Re: Why can pine trees stay green all year long, and leafy trees can not?

Hi, Neil.

I don't know if you made that up or not, it's entirely possible that you were taught that at one time or another since it does seem to follow the logic of evolution. However, I've done some research on it and found some other reasons which, althought they may not be the only reasons, are at least more probable than your hypothesis.

If you look at a deciduous leaf and then look at a pine needle, you will notice the large difference in surface area between the two (the amount of the leaf that is exposed to the air). The problem with the design of the broad, flat deciduous leaf is that in the winter, almost all of the leaf is exposed to the cold air and snow. Were the leaves to remain on the tree, the leaves would quickly freeze and the ice would damage the cells of the leaf. Furthermore, the tree would spend an inordinate amount of energy trying to keep the leaf warm -- energy which would be much better served feeding the tree.

Instead, the tree shifts its metabolism from a photosynthesis-based system, to one utilizing glucose and amino acids. This also helps keep the tree from freezing, acting as a kind of "antifreeze". A lot of the energy and resources to shift to this new system is taken from the leaves before they die and fall off.

The reason pine trees and other conifers don't do this is because the pine needles have much less surface area -- and are designed to allow water to flow off of them instead of retaining it like the deciduous leaves. Plus, the pine trees are always replacing their needles.

I hope this has answered your question. If you have any more questions, please feel free to E-mail be at: gt7418c@prism.gatech.edu