China News Service, Beijing, February 13th: Why does the cold Qinghai-Tibet Plateau have more thousand-year-old trees?
——Exclusive interview with Zhang Qibing, researcher at the Institute of Botany, Chinese Academy of Sciences
Author Li Hanxue Zhang Yangbin
Ancient trees have gone through years of vicissitudes and recorded rich climate and ecological historical information, which has incomparable value. However, there are not many ancient trees that can still survive after thousands of years. China's thousand-year-old trees are mainly distributed in the Qinghai-Tibet Plateau.
Why can the Qinghai-Tibet Plateau grow more thousand-year-old trees? How to determine its age? What historical information do these thousand-year-old trees record? Zhang Qibing, a researcher at the Institute of Botany of the Chinese Academy of Sciences who has been engaged in dendrochronology research on the Qinghai-Tibet Plateau for more than 20 years, recently accepted an exclusive interview with China News Service's "East-West Question" on this issue.
The interview transcript is summarized as follows:
China News Service reporter: How was the age of the ancient tree confirmed? Where are the thousand-year-old trees on the Qinghai-Tibet Plateau distributed?
Zhang Qibing:
The age of some ancient trees can be known by consulting literature records, interviewing local residents, and using methods such as estimating the empirical relationship between trunk diameter at breast height and tree age, but the errors are often large. The most accurate method is to use a tree growth cone to obtain a tree core sample and read the number of growth rings on the sample to determine the age of the tree.
The formation of tree rings is caused by the changes in the seasons. Between the bark and xylem of the tree trunk, there is a circle of cambial cells. When the tree grows in spring, these cambial cells divide inward to form xylem cells that are large in size, thin in wall, and lighter in color. They are called early wood; during the growing season The cells formed later are small in size, thick in wall and darker in color, and are called late wood. The combination of light-colored earlywood and dark-colored latewood is the wood formed by the tree in one year, which is the growth ring. There is a clear demarcation between the dark latewood of the first year and the lighter earlywood of the second year, allowing the growth rings of each year to be identified.
In August 2023, Zhang Qibing and his team discovered a thousand-year-old juniper juniper tree at an altitude of 4,260 meters in Angren County, Shigatse City, Tibet. Photo provided by interviewee
However, the number of growth rings visible on a tree core is not necessarily the actual age of the tree core. When the climate is abnormal or the trees are unhealthy, "pseudo growth rings" (two or more rings formed in a year) or "lost growth rings" (no rings formed in a year) will occur. Dendrochronology is to identify “pseudo annual rings” or “missing annual rings” by cross-dating tree ring samples from different individuals of the same tree species in the region, thereby determining the year of formation of each annual ring.
The tree ring samples we collected in Haibei Prefecture, Haixi Prefecture, Goluo Prefecture in Qinghai, Qamdo City, Nagqu City, Nyingchi City in Tibet and other places confirmed that there are many thousand-year-old trees on the Qinghai-Tibet Plateau, and the main tree species is Qilian Juniper. , large-fruited juniper, giant cypress and other cypress trees.
Reporter from China News Service: The Qinghai-Tibet Plateau has extreme environments such as high temperatures and cold temperatures. Why can ancient trees grow thousands of years ago? What “stories” can these thousand-year-old trees tell us?
Zhang Qibing:
The survival mechanism of longevity trees is still not clear yet. The mainstream view is that trees under certain adversity conditions can have a longer lifespan. A popular saying is "grow fast and die early."
The Chinese Giant Tree Scientific Expedition Team announced that the exact height of the Yunnan Huangguo fir discovered in Chayu County, Tibet is 83.4 meters. Photo courtesy of "Wild China" Studio
During their growth, trees not only passively respond to climate and environmental changes, but also resist and recover from external disturbances. This ability to proactively respond to external disturbances to maintain one's own health is ecological resilience. I think the ecological resilience of a tree has a significant impact on its longevity. As trees age, the thicker the trees, the greater their demand for photosynthetic products, water and various nutrient resources. When the supply of these resources cannot meet the demand, the ecological resilience of the trees will decrease, making it more difficult to withstand Affected by natural disasters such as extreme climate, pests and diseases during their growth, it is usually difficult for them to live to a thousand years old.
Cypress trees growing on the Qinghai-Tibet Plateau have adapted to adverse conditions such as high cold and drought over a long period of time and adopted a slow growth strategy to reduce the demand for various resources and maintain long-term ecological resilience. Therefore, more thousand-year-old trees can grow in adversity on the plateau. Research has found that the annual ring width of thousand-year-old cypress trees on the Qinghai-Tibet Plateau is particularly narrow, usually much less than 1 mm, and they have strong ecological resilience.
