Nathan Stephenson
Dr. Nathan Stephenson is a Scientist Emeritus at the Western Ecological Research Center.
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
Tree mortality from drought, insects, and their interactions in a changing climate
Temperate forest health in an era of emerging megadisturbance
Increasing elevation of fire in the Sierra Nevada and implications for forest change
Improving estimates of tree mortality probability using potential growth rate
Making the transition to the third era of natural resources management
Beyond reducing fire hazard: fuel treatment impacts on overstory tree survival
Rate of tree carbon accumulation increases continuously with tree size
Climatic correlates of tree mortality in water- and energy-limited forests
A natural resource condition assessment for Sequoia and Kings Canyon National Parks: Appendix 22: climatic change
A natural resource condition assessment for Sequoia and Kings Canyon National Parks: Appendix 11a: giant sequoias
Comment on "Changes in climatic water balance drive downhill shifts in plant species' optimum elevations"
Long-term effects of prescribed fire on mixed conifer forest structure in the Sierra Nevada, California
Science and Products
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Filter Total Items: 93
Tree mortality from drought, insects, and their interactions in a changing climate
Climate change is expected to drive increased tree mortality through drought, heat stress, and insect attacks, with manifold impacts on forest ecosystems. Yet, climate-induced tree mortality and biotic disturbance agents are largely absent from process-based ecosystem models. Using data sets from the western USA and associated studies, we present a framework for determining the relative contributiAuthorsWilliam R.L. Anderegg, Jeffrey A. Hicke, Rosie A. Fisher, Craig D. Allen, Juliann E. Aukema, Barbara Bentz, Sharon Hood, Jeremy W. Lichstein, Alison K. Macalady, Nate G. McDowell, Yude Pan, Kenneth Raffa, Anna Sala, John D. Shaw, Nathan L. Stephenson, Christina L. Tague, Melanie ZeppelTemperate forest health in an era of emerging megadisturbance
Although disturbances such as fire and native insects can contribute to natural dynamics of forest health, exceptional droughts, directly and in combination with other disturbance factors, are pushing some temperate forests beyond thresholds of sustainability. Interactions from increasing temperatures, drought, native insects and pathogens, and uncharacteristically severe wildfire are resulting inAuthorsConstance I. Millar, Nathan L. StephensonIncreasing elevation of fire in the Sierra Nevada and implications for forest change
Fire in high-elevation forest ecosystems can have severe impacts on forest structure, function and biodiversity. Using a 105-year data set, we found increasing elevation extent of fires in the Sierra Nevada, and pose five hypotheses to explain this pattern. Beyond the recognized pattern of increasing fire frequency in the Sierra Nevada since the late 20th century, we find that the upper elevationAuthorsMark W. Schwartz, Nathalie Butt, Christopher R. Dolanc, Andrew Holguin, Max A. Moritz, Malcolm P. North, Hugh D. Safford, Nathan L. Stephenson, James H. Thorne, Phillip J. van MantgemImproving estimates of tree mortality probability using potential growth rate
Tree growth rate is frequently used to estimate mortality probability. Yet, growth metrics can vary in form, and the justification for using one over another is rarely clear. We tested whether a growth index (GI) that scales the realized diameter growth rate against the potential diameter growth rate (PDGR) would give better estimates of mortality probability than other measures. We also tested whAuthorsAdrian J. Das, Nathan L. StephensonMaking the transition to the third era of natural resources management
We are entering the third era of National Park Service (NPS) natural resources management— an era defined by rapid and unprecedented global changes. This third era promises to overturn not only some of our most fundamental assumptions about parks and protected areas, but also many of the ideals we currently hold dear. A common initial reaction to the diverse challenges of this transition is to feeAuthorsNathan L. StephensonBeyond reducing fire hazard: fuel treatment impacts on overstory tree survival
Fuel treatment implementation in dry forest types throughout the western United States is likely to increase in pace and scale in response to increasing incidence of large wildfires. While it is clear that properly implemented fuel treatments are effective at reducing hazardous fire potential, there are ancillary ecological effects that can impact forest resilience either positively or negativelyAuthorsBrandon M. Collins, Adrian J. Das, John J. Battles, Danny L. Fry, Kevin Krasnow, Scott L. StephensRate of tree carbon accumulation increases continuously with tree size
Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle—particularly net primary productivity and carbon storage - increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves tAuthorsN.L. Stephenson, A.J. Das, R. Condit, S.E. Russo, P.J. Baker, N.G. Beckman, D.A. Coomes, E.R. Lines, W.K. Morris, N. Rüger, E. Álvarez, C. Blundo, S. Bunyavejchewin, G. Chuyong, S.J. Davies, Á. Duque, C.N. Ewango, O. Flores, J.F. Franklin, H.R. Grau, Z. Hao, M. E. Harmon, S.P. Hubbell, D. Kenfack, Y. Lin, J.-R. Makana, A. Malizia, L.R. Malizia, R.J. Pabst, N. Pongpattananurak, S.-H. Su, I-F. Sun, S. Tan, D. Thomas, P. J. van Mantgem, X. Wang, S.K. Wiser, M.A. ZavalaClimatic correlates of tree mortality in water- and energy-limited forests
Recent increases in tree mortality rates across the western USA are correlated with increasing temperatures, but mechanisms remain unresolved. Specifically, increasing mortality could predominantly be a consequence of temperature-induced increases in either (1) drought stress, or (2) the effectiveness of tree-killing insects and pathogens. Using long-term data from California’s Sierra Nevada mountAuthorsAdrian J. Das, Nathan L. Stephenson, Alan Flint, Tapash Das, Phillip J. van MantgemA natural resource condition assessment for Sequoia and Kings Canyon National Parks: Appendix 22: climatic change
Climate is a master controller of the structure, composition, and function of biotic communities, affecting them both directly, through physiological effects, and indirectly, by mediating biotic interactions and by influencing disturbance regimes. Sequoia and Kings Canyon National Park’s (SEKI’s) dramatic elevational changes in biotic communities -- from warm mediterranean to cold alpine -- arAuthorsAdrian J. Das, Nathan L. StephensonA natural resource condition assessment for Sequoia and Kings Canyon National Parks: Appendix 11a: giant sequoias
For natural resource managers in the southern Sierra Nevada, giant sequoia requires very little introduction. It receives great attention as an icon of western forests and as a common namesake with the areas where it occurs. While it is a single component of a very complex system, its attention in this assessment and in general is well deserved. Giant sequoia is one of the few "destination speAuthorsRobert A. York, Nathan L. Stephenson, Marc Meyer, Steve Hanna, Moody Tadashi, Anthony C. Caprio, John J. BattlesComment on "Changes in climatic water balance drive downhill shifts in plant species' optimum elevations"
Crimmins et al. (Reports, 21 January 2011, p. 324) attributed an apparent downward elevational shift of California plant species to a precipitation-induced decline in climatic water deficit. We show that the authors miscalculated deficit, that the apparent decline in species’ elevations is likely a consequence of geographic biases, and that unlike temperature changes, precipitation changes shouldAuthorsNathan L. Stephenson, Adrian J. DasLong-term effects of prescribed fire on mixed conifer forest structure in the Sierra Nevada, California
The capacity of prescribed fire to restore forest conditions is often judged by changes in forest structure within a few years following burning. However, prescribed fire might have longer-term effects on forest structure, potentially changing treatment assessments. We examined annual changes in forest structure in five 1 ha old-growth plots immediately before prescribed fire and up to eight yearsAuthorsPhillip J. van Mantgem, Nathan L. Stephenson, Eric Knapp, Jon E. Keeley - Software
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