For uptimum growth and development, tropical and temperate trees develope some adaptive features as highlighted below. In SUMMER, their broad green leaves help capture sunlight needed to make food through photosynthesis. As temperatures drop, the tree cuts off the supply of water to the leaves and seals off the area between the leaf stem and the tree trunk. With limited sunlight and water, the leaves are unable to continue producing chlorophyll (green pigment in leaves) causing them to change into the beautiful red, yellow and orange leaf colours of FALL. In WINTER, it is too cold for the trees to protect their leaves from freezing, so they simply loose them and seal up the places where the leaves attach to the branch. Losing their leaves helps trees to conserve water loss through transpiration. (Dried leaves continue to hang on the branches of some deciduous trees until the new leaves come out.) Before the leaves die, some of the food material they contain is drawn back into the twigs and branches where it is stored and used the following spring. The warmer temperatures of SPRING signal to the trees that they can grow new leaves again, and restart the cycle.
Posted on: Wed, 19 Jun 2013 08:32:19 +0000
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