Forest health and drought response Active
Tree mortality during extreme drought
view from Beetle Rock, Sequoia National Park, California
Characteristic bark beetle galleries
engraver beetle response to California’s extreme drought prove deadly to this white fir
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)
Below are publications associated with this project.
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
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
Causes and implications of the correlation between forest productivity and tree mortality rates
The contribution of competition to tree mortality in old-growth coniferous forests
- 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).
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... - Publications
Below are publications associated with this project.
Filter Total Items: 42Temperate 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. StephensonRate 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. KeeleyCauses and implications of the correlation between forest productivity and tree mortality rates
At global and regional scales, tree mortality rates are positively correlated with forest net primary productivity (NPP). Yet causes of the correlation are unknown, in spite of potentially profound implications for our understanding of environmental controls of forest structure and dynamics and, more generally, our understanding of broad-scale environmental controls of population dynamics and ecosAuthorsNathan L. Stephenson, Philip J. van Mantgem, Andrew G. Bunn, Howard Bruner, Mark E. Harmon, Kari B. O'Connell, Dean L. Urban, Jerry F. FranklinThe contribution of competition to tree mortality in old-growth coniferous forests
Competition is a well-documented contributor to tree mortality in temperate forests, with numerous studies documenting a relationship between tree death and the competitive environment. Models frequently rely on competition as the only non-random mechanism affecting tree mortality. However, for mature forests, competition may cease to be the primary driver of mortality.We use a large, long-term daAuthorsA. Das, J. Battles, N.L. Stephenson, Phillip J. van Mantgem