Trees have been around for a very, very long time; much longer than we have. Complex evolutionary forces have shaped trees and forests into their current robust configurations.
Trees are intimately connected with their ecosystems, and interact with their surroundings in both known and unknown ways. For example, it has been discovered recently that trees communicate with one another through chemical, hormonal and slow-pulsing electrical signals, including through the air, using pheromones and other scent signals 
Mother nature is complex. We do not have enough understanding of her complexity, and neither enough computational power to reliably model and subsequently change diverse ecosystems.
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