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 threatening forest sustainability. Using a number of complementary data sets, this project treats California’s recent hotter drought as a potential preview of the future, with the ultimate goal of providing forest managers with the information and adaptation tools they need to increase forest resistance and resilience to extreme droughts of the future.
Statement of Problem:
Ongoing global changes – particularly interacting changes in climate, land use, and disturbance regimes – are rapidly altering forests, often in undesirable ways. Such changes have been particularly evident in the western United States. This project explores the effects of climatic drivers on forest vegetation, ecological disturbance processes, mountain hydrology, and the coupled ecohydrological responses that determine vulnerability of western U.S. mountain landscapes to change.
Why this Research is Important:
Forests sequester the majority of the terrestrial biosphere’s carbon, making them key components of the global carbon cycle. For society to anticipate, mitigate, and adapt to these increasing threats to forests, we must improve our ability to understand and forecast forest response to environmental changes and management actions. We thus work closely with forest managers – particularly in the National Park Service and U.S. Forest Service – to provide concepts and tools for wise management of the nation’s forests. Our primary insights come from intensive, place-based study of a globally unique network of forest research plots in California’s Sierra Nevada mountain range, in which the fates of tens of thousands of trees have been followed for up to 36 years. Insights from this network, in turn, catalyze regional and global syntheses.
Linked to the Western Mountain Initiative (WMI) since 2003, this project explores effects of climatic drivers on forest vegetation, ecological disturbance processes, mountain hydrology, and the coupled ecohydrological responses that determine vulnerability of western U.S. mountain landscapes to change (see figure below).
Objective(s):
The effects of California’s extreme 2012-2016 drought were exacerbated by abnormally high temperatures, resulting in historically unprecedented tree mortality. To capture scientific information needed to prepare forest managers for similar events in the future, we launched the Leaf to Landscape project in 2014, with core funding from USGS, NPS, and USFS. Our 2014-2017 collection of “perishable” data was coordinated across spatial scales, from tree leaves to entire forested landscapes. Our globally-unique network of permanent forest plots in the Sierra Nevada has been a key component of this interdisciplinary effort.
Our primary goal for the next five years is to apply our existing Leaf to Landscape data and continued documentation of forest drought response and recovery to provide forest managers with key information and tools, as outlined the following six objectives:
Objective 1: Create and validate empirically derived, species-specific forest vulnerability maps, letting the trees themselves reveal which parts of the forested landscape are likely to be most vulnerable to future hotter droughts.
Objective 2: (i) Empirically identify areas that served as hydrologic refugia during the drought, (ii) quantify the extent to which they protected tree species, and (iii) determine whether tree species differed in the extent to which refugia protected them.
Objective 3: Provide a first real validation test of a state-of-the-art forest vulnerability model, determining how well it predicted actual patterns of tree mortality during the hotter drought.
Objective 4: Empirically quantify the effectiveness – or lack thereof – of past forest treatments in increasing tree survival during extreme drought.
Objective 5: Determine the species-specific timing, magnitude, and nature of lagged tree mortality following extreme drought.
Objective 6: Create and validate empirically derived giant sequoia vulnerability maps, and determine the role of bark beetles in drought-induced sequoia mortality.
The Western Mountain Initiative (WMI)
USGS Snow and Avalanche Project
Accelerating changes and transformations in western mountain lakes
Effects of disturbance and drought on the forests and hydrology of the Southern Rocky Mountains
Below are publications associated with this project.
Which trees die during drought? The key role of insect host-tree selection
Early-warning signals of individual tree mortality based on annual radial growth
Leaf to landscape responses of giant sequoia to hotter drought: An introduction and synthesis for the special section
Remote measurement of canopy water content in giant sequoias (Sequoiadendron giganteum) during drought
Landscape-scale variation in canopy water content of giant sequoias during drought
Patterns and correlates of giant sequoia foliage dieback during California’s 2012–2016 hotter drought
What mediates tree mortality during drought in the southern Sierra Nevada?
A synthesis of radial growth patterns preceding tree mortality
Why do trees die? Characterizing the drivers of background tree mortality
Does prescribed fire promote resistance to drought in low elevation forests of the Sierra Nevada, California, USA?
