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Bradford JB, Shriver RK, Robles MD, McCauley LA, Woolley TJ, Andrews CA, Crimmins M, Bell DM. Tree mortality response to drought‐density interactions suggests opportunities to enhance drought resistance. J Appl Ecol 2021. [DOI: 10.1111/1365-2664.14073] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- John. B. Bradford
- Southwest Biological Science Center U.S. Geological Survey Flagstaff AZ USA
| | - Robert K. Shriver
- Department of Natural Resources and Environmental Science University of Nevada Reno NV USA
| | - Marcos D. Robles
- Center for Science and Public Policy The Nature Conservancy Tucson AZ USA
| | - Lisa A. McCauley
- Center for Science and Public Policy The Nature Conservancy Tucson AZ USA
| | - Travis J. Woolley
- Center for Science and Public Policy The Nature Conservancy Tucson AZ USA
| | - Caitlin A. Andrews
- Southwest Biological Science Center U.S. Geological Survey Flagstaff AZ USA
| | - Michael Crimmins
- Department of Environmental Science University of Arizona Tucson AZ USA
| | - David M. Bell
- Pacific Northwest Research Station USDA Forest Service Corvallis OR USA
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Bradford JB, Andrews CM, Robles MD, McCauley LA, Woolley TJ, Marshall RM. Landscape-scale restoration minimizes tree growth vulnerability to 21 st century drought in a dry forest. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2021; 31:e2238. [PMID: 33067874 DOI: 10.1002/eap.2238] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 07/29/2020] [Accepted: 08/17/2020] [Indexed: 06/11/2023]
Abstract
Increasing aridity is a challenge for forest managers and reducing stand density to minimize competition is a recognized strategy to mitigate drought impacts on growth. In many dry forests, the most widespread and common forest management programs currently being implemented focus on restoration of historical stand structures, primarily to minimize fire risk and enhance watershed function. The implications of these restoration projects for drought vulnerability are not well understood. Here, we examined how planned restoration treatments in the Four Forests Restoration Initiative, the largest forest restoration project in the United States, would alter landscape-scale patterns of forest growth and drought vulnerability throughout the 21st century. Using drought-growth relationships developed within the landscape, we considered a suite of climate and treatment scenarios and estimated average forest growth and the proportion of years with extremely low growth as a measure of vulnerability to long-term decline. Climatic shifts projected for this landscape include higher temperatures and shifting seasonal precipitation that promotes lower soil moisture availability in the early growing season and greater hot-dry stress, conditions negatively associated with tree growth. However, drought severity and the magnitude of future growth declines were moderated by the thinning treatments. Compared to historical conditions, proportional growth in mid-century declines by ~40% if thinning ceases or continues at the status quo pace. By comparison, proportional growth declines by only 20% if the Four Forest Restoration Initiative treatments are fully implemented, and <10% if stands are thinned even more intensively than currently planned. Furthermore, restoration treatments resulted in dramatically fewer years with extremely low growth in the future, a recognized precursor to forest decline and eventual tree mortality. Benefits from density reduction for mitigating drought-induced growth declines are more apparent in mid-century and under RCP4.5 than under RCP8.5 at the end of the century. Future climate is inherently uncertain, and our results only reflect the climate projections from the representative suite of models examined. Nevertheless, these results indicate that forest restoration projects designed for other objectives also have substantial benefits for minimizing future drought vulnerability in dry forests and provide additional incentive to accelerate the pace of restoration.
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Affiliation(s)
- John B Bradford
- U.S. Geological Survey, Southwest Biological Science Center, Flagstaff, Arizona, 86011, USA
| | - Caitlin M Andrews
- U.S. Geological Survey, Southwest Biological Science Center, Flagstaff, Arizona, 86011, USA
| | - Marcos D Robles
- The Nature Conservancy, Center for Science and Public Policy, 1510 E Ft Lowell Road, Tucson, Arizona, 85719, USA
| | - Lisa A McCauley
- The Nature Conservancy, Center for Science and Public Policy, 1510 E Ft Lowell Road, Tucson, Arizona, 85719, USA
| | - Travis J Woolley
- The Nature Conservancy, Center for Science and Public Policy, 1510 E Ft Lowell Road, Tucson, Arizona, 85719, USA
| | - Robert M Marshall
- The Nature Conservancy, Center for Science and Public Policy, 1510 E Ft Lowell Road, Tucson, Arizona, 85719, USA
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Coop JD, Parks SA, Stevens-Rumann CS, Crausbay SD, Higuera PE, Hurteau MD, Tepley A, Whitman E, Assal T, Collins BM, Davis KT, Dobrowski S, Falk DA, Fornwalt PJ, Fulé PZ, Harvey BJ, Kane VR, Littlefield CE, Margolis EQ, North M, Parisien MA, Prichard S, Rodman KC. Wildfire-Driven Forest Conversion in Western North American Landscapes. Bioscience 2020; 70:659-673. [PMID: 32821066 PMCID: PMC7429175 DOI: 10.1093/biosci/biaa061] [Citation(s) in RCA: 107] [Impact Index Per Article: 26.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Changing disturbance regimes and climate can overcome forest ecosystem resilience. Following high-severity fire, forest recovery may be compromised by lack of tree seed sources, warmer and drier postfire climate, or short-interval reburning. A potential outcome of the loss of resilience is the conversion of the prefire forest to a different forest type or nonforest vegetation. Conversion implies major, extensive, and enduring changes in dominant species, life forms, or functions, with impacts on ecosystem services. In the present article, we synthesize a growing body of evidence of fire-driven conversion and our understanding of its causes across western North America. We assess our capacity to predict conversion and highlight important uncertainties. Increasing forest vulnerability to changing fire activity and climate compels shifts in management approaches, and we propose key themes for applied research coproduced by scientists and managers to support decision-making in an era when the prefire forest may not return.