We discovered five thousand-year-old cypress trees in Ru County, Nagqu City, Tibet. Their tree rings between 1260 and 1460 AD were very narrow, indicating that they experienced a difficult period of two hundred years and then returned to normal growth. This is the embodiment of ecological resilience. In addition, we also compared the changes in the width of tree rings between two disturbance events in history, and found that trees that recovered slowly after the previous disturbance will slow down the mutation process of tree ring width when encountering the next disturbance. This phenomenon suggests that trees may have accumulated a certain amount of "memory" during the recovery process, thereby enhancing ecological resilience in response to the next disturbance.
Of course, there are other reasons why more thousand-year-old trees can grow on the Qinghai-Tibet Plateau. For example, some longevity trees grow in environments that can avoid natural disasters such as snowstorms. In addition, due to the small population on the plateau, the trees are less disturbed by human activities. At the same time, local people regard the big cypress as a sacred tree. This kind of cultural belief It is also beneficial to the protection of ancient trees.
On December 22, 2023, research institutions, university experts and scholars, etc. inspected and investigated the area around Xindabu, the "Medog Tree King" in Medog County, Tibet, and took photos with the tree king. Photo by Li Pan
A lot of climate change information is recorded in the growth rings of ancient trees. For example, the tree rings of seven thousand-year-old cypress trees we found in Delingha City and Dulan County, Haixi Prefecture, Qinghai Province were wider between 929 and 1031 AD. Since the changes in the width of the tree rings here are positively correlated with the precipitation from May to June, this period of wider tree rings probably indicates that there were favorable moisture conditions during the Medieval Warm Period.
The growth ring information of thousand-year-old trees also plays an important role in archaeological work. For example, in the dating of the Shuishui tombs in Dulan County, Qinghai Province, researchers used tree-ring data collected over thousands of years of Qilian juniper in the wild mountains to determine the formation of the outermost tree rings of the logs buried in the ancient tombs. The year helps determine the construction period of the tomb between the late 7th century AD and the mid-to-late 8th century AD.
Reporter from China News Service: Extreme weather has occurred frequently in recent years, and the public has become more concerned about the fate of ancient trees under global climate change. What impact do you think global climate change will have on the survival of thousand-year-old trees? How to deal with it?
Zhang Qibing:
Many studies have shown that thousand-year-old trees play an important role in maintaining ecosystem functions. For example, ancient trees are habitats for many animals above and below the ground, effectively protecting biodiversity and maintaining the long-term stability of the habitat.
On December 18, 2023, an alpine coniferous forest in Medog County, Tibet was covered with snow, and there were epiphytes on the branches. Medog is known as the treasure house of biological diversity. Photo by Jiang Feibo
In recent years, the trend of global warming has been obvious, and the intensity and frequency of extreme climate events have continued to increase. The Qinghai-Tibet Plateau, with an average altitude of over 4,000 meters, is more sensitive to global climate change. Although the alpine adversity contributes to the longevity of the ancient trees here, if the damage to the habitat of the ancient trees due to extreme climate and natural disasters exceeds historical extremes, the ancient trees may be affected. If the impact on growth exceeds the threshold of ecological resilience, it may cause its growth to decline and be difficult to recover, eventually causing tree death.
In order to slow down the process of climate warming, the United Nations has always advocated controlling the continued accumulation of greenhouse gases in the atmosphere. China has also clearly proposed a "double carbon" goal in 2020. On September 1, 2023, the "Qinghai-Tibet Plateau Ecological Protection Law of the People's Republic of China" was officially implemented. Under the guiding principles of "respecting nature, complying with nature, and protecting nature", a series of regulations on the authenticity and stability of the forest ecological environment were formulated. Conservation Regulations. In addition, what factors determine the longevity of ancient trees is still a scientific question that has not yet been fully answered. Scientific research in this field needs to be strengthened to better serve the protection of thousand-year-old trees. (over)
Interviewee profile:
Zhang Qibing, a researcher at the Institute of Botany, Chinese Academy of Sciences, received his PhD from the University of Victoria in Canada in 2000. He is currently the executive director and deputy secretary-general of the China Scientific Exploration Association, deputy director of the Tree Ring Branch of the Chinese Geographical Society, and a member of the Academic Committee of the National Forestry and Grassland Ancient Tree Health and Ancient Tree Culture Engineering Technology Research Center of Beijing Agricultural College. Since 2001, he has been mainly engaged in the study of tree ring ecology on the Qinghai-Tibet Plateau. He has conducted on-site inspections of major forest areas on the plateau, obtained a large amount of first-hand tree ring data on the plateau, and elaborated on the north-south space of climate change on the Qinghai-Tibet Plateau over the past few hundred years. Characteristics, proposed a method to extract life signals of tree growth by comparing tree ring change information of individual trees to understand forest ecological processes, quantitatively assessed the role of tree ecological resilience in forests coping with extreme climates, and identified the age of ancient trees in many places and growth history.