Final answer:
Deciduous trees, such as maples, lose their leaves in autumn in response to shorter days and cooler temperatures, conserving water and energy during the winter when photosynthesis can't occur. They regrow leaves in spring which requires a significant amount of energy.
Step-by-step explanation:
Maples and other deciduous trees lose their leaves in the autumn as part of their adaptation to seasonal changes in their environment. This process occurs in response to shorter days and cooler temperatures which signal the approach of winter. As daylight decreases, trees begin to produce less chlorophyll, the pigment responsible for the green color in leaves, allowing other pigments to show and leading to the colorful display of fall foliage. After the leaves turn color, they fall off, preparing the plant for a period of dormancy.
The leaf shedding is a strategy to reduce water loss during the winter when water may be less available, and the ground may be frozen. This survival strategy is critical for conserving resources, such as water and nutrients. Leaf drop also allows deciduous trees to "bank" energy over the colder months, since maintaining leaves would require energy that the tree can't afford to spare when photosynthesis is not possible.
In the spring, as temperatures rise, these trees must expend a significant amount of energy and matter to grow new leaves. This cycle of growth and dormancy affects the net primary productivity of temperate forests, where deciduous trees are a dominant plant form, making it lower than in tropical wet forests where plants grow year-round.