What natural force helps leaves from the trees in why leaves turn color in the fall

http://blog.nwf.org/2014/09/why-leaves-fall-from-trees-in-autumn/

http://www.esf.edu/pubprog/brochure/leaves/leaves.htm

The natural force that helps leaves fall from trees in the fall is gravity. However, the change in leaf color during autumn is not directly caused by gravity. The color change is actually a result of a process called leaf senescence, which is triggered by changes in daylight and temperature.

To understand why leaves turn color in the fall, we need to delve into the biology of leaves. Leaves contain pigments, such as chlorophyll, which give them their green color. Chlorophyll plays a vital role in photosynthesis, the process by which plants convert sunlight into energy.

During the summer, there is an abundance of sunlight, so chlorophyll production is high. This masks other pigments present in the leaves, such as carotenoids (which produce yellow and orange colors) and anthocyanins (which produce red and purple colors).

As autumn approaches, the days become shorter, and temperatures decrease. These environmental cues trigger several changes in the tree's physiology. One of these changes is the reduction in chlorophyll production. As the chlorophyll levels decrease, the green color fades, and the underlying pigments, like carotenoids and anthocyanins, become more visible.

However, unlike chlorophyll, carotenoids are more stable and are not dependent on sunlight for their production. As a result, the carotenoids that were there all along start to show, giving the leaves their yellow and orange hues.

Anthocyanins, on the other hand, are not always present in leaves during the growing season. They are produced primarily in response to certain environmental conditions, such as cool temperatures and bright sunlight. These conditions can trigger the production of anthocyanins, which are responsible for the vibrant reds and purples seen in some trees during fall.

Ultimately, as the days get shorter and temperatures continue to drop, the combination of reduced chlorophyll production and the appearance of carotenoids and anthocyanins leads to the dramatic color change in leaves. Gravity then plays its role by pulling the leaves downward, causing them to detach from the trees and fall to the ground.