Farmers cleared land for planting, and they didn't do that much of it before the 1800's. There just wasn't that much population.
Indians were fire-bugs. They would set forest fires all over. The reason was that deer eat grasses and tree shoots. Their ecological niche is at the interface between woods and meadow. Large forests of large mature trees do not provide food for deer. The ideal hunting environment involved lots of meadows.
That said, the conclusion is silly. The Earth's main carbon sink is the ocean. Warm oceans hold less carbon than cold oceans. For that reason, CO2 levels FOLLOW temperature changes, rather than causing them.
How does that account for the deer foraging on acorns? Are they all community organizers?
We all know...deer eat meat. Fact.