What is the evolutionary benefit of some trees dropping their leaves and others not?

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Offline thedoc

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Jonas Jacobson asked the Naked Scientists:
   Science question on trees & leaves:
In colder climates, many leaf trees drop their leaves during the autumn. Is there an average percentage amount of biomass that a tree drops through their leaves in a season?
And related to that, some trees do not drop their leaves even in colder climates, so why is it evolutionary beneficial for some trees to drop their leaves (i.e. why didn't only the leave-keeping trees / evergreens come out on top)?

Thank you,
Jonas, a Swede in Switzerland
What do you think?
« Last Edit: 07/05/2016 21:50:01 by _system »

Offline evan_au

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I see that some trees that keep their leaves in snow season tend to have very spiky leaves. This small surface area (compared to wide, flat leaves) might reduce water loss in winter?

I live in Australia, where very few areas freeze during winter. Keeping leaves all year allows the trees to continue growing all year.

See: https://en.wikipedia.org/wiki/Deciduous#Function

Offline puppypower

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The reason trees loose leaves is to prevent loss of water during the winter. In the winter, the ground and the surface water is often frozen, while the air is very dry. The result is leaves provide too much surface area for water loss. This loss can exceed water the roots can find, so the tree loses it leaves. 

Pine trees contain a lot of sap, from which kerosene is extracted. I would guess the organic sap seals the leaves and reduces the amount of water loss; surface tension.

Offline Ophiolite

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Or consider the waxy coating of a holly leave, which is certainly not pine needle shape. That is another mechanism for controlling water loss.

Nature is versatile in its designs.
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