Why do leaves on the last fall?

In temperate regions, whenever autumn comes, the trees change color from green to yellow, finally unloading this shirt, naked to welcome the coming winter. If you pay a little attention, you will see that the leaves on the main branch change color first, then gradually spread to the tops of the trees and branches. The same is true for deciduous, fallen below, to the top, the more slowly the leaves fall.

You may say, it is a natural phenomenon of the biological world, getting old first to die first. The lower leaf comes first, the first branch should fall earlier. This is an explanation, but there is a deeper understanding.

When the top of a tree grows to a certain extent, growth slows down.

During growth, every tree reaches its fullest growth, so it always brings a lot of food to the top to accelerate growth . The tops of branches are provided with many nutrients. When the top of a tree grows to a certain extent, growth slows down. At this time, deciduous trees are due to two conditions: Inside, the supply of nutrients is limited and outside, the weather conditions change in the unfavorable direction , the function of food synthesis of leaves is worse, leaves do not exist anymore, falling faintly.

But even so, the top of the tree is still prioritized to take care of, the food is provided the most, so although the tree stops putting food to the top, thanks to the reserves it will survive for some time. At the same time, the chlorophyll in the leaves has not been destroyed, still synthesizing some nutrients. Thus, the leaves on the top of the tree will fall later than in other parts of the tree.

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