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
Forest health and drought response
Forests provide society with economically important and often irreplaceable goods and services, such as wood products, carbon sequestration, clean water, biodiversity, and recreational opportunities. Yet hotter droughts (droughts in which unusually high temperatures exacerbate the effects of low precipitation) are projected to increase in frequency and intensity in coming decades, potentially...
Post-Fire Conifer Regeneration Under a Warming Climate: Will Severe Fire Be a Catalyst for Forest Loss?
The Southwest U.S. is experiencing hotter droughts, which are contributing to more frequent, severe wildfires. These droughts also stress vegetation, which can make it more difficult for forests to recover after fire. Forest regeneration in burned areas may be limited because seeds have to travel long distances to recolonize, and when they do arrive, conditions are often unfavorably hot and...
Adaptations to Rapid Change
Management decisions are made at the intersection of facts and values, and WERC's role is to assist decision-makers by bringing the best available science to the table. Dr. Nathan Stephenson seeks to help managers and policy makers reassess their missions in light of rapid and unprecedented changes, develop broad concepts relevant to adapting to such changes, and provide hands-on assistance...
Improving Understanding of Forest and Carbon Dynamics
The community's ability to understand and predict changes in forests and their feedbacks to the global carbon cycle increasingly relies on models spanning several scales of biological organization – from tree leaves to entire forested landscapes. Yet many model assumptions about key processes – such as tree growth and mortality – require long-term data that are sometimes difficult and time-...
Detection, Attribution, and Interpretation of Forest Changes
Dr. Nathan Stephenson and colleagues seek to determine what changes are occurring in forests, why they are occurring, and what they mean. For example, they have documented a long-term, apparently climatically-induced increase of tree mortality rates in otherwise undisturbed old forests across the western U.S., implying that these forests could become net sources of atmospheric carbon dioxide...
Sequoia and Kings Canyon Field Station
The Sequoia and Kings Canyon Field Station is home to research programs that focus on wildfire patterns in Southern California, and the effects of drought on Sierra Nevada forests. Select the "Science" tab for a more comprehensive summary.
Fighting Drought with Fire: A Comparison of Burned and Unburned Forests in Drought-Impacted Areas of the Southwest
Drought is one of the biggest threats facing our forests today. In the western U.S., severe drought and rising temperatures have caused increased tree mortality and complete forest diebacks. Forests are changing rapidly, and while land managers are working to develop long-term climate change adaptation plans, they require tools that can enhance forest resistance to drought now. To address this...
Characterizing a link in the terrestrial carbon cycle: a global overview of individual tree mass growth
Forests sequester the majority of the terrestrial biosphere’s carbon and are key components of the global carbon cycle, potentially contributing substantial feedbacks to ongoing climatic changes. It is therefore remarkable that no consensus yet exists about the fundamental nature of tree mass growth (and thus carbon sequestration rate). Specifically, does tree mass growth rate increase,...
The influence of pre-fire growth patterns on post-fire tree mortality for common conifers in western U.S. parks
Fire severity in forests is often defined in terms of post-fire tree mortality, yet the influences on tree mortality following fire are not fully understood. For trees that are not killed immediately by severe fire injury, pre-fire growth may partially predict post-fire mortality probabilities for conifers of the western U.S. Here, we consider the...
van Mantgem, Phillip; Falk, Donald A.; Williams, Emma C.; Das, Adrian J.; Stephenson, Nathan L. Tree mortality in blue oak woodland during extreme drought in Sequoia National Park, California
Blue oak woodlands in California have been a focus of conservation concern for many years. Numerous studies have found that existing seedling and sapling numbers are inadequate to sustain current populations, and recent work has suggested that blue oak woodlands might be particularly vulnerable to a warming climate. California has recently...
Das, Adrian J.; Ampersee, Nicholas J.; Pfaff, Anne Hopkins; Stephenson, Nathan L.; Swiecki, Tedmund J; Bernhardt, Elizabeth A; Haggerty, Patricia; Nydick, Koren R. Size matters, but not consistently
E. Pennisi (“Forest giants are the trees most at risk,” News, 6 September, p. 962) interprets presentations of three studies as suggesting that “for trees, size is not strength, and forest giants are disproportionately vulnerable.” However, this conclusion is not well supported. The observation that lightning is a major cause of large-tree...
Stephenson, Nathan L.; Das, Adrian J. Giant sequoias: Drama on a grand scale
No abstract available.
Stephenson, Nathan L. Negative impacts of summer heat on Sierra Nevada tree seedlings
Understanding the response of forests to climate change is important for predicting changes in biodiversity and ecosystem services, including carbon storage. Seedlings represent a key demographic stage in these responses, because seedling establishment is necessary for population persistence and spread, and because the conditions allowing...
