Climate change – 83 percent of tree species under pressure from human activities

According to a global study of more than 46,000 tree species, about 83 percent are under pressure from human activities, and 15 percent are under severe to very severe pressure. As the international research team, which includes Peter Hietz ​​from BOKU, reports in the journal “PNAS”, half of the distribution area of ​​certain tree species is located in landscapes without protection status. One in seven grows exclusively in unprotected regions.

About 64,000 species of trees are already known. Another 9,000 are still growing incognito in forests around the world, according to a study published earlier this year in the journal PNAS involving scientists from the International Institute for Applied Systems Analysis (IIASA) in Laxenburg near Vienna.

In the current publication, researchers led by Jens-Christian Svenning of Aarhus University analyzed a database of 46,752 tree species and calculated their geographic distribution (in 110-kilometer grid cells). They combined this with a global map showing how intensely human activities affect nature, as well as information on more than 200,000 protected areas around the world.

Every seventh tree species grows in unprotected areas

Accordingly, 50.2 percent of the distribution area of ​​certain tree species is located in landscapes without protection. A total of 6,377 (13.6 percent) with very limited distribution are completely unprotected.

On average, 14.8 percent of the studied tree species are exposed to high or very high human pressure, 68.5 percent are under moderate pressure – a total of about 83 percent. Only 17 percent of species are not stressed by human activity.

The researchers emphasize that this data can now be used to calculate where it is most important to preserve or restore natural areas in order to effectively protect biodiversity. They also calculated the most suitable locations for potential protected areas to preserve diversity.

“We did this not only with regard to the number of species, but also their evolutionary and functional differences, i.e. we distinguished three categories of biodiversity”, emphasized Peter Hietz ​​​​from the Department of Integrative Biology and Biodiversity Research at the University of Natural Resources and Life Sciences ( BOKU) Vienna APA. It is not only about protecting individual species, but also about protecting functional and phylogenetic diversity.

Functional diversity is beneficial

“Ten species of trees that all have very similar properties are ten different species, but the diversity of their functions, such as how they respond to the environment and what adaptation mechanisms they have, is relatively low,” says Hietz. On the other hand, in view of global changes, the advantage is the greatest possible functional diversity with many different functions and strategies.

Phylogenetic diversity primarily refers to how closely related species are. “There are about 500 oak species. If one of them goes extinct, it’s less severe in terms of genetic diversity than if the only extant ginkgo species goes extinct, which has no living relatives far away and has a lot of genes that don’t exist anywhere else,” Hietz ​​said.

In another paper in which Hietz ​​was involved, published in the journal Nature Communications, an international team of researchers analyzed the characteristics of about 50,000 tree species. They have created what they claim is the largest database of leaf, seed, bark, wood, canopy and root properties, among others.

The aim was to identify patterns in tree characteristics, for example which often occur together and how they influence each other. “You can see obvious reciprocal relationships, for example that tree height is related to crown diameter, but also less obvious ones, for example that nitrogen content is more related to leaf thickness than phosphorus,” says Hietz.

All this is important in relation to climate change: “If you put the results in relation to climate parameters such as precipitation or temperature, you can tell from easily measurable characteristics how the spectrum of tree species with certain functional properties will shift when climate changes to this or that way,” Hietz ​​said. It can also be used to identify which tree species are better adapted to drought and the increasing number of wildfires. (apa)

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