When a disaster strikes, animals will run away, and humans will invent various technologies to reduce damage. Then, what will the trees that will not “walk” or “run” do?
Will the trees collectively “move”?
In 2017, ecologists at Purdue University in the U.S. used data from the U.S. Forest Service to study the distribution of 86 species of trees in the U.S. between 1980-1995 and 2013-2015. They want to see whether climate or environmental changes will affect the distribution of trees. The calculation results show that in the past 30 years, most tree species have been “moving”.
More than half of the tree species studied are migrating northward at an average rate of 11 kilometers every 10 years. These tree species are usually gymnosperms composed of North American conifers (in seed plants, plants with ovules on the upper edge or leaf surface of the open spores); and about 3/4 of the flowering trees in the forests of the eastern United States, such as white Oak trees, sugar maple trees, and holly plants have moved westward at a rate of 15.4 kilometers every 10 years since 1980. Hardly any kind of tree moves south or east.
Of course, trees are not like animals that can “walk around” at will, but trees also have their own way of “moving”. As time goes by, new saplings can grow in a new area, while old trees growing in other areas will slowly wither, eventually shifting the distribution center of the entire population.
So why do trees move?
Trees are also afraid of “heat”
Part of the reason can be attributed to global warming. For trees, too much heat is as deadly as lack of water. For photosynthesis, the tiny pores on the leaves-the stomata will take in carbon dioxide from the air. Then photosynthesis converts carbon dioxide into carbohydrates-the nutrients of leaves and tree trunks. In this process, a small part of the tree’s own water will evaporate through its stomata, creating negative pressure. This negative pressure helps the tree to transport the water inhaled from the soil through the trunk to the canopy, supplying the entire tree for photosynthesis.
However, as the temperature increases, the water vapor evaporation of the trees themselves will also increase, and the final evaporation rate is greater than the rate at which the trees absorb water from the environment. In this case, the tree will close the stomata on the leaves to avoid the rapid loss of water vapor, but doing so also means that photosynthesis cannot be carried out, and eventually its cells will lose their nutrient supply and die. Even if it does not die, after the loss of its own water, the toxic sap that defends against pests will dry out, and the defense power will decrease. The pests can sensitively detect this change through the smell, and magnificently erode trees.
These factors can explain why many evergreen coniferous species such as American firs, spruces and pine trees migrate north. They have adapted to the cold climate. When the environment becomes warmer, they can only move north. Similar situations are happening all over the world. Since the Arctic is warming at about twice the rate of the rest of the world, the researchers predict that by 2100, as the ice in the Arctic region melts, the tree species that now grow in the Arctic Circle will migrate 500 kilometers northward. By then, Half of the Arctic tundra from Siberia to Canada may disappear and be covered by forests.
The still unsolved mystery
However, global warming may only explain part of the reason. In this study, scientists at Purdue University in the United States also found that trees are moving to the west, which is faster than the speed of trees moving to the north. How can this be explained?
Although climate warming has increased the temperature in the eastern United States, it has also significantly changed local rainfall. Since 1980, the annual precipitation in the eastern United States has increased a lot. Although the precipitation in the western part of the United States has also increased, the average annual precipitation in the western region is still lower than that in the eastern part. Why do angiosperms that prefer rain, such as deciduous trees and broad-leaved forests, migrate from the east to the west?
Researchers speculate that the dense population of the eastern United States, changes in land use, the frequency of forest fires, pests or lights may all affect the distribution of trees. However, no one has figured out why the trees still migrate to the west.
However, even if trees are “moving” to reduce the risk of group extinction, in order to cope with the increase in carbon dioxide concentration in the atmosphere, some small trees will increase water use efficiency. However, if the climate warms and droughts intensify, then the global forests will actually In general, there will be a large reduction.