A fellow Octopus Overlords forumite pointed me to a New York Times piece on how deforestation may not be as severe a problem as we thought. As people leave their farms for jobs in the city, the farmlands revert to forests. Because these forests absorb carbon dioxide and become new habitats for wildlife, they counterbalance some of the negative impact of rainforest destruction. The effect could be significant because forest growth is outpacing forest loss in terms of acreage.
As some of the authorities quoted in the article argue, though, these new forests are no substitute for old-growth forests. The species displaced by rainforest destruction usually have no way to relocate to the new forests. Even if they did, the new forests may not be sufficiently developed to suit them as habitats. Furthermore, city workers affected by the global recession may move out and raze the forests to build farmland again.
The article didn't mention it, but I wonder whether the global warming phenomenon facilitates the growth of these new forests. Does rainforest destruction, by contributing to global warming, speed the regeneration of forests in other tropical areas?
I also wonder whether the forests you chop down in the Age of Empires games ought to regenerate a bit as you progress through the ages.