Discussions on general biology and biological evolution, genetics, zoology, ecology, botany, etc.


Postby pgrudzi on April 16th, 2012, 7:34 pm 

Hello, I have gotten some really good answers here in the past so I thought I would pose another question. This one deals with trees. My question is decidious trees lose their leaves in the fall. What causes them to do this? Is it temperature, amount of sunlight etc. When the tree doesn't have leaves is it still alive and able to photosynthesis (my guess is no). If not how does it surive to the next spring and grow leaves again. What causes them to grow leaves again?
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Re: Trees

Postby wolfhnd on April 16th, 2012, 11:13 pm 

A tree is full of vascular cells that transport water and sap throughout, from root to leaf tip. As the amount of sunlight decreases in autumn, the veins that transport sap into and out of a leaf slowly close off. Then a layer of cells, called the separation or abscission layer, develops at the base of the leaf's stem. When this layer is completely formed, the leaf falls off.

This process happens in all deciduous trees (trees that annually shed their foliage), with oak leaves as a notable exception. In oaks, the separation layer doesn't fully allow the oak leaves to detach. That's why most dead oak leaves remain on the tree through winter and even into early spring (much to the perpetual leaf-raking consternation of home owners with oak trees on their property). ... -in-winter
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