In order to answer this question, you need to take a certain interest in the role of leaves in the life of a tree.
The function of the latter is to capture the sun's rays so that the tree can transform light energy using photosynthesis.
Regarding deciduous trees, the drop in light levels and temperatures during the autumn season reduces the effectiveness of the leaves. A seal forms at their base, thereby cutting off the fluid exchanges with the tree. They dry up and fall. The tree, which is then deprived of its energy source, becomes dormant and consumes fewer nutrients in order to withstand the severity of the winter. As spring returns, it deploys a lot of energy to create new leaves.
As for the evergreen trees, like holly or conifers, they adopt a completely different strategy.
They keep their leaves from one year to the next. They often have highly resistant leaves with a small surface area that can photosynthesise, even when there is little sunlight. The sap continues to run through the leaves and branches despite the cold. Thanks to a layer of wax, these leaves or needles are protected from the frost in the winter and from drying up in the summer.
These trees lose their leaves gradually as new ones grow thereby replacing the older leaves without requiring any particular effort
Regardless of the method employed, it is always a matter of adapting as effectively as possible to the environment of the tree !