Montane Forests
Tree mortality from drought, insects, and their interactions in a changing climate
- Overview
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 threatening forest sustainability. Using a number of complementary data sets, this project treats California’s recent hotter drought as a potential preview of the future, with the ultimate goal of providing forest managers with the information and adaptation tools they need to increase forest resistance and resilience to extreme droughts of the future.
Statement of Problem:
Ongoing global changes – particularly interacting changes in climate, land use, and disturbance regimes – are rapidly altering forests, often in undesirable ways. Such changes have been particularly evident in the western United States. This project explores the effects of climatic drivers on forest vegetation, ecological disturbance processes, mountain hydrology, and the coupled ecohydrological responses that determine vulnerability of western U.S. mountain landscapes to change.
Why this Research is Important:
Forests sequester the majority of the terrestrial biosphere’s carbon, making them key components of the global carbon cycle. For society to anticipate, mitigate, and adapt to these increasing threats to forests, we must improve our ability to understand and forecast forest response to environmental changes and management actions. We thus work closely with forest managers – particularly in the National Park Service and U.S. Forest Service – to provide concepts and tools for wise management of the nation’s forests. Our primary insights come from intensive, place-based study of a globally unique network of forest research plots in California’s Sierra Nevada mountain range, in which the fates of tens of thousands of trees have been followed for up to 36 years. Insights from this network, in turn, catalyze regional and global syntheses.
Linked to the Western Mountain Initiative (WMI) since 2003, this project explores effects of climatic drivers on forest vegetation, ecological disturbance processes, mountain hydrology, and the coupled ecohydrological responses that determine vulnerability of western U.S. mountain landscapes to change (see figure below).
(Credit: Baron. Public domain) Objective(s):
The effects of California’s extreme 2012-2016 drought were exacerbated by abnormally high temperatures, resulting in historically unprecedented tree mortality. To capture scientific information needed to prepare forest managers for similar events in the future, we launched the Leaf to Landscape project in 2014, with core funding from USGS, NPS, and USFS. Our 2014-2017 collection of “perishable” data was coordinated across spatial scales, from tree leaves to entire forested landscapes. Our globally-unique network of permanent forest plots in the Sierra Nevada has been a key component of this interdisciplinary effort.
Our primary goal for the next five years is to apply our existing Leaf to Landscape data and continued documentation of forest drought response and recovery to provide forest managers with key information and tools, as outlined the following six objectives:
Objective 1: Create and validate empirically derived, species-specific forest vulnerability maps, letting the trees themselves reveal which parts of the forested landscape are likely to be most vulnerable to future hotter droughts.
Objective 2: (i) Empirically identify areas that served as hydrologic refugia during the drought, (ii) quantify the extent to which they protected tree species, and (iii) determine whether tree species differed in the extent to which refugia protected them.
Objective 3: Provide a first real validation test of a state-of-the-art forest vulnerability model, determining how well it predicted actual patterns of tree mortality during the hotter drought.
Objective 4: Empirically quantify the effectiveness – or lack thereof – of past forest treatments in increasing tree survival during extreme drought.
Objective 5: Determine the species-specific timing, magnitude, and nature of lagged tree mortality following extreme drought.
Objective 6: Create and validate empirically derived giant sequoia vulnerability maps, and determine the role of bark beetles in drought-induced sequoia mortality.
