Answer:
Chopping down half of the trees in a forest would upset the existing ecosystem and the mall could be built somewhere else or trees replanted.
Step-by-step explanation:
By this I mean that many animals would be without the food or homes that they had in and around the trees. This would cause populations of animals to decrease as a result.
By putting the mall somewhere else that would mean even more work in planing because the terrain may be different, but as a trade off the forests are not being damaged.
There also is the possibility of just building where planned and just replanting the trees or just planting new ones around the mall. The problem with planting new ones is that trees take a while to grow.