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Affiliation(s)
- Jonathan D Coop
- School of Environment and Sustainability, Western Colorado University, Gunnison
| | - Sean A Parks
- Research ecologist with the Aldo Leopold Wilderness Research Institute, Rocky Mountain Research Station, US Forest Service, Missoula, Montana
| | | | - Shelley D Crausbay
- Senior scientist with Conservation Science Partners, Fort Collins, Colorado
| | - Philip E Higuera
- Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, Montana
| | | | - Alan Tepley
- Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta, Canada
| | - Ellen Whitman
- Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta, Canada
| | - Timothy Assal
- Department of Geography, Kent State University, Kent, Ohio
| | - Brandon M Collins
- Fire Research and Outreach, University of California, Berkeley, Berkeley, California, and with the Pacific Southwest Research Station, US Forest Service, in Davis, California
| | - Kimberley T Davis
- Department of Ecosystem and Conservation Sciences, University of Montana, Missoula
| | | | - Donald A Falk
- Natural Resources and the Environment, University of Arizona, Tucson
| | - Paula J Fornwalt
- Rocky Mountain Research Station, US Forest Service, Fort Collins, Colorado
| | - Peter Z Fulé
- School of Forestry, Northern Arizona University, Flagstaff
| | - Brian J Harvey
- School of Environmental and Forest Sciences, University of Washington, Seattle
| | - Van R Kane
- School of Environmental and Forest Sciences, University of Washington, Seattle
| | - Caitlin E Littlefield
- Caitlin Littlefield is a postdoctoral research associate, Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington
| | - Ellis Q Margolis
- US Geological Survey, New Mexico Landscapes Field Station, Santa Fe
| | - Malcolm North
- US Forest Service, Pacific Southwest Research Station, Mammoth Lakes, California
| | - Marc-André Parisien
- Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta, Canada
| | - Susan Prichard
- School of Environmental and Forest Sciences, University of Washington, Seattle
| | - Kyle C Rodman
- Department of Forest and Wildlife Ecology, University of Wisconsin, Madison
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Chapman TB, Schoennagel T, Veblen TT, Rodman KC. Still standing: Recent patterns of post-fire conifer refugia in ponderosa pine-dominated forests of the Colorado Front Range. PLoS One 2020; 15:e0226926. [PMID: 31940320 PMCID: PMC6961861 DOI: 10.1371/journal.pone.0226926] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2019] [Accepted: 12/06/2019] [Indexed: 11/19/2022] Open
Abstract
Forested fire refugia (trees that survive fires) are important disturbance legacies that provide seed sources for post-fire regeneration. Conifer regeneration has been limited following some recent western fires, particularly in ponderosa pine (Pinus ponderosa) forests. However, the extent, characteristics, and predictability of ponderosa pine fire refugia are largely unknown. Within 23 fires in ponderosa pine-dominated forests of the Colorado Front Range (1996-2013), we evaluated the spatial characteristics and predictability of refugia: first using Monitoring Trends in Burn Severity (MTBS) burn severity metrics, then using landscape variables (topography, weather, anthropogenic factors, and pre-fire forest cover). Using 1-m resolution aerial imagery, we created a binary variable of post-fire conifer presence ('Conifer Refugia') and absence ('Conifer Absence') within 30-m grid cells. We found that maximum patch size of Conifer Absence was positively correlated with fire size, and 38% of the burned area was ≥ 50m from a conifer seed source, revealing a management challenge as fire sizes increase with warming further limiting conifer recovery. In predicting Conifer Refugia with two MTBS-produced databases, thematic burn severity classes (TBSC) and continuous Relative differenced Normalized Burn Ratio (RdNBR) values, Conifer Absence was high in previously forested areas of Low and Moderate burn severity classes in TBSC. RdNBR more accurately identified post-fire conifer survivorship. In predicting Conifer Refugia with landscape variables, Conifer Refugia were less likely during burn days with high maximum temperatures: while Conifer Refugia were more likely on moister soils and closer to higher order streams, homes, and roads; and on less rugged, valley topography. Importantly, pre-fire forest canopy cover was not strongly associated with Conifer Refugia. This study further informs forest management by mapping post-fire patches lacking conifer seed sources, validating the use of RdNBR for fire refugia, and detecting abiotic and topographic variables that may promote conifer refugia.
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Affiliation(s)
- Teresa B. Chapman
- The Nature Conservancy, Boulder, Colorado, United States of America
- Department of Geography, University of Colorado Boulder, Boulder, Colorado, United States of America
| | - Tania Schoennagel
- Department of Geography, University of Colorado Boulder, Boulder, Colorado, United States of America
- Institute of Arctic and Alpine Research (INSTAAR), University of Colorado Boulder, Boulder, Colorado, United States of America
| | - Thomas T. Veblen
- Department of Geography, University of Colorado Boulder, Boulder, Colorado, United States of America
| | - Kyle C. Rodman
- Department of Geography, University of Colorado Boulder, Boulder, Colorado, United States of America
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