Arbor Day丨Can towering trees really "reach the sky"? How tall can trees really grow?

It is said that "ancient trees are towering", and the lifespan of a tree is much longer than you think. In Dinglin Temple in Fulaishan Scenic Area, Ju County, Rizhao City, Shandong Province, there is a ginkgo tree that is thousands of years old. It is still full of vitality and enjoys the reputation of "the best ginkgo tree in the world".

A tree starts to grow continuously from the moment it sprouts. Although the ginkgo tree is long-lived, its growth rate is very slow. But for some trees, growing taller is their ultimate goal. It is understood that the tallest tree in the world is an American redwood, which is 116.07 meters high, equivalent to the height of more than 30 floors. It can be said to be truly "towering into the sky".

As long as a tree does not die, it will grow taller almost every day. So how tall can trees grow? If there are no special circumstances, will they continue to grow indefinitely and get taller?

How do trees grow?

Most trees go through four stages of growth: germination, development, growth, flowering and fruiting. During the growth process, the leaves will continuously absorb sunlight, perform photosynthesis, form nutrients needed by the tree, and continuously transport them to various parts of the plant. In addition, the roots will also absorb water and various nutrients from the soil to promote the growth of various parts.

Through the synthesis of nutrients year after year, the cells will divide many times, the tree will grow taller and taller, and the trunk will become thicker and thicker. The trunk of a tree like a poplar can be divided from the outside to the inside: bark, phloem, cambium, xylem and pith. The bark is the surface layer of the trunk, which has the function of protecting the tree and preventing pests.

The phloem is composed of fibrous tissue, which is mainly responsible for transporting sugar to the roots of the tree and promoting the growth of the roots. The cambium is relatively thin, but it is the growing part of the trunk. The cells of other parts of a tree are all produced from the cambium, so it can be seen that its role is very important. There are conducting tissues in the xylem that can transport water from the roots to various parts, helping the tree to form nutrients.

Internal factors limit tree growth

The shape of a tree is determined by its genes and the environment it lives in. Some trees are tall, some are short, some grow fast, and some grow slowly. If there is no "tall" label in the gene, no matter how good the environment is, it will not grow indefinitely. However, genes cannot determine everything, and the influence of the external environment is still crucial to the growth of trees.

External factors also affect the performance of trees.

The tree that seems to be growing forever cannot actually grow infinitely tall. The main reason is the existence of gravity. As we all know, the growth of plants mainly relies on the evaporation of water from the stomata on the surface of the leaves to generate power, which in turn enables the vessels of the root stem to transport water to the branches and leaves, and combined with photosynthesis, to provide themselves with the necessary nutrients for growth.

The direction of water transport by the duct is exactly opposite to the direction of gravity. In order to transport water smoothly to each branch and leaf, it is necessary to overcome the obstacles of gravity and the friction of the duct itself. The interweaving of these forces makes it difficult to transport water to the top of a very high tree.

By measuring the water tension in the top tissues of trees, we can determine the growth limit of the tree. In the article "Why Trees Can't Grow Infinitely" in the magazine "Science and Culture" (2005), Dr. George Koch of Arizona State University in the United States once found leaves in a state of extreme water shortage at the top of a 100-meter-high tree. Although there is plenty of water in the local soil, it takes up to 24 days for water to be transported from the roots to the top.

Through this research, scientists concluded that the maximum height of trees on Earth is 122-130 meters. If the height exceeds this, it will be extremely difficult for water to reach the top of the tree, and photosynthesis at the top of the tree will not be able to proceed normally.

The proverbs such as "A tree that stands out in the forest will be destroyed by the wind" and "A tall tree attracts the wind" also show us that the fact that trees cannot grow infinitely tall is also the result of natural selection. In coastal areas, before a typhoon arrives, the urban greening department will do a special job: pruning street trees. Pruning trees can not only improve their wind resistance, but also reduce the chance of broken branches and lodging.

In nature, the larger the tree, the more vulnerable it is to natural disasters such as strong winds, heavy rains, and lightning. It may also be affected by insufficient supply of sunlight, oxygen, water, nutrients, and temperature. Therefore, as trees continue to evolve, their height is gradually restricted. Their inability to grow indefinitely is also the result of natural selection.