In the past 80 years, the alpine shrub line of the willow genus on the Qinghai-Tibet Plateau has climbed 59.3 meters!

Recently, the Ecosystem Pattern and Process Team of the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences and the School of Biology and Environment of Nanjing Forestry University found that from 1939 to 2010, climate warming led to an increase in the renewal rate of alpine shrubs of the genus Willow on the Qinghai-Tibet Plateau and an expansion of their distribution space, which is one of the factors that promoted the greening of the Qinghai-Tibet Plateau. In the past 10 years, the renewal rate of alpine shrubs of the genus Willow has shown a downward trend, and the shrub line tends to remain static. Over the past 80 years, the alpine shrub line of the genus Willow on the Qinghai-Tibet Plateau has risen significantly, with a maximum rise of 59.3 meters and an average climbing rate of about 5.16 meters per decade.

This result was recently published in "Ecography", laying a data and theoretical foundation for predicting the evolution trend of alpine shrub ecosystems under climate change and providing a scientific basis for high-altitude ecological management.

Liang Eryuan, a researcher at the Institute of Tibetan Plateau Research, Chinese Academy of Sciences and the corresponding author of the article, said that the alpine shrub line refers to the upper limit of the altitude boundary of shrub distribution. On the alpine shrub line, the climate is harsh and unstable, and such climate characteristics restrict key ecological processes such as shrub growth and renewal. Since the environmental conditions of the alpine shrub line are the limit of what the shrubs can bear physiologically, in theory, the alpine shrub line can respond quickly to global changes and is considered a natural laboratory for exploring the response and adaptation of alpine ecosystems to global changes and a "warning line" for global warming.

Figure 1 Landscape of mountain willow shrubs on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau has rich shrub resources such as juniper, rhododendron, berberis, caragana, willow, rose, potentilla, sophora, honeysuckle, sea buckthorn, wolfberry, and spiraea, forming a continuous natural shrub line. Studies have shown that the Qinghai-Tibet Plateau is home to the world's highest evergreen cedar shrub line (5,280 meters above sea level).

Based on the field research data of the past five years, the research team found that Salix alpina is a typical deciduous shrub that forms the alpine shrub line, with the highest altitude reaching 4,960 meters. However, it is still unclear what changes have occurred in the structure and pattern of the Salix alpina shrub line on the Qinghai-Tibet Plateau under the background of climate warming?

Fig. 2 Spatial distribution of Salix alba shrub line plots on the Qinghai-Tibet Plateau

Wang Yafeng, associate professor of the School of Biology and Environment at Nanjing Forestry University and the first author of the article, introduced that the research team established 24 mountain willow shrub line plots along the 900-kilometer latitude gradient in the eastern Qinghai-Tibet Plateau, and obtained parameters including coordinates, plant height, base diameter, crown width, age, and habitat conditions. Combined with climate change and remote sensing satellite data, the team systematically revealed the spatiotemporal changes in the location and population renewal of mountain willow shrub lines over the past 80 years.

Figure 3 Shrub line landscape of the Qinghai-Tibet Plateau

The study showed that between 1939 and 2010, warming led to an increase in alpine shrub renewal and a significant rise in the shrub line. In the past decade, the shrub renewal rate has been on a downward trend, the shrub line has slowed down, and has tended to remain static. The study also interpolated and estimated the relationship between the shrub line and temperature and found that 8.5°C is an important temperature threshold for mountain willow shrubs. When the average summer temperature is between 5-8.5°C, the change of the shrub line is driven by temperature, and when the average summer temperature is above 8.5°C, the change of the shrub line is limited by humidity. As warming exacerbates water deficits in high-altitude cold areas, the mountain willow shrub line changes from being limited by temperature to being limited by humidity. Therefore, continued warming will threaten the stability of alpine shrub ecosystems and deserves further attention.

This research was funded by the National Natural Science Foundation of China and the Second Comprehensive Scientific Expedition and Research Project on the Qinghai-Tibet Plateau.

Author: Wang Yafeng, Liu Xiaoqian

Source: Institute of Tibetan Plateau Research, Chinese Academy of Sciences