Council-Strategic Topics Grant STG2/P-705/24-R, the University of Hong Kong HKU-100 Scholars Fund, and the HKU Social Sciences Internal Seed Grant Scheme, and.
About the SCL:
SUSTAINABLE CITIES LAB (SCL) aims to leverage geospatial and remote sensing big data and advanced interdisciplinary approaches including remote sensing, geographic information system, regional and global climate modelling, and integrated assessment modelling to understanding the problems of environmental change and their potential solutions for a sustainable environment. SCL lab's research focuses on six primary directions: (1) Urbanisation mapping & modelling; (2) Urban environmental changes; (3) Urban energy use and emissions; (4) Urban sustainability; (5) Water-energy-food nexus; (6) Climate change impacts, adaption, and vulnerability.
To promote knowledge exchange, more recent research activities can be viewed through https://www.scl.hku.hk/
