Mountain forests are refuges for many rare animal and plant species, but they are threatened. A global survey that has examined the loss of mountain forests since 2001 shows how much. According to this, 78.1 million hectares of mountain forest have been lost in the last 20 years or so, which corresponds to more than seven percent of the total stock. In addition, the loss of mountain forests has accelerated by more than one and a half times since 2010, and forest loss has even doubled in the particularly species-rich mountain forests of the tropics. The main causes are targeted clearing, forest fires and the advance of cultivated areas to ever higher altitudes.
Mountain forests protect the mountain slopes from erosion, stop avalanches and provide a refuge for many animal species. Due to the small-scale and climatic conditions that vary depending on the altitude, they are important habitats, especially for rare species with a small distribution area. More than 85 percent of the world’s bird, mammal and amphibian species live in the mountain regions, and the high and cloud forests of the tropical mountain regions are often home to unique animal and plant life. For a long time, the mountain forests were also protected from large-scale clearing because of their often inaccessible location, the steep slopes and great heights. Because the mountain slopes were hardly worth cultivating anyway, the forests were left largely unmolested.
Ever faster loss of mountain forests
But that has now changed. “Since the beginning of the 21st century, the mountain forests have also been increasingly exploited for timber and wood products, but also to enable new agricultural crops, such as tree-based plantations in Southeast Asia,” explain Xinyue He of the South University of Science and Technology in Shenzhen and his colleagues. In order to determine the extent of forest loss in mountain regions, they evaluated satellite images and national data on forest cover and forest use in the period from 2001 to 2018. They analyzed increases and decreases in forest cover by forest type, altitude and region. “Knowing the dynamics of forest loss along altitudinal gradients is crucial to understanding how habitats for forest-dwelling species change and will change as they change their ranges in the wake of climate change, for example,” explains the team. Because when temperatures rise, the cooler, higher mountain forests are important alternative areas for many species.
The analyzes showed that the area of global mountain forests has decreased by 78.1 million hectares since the turn of the millennium, which corresponds to 7.1 percent of the total area. The mountain forests in tropical regions, which are particularly rich in species, are hardest hit. “At 32.9 million hectares, tropical montane forest accounted for 42 percent of global montane forest loss,” He and his colleagues report. In the tropical regions, especially in Asia, forest loss has also accelerated the most: Since 2010, mountain forests worldwide have shrunk one and a half times faster than in the same period before. In the tropical montane forests, however, the rate of annual montane forest loss from 2010 was even twice as high as before. After all, if the deforested area in these regions is left to its own devices, the forest there will grow back the fastest. However, the amount of renatured areas is not sufficient to compensate for the loss, as the researchers explain.
Agriculture as the biggest driver in the tropics
The main driver of mountain forest loss in the tropics is primarily land use change – the clearing and burning of forests to make room for fields and plantations. “The dominant drivers there were shifting cultivation at 44 percent, the cultivation of food and feed for export at 28 percent and commercial logging at 24 percent,” report He and his team. The mountain forests in temperate latitudes, such as in North America, on the other hand, were cleared primarily for the extraction of wood and wood products. “More than 75 percent of the loss there goes back to this sector,” the scientists said. However, their analyzes also show that nature protection areas can at least slow down the loss of mountain forests: “In all mountain biodiversity hotspots, the relative forest loss was lower inside the protected areas than outside,” the researchers report. However, there are also exceptions: In some countries such as Haiti, the Ivory Coast or Nicaragua, even more protected mountain forests have been lost since 2001 than unprotected ones. The same was true in Russia, where forest fires were primarily responsible for forest loss.
According to the scientists, their results underline that the mountain forests, which are important for biodiversity, must be better protected. This is all the more important in times of climate change, because the higher altitudes then become a refuge for many animals against the progressive warming. “We need to preserve the integrity of the forests over a large enough area to give the migratory species enough space to do this,” emphasize He and his colleagues. At the same time, however, it is also important to include the people living in the mountain regions and their needs. “Any measure to protect mountain forests must be adapted to local conditions and also take into account the local well-being and livelihood security of residents.”
Source: Xinyue He (Southern University of Science and Technology, Shenzhen) et al., One Earth, doi: 10.1016/j.oneear.2023.02.005