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,...
Seed production patterns of surviving Sierra Nevada conifers show minimal change following drought
Reproduction is a key component of ecological resilience in forest ecosystems, so understanding how seed production is influenced by extreme drought is key to understanding forest recovery trajectories. If trees respond to mortality-inducing drought by preferentially allocating resources for reproduction, the recovery of the stand to pre-drought...
Wright, Micah Charles; van Mantgem, Phillip J.; Stephenson, Nathan L.; Das, Adrian; Keeley, Jon Effects of postfire climate and seed availability on postfire conifer regeneration
Large, severe fires are becoming more frequent in many forest types across the western United States and have resulted in tree mortality across tens of thousands of hectares. Conifer regeneration in these areas is limited because seeds must travel long distances to reach the interior of large burned patches and establishment is jeopardized by...
Stewart, Joseph A E; van Mantgem, Phillip J.; Young, Derek J N; Shive, Kristen L.; Preisler, Haiganoush K.; Das, Adrian; Stephenson, Nathan L.; Keeley, Jon; Safford, Hugh D.; Wright, Micah Charles; Welch, Kevin R; Thorne, James H. Mortality predispositions of conifers across western USA
Conifer mortality rates are increasing in western North America, but the physiological mechanisms underlying this trend are not well understood.We examined tree‐ring‐based radial growth along with stable carbon (C) and oxygen (O) isotope composition (δ13C and δ18O, respectively) of dying and surviving conifers at eight old‐growth forest sites...
Wang, Wenzhi; English, Nathan B.; Grossiord, Charlotte; Gessler, Arthur; Das, Adrian; Stephenson, Nathan L.; Baisan, Christopher H.; Allen, Craig D.; McDowell, Nate G. Compounding effects of white pine blister rust, mountain pine beetle, and fire threaten four white pine species
Invasive pathogens and bark beetles have caused precipitous declines of various tree species around the globe. Here, we characterized long‐term patterns of mountain pine beetle (Dendroctonus ponderosae; MPB) attacks and white pine blister rust, an infectious tree disease caused by the pathogen, Cronartium ribicola. We focused on four dominant...
Dudney, Joan C; Nesmith, Jonathan C B; Cahill, Matthew C; Cribbs, Jennifer E; Duriscoe, Dan M; Das, Adrian; Stephenson, Nathan L.; Battles, John J. Height-related changes in forest composition, not tree vulnerability, explain increasing mortality with height during an extreme drought
Recently, Stovall et al.1 (hereafter SSY) showed that during an extreme drought, remotely sensed mortality of tall trees was more than double that of short trees. They interpreted this to be a consequence of inherently greater hydraulic vulnerability of tall trees, and suggested that tall-tree vulnerability should thus generalize more broadly....
Stephenson, Nathan L.; Das, Adrian The Fire and Tree Mortality Database, for empirical modeling of individual tree mortality after fire
Wildland fires have a multitude of ecological effects in forests, woodlands, and savannas across the globe. A major focus of past research has been on tree mortality from fire, as trees provide a vast range of biological services. We assembled a database of individual-tree records from prescribed fires and wildfires in the United States. The Fire...
Cansler, C. Alina; Hood, Sharon M.; Varner, J. Morgan; van Mantgem, Phillip J.; Agne, Michelle C.; Andrus, Robert A.; Ayres, Matthew P.; Ayres, Bruce D.; Bakker, Jonathan D.; Battaglia, Michael A.; Bentz, Barbara J.; Breece, Carolyn R.; Brown, James K.; Cluck, Daniel R.; Coleman, Tom W.; Corace, R. Gregory; Covington, W. Wallace; Cram, Douglas S.; Cronan, James B.; Crouse, Joseph E.; Das, Adrian; Davis, Ryan S.; Dickinson, Darci M.; Fitzgerald, Stephen A; Fule, Peter Z.; Ganio, Lisa M.; Grayson, Lindsay M.; Halpern, Charles B.; Hanula, Jim L.; Harvey, Brian J.; Hiers, J. Kevin; Huffman, David W.; Keifer, MaryBeth; Keyser, Tara L.; Kobziar, Leda N.; Kolb, Thomas E.; Kolden, Crystal A.; Kopper, Karen E.; Kreitler, Jason R.; Kreye, Jesse K.; Latimer, Andrew M.; Lerch, Andrew P.; Lombardero, Maria J.; McDaniel, Virginia L.; McHugh, Charles W.; McMillin, Joel D.; Moghaddas, Jason J.; O'Brien, Joseph J.; Perrakis, Daniel D. B.; Peterson, David W.; Pritchard, Susan J.; Progar, Robert A.; Raffa, Kenneth F.; Reinhardt, Elizabeth D.; Restaino, Joseph C.; Roccaforte, John P.; Rogers, Brendan M.; Ryan, Kevin C.; Safford, Hugh D.; Santoro, Alyson E.; Shearman, Timothy M.; Shumate, Alice M.; Sieg, Carolyn H.; Smith, Sheri L.; Smith, Rebecca J.; Stephenson, Nathan L.; Stuever, Mary; Stevens, Jens; Stoddard, Michael T.; Thies, Walter G.; Vaillant, Nicole M.; Weiss, Shelby A.; Westlind, Douglas J.; Woolley, Travis J; Wright, Micah Charles 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.
12 Days of Conifers: A Tale of Two Conifers: Incense Cedar and Sugar Pine
For Day 9 of 12 Days Of Conifers, we feature two very different conifer species: incense cedar (Calocedrus decurrens) and sugar pine (Pinus lambertiana)--and the role of tree species in determining what trees die during drought.
12 Days of Conifers: Red Firs in the Forest
It’s Day 6 of 12 Days Of Conifers, and we’ve got a wintry scene in a red fir forest--a forest that likely looked very different a century ago.
12 Days of Conifers: How to Measure a Giant Sequoia
It’s Day 4 of 12 Days Of Conifers and it’s giant sequoia time. We'll also learn about how scientists measure sequoias and other trees.
12 Days of Conifers: Five Needles on a Foxtail
For Day 3 of 12 Days Of Conifers, we're featuring the long-lived foxtail pine (Pinus balfouriana) and a close-up on its cones.
To manage forest response to drought, pay attention to "the little things that run the world"
This article is a part of the Fall 2019 issue of the Earth Science Matters Newsletter.
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
Giant sequoia responses to extreme drought
This article is part of the Spring 2019 issue of the Earth Science Matters Newsletter.
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.
Leaf to Landscape: Understanding and Mapping Forest Vulnerability to Hotter Droughts
This article is part of the Spring 2016 issue of the Earth Science Matters Newsletter.
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.