What is the geographical relationship between tree rings and climate?

Tree rings are textures on wood. When spring returns to the earth, the cells next to the bark begin to divide; The divided cells are big and thick, with bright colors, which scientists call early wood, and the dark annual rings on the trunk are formed by early wood. 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 obvious in conifers, but not in most temperate deciduous trees, but not at all in many tropical trees.

Nowadays, tree rings have become an important field of scientific research. Trees are called living files, and tree rings 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. So as long as we know how to reveal the secret of the tree, it will tell us a lot about what happened around it from its birth. Now, the hot topic of this subject is to measure the past meteorology and major meteorological changes from tree rings.

The research results of using tree rings began at the beginning of this century. Douglas, an American scholar, visited a logging camp in 190 1, looking for evidence that sunspot activity with a period of 1 1 was recorded in these tree rings. He didn't find evidence immediately, but he noticed that the pattern of annual rings in one area and another seemed to be the same. For example, a newly cut tree in a logging camp has two thin rings inside and three thick rings outside, and so do the newly cut trees in other camps. It can be inferred that this pattern shows that two years is bad weather and three years is good weather. Douglas noticed that this type of halo he found seemed to be everywhere in northern Arizona.

In the first 20 years of this century, Douglas continued to study the pattern of tree rings. It is Douglas's pioneering work to determine the age of ancient buildings by identifying tree rings. The ruins of Indian villages in the southwestern United States have long attracted the interest of archaeologists. Those villages were first carefully built by craftsmen, and many of them have obviously been used for centuries, but then they were abandoned somehow. It is estimated that these villages existed as early as 2000 BC. Douglas began to investigate the residual wood in the ruins of Indian villages from 19 16, and studied its annual rings to determine its age. By 1929, he finally made a "floating" chronology.

Where there is a civilized tradition, the use of tree rings may be unexpected and surprising. For example, in Novgorod, Russia in the Middle Ages, the streets were muddy, and citizens paved roads with logs. When one layer sinks into the mud, spread another layer. Up to now, at least 28 streets have been filled with layers of logs. These logs date from 953 A.D. to 182, which is really an annual ring market. Another example is the oil paintings of masters such as Rembrandt and Rubens. By analyzing the annual ring patterns on their oak oil paintings, we can know the age of the paintings.

Modern dendrology can be said to have originated from the research work of biologist Fritz of the University of Arizona in the 1960s. Fritz and his colleagues carefully investigated the growth process of some trees near Tucson. They cover branches or even the whole tree with plastic film to determine how many gases a tree actually ingests and releases. After eight years of work, they finally got a detailed understanding of the whole process of the growth of an annual ring.

They collected the data of tree rings around the southwestern United States and compared them with the meteorological records of the past 80 years, so we can see how tree rings reflect the climate. So for the period without meteorological records, we can infer the climate at that time from the formation of a ring. In this way, Fritz compiled the meteorological map of the United States and the North Pacific Ocean about AD 1600.

Tree ring experts also studied the effects of acid rain on forests in the eastern United States. Gordon jacoby of Columbia University explained that as trees get older, the rings become thinner and thinner. This is a normal aging process. Therefore, it can be concluded that the effect of acid rain on trees is opposite. It is also necessary to compare meteorological data to rule out other possible reasons for the slow growth of trees. In order to confirm the influence of acid rain, it is necessary to find out the growth retardation outside normal conditions. Jacoby saw that three of the areas delineated by 12 around New England were affected by acid rain, and the other nine areas were not.

In addition, tree rings also record natural phenomena such as volcanic eruptions and earthquakes. For example, when Mount St. hellens erupted, a lot of dust and gas entered the stratosphere, blocking a large area of sunlight. This will drop the temperature below freezing point and leave a special mark on the tree, called the frost wheel. Earthquakes will damage trees, making them produce thinner rings in the next few years.

In some cases, tree rings can also be used to prove the impact of environmental pollution. Due to the continuous burning of coal and oil for centuries, a large amount of carbon dioxide has accumulated in the atmosphere, which will lead to the future temperature rise of the earth. The data of the international plan on meteorological relations of tree rings will be extended to 1700, which is much earlier than the industrial revolution burning coal and oil. The researchers said: "Without this data base, it may take 8 to 20 years for atmospheric scientists to observe the temperature and carbon dioxide if they want to know the warming trend exactly. By then, I am afraid it will be too late. "