Needles have a low evaporation rate.
Leaf fall is an adaptation of trees to unfavorable conditions, especially to cold. Leaves, even on frosty days, would evaporate such an amount of water that the roots would be unable to extract it from the frozen soil. Moreover, the rising moisture could freeze in the trunk, leading to its destruction.
Needles evaporate about ten times less moisture compared to leaves. Therefore, most coniferous trees do not shed their needles but renew them over several years.
Only a small portion of the needles turns yellow and is ready to fall, so at any moment the tree remains almost completely green.
