What can tree rings tell us?

After the trees are cut down, we can see many concentric rings on the stump, which are called rings in botany. Tree rings are formed by the influence of seasons in the process of tree growth, and one ring is produced every year. Every spring, the climate is mild, the rainfall is abundant, the trees grow rapidly, and the cells formed are large in volume and quantity, thin in cell wall, loose in material and light in color, which are called early wood or spring wood; In autumn, the temperature is getting colder, the rainfall is scarce, the trees grow slowly, and the cells formed are small in size, few in number, thick in cell wall, dense in material and dark in color, which is called late wood or autumn wood. Spring wood and autumn wood in the same year are collectively called annual rings. There is an obvious line between the autumn timber in the first year and the spring timber in the second year, which becomes the annual ring line, marking the turning point of the annual growth alternation of timber and wood. Therefore, from the number of rings at the base of the trunk, you can know the age of the tree.

Trees growing in temperate and tropical areas with alternating rainy and dry seasons have annual rings, while trees growing in areas with little climate change in four seasons have no obvious annual rings. Tree rings contain a lot of historical information about climate, astronomy, medicine and environment. At the same time, tree rings also play an important role in historical archaeology, forestry research, geology and public security.

In history, tree rings are often used to calculate the specific age of some historical events. For example, in the vast sea, there are large and small ships that have sunk in past dynasties, and the tree species of shipbuilding can be determined according to the patterns (annual rings) of wooden ships; According to the corrosion of materials, the age of the sunken ship and some historical events related to this age are determined.

In meteorology, we can know the climate situation of each year by the width of annual rings, and we can infer the climate change for thousands of years by using the information on annual rings. The width of the annual rings indicates that there was plenty of sunshine and good weather in that year; If the annual rings are narrow, it means that the temperature was low, the rainfall was low and the climate was bad. If the climate in a certain place has a certain periodicity, it will also show the corresponding width and periodic change of width in the annual rings. Through the study of tree rings, American scientists found that the grassland in the western United States had a drought every 1 1 year, and applied this law to correctly predict the drought in 1976. Meteorologists in China studied the annual rings of an ancient cypress tree in Qilian Mountain, and made scientific corrections at different growth stages. It is estimated that the climate in China in recent thousand years is dominated by cold, and the period from the 1920s in 17 to the 1970s in 19 is the longest cold period in recent dry years, lasting for 250 years.

In environmental science, tree rings can help people understand the history of pollution. German scientists studied tree rings in Franken and other three areas by spectroscopy, and found out the pollution of lead, zinc and manganese in these areas in recent 120 ~ 160 years. By comparing the pollution levels in different periods, the main causes of environmental pollution were found out.

In medicine, tree rings play a certain role in exploring the causes of endemic diseases. In some areas where Keshan disease occurs, such as Heilongjiang and Shandong, the platinum content in tree rings in high incidence years is lower than that in normal years. This is very consistent with the research results of geochemical etiology at present.

In the investigation of forest resources, we can know the growth of trees in the past few years according to the width of tree rings, and predict the future growth dynamics, which provides scientific basis for formulating forestry planning, determining reasonable cutting volume and adopting different management measures.

In recent years, the United States has introduced tree rings into earthquake research. They believe that after the earthquake caused the ground to move and tilt, the tree rings left traces of the trunk's efforts to ensure straight growth; Another example is that the root system passes through the fault or is located near the fault. Because the growth was blocked, the annual rings formed in that year were relatively small. According to this, we can know the time and intensity of the earthquake at that time, reveal the history and period of the earthquake, and then make earthquake prediction.

People have realized that tree rings record the ever-changing traces of nature and are extremely precious scientific data. In order to observe the annual rings, people can use a special drilling tool to drill into the tree core from the bark, and then take out a thin sheet with all the annual rings on it. In this way, the age of the tree can be known without cutting it down, thus providing research materials for scientists. In recent years, Japan has developed a new method to observe tree rings-CT scanning. This method can not only observe the growth of trees, but also understand the internal situation of ancient buildings and sculptures.