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Many tree species are moving to colder and wetter regions

Climate change is likely to push tree species toward the colder and wetter parts of their geographical distribution, according to new research led by the University of Alcalá (UAH) in Spain. 

The study, published in the Proceedings of the National Academy of Sciences (PNAS), provides the first quantitative evidence that climate change is causing this shift in tree density across temperate forests on a continental scale.

“Although climate change is expected to drive tree species toward colder and wetter regions of their distribution, broadscale empirical evidence is lacking,” noted the study authors. “One possibility is that past and present human activities in forests obscure or alter the effects of climate.”

Most tree species can acclimate

The researchers analyzed data from over two million trees, representing 73 species widely distributed across Europe and the United States. 

They explored whether changes in tree density could be attributed to specific characteristics of each species, such as tolerance to arid conditions or dispersal capacity. However, the study did not identify any single trait as decisive for these changes.

“This lack of a definitive trait suggests that most species possess a degree of acclimation capability,” said lead author Julen Astigarraga, a postdoctoral fellow at UAH.

Tree species used for ecosystem restoration 

Understanding how forest species respond to climate change by increasing their density in more northerly regions is crucial for planning ecosystem conservation, management, and restoration. 

“Some tree species which are currently used for ecosystem restoration in Europe may no longer be suitable in these regions in the near future,” said co-author Thomas Pugh, a climate scientist at the University of Birmingham and Lund University. 

“In addition, massive reforestation programs planned as a solution for capturing and storing carbon dioxide from the atmosphere might be limited in their effectiveness if they do not account for these responses.”

International collaboration 

The study represented a significant international collaboration, involving scientists from 12 countries and data analysis from more than 125,000 forest plots across Europe and North America. 

“This study required a significant international effort to pull together and harmonize data from many different sources. The data from these forest inventories is crucial for advancing our understanding of forest dynamics and their resilience to climate change,” explained co-author Adriane Esquivel Muelbert, an expert in forest ecology at Birmingham.

These findings underscore the importance of considering climate-driven changes in tree species distribution when developing strategies for ecosystem restoration and reforestation.


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