Why do trees shed their leaves in autumn? Causes of autumn leaf fall

Autumn is a great time. The fact that it has come can already be judged by the fact that the leaves on the trees and shrubs change their color. At this time, the leaves have an extremely rich palette of colors. Nature itself paints them in different shades, so much so that any artist would envy. Why does this happen every year? Why do trees shed their leaves in autumn? This issue should be examined in more detail.

What assumptions might arise?

Why do trees shed their leaves in autumn? Various associations immediately arise in my head about what is happening:

• The foliage of the trees has grown old, it has become cold, and therefore there is a fall.
• In autumn, the leaves no longer have enough light for their growth.
• The reason that the leaves fall is the wind.

Naturally, all these assumptions are subject to verification to determine the true causes.

What role do leaves play in the life of trees?

The structure of the leaf is represented by two parts: the leaf blade and the petiole, which is its stalk. The structure of the plate is represented by veins. They are especially clearly visible from below. It turns out that they are vessels designed to move water. Each leaf contains green chlorophyll grains. They are so small that they are not visible to the naked eye. Grains can be compared to tiny factories. They are cooking for the whole tree. They build the material from which new branches, buds, roots and, of course, the trunk itself are formed.

They get energy for their production from the sun. The absorption of light by them is carried out throughout the daylight hours. Chlorophyll is unstable and is constantly being destroyed. But at the same time there is a regular recovery. For any tree, a green leaf is essential. But the yellow leaf does not nourish the tree, but only takes moisture from it.

Why does the color change?

Simultaneously with the destruction of chlorophyll, the process of its restoration takes place. Moreover, the formation of green matter does not lag behind its destruction. As long as there is enough light, there is a certain balance between these processes, an equilibrium. With the onset of autumn, due to the lengthening of nights, daylight hours become shorter. Being destroyed, chlorophyll simply does not have time to recover in a day. Therefore, it is not green, but yellow that becomes predominant. But not only this color there are withering leaves. They can acquire red, crimson, other colors. This is determined by which coloring matter is predominant in the withering leaf.

Foliage also varies in brightness. It depends on what the weather is like in autumn. The abundance of rain causes excessive saturation of the foliage with moisture. From this they become dull in nature. Alder and lilac lose their foliage regardless of the weather. In them, chlorophyll is simply represented by the only coloring matter.

Various folk signs

For many years man has been constantly observing nature. Thanks to this, many folk signs were formed. Many of them are also associated with a change in the color of the foliage:

1. If the leaf has turned yellow, but the process of falling off is not expressed, then frost is still far away.
2. Trees prematurely covered with yellow foliage - autumn will be early.
3. Despite the snowfall, winter will not come as long as the leaves remain on the cherry tree.
4. Bone tree with its leaves is able to predict the weather. Twisting down speaks of good days. Otherwise, the weather will be bad.
5. If the leaves appear on the birch earlier than on the alder, then the summer will be windy in nature. If the birch is ahead of the alder, then the summer will be cold and rainy.
6. Early spring is predicted by early yellowness at the top of a birch in autumn. If the birch begins to turn yellow from below, then this indicates a late onset of spring.
7. The appearance of buds and foliage on the oak before the ash indicates the humidity and coolness of the upcoming summer. But if the ash is ahead of the oak, then we should expect a warm and dry summer.

The onset of leaf fall

The autumn tree never waits for a command to shed its leaves. This happens spontaneously. Why do trees shed their leaves in autumn? With the onset of coolness, the color of the leaves changes. Petioles also undergo certain changes. The "bricks" of foliage are connected to each other by strong bonds. The leaf is also firmly attached to the branch. It is not so easy, for example, to separate a leaf from a branch near a birch. In autumn, with a change in color, these bonds are destroyed. Therefore, the leaf is very loosely attached to the branch. Sometimes it is enough just to touch him, as he immediately falls.

This is due to the formation of a special cork layer. It seems to separate the petiole from the branch, becoming a real barrier between them. The sheet is fastened only with the help of thin tubes. Therefore, we can conclude that there is not a leaf breaking off from a branch, but a separation in a certain place. This is observed exactly where the formation of the cork layer occurred.

Which trees are the first to shed their leaves in autumn

Calendar autumn begins on the first of September. But by astronomical standards, its beginning is considered the day of the autumn equinox, which falls on September 21. According to phenologists, as soon as the leaves begin to turn yellow and fall, we can talk about the coming autumn.

