Mountain forests are normally among the most diverse habitats in alpine regions. Yet, as a team from the Alfred Wegener Institute discovered in the Tibetan Plateau, the higher, treeless areas are home to far more species.
Their findings, which were just published in the journal Nature Communications, can help to predict how the biodiversity of alpine regions will decline in response to global warming when the mountain forests spread to higher elevations.
As anyone who has ever hiked in the mountains knows, the landscape changes with the elevation. At first, for a long time, you trek uphill through forests, until they open up into the first meadows and pastures, where a wide range of plant species bloom in the spring.
Farther up, the landscape becomes more barren. Only those plants that have adapted to the alpine climate can thrive here. In order to map the vegetation of the alpine world, biologists most often investigate plant diversity along so-called elevation levels.
First they examine the plants in the sprawling forests, then in the alpine meadows, and then in the rocky upper reaches. No matter where researchers do so in the Alps, the Caucasus or the Rocky Mountains, the results are always similar.
More species in treeless areas
If the evolution of mountain ranges in the course of millennia is considered, it becomes clear that the landscape above the treeline contains many more species than the mountain forests.
As Herzschuh and her colleagues report in the journal Nature Communications, they succeeded in reconstructing the evolution of plant diversity in the Tibetan Plateau over the past 17,000 years.
What they found: When, in colder phases, the forests retreated to lower regions and the treeline followed suit, the alpine meadows and alpine landscape grew — and with them, the number of species.
Ancient sediments from a Tibetan alpine lake
The southeast Tibetan Plateau is one of the most species-rich mountainous regions in the world, and a so-called biodiversity hotspot. Further, since the region is at such a high elevation, at the end of the last ice age it was heavily glaciated; it was only with the gradual warming of the planet that the forests reclaimed parts of the Plateau.
In order to determine how biodiversity changed with the disappearance and return of the forests, Herzschuh and her team assessed the sediments from an ancient lake in the Hengduan Mountains of eastern Tibet. Since the lake was formed after the last ice age, sand, dust and plant remains had gathered there for over 17,000 years.
The researchers extracted ancient fragments of DNA strands from the sediments, allowing them to identify which plants lived there at which times. They then combined these biological findings with analyses provided by a mathematical ice model, which can be used to reconstruct the glaciers’ changing positions.