why do trees drop their leaves?
Why do trees drop their leaves? Janzen says that leaf drop may be a response to • increased shading due to the more leaves growing overhead within the tree’s crown or in other trees’ crowns • damage by herbivores, wind, or falling debris • dry weather Increased shading. If there is a gap in the forest or if the area is disturbed, pioneer species of trees will come in, and for these species here is a premium on rapid vertical growth. In these circumstances, “…leaves tend to be shed almost as soon as a shadow is cast upon them. If minerals can be thoroughly extracted from leaves before discarding…the cellulose skeleton that is lost means relatively little to the plant in a light-rich habitat.” [Janzen] Aha! This seems to me the perfect explanation for the Cecropia behavior. Here’s a leaf about to drop from a young Cecropia – zooming in on it in the adjacent image. Doesn’t that leaf look like it’s had all its minerals and other goodies extracted? The petioles (leaf stalks) are quite long
