Drought disturbance from climate change: response of United States forests

Predicted changes in climate have raised concerns about potential impacts o n terrestrial forest ecosystem productivity, biogeochemical cycling, and th e availability of water resources. This review summarizes characteristics o f drought typical to the major forest regions of the United States, future drought projections, and important features of plant and forest community r esponse to drought. Research needs and strategies for coping with future dr ought are also discussed. Notwithstanding uncertainties surrounding the mag nitude and direction of future climate change, and the net impact on soil w ater availability to forests, a number of conclusions can be made regarding the sensitivity of forests to future drought. The primary response will be a reduction in net primary production and stand water use, which are drive n by reductions in stomatal conductance. Mortality of small stature plants (i.e. seedlings and saplings) is a likely consequence of severe drought. In comparison, deep rooting and substantial reserves of carbohydrates and nut rients make mature trees less susceptible to water limitations caused by se vere or prolonged drought. However, severe or prolonged drought may render even mature trees more susceptible to insects or disease. Drought-induced r eductions in decomposition rates may cause a buildup of organic material on the forest floor, with ramifications for fire regimes and nutrient cycling . Although early model predictions of climate change impacts suggested exte nsive forest dieback and species migration, more recent analyses suggest th at catastrophic dieback will be a local phenomenon, and changes in forest c omposition will be a relatively gradual process. Better climate predictions at regional scales, with a higher temporal resolution (months to days), co upled with carefully designed, field-based experiments that incorporate mul tiple driving variables (e.g. temperature and CO2), will advance our abilit y to predict the response of different forest regions to climate change. (C ) 2000 Elsevier Science B.V. All rights reserved.