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Decades of climate change in the mountains do not cause a shift in the tree line

Decades of climate change in the mountains are not shifting the treeline

View of the tree line at the Lefka Ori mountain range on the island of Crete. Credit: Dimitris Poursanidis.

Living conditions of high-altitude forests have changed significantly in recent decades as a result of climate change. In many mountain areas they have become more favorable above the tree line than in lower forested areas. However, climate change has not yet resulted in forests adapting directly to this change and shifting to higher elevations. This is confirmed by a new biogeographical study from the University of Bayreuth using the example of the Mediterranean island of Crete. The scientists present their research results in the journal Forest ecosystems† They warn of the possible consequences.

The comparison of climate data and archived aerial photographs from the years 1945 to 2015 shows that the trees in the Lefka Ori mountain range, the “White Mountains” of Crete, have been colonizing the same areas for decades – and this despite the fact that their living conditions are noticeably deteriorated as a result of the climate-induced temperature rise during this period.

“Our study shows that ecosystems do not always respond to climate change with the necessary adaptive measures to compensate for the deterioration of their site conditions. Even in many other regions of the world where the effects of global climate change are observable, there is no evidence that disadvantaged or even endangered montane forests move to higher altitudes as a result. The treeline shift expected in models often does not take place in practice. This makes it all the more important for politicians and society in general to respond to the associated dangers. Location in the Mediterranean region increases the risk of forest fires or drought damage in forests below the tree line This in turn weakens the ecologically important function of montane forests in carbon storage It can also exacerbate erosion In addition, especially in Crete, many endemic species are becoming increasingly threatened,” says Prof. dr. Carl Beierkuhnlein, who coordinated the research work.

To investigate the question of whether global climate change is causing a shift in tree lines, the Bayreuth researchers chose the Mediterranean island of Crete because the conditions there were unusually favorable for such a study. “It’s a rare coincidence for research that relatively high-resolution aerial photographs of a mountainous region, spanning a 70-year period, allow us to see with sufficient accuracy whether tree populations have changed. Using climate data and new geo computer science methods, we were able to document decades of climate change while proving that the trees native to the mountains of Crete have not moved to higher elevations,” said first author Mirela Beloiu, who obtained her PhD from the University of Bayreuth. and is now a postdoctoral researcher at ETH Zurich. The research in Crete was carried out in close collaboration with the Remote Sensing Laboratory of the Institute of Applied and Computational Mathematics of the Foundation for Research and Technology Hellas (FORTH). The institute also provided the historical and recent aerial images.

Decades of climate change in the mountains are not shifting the treeline

Trees on the steep slopes of the Lefka Ori massif (White Mountains). Credit: Dimitris Poursanidis

In their study, the researchers identify several climatic and topographical factors that may contribute to the survival of Crete’s montane forests in their decades-old sites. During the study period, the average annual temperature at the treeline increased by 0.81 degrees Celsius, while the average rainfall decreased by 170 millimeters. Increasing drought is apparently a stressor that inhibits the spread of plants. In addition, regions above the treeline are exposed to very high winds. As a result, young trees do not find the protection they need to establish themselves at higher altitudes. “If ecosystems, such as the high montane forests of Crete, are unable to respond to climate change and protect themselves adequately due to topographical conditions, then how humans can enhance their adaptation through creative nature management should be explored,” says Beierkühnlein.

Climate change increases risk of tree death

More information:
Mirela Beloiu et al, No treeline shift despite climate change over the past 70 years, Forest ecosystems (2022). DOI: 10.116/j.fecs.2022.100002

Provided by Bayreuth University

Quote: Decades of climate change in the mountains are not causing treeline shifts (2022, June 23) retrieved June 23, 2022 from https://phys.org/news/2022-06-decades-climate-mountains-shift-boom.html

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