Answer
Erosion resulting from the removal of trees washes more nutrient-rich soil and detritus out into rivers while also removing much of the nutrients from the ecosystem in the form of the trees themselves.
Work Step by Step
There are two pieces to this: One is that erosion can remove nutrient-rich topsoil and the detritus on the forest floor that helps enrich it, and the other is that the trees themselves contain a massive proportion of the nutrients present in this ecosystem.
