Ecological Applications, 17(8), 2007, pp. 2145–2151Ó 2007 by the Ecological Society of AmericaCLIMATE CHANGE AND FORESTS OF THE FUTURE:MANAGING IN THE FACE OF UNCERTAINTYCONSTANCE I. MILLAR,1,4NATHAN L. STEPHENSON,2AND SCOTT L. STEPHENS31USDA Forest Service, Sierra Nevada Research Center, Pacific Southwest Research Station, 800 Buchanan Street,Albany, California 94710 USA2U.S. Geological Survey, Sequoia–Kings Canyon Field Station, 47050 Generals Highway, Three Rivers, California 93271 USA3Division of Ecosystem Science, Department of Environmental Science, Policy, and Management, 137 Mulford Hall,University of California, Berkeley, California 94720-3114 USAAbstract. We offer a conceptual framework for managing forested ecosystems under anassumption that future environments will be different from present but that we cannot becertain about the specifics of change. We encourage flexible approaches that promotereversible and incremental steps, and that favor ongoing learning and capacity to modifydirection as situations change. We suggest that no single solution fits all future challenges,especially in the context of changing climates, and that the best strategy is to mix differentapproaches for different situations. Resources managers will be challenged to integrateadaptation strategies (actions that help ecosystems accommodate changes adaptively) andmitigation strategies (actions that enable ecosystems to reduce anthropogenic influences onglobal climate) into overall plans. Adaptive strategies include resistance options (forestallimpacts and protect highly valued resources), resilience options (improve the capacity ofecosystems to return to desired conditions after disturbance), and response options (facilitatetransition of ecosystems from current to new conditions). Mitigation strategies include optionsto sequester carbon and reduce overall greenhouse gas emissions. Priority-setting approaches(e.g., triage), appropriate for rapidly changing conditions and for situations where needs aregreater than available capacity to respond, will become increasingly important in the future.Key words: carbon sequestration; climate change; desired con ditions; ecosystem management;facilitated conservation; forest management; historical variability; resilience; resistance; wildfire.INTRODUCTIONDuring the last several decades, forest managers haverelied on paradigms of ecological sustainability, histor-ical variability, and ecological integrity to set goals andinform management decisions (Lackey 1995, Landres etal. 1999). These concepts commonly use historical forestconditions, usually defined as those that occurred beforeEuro-Americans dominated North American land-scapes, as a means of gaining information about howhealthy forests should be structured. There is no doubtthat historical data have immense value in improvingour understanding of ecosystem responses to environ-mental changes and setting management goals (e.g.,Swetnam et al. 1999). However, many forest managersalso use the range of historical ecosystem conditions as amanagement target, assuming that by restoring andmaintaining historical conditions they are maximizingchances of maintaining ecosystems (their goods, servic-es, amenity values, and biodiversity) sustainably into thefuture. This approach is often taken even as ongoingclimate changes push gl obal and regional climatesbeyond the bounds of the last several centuries tomillenia (Intergovernmental Panel on Climate Change2007). As importantly, novel anthropogenic stressorssuch as pollution, habitat fragmentation, land-usechanges, invasive plants, animals, and pathogens, andaltered fire regimes interact with climate change at localto global scales. The earth has entered an era of rapidenvironmental changes that has resulted in conditionswithout precedent in the past no matter how distantlywe look. Attempts to maintain or restore past conditionsrequire increasingly greater inputs of energy frommanagers and could create forests that are ill adaptedto current conditions and more susceptible to undesir-able changes. Accepting that the future will be differentfrom both the past and the present forces us to manageforests in new ways. Further, although quantitativemodels can estimate a range of potential directions andmagnitudes of environmental changes and forest re-sponses in the future, models rarely can predict thefuture with the level of accuracy and precision needed byresource managers (Pilkey and Pilkey-Jarvis 2007). Wemight feel confident of broad-scale future environmentalchanges (such as global mean temperature increases),but we cannot routinely predict even the direction ofchange at local and regional scales (such as increasing ordecreasing precipitation). A healthy skepticism leads usto use models to help organize our thinking, gamedifferent scenarios, and gain qualitative insight on theManuscript received 11 October 2006; revised 14 May 2007;accepted 15 May 2007. Corresponding Editor: D. McKenzie.4E-mail: [email protected] of magnitudes and direction of possible futurechanges without committing to them as forecasts.Facing an unknowable and uncertain future, however,does not mean ‘‘anything goes’’ for natural resourcemanagement. Managing in the face of uncertainty willrequire a portfolio of approaches, including short-termand long-term strategies, that focus on enhancingecosystem resistance and resilience as well as assistingforested ecosystems to adapt to the inevitable changes asclimates and environments continue to shift. Historicalecology becomes ever more important for informing usabout environmental dynamics and ecosystem responseto change. We offer here a conceptual framework fordeveloping forest management strategies in a context ofchange.FOREST AND ECOSYSTEM MANAGEMENTIN THEFACE OF CHANGEThe premise of an uncertain but certainly variablefuture is effectively best addressed with approaches thatembrace strategic flexibility, characterized by risk-taking(including decisions of no action), capacity to reassessconditions frequently, and willingness to change courseas conditions change (Hobbs et al. 2006). Learning fromexperience and iteratively incorporating lessons intofuture plans (adaptive management in its broadest sense)is the necessary lens through which natural resourcemanagement must be conducted (Spittlehouse andStewart 2003, Stephens and Ruth 2005). Decisions thatemphasize ecological process, rather than structure