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A collaborative study by researchers from The Chinese University of Hong Kong (CUHK) and the University of Illinois Urbana-Champaign has revealed that vegetation recovery following sudden permafrost collapse varies dramatically across regions, ranging from less than a decade to over a century. The study identifies gross primary productivity – a measure of plants’ photosynthetic capacity – as the key factor determining how quickly affected landscapes regain their greenness, and allows scientists to accurately predict how long it will take a specific site to recover after a permafrost collapse. The findings have been published in leading journal Nature Climate Change.

The study was co-led by Professor Liu Lin of CUHK’s Department of Earth and Environmental Sciences, Professor Mark Lara, a professor of plant biology at the University of Illinois Urbana-Champaign, and his postdoctoral researcher Dr Summer Xia Zhuoxuan, who is also a PhD graduate of CUHK.

The research focuses on a phenomenon known as retrogressive thaw slumps, a form of abrupt permafrost collapse triggered when large volumes of ground ice melt, destabilising frozen terrain. These landslide-like events can affect extensive areas, uprooting vegetation and releasing stored soil organic carbon into the environment.

“Thaw slumps fundamentally reshape Arctic and high-mountain landscapes,” said Professor Liu. “Understanding how vegetation recovers after these disturbances is crucial to predict long-term ecosystem changes and their implications for the global carbon cycle.” Abrupt thaw features like thaw slumps currently affect about 5% of the global permafrost, amounting to roughly 905,000 square kilometres of territory.

The research team believes that understanding how plants reestablish themselves in areas degraded by thaw slumps can help scientists make better predictions about how these events may affect carbon cycling and contribute to or even mitigate the negative effects of climate change.

Tracking vegetation greenness across Arctic and high-mountain regions

Using decades of satellite observations combined with uncrewed aerial surveys, the study analysed vegetation recovery across eight permafrost regions in Alaska, northern and northwestern Canada, Siberia and the Qinghai-Tibet Plateau. By tracking changes in surface greenness, the team reconstructed recovery timelines following thaw-slump events. The study covers both Arctic and high-elevation regions, which allows the research team to compare how recovery processes differ across climatic and ecological conditions.

It found that areas affected by thaw slumps in higher Arctic latitudes and high-elevation regions took much longer to recover their surface greenness than those in the lower Arctic latitudes. “Low-Arctic regions can regain vegetation cover within about 10 years, while high-Arctic and high-altitude regions may require from several decades to more than 100 years,” said Dr Xia. The recovery time was closely linked to a site’s gross primary productivity, enabling scientists to predict how long vegetation recovery is likely to take following a collapse. The team validated its model using additional permafrost sites and found particularly high predictive accuracy in more productive regions.

While vegetation may recover in appearance, the researchers note that plant composition and diversity often change and are unlikely to quickly go back to their original state. Fast-growing, woody plants (if present), tend to colonise disturbed areas quickly, helping stabilise soil and potentially enhancing carbon uptake.

“The plants can’t uptake the amount of carbon that we’re releasing from permafrost as it warms and thaws. But plants might be able to offset some of that loss,” added Professor Lara.

Professor Liu was among the first cohort of Hong Kong scientists to join China’s Scientific Expedition to Antarctica. Alongside colleagues and students from CUHK’s Department of Earth and Environmental Sciences and the School of Life Sciences who have conducted expeditions to both the Arctic and Antarctica, he is helping to drive a dynamic new polar research initiative led by the University. Looking ahead, Professor Liu is collaborating with environmental chemists, life scientists, and robotics engineers at CUHK in an interdisciplinary effort to comprehensively study polar environmental responses to climate change.

The study was supported by funding from the Research Grants Council of the Hong Kong Special Administrative Region of the People’s Republic of China, the National Key Research and Development Program of China, the Guangdong Science and Technology Department, the CUHK Resource Allocation Committee, and US funding agencies.