Moran, Emily V; Das, Adrian J.; Keeley, Jon; Stephenson, Nathan L. Which trees die during drought? The key role of insect host-tree selection
1. During drought, the tree subpopulations (such as size or vigor classes) that suffer disproportionate mortality can be conceptually arrayed along a continuum defined by the actions of biotic agents, particularly insects. At one extreme, stress dominates: insects are absent or simply kill the most physiologically stressed trees. At the...
Stephenson, Nathan L.; Das, Adrian J.; Ampersee, Nicholas J.; Bulaon, Beverly M; Yee, Julie L. Pre‐fire drought and competition mediate post‐fire conifer mortality in western U.S. National Parks
Tree mortality is an important outcome of many forest fires. Extensive tree injuries from fire may lead directly to mortality, but environmental and biological stressors may also contribute to tree death. However, there is little evidence showing how the combined effects of two common stressors, drought and competition, influence post‐fire...
van Mantgem, Phillip J.; Falk, Donald A.; Williams, Emma C.; Das, Adrian J.; Stephenson, Nathan L. Leaf to landscape responses of giant sequoia to hotter drought: An introduction and synthesis for the special section
Hotter droughts are becoming more common as climate change progresses, and they may already have caused instances of forest dieback on all forested continents. Learning from hotter droughts, including where on the landscape forests are more or less vulnerable to these events, is critical to help resource managers proactively prepare for the future...
Nydick, Koren R.; Stephenson, Nathan L.; Ambrose, Anthony R.; Asner, Gregory P.; Baxter, Wendy L.; Das, Adrian J.; Dawson, Todd E.; Martin, Roberta E.; Paz-Kagan, Tarin Remote measurement of canopy water content in giant sequoias (Sequoiadendron giganteum) during drought
California experienced severe drought from 2012 to 2016, and there were visible changes in the forest canopy throughout the State. In 2014, unprecedented foliage dieback was recorded in giant sequoia (Sequoiadendron giganteum) trees in Sequoia National Park, in the southern California Sierra Nevada mountains. Although visible changes in sequoia...
Martin, Roberta E.; Asner, Gregory P.; Francis, Emily; Ambrose, Anthony; Baxter, Wendy; Das, Adrian J.; Vaughn, Nicolas R.; Paz-Kagan, Tarin; Dawson, Todd E.; Nydick, Koren R.; Stephenson, Nathan L. Landscape-scale variation in canopy water content of giant sequoias during drought
Recent drought (2012–2016) caused unprecedented foliage dieback in giant sequoias (Sequoiadendron giganteum), a species endemic to the western slope of the southern Sierra Nevada in central California. As part of an effort to understand and map sequoia response to droughts, we studied the patterns of remotely sensed canopy water content (CWC),...
Paz-Kagan, Tarin; Vaughn, Nicolas R.; Martin, Roberta E.; Brodrick, Philip G.; Stephenson, Nathan L.; Das, Adrian; Nydick, Koren R.; Asner, Gregory P. Patterns and correlates of giant sequoia foliage dieback during California’s 2012–2016 hotter drought
Hotter droughts – droughts in which unusually high temperatures exacerbate the effects of low precipitation – are expected to increase in frequency and severity in coming decades, challenging scientists and managers to identify which parts of forested landscapes may be most vulnerable. In 2014, in the middle of California’s historically...
Stephenson, Nathan L.; Das, Adrian J.; Ampersee, Nicholas J.; Cahill, Kathleen G.; Caprio, Anthony C.; Sanders, John E.; Williams, A. Park Navigating translational ecology: Creating opportunities for scientist participation
Interest in translational ecology (TE) – a research approach that yields useful scientific outcomes through ongoing collaboration between scientists and stakeholders – is growing among both of these groups. Translational ecology brings together participants from different cultures and with different professional incentives. We address ways to...
Hallett, Lauren M.; Morelli, Toni Lyn; Gerber, Leah R.; Moritz, Max A.; Schwartz, Mark W.; Stephenson, Nathan L.; Tank, Jennifer L.; Williamson, Matthew A.; Woodhouse, Connie A.
What’s It Like To Be a Tree in California Today? WERC Forest Ecologist Weighs In (Mashable)
Dr. Nate Stephenson says the rules are changing for Sierra Nevada trees
How Is A 1,600-Year-Old Tree Weathering California's Drought? (NPR)
SEQUOIA NATIONAL PARK, California — Nate Stephenson was a guest on NPR's "All Things Considered." The segment featured collaborative research on the drought's effects on giant sequoias.
Hotter Droughts, Forests and the Leaf to Landscape Project
California's hotter droughts are a preview of a warmer future world.
Large Old Trees Grow Fastest, Storing More Carbon
Trees do not slow in their growth rate as they get older and larger — instead, their growth keeps accelerating, according to a study published today in the journal Nature.