GEOGRAPHY

Phenological evidence of high-altitude forest expansion found!


Over the past 100 years, global warming has caused most high-altitude forests to climb to higher altitudes. On July 10, the Institute of Tibetan Plateau of the Chinese Academy of Sciences announced that the research of the Institute of Ecosystem Pattern and Process found that under the background of global warming, the spring growth and development of trees is advanced, and the competitive advantage between species increases, promoting the climb of alpine tree lines to higher altitudes. The results were recently published in the international academic journal National Science Review.

The alpine tree line is the upper elevation limit of the distribution of erect trees, and vegetation growth on this ecological transition zone is generally limited by low temperatures and sensitive to climate warming. In addition to climatic factors, interspecies competition between trees and shrubs is also an important factor in regulating tree line position changes.

Phenology refers to the cyclical changes of plants that adapt to light, precipitation, temperature and other conditions for a long time, forming a corresponding growth and development law, which is an important factor determining the distribution range of species and the key to measuring the competitiveness between species. The slight change of phenological differences between plant species significantly affects the competitiveness and niche differentiation of coexisting species. The results have shown that in the cold and humid environment of southeast Tibet, the atmospheric minimum temperature threshold can regulate the phenology of the tree formation layer (that is, the time of the beginning and end of cell division), and then control the length of the plant growing season and the formation of alpine tree lines. Therefore, from the perspective of phenology, this paper discusses how the changes in the formation layer of trees and shrubs on alpine tree lines respond to climate warming, which can provide a new scientific explanation for analyzing the competition intensity between trees and shrubs under the background of warming and predicting the position change of alpine tree lines.

Li Xiaoxia, the first author of the paper and associate researcher of the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, introduced that the team used the 8-10 years of continuous formation layer phenological observation data of the comprehensive observation and research station of alpine environment in southeast Tibet, combined with the simulated phenological data of 11 sample points in the northern hemisphere, to systematically study the changes and mechanisms of the spring growth and development of trees and shrubs on the alpine tree line under the background of climate warming.

The researchers found that the phenology of trees (sharp-pointed long-bracted fir) and shrubs (Rhododendron thin-haired sponge) on the typical alpine tree line of the Sejila Mountains in southeastern Tibet were not synchronized in response to spring warming. Spring warming is 1 degree, arbor growth recovery is 2-4 days earlier, shrubs are delayed by 3-8 days; The spring warming is 2 degrees, and the start time of the formation layer activity between the two is about 20 days. The main reason for this phenomenon is that the shrub needs more winter low temperature stimulation (cold shock) to restore growth, resulting in delayed spring phenology; Arbor is less dependent on low temperature stimuli, allowing it to resume growth early in the warm spring.

The research team further constructed the wheel width dataset of trees and shrubs of 11 alpine tree lines in the northern hemisphere, combined with the growth process model, simulated the formation layer phenology of trees and shrubs in the northern hemisphere from 1960 to 2000. The comparison results further confirmed that shrubs were more sensitive to low temperature stimuli in winter than trees, and trees were more sensitive to changes in accumulated temperature (spring temperature). Since 1990, climate warming has promoted the growth of trees on alpine tree lines, and shrubs have not responded significantly to warming.

Liang Eryuan, the corresponding author of the article and a researcher at the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences, said that under the background of global warming, the warming rate in high-altitude areas is significantly higher than that in low-altitude areas, and the warming rate in winter is much greater than that in spring, which may increase the phenological differences between alpine treeline trees and shrubs. Earlier spring phenology gives trees a competitive advantage by promoting growth, carbon gain, and resource availability, which in turn promotes alpine tree line migration to higher altitudes.

This study provides a physiological explanation for the study of the dynamic changes of alpine tree lines under climate change from the perspective of phenological changes between plant species, and is an important theoretical progress in the study of the driving mechanism of alpine tree line changes. (Source: China Science News Han Yangmei)

Related paper information:https://doi.org/10.1093/nsr/nwad182

Schematic diagram of the influence of phenological differences between trees and shrubs caused by climate warming on the position change of alpine tree lines. Photo courtesy of interviewee



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