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 herself paints them in different shades, so much so that any artist will envy. Why does this happen every year? Why do trees drop leaves in the fall? This issue should be addressed in more detail.
What assumptions may arise?
Why do trees drop leaves in autumn? In the head, various associations immediately arise about what is happening:
- The foliage of the trees has grown old, it has become cold, and therefore falling off.
- In autumn, the leaves no longer have enough light for their growth.
- The reason the leaves fall is the wind.
Naturally, all these assumptions are subject to verification to find out the true reasons.
What role do leaves play in tree life?
The structure of the leaf is represented by two parts: the leaf blade and the petiole, which is its stem. The structure of the plate is represented by veins. They are especially clearly visible from below. It turns out that they are vessels designed for the movement of 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 little plants. They are preparing food for the whole tree. They build the material from which new branches, buds, roots and, of course, the trunk itself are formed.
They receive energy for their production from the sun. The absorption of light by them is carried out throughout the daylight hours. Chlorophyll is unstable and constantly undergoes destruction. But at the same time, its regular recovery is taking place. For any tree, a green leaf is essential. But the tree does not nourish the yellow leaf, but only takes moisture from it.
Why is the color changing?
Along with the destruction of chlorophyll, the process of its recovery is in progress. Moreover, the formation of green matter does not lag behind its destruction. As long as there is enough light, between these processes there is a certain balance, balance. 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, the predominant is not green, but yellow. But not only this color there are fading leaves. They can acquire a red, crimson, other color. This is determined by which coloring matter is predominant in the fading sheet.
Different foliage also happens in brightness. It depends on what the weather is like in autumn. The abundance of rain causes excessive saturation of the leaves with moisture. From this they become dull in nature. Alder and lilac lose their foliage regardless of the weather. In them, simply chlorophyll is represented by the only coloring matter.
Various folk signs
For many years, man has constantly monitored nature. Thanks to this, many national signs were formed. A lot of them are also associated with a change in the color of the foliage:
- If the leaf is yellowed, but the process of decay is not expressed, then it is still far from frost.
- Trees are covered with yellow foliage ahead of time - autumn will be early.
- Despite the snow falling, winter will not come until the leaves keep on the cherry.
- Bones with their leaves can predict the weather. Twisting down says good days. If on the contrary, the weather will be bad.
- If leaves appear on a birch earlier than on an alder, then summer will be windy in nature. If the birch is outstripped by an alder, then the summer will be cold and rainy.
- Early spring is predicted by early yellowness at the top of birch trees in autumn. If the birch begins to turn yellow below, then this indicates a late spring.
- The appearance of buds and foliage on an oak tree before ash indicates the humidity and coolness of the coming summer. But if ash is ahead of oak, then you should expect a warm and dry summer.
Offensive leaf fall
An autumn tree never waits for foliage dumping. This happens spontaneously. Why do trees drop leaves in autumn? With the onset of coolness, the color of the leaves changes. The petioles are also undergoing certain changes. The “bricks” of the foliage are connected to each other by strong bonds. The leaf is also firmly attached to the branch. It is not so simple, for example, to separate a leaf from a branch near a birch. In the fall, with a change in color, these bonds are destroyed. Therefore, the leaf is very loosely attached to the branch. Sometimes it’s 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 stalk from the branch, it becomes a real barrier between them. Fastening the sheet is carried out only with the help of thin tubes. Therefore, we can conclude that there is no tearing off the leaf from the branch, but separation in a certain place. This is observed exactly where the formation of the cork layer occurred.
Which trees first drop leaves in the fall
Calendar autumn begins on the first of September. But by astronomical standards, its beginning is considered the day of the autumnal 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 upcoming autumn.
What trees drop leaves first in the fall? 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 occurs with a different sequence. For a long time, oaks cannot part with their foliage. But after all, the appearance of leaves in them is observed later than in other species of trees. There are individual specimens in which leaves do not fall at all. This phenomenon has not yet been explained by scientists.
Before all, foliage falls from linden, birch and elm. They are subject to leaf fall already in early autumn. Loss of leaves in different parts of the tree also occurs unevenly. For example, large poplar branches are the first to lose leaves at poplar. Then the "middle" becomes the middle part, and this is the last thing that touches the crown. Elm or poplar behaves somewhat differently. He begins to lose his leaves, on the contrary, from the top. The crown begins to melt gradually, more and more exposing the trunk.
Some autumn trees retain foliage even with the first frosts. This situation is observed in the case of aspen and maple. Only spruce and pine do not drop their needles with the onset of autumn. They will remain green all winter.
Which tree is the last to drop leaves in the fall
The phenomenon of leaf fall is associated with a seasonal nature. In this way, plants adapt to winter. Frosts have not yet come, and the foliage of plants has already begun to blaze with different colors. In a number of trees, this phenomenon can be observed already in early August. The crowns of linden are gilded. 2-3 weeks will pass, and the foliage will literally begin to burn from gold. A similar outfit by this time is already observed on birches. Aspen trees look as if they were covered by a couch. Already among the mountain ash, red leaves are visible. By the end of September, the crowns of many trees are exposed.
In early October, a weeping willow ends its leaf fall. By the end of September, leaf fall ended with elm and bird cherry. Birch, maple and walnut are in no hurry to give their foliage. Individual leaves on them hold until mid-October. But all these are average indicators. Naturally, they can change in one direction or another. It depends on the region where the trees grow and the weather conditions that developed precisely this fall.
What is the purpose of leaf fall?
What are the causes of fall foliage in the fall? It is no coincidence that trees dump their foliage. This is their protection against various damage to the mechanical plan. In winter, there are often snowfalls, accompanied by a strong wind. Not only foliage can suffer from their pressure, but even branches and trees break. Damage will be even greater if the foliage will retain snow on its surface.
Why do trees drop leaves in autumn? Minerals that accumulated in sufficient quantities over the summer are removed with leaf fall. For plants, they already do not 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 still useful to plants. This circumstance explains the need for leaf fall. This situation has developed over millions of years. With the advent of winter only those trees that survived in winter dropped the maximum number of leaves were able to survive.
Do I need to burn foliage in the fall?
Now it’s clear why trees drop leaves in the fall. Do you need to burn them? The earth is covered with leaves and other parts of trees. All of this is defined as litter. In forests dominated by deciduous trees, it reaches 4 tons per hectare of land. It is slightly smaller 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 soil. If the litter is loose, then its decomposition is easy, and water enters the soil. The process of decay of a 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 the humus, the soil becomes dark in color, and therefore the sun warms up more strongly. Cooling is slow, which favors the reproduction of beneficial microflora in the soil. If you remove the sheet litter, then the growth of plantings will decrease by 11%.
Why doesn’t the needles fall?
In the life of any tree or shrub, the leaves play a rather significant role. They create and accumulate substances necessary for the nutrition of the tree. For the reason that in winter there is not enough light, useful components are intensively consumed and moisture evaporation occurs too intensively.
The habitat of conifers is, as a rule, the area where the harsh climate is present. Such plants need enhanced nutrition, and therefore their needles for the winter period do not fall. They contain a large amount of chlorophyll, through which the conversion of nutrients occurs. A small needle area significantly reduces evaporation. It also has protection from the cold, 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
Such representatives of the foliage does not fall even with the advent of cold weather. They are constantly present with leaves that can survive any weather conditions. Naturally, their foliage is constantly updated. But this happens gradually. Such plants can be found where the climate is mild and warm in nature. In such places it is warm even in winter. But they can also be found where the climate is severe. As an example, it is easy to cite the blue fan palm, which can be found in California.