Which trees shed their leaves first in autumn? The intensity of leaf fall is different. This applies not only to different types of trees, but also to different representatives of the same species. The situation depends on many factors and is determined by the nature of the weather, the age of the tree, its individual characteristics. Leaf fall proceeds with a different sequence. For quite a long time, oaks cannot part with their foliage. But after all, the appearance of leaves in them is observed later than in other types of trees. There are individual specimens in which leaves do not fall at all. This phenomenon has not yet been explained by scientists.

The linden, the birch and the elm fall the earliest. They are subject to leaf fall in early autumn. The loss of leaves by different parts of the tree also occurs unevenly. For example, in a poplar, the large lower branches are the first to lose their leaves. Then the middle part becomes “naked”, and this concerns the top of the head last. Elm or poplar behaves somewhat differently. It begins to lose its leaves, on the contrary, from the top. The crown begins to melt gradually, exposing the trunk more and more.

Some autumn trees retain their foliage even with the first frost. This situation is observed in the case of aspen and maple. Only spruce and pine do not shed their needles with the onset of autumn. They will stay green all winter.

Which tree is the last to shed its leaves in autumn?

The phenomenon of leaf fall is associated with a seasonal nature. In this way, plants adapt to winter. The frosts have not yet come, and the foliage of the plants has already begun to blaze with different colors. In a number of trees, this phenomenon can be observed already in early August. Linden crowns are painted with gilding. It will take 2-3 weeks, and the foliage will literally begin to burn with gold. By this time, a similar outfit is already observed on birch trees. The aspens look as if they were covered with a kumach. Even among the mountain ash, red leaves are visible. By the end of September, the crowns of many trees are bare.

In early October, the weeping willow ends its leaf fall. By the end of September, the leaf fall ended at the elm and bird cherry. Birch, maple and walnut are in no hurry to give up their foliage. Separate leaves on them keep until mid-October. But these are all averages. Naturally, they can change in one direction or another. It depends on the region where the trees grow and the weather conditions that prevailed in this particular autumn.

What is the purpose of leaf fall?

What are the causes of leaf fall in autumn? Trees shed their leaves for a reason. This is their protection from various damages of the mechanical plan. In winter, snowfalls are often accompanied by strong winds. From their pressure, not only foliage can suffer, but even branches and trees break. Damage will be even greater if the foliage traps snow with its surface.

Why do trees shed their leaves in autumn? With leaf fall, minerals are removed that have accumulated in sufficient quantities over the summer. For plants, they no longer bring benefits, on the contrary, they can only cause harm. Leaves, falling to the ground, rot and contribute to the return of minerals to the soil. They are good for plants too. This circumstance explains the need for leaf fall. This situation has been going on for millions of years. With the advent of winter, only those trees that shed the maximum number of leaves for the winter turned out to be able to survive.

Should I burn leaves in the fall?

Now I understand why trees shed their leaves in autumn. Should they be burned? The ground is covered with leaves and other parts of trees. All this is defined as bedding. In forests dominated by deciduous trees, it reaches 4 tons per hectare of land. Slightly less of it among pine representatives. The figure is approaching 3.5 tons. It accumulates not just like that, but has a certain value. It contributes to the accumulation of humus and minerals in the composition of the soil. If the litter is loose in nature, then its decomposition occurs easily, and water enters the soil. The process of rotting dense litter takes a very long time and is accompanied by a sour smell. It does not allow the soil and plant roots to freeze strongly.

Due to humus, the soil acquires a dark color, and therefore the sun warms up more strongly. Cooling occurs slowly, which favors the reproduction of beneficial microflora in the soil. If the leaf litter is removed, then the growth of plantations will decrease by 11%.

Why doesn't the needles fall off?

Leaves play an important role in the life of any tree or shrub. They create and accumulate the substances necessary to nourish the tree. Due to the fact that in winter there is not enough light, useful components are intensively consumed and moisture evaporates too intensively.

The habitat of coniferous plants is, as a rule, an area where there is a harsh climate. Such plants need enhanced nutrition, and therefore their needles do not fall off for the winter period. They contain a large amount of chlorophyll, with the help of which the transformation of nutrients takes place. The small area of ​​the needle significantly reduces evaporation. It also has protection from the cold, which is due to the wax coating. Thanks to this, the needles are not able to freeze even in severe frosts.

The only plant with needles that loses foliage for the winter is larch.

evergreens

In such representatives, the foliage does not fall even with the advent of cold weather. They constantly have leaves that can survive any weather conditions. Naturally, their foliage is constantly updated. But it happens gradually. Such plants can be found where the climate is mild and warm in nature. In such places, even in winter it is warm. But they can also be found where the climate is severe. As an example, it is easy to cite the blue one that can be found in California.