- Science
The Western Mountain Initiative (WMI)
Western Mountain Initiative (WMI) is a long-term collaboration between FORT, WERC, NOROCK, USFS, NPS, LANL, and universities worldwide to address changes in montane forests and watersheds due to climate change. Current emphases include altered forest disturbance regimes (fire, die-off, insect outbreaks) and hydrology; interactions between plants, water, snow, nutrient cycles, and climate; and...USGS Snow and Avalanche Project
Snow avalanches are a widespread natural hazard to humans and infrastructure as well as an important landscape disturbance affecting mountain ecosystems. Forecasting avalanche frequency is challenging on various spatial and temporal scales, and this project aims to fill a gap in snow science by focusing on reconstructing avalanche history on the continental mountain range scale - throughout the...Accelerating changes and transformations in western mountain lakes
While research into eutrophication has been a cornerstone of limnology for more than 100 years, only recently has it become a topic for the remote alpine lakes that are icons of protected national parks and wilderness areas. National park lakes in the western U.S. are threatened by global change, specifically air pollution, warming, and their interactions, and the problem is quickly worsening...Effects of disturbance and drought on the forests and hydrology of the Southern Rocky Mountains
Climate-related forest disturbances, particularly drought-induced tree mortality and large, high-severity fires from increasingly warm and dry conditions, are altering forest ecosystems and the ecosystem services society depends on (e.g., water supplies). Our research combines long-term place-based ecological data, diverse methods (e.g., paleo, remote-sensing), and networking approaches to... - Publications
Below are publications associated with this project.
Filter Total Items: 42Which 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 opposite extreme, host selection dominates: outbreakingAuthorsNathan L. Stephenson, Adrian J. Das, Nicholas J. Ampersee, Beverly M Bulaon, Julie L. YeeEarly-warning signals of individual tree mortality based on annual radial growth
Tree mortality is a key driver of forest dynamics and its occurrence is projected to increase in the future due to climate change. Despite recent advances in our understanding of the physiological mechanisms leading to death, we still lack robust indicators of mortality risk that could be applied at the individual tree scale. Here, we build on a previous contribution exploring the differences in gAuthorsMaxime Cailleret, Vasilis Dakos, Steven Jansen, Elisabeth M. R. Robert, Tuomas Aakala, Mariano M. Amoroso, Joe A. Antos, Christof Bigler, Harald Bugmann, Marco Caccianaga, Jesus-Julio Camarero, Paolo Cherubini, Marie R. Coyea, Katarina Cufar, Adrian J. Das, Hendrik Davi, Guillermo Gea-Izquierdo, Sten Gillner, Laurel J. Haavik, Henrik Hartmann, Ana-Maria Heres, Kevin R. Hultine, Pavel Janda, Jeffrey M. Kane, Viachelsav I. Kharuk, Thomas Kitzberger, Tamir Klein, Tom Levanic, Juan-Carlos Linares, Fabio Lombardi, Harri Makinen, Ilona Mészáros, Juha M. Metsaranta, Walter Oberhuber, Andreas Papadopoulos, Any Mary Petritan, Brigitte Rohner, Gabriel Sanguesa-Barreda, Jeremy M. Smith, Amanda B. Stan, Dejan B. Stojanovic, Maria-Laura Suarez, Miroslav Svoboda, Volodymyr Trotsiuk, Ricardo Villalba, Alana R. Westwood, Peter H. Wyckoff, Jordi Martínez-VilaltaLeaf 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. As part of our Leaf to Landscape Project, we measAuthorsKoren R. Nydick, Nathan L. Stephenson, Anthony R. Ambrose, Gregory P. Asner, Wendy L. Baxter, Adrian J. Das, Todd E. Dawson, Roberta E. Martin, Tarin Paz-KaganRemote 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 canopies can be recorded, biochemical and physiologicAuthorsRoberta E. Martin, Gregory P. Asner, Emily Francis, Anthony Ambrose, Wendy Baxter, Adrian J. Das, Nicolas R. Vaughn, Tarin Paz-Kagan, Todd E. Dawson, Koren R. Nydick, Nathan L. StephensonLandscape-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), both within and among sequoia groves in two successiveAuthorsTarin Paz-Kagan, Nicolas R. Vaughn, Roberta E. Martin, Philip G. Brodrick, Nathan L. Stephenson, Adrian Das, Koren R. Nydick, Gregory P. AsnerPatterns 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 unprecedented 2012–2016 hotter drought, we noticed apparentlyAuthorsNathan L. Stephenson, Adrian J. Das, Nicholas J. Ampersee, Kathleen G. Cahill, Anthony C. Caprio, John E. Sanders, A. Park WilliamsWhat mediates tree mortality during drought in the southern Sierra Nevada?
