Researchers from the Institute of Applied Ecology, Chinese Academy of Sciences (CAS), have revealed the mechanism underlying the dieback of natural Mongolian pine (Pinus sylvestris var. mongolica) forests on sandy land. Their findings, titled “Anthropogenic fire suppression and climate change-driven winter warming inducing the dieback of natural Pinus sylvestris var. mongolica forests on sandy land” were published in Forest Ecology and Management.

Natural Mongolian pine distributed in Hulunbuir sandy land near the Greater Khingan Mountains of China, exhibits remarkable ecological adaptations to extreme conditions, which make it a keystone species for establishing windbreak and sand-fixation forests in arid and semi-arid regions. However, widespread dieback of natural Mongolian pine forests has occurred since 2018, raising concerns about their sustainability in afforestation programs.

Led by Professor Zhu Jiaojun, the research team hypothesized that this dieback is driven by two interrelated mechanisms, anthropogenic fire suppression disrupting the natural fire regime, and climate change-induced winter warming reducing snow cover duration and depth. To test these, the research team quantified dieback using Green Normalized Difference Vegetation Index (GNDVI) across stands with varying fire histories via UAV-based multispectral imagery, alongside long-term climatic observations (1960–2024) of temperature, precipitation, and snow dynamics from meteorological stations combined with remote sensing datasets.

The research team identified an abrupt change point in 2018 for both annual precipitation and mean temperature, coinciding with the natural Mongolian pine dieback. A significant negative linear relationship was found between GNDVI (forest health) and the last fire interval, indicating that prolonged fire exclusion exacerbates dieback, possibly through pathogen/pest accumulation. Winter temperature rose significantly during 1960–2023, with notable acceleration following an abrupt change point in 1987. Concurrently, winters during 2018–2023 exhibited pronounced warming, with snow cover duration reduced by 23 days and snow depth diminished by 7.6 cm. These conditions reduced snowmelt-derived soil moisture (critical water source) recharge in early spring, exacerbating drought stress during critical growth periods and predisposing trees to pest and disease infestations. Their findings supported both hypotheses, demonstrating that dieback was synergistically driven by fire regime alteration and climate-mediated snowpack reductions.

The researchers proposed some adaptive management strategies, such as planned and controlled low-intensity prescribed burning and converting pure pine forests into mixed pine-broadleaf forests via differentiated water sources, to restore ecological resilience in these vulnerable sandy ecosystems.

Figure 1. Long-term trends in (a) snow-cover duration and (b) snow depth in the Mongolian pine forest region (Image by SONG Lining).