" reforestation programs introduce spruce and pines to areas where they are not native, and the newcomers experience substantial problems in their new habitats. Usually, they are brought to low elevations that are too warm and dry for conifers to thrive. As a result, the air is dustier, as you can clearly see when the dust motes are backlit by sun streaming down on a summer’s day. And because the spruce and pines are constantly in danger of dying of thirst, they are easy prey for bark beetles, which come along to make a meal of them. At this point, frantic scent-mails begin to swirl around in the canopy. The trees are “screaming” for help and activating their arsenal of chemical defenses. You absorb all of this with every breath of forest air you take into your lungs. "

― Peter Wohlleben , The Hidden Life of Trees: What They Feel, How They Communicate: Discoveries from a Secret World