Investigation of the relationship between treeline migration and changes in temperature and precipitation for the northern hemisphere and sub-regions

Purpose of Review: Numerous studies have reported that treelines are moving to higher elevations and latitudes over the last few decades. Climate change is assumed to be the main driver behind the observed migration of treelines. Predicting how treelines are likely to move in the future is important to identify impacts on sensitive high-alpine ecosystems and help model potential climatic feedback mechanisms associated with the expansion of alpine and arctic forests. Recent Findings: Here, we examine the correlation between treeline movements and recent climate change to better understand the drivers of treeline migration. Changes in monthly minimum and maximum temperature and precipitation between 1961 and 1970 and 2009 and 2018 for 256 treeline sites in the Northern Hemisphere were analysed through logistic regression modelling. The model was run at various spatial scales to assess if globally significant climatic drivers are applicable at regional scales. Summary: Our analysis revealed that the rate of temperature change during the northern hemisphere autumn, particularly in October, was a significant predictor of treeline movement. At the end of the growing season, increased minimum temperatures corresponded with treeline migration. At warmer maximum summer temperatures, treelines were more likely to remain stationary. While statistically significant correlations were identified at global scales, there were also substantial regional correlations of treeline movement regarding warmer temperatures. Changes in precipitation correlated with treeline migration were not statistically significant. Continued warming is likely to further extend the growing season for alpine forests, promoting continued encroachment of forests into alpine grassland and tundra in areas where moisture availability does not present a limiting factor for tree survival.