In the past, people could perhaps maintain a forest's area by replacing the trees chopped down each year with a year of planting, but today Man can cut down the trees planted over a century in a single year.
前人或許砍一年樹、種一年樹，仍可維持森林面積不變，今人則一年之內就可以把一千年甚至一萬年所種的樹砍完。