Does anybody know if/how Ecosia tackles long-term viability of their trees?

Edit: From their site: "Of course, not all trees survive; that never happens. Ecosia therefore only counts trees that will survive for more than three years – a time when they’re robust enough to face most natural threats.

For instance, if we plant 1000 trees and know from experience that the mortality rate in this area is 25%, we’ll only add 750 trees to our tree counter. We continually measure the survival rate of the trees we plant, through inventories and satellite technology, and adjust our tree counter accordingly."

(https://blog.ecosia.org/how-do-ecosia-trees-survive-cut-down...)