As a result of the climate and highly fertile land, agriculture is a major activity in the Mont Saint-Hilaire Biosphere Reserve. Corn is the principal crop, while cows are the main livestock raised. Agricultural development has led to marked deforestation throughout the region. That in turn has made it possible for certain species of plants and animals to proliferate dramatically. A case in point is the white-tailed deer, which delights hikers but is a considerable annoyance for farmers and apple-growers alike.