Science Questions

Why do trees lose their leaves in temperate climates?

Sun, 23rd Nov 2008

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Eduardo asked:

Why do trees lose their leaves in temperate climates?


Kat - The only trees that lose their leaves are deciduous trees. Theyíre different from coniferous trees. The reason they do this mainly is because leaves fulfil an interesting function for trees. Not only do they help them produce energy from photosynthesis, thatís where the pigments live that help trees to make energy from sunlight from carbon dioxide and water but also they act as the treeís disposal system. Throughout the year the tree will grow, produce energy, sugars and all sorts of things in its leaves and its waste products get put back into the leaves. Now very Autumn, basically because trees do need a lot of water, they start to have a less reliable supply of water, less light so the trees decide ok, now is the time to get rid of our leaves. They lose them and itís basically tress are getting rid of their waste products. Itís also why theyíre changing in colour as well because these waste products are different colours to the green chlorophyll pigment that helps them to make energy.  Basically, deciduous trees will lose their energy in this way but coniferous trees so pine trees: all these things with little needles, they donít produce energy in quite the same way. They also donít have this need for water. They have thin, very thin leaves that lose less water and they have a very waxy cuticle on them. Deciduous trees are basically throwing out the garbage when they get rid of their leaves.

Chris - i did also hear thereís quite a clever trick that researchers at Colgate University in the US discovered that acer trees also use this as the tree equivalent of chemical warfare. They pump into their leaves various toxins, which when the leaves fall to the ground, suppress the growth of other plants and things that would normally grow in the ground. This means that when their seeds try and germinate they have much less competition. The researchers who did this showed that they could kill lettuce plants with the leaf extract from these trees. You could say that when it comes to giving their offspring a fighting chance theyíve got an ace up their leaves.


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