Subject: why are some trees evergreen?

From: [email-masked]
Date: Thu, 31 Aug 95 15:41:52 WST

For your information from the Botany News Group[

MB>>1. Why are some trees and bushes evergreen and why are some deciduous?

MB>Evergreen may best be considered as the "normal" or "initial" condition.  Th
MB>seasonal shedding of leaves is an adaptation to draught. The water-household
MB>is very essential in plants. Leaves evaporate water, but when there is no 
MB>water available to the roots, the plant will dry out. Shedding of the leaves
MB>in a dry  period is an (evolutionary) answer to this problem.

MB>Cold, in a way, is exactly the same problem. When the water in the ground 
MB>freezes, it becomes inaccessable for the plant, and it is in fact the same a
MB>draught.

MB>Another answer to this problem is having very small leaves, like needles, th

MB>don't evaporate much.

MB>>2. What mechansim allows some trees to stay green all year?
MB>Wrong question. You should ask what the mechanism is to shed leaves. This is
MB>very complex. What would happen when you place a deciduous tree in a climate
MB>with no seasonal differences, an all-year-round optimal climate?  I think it
MB>would still shed it's leaves in October. It is probably a genetically 
MB>programmed phenomenon. Temperature and draught help to determine the exact 
MB>moment. It is not just that the leaves die and fall off, but it is an active
MB>process: first some of the nutricious substances of the leaves are retrieved
MB>from them (causing autumn colors), then a scar tissue is formed at a precise
MB>place at the leave base.

MB>>3. Can evergreens be found in all climates?
MB>Yes. There are also other ways to adapt to draught. Except of course on the 
MB>North Pole and in the Sahara [the Date Palm is evergreen tho... but that's a
MB>oasis].

MB>>4. Do evergreens reproduce the same way that deciduous trees do?
MB>Evergreen is not the same as Coniferous. A Conifer like Larix is a deciduous
MB>tree (with spectacular aurumn colors). Reproduction has not much to do with 
MB>the topic of evergreen/deciduous.

MB>Hope this helpes, bye, Marco

MB><[email-masked]>------------<http://www.euronet.nl/users/mbleeker/>
MB>>-------------<Plants, Programs, Primitive creatures>------------------<
MB><Marco Bleeker>------------<nl-en-de-fr>------------<Amsterdam, Holland>

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