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Tree species diversity shaped by climate change for 21,000 years

A team of researchers led by Aarhus University in Denmark has recently conducted a global survey of 1,000 forest areas to examine the impact of climate change during the past 21,000 years on today’s diversity and distribution of tree species. Such an analysis could help scientists predict how ecosystems will react to future climatic changes and thus benefit conservation management.

By focusing on “beta diversity” – a measure of the variation of species between different habitats or areas that is helpful for understanding the diversity of life in a specific region or ecosystem by comparing the number and types of species present in different locations – the experts found that angiosperm tree species worldwide have been significantly affected by temperature changes since the peak of the last Ice Age about 21,000 years ago.

According to the scientists, climatic changes affected two different components of forests’ beta-diversity: turnover, referring to changes due to species replacement (such as when a species goes extinct and another one fills its ecological role); and nestedness, referring to a pattern in which the composition of species in a diverse habitat is a subset of the species composition in another, less diverse habitat, such that the more diverse habitat contains all the species found in the less diverse one, as well as several additional species.

While habitats with nested species compositions may have lower overall diversity, they may contain species not found in other habitats, thus making them essential for preserving overall diversity.

The investigation revealed that the greater temperature changes an area has experienced, the less turnover and the more nestedness have occurred, thus leading to the loss of a variety of local species that have not been replaced.

Moreover, while in tropical areas turnover was the leading factor in determining changes in species composition between habitats due to rapid species change, in temperate regions nestedness was the main mechanism for determining changes in species composition, since species richness declines as we get closer to the poles.

“Trees and tree diversity play crucial roles for terrestrial ecosystems, global biodiversity, and humans. This study confirms and extends our previous findings of the high sensitivity of tree diversity to paleoclimatic changes on a global scale. It also suggests that ongoing climate change has the potential to dramatically influence global biodiversity and ecosystem properties not just via direct effects, but also via its effects on trees as ecosystem engineers,” said co-author Jens-Christian Svenning, a professor of Ecology at Aarhus.

“I hope these findings can aid the development of conservation and management plans that consider the long-term and diverse impacts of climate change on all biodiversity dimensions. Only then is there a realistic chance that we will reach goal A of Kunming-Montreal’s Sustainable Development Goals for 2050,” concluded senior author Alejandro Ordonez, an expert in Global Change Biology at the same university.

The study is published in the journal Science Advances.

By Andrei Ionescu, Staff Writer


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