Why do evergreen trees do not lose their leaves in winter?

Answer 1

A simple answer is that, wheras deciduous trees lose their leaves in winter, evergreen trees also lose their leaves, but all year round. Some evergreen trees, such as the Australian Eucalypts shed leaves, and even drop whole branches during dry periods, to limit loss of water.

Answer 2

Making leaves requires a big input of resources, so it's advantageous for trees to hang onto their leaves. On the other hand, leaves lose a lot of water, which can kill plants. And winters are functionally dry for plants since the moisture is frozen, and there are cold evaporative winds.

Evergreen trees have evolved to protect their leaves through a thick waxy coating on the needles, which controls evaporation and allows them to keep their needles for several years. Deciduous trees in cold climates have taken another approach--they make leaves with a large surface area to take in a lot of sunlight during the summer. At the end of the season, they suck back a lot of the minerals and other resources from the leaves into the tree, and then drop the leaves so that they don't lose water to evaporation during the winter.

Answer 3

Evergreens stay green all the year around because they don't lose their leaves. Deciduous trees lose their leaves because in Winter, they lose too much moisture through the leaves to make it worthwhile keeping them. They don't gain enough from the small amount of sunlight in winter to compensate. There are a few different types of evergreens which have different reasons for not losing their leaves.

1. Conifers have needles instead of broad leaves, so they don't lose much moisture through them making it practical to keep them throughout the year.

2. Some broad-leaved trees such as Evergreen Oaks and Laurels have a waxy coating on the leaves so they don't lose moisture.

3. Trees in tropical rainforests don't experience any winter so they are green all the year round.