Declining biodiversity in mountainous Tibet in response to climate change – sciencedaily
Normally, mountain forests are among the most diverse habitats in alpine regions. Yet, as a team from the Alfred Wegener Institute discovered in the Tibetan Plateau, the taller, treeless areas are home to many more species. Their conclusions, which have just been published in the journal Nature communications, can help predict how the biodiversity of alpine regions will decline in response to global warming – when mountain forests spread to higher elevations.
As anyone who has ever hiked the mountains knows, the scenery changes with the elevation. At first, for a long time, you climb through the forests, until they open up to the first meadows and pastures, where a wide range of plant species blooms in the spring. Higher up, the landscape becomes more arid. Only plants that have adapted to the alpine climate can thrive there. In order to map the vegetation of the Alpine world, biologists most often study plant diversity along what are called elevation levels. They first examine the plants in the sprawling forests, then in the alpine meadows, then in the rocky upper parts. No matter where the researchers do it – in the Alps, the Caucasus or the Rocky Mountains – the results are always similar: vast forests are the region with the most species. With increasing elevation, biodiversity steadily decreases.
More species in treeless areas
A team led by biologist Prof Ulrike Herzschuh of the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) in Potsdam has now concluded that this thesis is not necessarily correct: forests should in no way be the most diverse part of alpine regions. If we consider the evolution of mountain ranges over the millennia, it becomes clear that the landscape above the treeline contains many more species than the mountain forests. As Herzschuh and his colleagues report in the newspaper Nature communications, they have succeeded in reconstructing the evolution of plant diversity on the Tibetan plateau over the past 17,000 years. What they found: When, in the colder phases, the forests retreated to the lower regions and the treeline followed suit, the alpine meadows and alpine landscape increased – and with them, the number of cash. In the warmer phases, the forests spread higher and the number of species decreased. “If we assume the same size, there are more species in the higher treeless areas than in the forests,” Herzschuh says. “It also surprised us, because conventional studies, which always reflect elevation levels, have always indicated the exact opposite.”
A wider range of habitats
The authors of the study do not yet have a definitive explanation for their discovery. “However, it is safe to assume that there are now more species in the forest areas because they are more extensive than the more barren areas near the mountain peaks,” says Sisi Liu, the study’s first author and member of the AWI Polar Terrestrial research section. Environmental systems. As a result, there is much more forest available today, which can contain various types of habitat, such as forest clearings and streams. If the alpine areas were instead larger, as Liu and his colleagues assume, the result would be much more diverse habitats than those found in forests – shady and sunny and dry areas or areas with sparse vegetation, poor in nutrients and loamy soils. – and therefore, a wide range of parameters for a diverse flora.
Ancient sediments of a Tibetan alpine lake
The Southeast Tibetan Plateau is one of the most species-rich mountain regions in the world and a so-called biodiversity hotspot. Also, because the area is at such a high altitude, at the end of the last Ice Age it was heavily glacial; it was only with the gradual warming of the planet that the forests recovered parts of the Plateau. To determine how biodiversity has changed with the disappearance and return of forests, Herzschuh and his team assessed sediments from an ancient lake in the Hengduan Mountains in eastern Tibet. Since the lake formed after the last ice age, sand, dust and plant remains have gathered there for over 17,000 years. The researchers extracted old fragments of DNA strands from the sediments, allowing them to identify which plants lived there and when. They then combined these biological results with analyzes provided by a mathematical model of ice, which can be used to reconstruct the changing positions of glaciers. According to Herzschuh: “With the help of an ice model developed by our colleagues at the German Geoscience Research Center in Potsdam, we were able to trace precisely how the plant community changed with the rise of the glacier and the displacement of the treeline. “
More forest means less diversity
Interestingly, ca. 8,000 years ago there was a warm phase in which forests “migrated” further upstream than they do today – and the number of species present in sediment data has declined dramatically. The findings gleaned by Herzschuh, her doctoral student Sisi Liu and other colleagues are important in terms of our ability to predict how the biodiversity of mountainous regions around the world might be affected by climate change; what they learned about the situation in Tibet can also be applied to other Alpine regions. “Our data could potentially help develop new management strategies to tackle the loss of diversity,” says Herzschuh. Either way, she argues, the stereotypical image of the mountain forest being the most species-rich type of region needs to be critically reconsidered.