Agriculture is one of the primary drivers of deforestation — both in modern times and in ancient times. The vast old-growth forests that once covered much of the world have largely been cut and burned down because of agriculture. Even when such agricultural-land is reclaimed by nature it generally lacks the great biodiversity that was found there previously, being replaced largely by fast-growing plants and ‘weeds’ that favor the depleted soil. Subsistence-farming accounts for 48% of deforestation, and commercial agriculture for a further 32% of deforestation, according to the United Nations Framework Convention on Climate Change.
Even the most efficient agricultural systems and practices inevitably lead to nutrient loss unless supplemented with fertilizer brought in from elsewhere — this nutrient-loss is especially pronounced with GMO (genetically modified food) agriculture. And this, along with the soil erosion that accompanies the loss of large vegetation, further contributes to the soil erosion and desertification that seems to almost inevitably follow deforestation in the long term.