Explain how this human impact on a forest ecosystem might affect the ability of some species to move to more suitable habitats as earth's climate changes

The possibility human impact refered to in the statement is deforestation. Deforestation is the widespread removal of trees and other vegetation from forested areas for purposes such as agriculture, road construction and other infrastructural development.

Removing sections of forest can create a disconnect between areas of the forest preventing species from moving and otherwise confining them to smaller regions of the forest.