Why do deciduous trees lose their leaves?
It’s survival not just of the fittest, but of the wisest.
Deciduous trees drop their leaves in order to survive. As days grow shorter and colder, deciduous trees shut down veins and capillaries (that carry water and nutrients) with a barrier of cells that form at the leaf’s stem.
Called “abscission” cells, the barrier prevents the leaf from being nourished. Eventually, like scissors, the abscission cells close the connection between leaf and branch and the leaf falls.
Had the leaves remained on branches, the leaves would have continued to drink and, once temperatures drop to freezing, the water in the tree’s veins would freeze, killing the tree.
Further, with leaves fallen, bare branches are able to carry what little snow collects on them, protecting them from being broken under the weight of the snow. So, by cutting off their food supply (leaves), deciduous trees survive winter.
The fallen leaves continue to benefit the tree through winter, spring and summer by creating a humus on the forest floor that insulates roots from winter cold and summer heat, collect dew and rainfall, and decompose to enrich the soil and nurture life.
It’s a cycle of survival, planned wisely.
Deciduous conifers that drop leaves at once include: Larch, Bald Cyprus and Dawn Redwood.
In snowy regions, evergreen trees are able to carry snow because the waxy coating on needles, along with their narrow shape, allows them to retain water better by keeping it from freezing inside (which would otherwise destroy the leaf).
Needles also prevent snow from weighing down and breaking branches. Finally, needles allow an evergreen tree to sustain the production (though slowed) of chlorophyll through winter. Whereas, broadleaved deciduous trees would be damaged if they kept producing chlorophyll and didn’t drop their leaves.
Evergreen trees do lose their leaves and the leaves do change color. It just isn’t as spectacular.
I love your site, so I hope you excuse the pedantic comment I’m about to make:
Larches are deciduous conifers, not evergreens. If they were evergreens, well, they would be ever green.
Again, thanks for putting together so a great site.
Derek, Thanks greatly for the clarification on larches. I will correct past posts to note the difference and welcome other info you might provide. I’m a journalist with a love of forests, but not a forester (my father was one). So, my knowledge comes mostly from reference literature and my own mistaken beliefs. That’s why I so appreciate comments and corrections by readers. JP