Development history of tree climatology

At the beginning of the 20th century, A.E. Douglas of the United States first demonstrated the relationship between the change of tree ring width and precipitation, and established a laboratory specializing in tree ring research in 1930s. Since then, tree climatology has made a detailed study on the relationship between the physiological process of tree ring formation and climate, made progress in the selection of sample tree species and the statistical analysis technology of tree ring sequence, and gradually established the basic principles and analysis methods of tree climatology.

When selecting samples, the trees whose growth conditions are most limited by a certain climatic factor (temperature or precipitation) should be selected. For example, trees growing in the upper boundary of forests in high latitudes or alpine mountains can often reflect the changes of cold and warm well due to the limitation of insufficient heat; In arid and semi-arid areas, the trees at the edge of the forest, which are in transition from forest to grassland or desert, can often reflect the change of dryness and wetness due to the limitation of insufficient rainfall. In practical application, multiple repeated samples are often selected in the same place and compared with each other to accurately determine the year and exclude the influence of non-climatic factors. In addition, the change of ring width should be corrected according to the growth of trees with age and checked with the existing data. After strict verification, tree ring sequence can reflect large-scale climate change. For example, the annual ring sequence taken by American V.C. Lamac near the upper distribution limit of slash pine in Whitney Mountain, California, USA is consistent with the temperature change trend in Europe (central England). In the early 1970s, H.C. Fritz of the United States drew the average circulation map of the western half of the northern hemisphere every ten years since 1700 according to the relationship between the change of ring width and atmospheric pressure anomaly. China began to study tree climatology in 1930s. The research shows that it is very valuable to use tree ring analysis to understand the climate change in historical period, especially to reflect the change of precipitation in the vast areas of North China and Northwest China. At the end of 1970s, this work was widely carried out in many northern provinces (autonomous regions) and the Qinghai-Tibet Plateau. Many time series reflecting the temperature or precipitation for hundreds of years have been obtained in various places, which provides more evidence for studying the historical facts of climate change in historical periods.

Carpenters have long known that there are tree rings on the trunk, and with them, there are textures on the wood. As far as people know, Aristotle's colleagues mentioned the New Year's Ring, but this is the first time that arrival Finch proposed to increase the ring once a year. Today, as we all know, spring returns to the earth, everything recovers, and the cells next to the bark begin to divide; Divided cells are large, thick and bright in color, which scientists call early wood; After that, the cell growth slows down, the wall thickens, the volume shrinks and the color darkens. This is called houmu, and the dark annual rings on the trunk are formed by houmu. After that, the tree enters the winter dormancy period again, and it goes on and on. In this way, many trees will generate rings of light and dark on the trunk, and each ring is part of the annual growth. This kind of ring is most obvious in coniferous trees, but not obvious in most temperate deciduous trees, and it is not found in many tropical trees at all.

Trees are living archives, and the annual rings on the trunk are records. It not only shows the age of the trees themselves, but also shows the changes of annual precipitation and temperature. Tree rings can also record forest fires, early frost and chemicals absorbed from the surrounding environment. Therefore, as long as people know how to reveal the secret of the tree, it will tell people a lot of things that have happened around it since its birth. Trees can tell people what happened in the past and what will happen in the future. Trees' records of meteorology can help people understand the natural forces that contribute to meteorology, which in turn can help people predict the future.