Nathan Stephenson
Biography
Earth’s vast forests provide human communities with irreplaceable goods and services such as carbon sequestration, hydrologic regulation, clean water, biodiversity, critical wildlife habitat, wood products, and recreational and spiritual opportunities. An overarching goal of Dr. Nathan Stephenson's research is to improve scientists' and land managers' ability to understand, forecast, and adapt to the effects of ongoing global changes – particularly changing climatic and disturbance regimes – on forests. Accordingly, most of his research falls in three broad, complementary themes: (1) improving mechanistic understanding of forest and carbon dynamics, (2) detection, attribution, and interpretation of forest changes, and (3) adaptations to rapid global changes. The last theme extends well beyond forests, to natural areas in general.
RESEARCH INTERESTS
- Forest ecology
- Global change biology
- Climate change
- Fire ecology
- Natural areas management
- Adaptation
EDUCATION
- Ph.D., Ecology and Systematics, Cornell University, 1988
- B.S., Biological Sciences, University of California, Irvine, 1979
Science and Products
National parks: Chapter 4
Covering about 4% of the United States, the 338,000 km² of protected areas in the National Park System contain representative landscapes of all of the nation’s biomes and ecosystems. The U.S. National Park Service Organic Act established the National Park System in 1916 “to conserve the scenery and the natural and historic objects and the wild...
Julius, Susan Herrod; West, Jordan M.; Baron, Jill S.; Allen, Craig D.; Fleishman, Erica; Gunderson, Lance; McKenzie, Don; Meyerson, Laura A.; Oropeza, Jill; Stephenson, Nathan L. Naturalness and beyond: Protected area stewardship in an era of global environmental change
For most large U.S. parks and wilderness areas, enabling legislation and management policy call for preservation of these protected areas unimpaired in perpetuity. Central to the notions of protection, preservation, and unimpairment has been the concept of maintaining “naturalness,” a condition imagined by many to persist over time in the absence...
Cole, David N.; Yung, Laurie; Zavaleta, Erika S.; Aplet, Gregory H.; Chapin, F. Stuart; Graber, David M.; Higgs, Eric S.; Hobbs, Richard J.; Landres, Peter B.; Millar, Constance I.; Parsons, David J.; Randall, John M.; Stephenson, Nathan L.; Tonnessen, Kathy A.; White, Peter S.; Woodley, Stephen Apparent climatically induced increase of tree mortality rates in a temperate forest
We provide a first detailed analysis of long-term, annual-resolution demographic trends in a temperate forest. After tracking the fates of 21 338 trees in a network of old-growth forest plots in the Sierra Nevada of California, we found that mortality rate, but not the recruitment rate, increased significantly over the 22 years of measurement (...
van Mantgem, P.J.; Stephenson, N.L. Climate change and forests of the future: Managing in the face of uncertainty
We offer a conceptual framework for managing forested ecosystems under an assumption that future environments will be different from present but that we cannot be certain about the specifics of change. We encourage flexible approaches that promote reversible and incremental steps, and that favor ongoing learning and capacity to modify direction as...
Millar, C.I.; Stephenson, N.L.; Stephens, S.L. Response of western mountain ecosystems to climatic variability and change: The Western Mountain Initiative
Mountain ecosystems within our national parks and other protected areas provide valuable goods and services such as clean water, biodiversity conservation, and recreational opportunities, but their potential responses to expected climatic changes are inadequately understood. The Western Mountain Initiative (WMI) is a collaboration of scientists...
Stephenson, Nathan L.; Peterson, Dave; Fagre, Daniel B.; Allen, Craig D.; McKenzie, Donald; Baron, Jill S.; O'Brian, Kelly The relationship between tree growth patterns and likelihood of mortality: A study of two tree species in the Sierra Nevada
We examined mortality of Abies concolor (Gord. & Glend.) Lindl. (white fir) and Pinus lambertiana Dougl. (sugar pine) by developing logistic models using three growth indices obtained from tree rings: average growth, growth trend, and count of abrupt growth declines. For P. lambertiana, models with average growth, growth trend, and count of...
Das, A.J.; Battles, J.J.; Stephenson, N.L.; van Mantgem, P.J. Response of western mountain ecosystems to climatic variability and change: The Western Mountain Initiative
Mountain ecosystems within our national parks and other protected areas provide valuable goods and services such as clean water, biodiversity conservation, and recreational opportunities, but their potential responses to expected climatic changes are inadequately understood. The Western Mountain Initiative (WMI) is a collaboration of scientists...
Stephenson, Nathan L.; Peterson, David A.; Fagre, Daniel B.; Allen, Craig D.; McKenzie, Donald; Baron, Jill S.; O'Brien, K. Forest reproduction along a climatic gradient in the Sierra Nevada, California
To elucidate broad-scale environmental controls of coniferous forest reproduction in the Sierra Nevada, California, we monitored reproduction for 5 years in 47 plots arrayed across a steep elevational (climatic) gradient. We found that both absolute seedling densities (stems < 1.37 m) and seedling densities relative to overstory...
van Mantgem, Phillip J.; Stephenson, Nathan L.; Keeley, Jon E. Forest turnover rates follow global and regional patterns of productivity
Using a global database, we found that forest turnover rates (the average of tree mortality and recruitment rates) parallel broad-scale patterns of net primary productivity. First, forest turnover was higher in tropical than in temperate forests. Second, as recently demonstrated by others, Amazonian forest turnover was higher on fertile than...
Stephenson, N.L.; van Mantgem, P.J. The accuracy of matrix population model projections for coniferous trees in the Sierra Nevada, California
1 We assess the use of simple, size-based matrix population models for projecting population trends for six coniferous tree species in the Sierra Nevada, California. We used demographic data from 16 673 trees in 15 permanent plots to create 17 separate time-invariant, density-independent population projection models, and determined differences...
van Mantgem, P.J.; Stephenson, N.L. Does coring contribute to tree mortality?
We assess the potential of increment coring, a common method for measuring tree ages and growth, to contribute to mortality. We used up to 21 years of annual censuses from two cored and two uncored permanent plots in the Sierra Nevada of California, to detect changes in mortality rates 12 years following coring for individuals >5 cm DBH from...
van Mantgem, P.J.; Stephenson, N.L. Effects of an introduced pathogen and fire exclusion on the demography of sugar pine
An introduced pathogen, white pine blister rust (Cronartium ribicola), has caused declines in five-needled pines throughout North America. Simultaneously, fire exclusion has resulted in dense stands in many forest types, which may create additional stress for these generally shade-intolerant pines. Fire exclusion also allows fuels to accumulate,...
van Mantgem, Phillip J.; Stephenson, Nathan L.; Keifer, MaryBeth; Keeley, Jon E.