1) Biological process 2) Organic process 3) Removal of shoots 4) The loss of foliage 
• (n.) The separation of ripened leaves from a branch or stem; the falling or shedding of the leaves.
(from the article `woodrat`) Woodrats are usually common within their ranges, but Allegheny woodrat populations are declining, possibly because of forest defoliation by gypsy ...
Loss of leaves.Removal of shoots.
De·fo`li·a'tion noun [ Late Latin defoliare , defoliatum , to shed leaves; Latin de- + folium leaf: confer French défoliation .] The separation of ripened leaves from a branch or stem; the falling or shedding of the leaves. 
The casting or falling of the leaves.
When the leaves fall off your plant too early. Can be caused by lack of water, insects, or plant diseases.
[n] - the loss of foliage 2. [n] - causing the leaves of trees and other plants to fall off (as by the use of chemicals)
noun causing the leaves of trees and other plants to fall off (as by the use of chemicals)
The premature falling off of leaves. May be caused by disease, insects or too much or too little moisture.
The loss of leaves from trees and shrubs.