
In the average forested 250 x 250 tile area (including a river running through the middle), there are approximately 700 trees. There are 400 such size areas on any given super-grid (a super-grid is 5000 x 5000 tiles).
If we assume this as a standard measure, that equates to 280,000 trees per super-grid.
If we assume that there are currently 49 super-grids in the world, then that equates to 13,720,000 trees.
It takes approximately 10 seconds to cut down a tree. That equates to 137,200,000 seconds; 38,111 hours; 1,588 days or 4.3 years non-stop to cut down all the trees in the world.
It will take 32 days of non-stop tree cutting in order to clear a single super-grid.
Have fun!