Question

why is tropical rainforests known as evergreen forest?

Answer 1

Bcz they every year gets evergreened again and the region in which they lie are hot and receive rainfall in a heavy amount but evergreen again...Also
The trees and plants shed their leaves every year.

Answer 2

These forests are dense and the trees grow to a great height. The trees and plants shed their leaves during the year at the same time.Hence they are evergreen.
Eg:- Teak,Rosewood,Champa etc.
I guess...
Hope this is it....