Severe drought has the potential to cause selective mortality within a forest, thereby inducing shifts in forest species composition. The southern Sierra Nevada foothills and mountains of California have experienced extensive forest dieback due to drought stress and insect outbreak. We used high-fidelity imaging spectroscopy (HiFIS) and light detection and ranging (LiDAR) from the Carnegie AirbornAuthorsTarin Paz-Kagan, Philip Brodrick, Nicholas R. Vaughn, Adrian J. Das, Nathan L. Stephenson, Koren R. Nydick, Gregory P. AsnerA synthesis of radial growth patterns preceding tree mortality
Tree mortality is a key factor influencing forest functions and dynamics, but our understanding of the mechanisms leading to mortality and the associated changes in tree growth rates are still limited. We compiled a new pan-continental tree-ring width database from sites where both dead and living trees were sampled (2970 dead and 4224 living trees from 190 sites, including 36 species), and comparAuthorsMaxime Cailleret, Steven Jansen, Elisabeth M.R. Robert, Lucia Desoto, Tuomas Aakala, Joseph A. Antos, Barbara Beikircher, Christof Bigler, Harald Bugmann, Marco Caccianiga, Vojtech Cada, Jesus J. Camarero, Paolo Cherubini, Herve Cochard, Marie R. Coyea, Katarina Cufar, Adrian J. Das, Hendrik Davi, Sylvain Delzon, Michael Dorman, Guillermo Gea-Izquierdo, Sten Gillner, Laurel J. Haavik, Henrik Hartmann, Ana-Maria Heres, Kevin R. Hultine, Pavel Janda, Jeffrey M. Kane, Vyacheslav I. Kharuk, Thomas Kitzberger, Tamir Klein, Koen Kramer, Frederic Lens, Tom Levanic, Juan C. Linares Calderon, Francisco Lloret, Raquel Lobo-Do-Vale, Fabio Lombardi, Rosana Lopez Rodriguez, Harri Makinen, Stefan Mayr, IIona Meszaros, Juha M. Metsaranta, Francesco Minunno, Walter Oberhuber, Andreas Papadopoulos, Mikko Peltoniemi, Any M. Petritan, Brigitte Rohner, Gabriel Sanguesa-Barreda, Dimitrios Sarris, Jeremy M. Smith, Amanda B. Stan, Frank Sterck, Dejan B. Stojanovic, Maria L. Suarez, Miroslav Svoboda, Roberto Tognetti, Jose M. Torres-Ruiz, Volodymyr Trotsiuk, Ricardo Villalba, Floor Vodde, Alana R. Westwood, Peter H. Wyckoff, Nikolay Zafirov, Jordi Martínez-VilaltaWhy do trees die? Characterizing the drivers of background tree mortality
The drivers of background tree mortality rates—the typical low rates of tree mortality found in forests in the absence of acute stresses like drought—are central to our understanding of forest dynamics, the effects of ongoing environmental changes on forests, and the causes and consequences of geographical gradients in the nature and strength of biotic interactions. To shed light on factors contriAuthorsAdrian J. Das, Nathan L. Stephenson, Kristin P. DavisDoes prescribed fire promote resistance to drought in low elevation forests of the Sierra Nevada, California, USA?
Prescribed fire is a primary tool used to restore western forests following more than a century of fire exclusion, reducing fire hazard by removing dead and live fuels (small trees and shrubs). It is commonly assumed that the reduced forest density following prescribed fire also reduces competition for resources among the remaining trees, so that the remaining trees are more resistant (more likelAuthorsPhillip J. van Mantgem, Anthony C. Caprio, Nathan L. Stephenson, Adrian J. DasMontane Forests
This long-anticipated reference and sourcebook for California’s remarkable ecological abundance provides an integrated assessment of each major ecosystem type—its distribution, structure, function, and management. A comprehensive synthesis of our knowledge about this biologically diverse state, Ecosystems of California covers the state from oceans to mountaintops using multiple lenses: past and prAuthorsMalcolm P. North, Brandon M. Collins, Hugh D. Safford, Nathan L. StephensonTree 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 Zeppel