Numerous studies have tried to project the effects of climate change on forest productivity and carbon balance through modeling simulations and manipulative experiments. Studies of CO2 fertilization indicate that productivity may generally increase across the Upper Midwest. Warmer temperatures may speed nutrient cycling and increase photosynthetic rates for most tree species. Longer growing seasons could also result in greater growth and productivity of trees and other vegetation, but only if sufficient water and nutrients are available. Episodic disturbances such as fires, wind events, droughts, and pest outbreaks may reduce productivity in certain areas over different time scales. In addition, lags in the migration of species to newly suitable habitat may reduce productivity until a new equilibrium is reached. For these reasons, future forest productivity is dependent upon complex interactions among the degree of warming, ecosystem water balance, and disturbance events.