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      Land management explains major trends in forest structure and composition over the last millennium in California’s Klamath Mountains

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          Significance

          We provide the first assessment of aboveground live tree biomass in a mixed conifer forest over the late Holocene. The biomass record, coupled with local Native oral history and fire scar records, shows that Native burning practices, along with a natural lightning-based fire regime, promoted long-term stability of the forest structure and composition for at least 1 millennium in a California forest. This record demonstrates that climate alone cannot account for observed forest conditions. Instead, forests were also shaped by a regime of frequent fire, including intentional ignitions by Native people. This work suggests a large-scale intervention could be required to achieve the historical conditions that supported forest resiliency and reflected Indigenous influence.

          Abstract

          For millennia, forest ecosystems in California have been shaped by fire from both natural processes and Indigenous land management, but the notion of climatic variation as a primary controller of the pre-colonial landscape remains pervasive. Understanding the relative influence of climate and Indigenous burning on the fire regime is key because contemporary forest policy and management are informed by historical baselines. This need is particularly acute in California, where 20th-century fire suppression, coupled with a warming climate, has caused forest densification and increasingly large wildfires that threaten forest ecosystem integrity and management of the forests as part of climate mitigation efforts. We examine climatic versus anthropogenic influence on forest conditions over 3 millennia in the western Klamath Mountains—the ancestral territories of the Karuk and Yurok Tribes—by combining paleoenvironmental data with Western and Indigenous knowledge. A fire regime consisting of tribal burning practices and lightning were associated with long-term stability of forest biomass. Before Euro-American colonization, the long-term median forest biomass was between 104 and 128 Mg/ha, compared to values over 250 Mg/ha today. Indigenous depopulation after AD 1800, coupled with 20th-century fire suppression, likely allowed biomass to increase, culminating in the current landscape: a closed Douglas fir–dominant forest unlike any seen in the preceding 3,000 y. These findings are consistent with precontact forest conditions being influenced by Indigenous land management and suggest large-scale interventions could be needed to return to historic forest biomass levels.

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          Most cited references90

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          TOLERANCE TO SHADE, DROUGHT, AND WATERLOGGING OF TEMPERATE NORTHERN HEMISPHERE TREES AND SHRUBS

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            Vegetation mediated the impacts of postglacial climate change on fire regimes in the south-central Brooks Range, Alaska

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              Archaeological assessment reveals Earth’s early transformation through land use

              Environmentally transformative human use of land accelerated with the emergence of agriculture, but the extent, trajectory, and implications of these early changes are not well understood. An empirical global assessment of land use from 10,000 years before the present (yr B.P.) to 1850 CE reveals a planet largely transformed by hunter-gatherers, farmers, and pastoralists by 3000 years ago, considerably earlier than the dates in the land-use reconstructions commonly used by Earth scientists. Synthesis of knowledge contributed by more than 250 archaeologists highlighted gaps in archaeological expertise and data quality, which peaked for 2000 yr B.P. and in traditionally studied and wealthier regions. Archaeological reconstruction of global land-use history illuminates the deep roots of Earth’s transformation and challenges the emerging Anthropocene paradigm that large-scale anthropogenic global environmental change is mostly a recent phenomenon.
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                Author and article information

                Journal
                Proc Natl Acad Sci U S A
                Proc Natl Acad Sci U S A
                pnas
                PNAS
                Proceedings of the National Academy of Sciences of the United States of America
                National Academy of Sciences
                0027-8424
                1091-6490
                14 March 2022
                22 March 2022
                14 March 2022
                : 119
                : 12
                : e2116264119
                Affiliations
                [1] aUS Geological Survey , Menlo Park, CA 94025;
                [2] bDepartment of Environmental Science, Policy, and Management, University of California , Berkeley, CA 94720;
                [3] cDepartment of Geography, Geology and Environment, University of Hull , Hull HU6 7RX, United Kingdom;
                [4] dThe Yurok Tribe’s Cultural Resources Manager , Klamath, CA 95548;
                [5] eUSDA Forest Service, Deschutes National Forest , Bend, OR 97701;
                [6] fDepartment of Geography, California State University , Sacramento, CA 95819;
                [7] gPacific Southwest Research Station, USDA Forest Service , Redding, CA 96002;
                [8] hPacific Southwest Research Station, USDA Forest Service , Arcata, CA 95521;
                [9] iDepartment of Geography, University of Nevada , Reno, NV 89557;
                [10] jDepartment of Geography, University of California , Berkeley, CA 94720;
                [11] kThe Karuk Tribe’s Department of Natural Resources , Orleans, CA 95556
                Author notes
                1To whom correspondence may be addressed. Email: cknight@ 123456usgs.gov .

                Edited by F. Stuart Chapin III, University of Alaska Fairbanks, Fairbanks, AK; received October 4, 2021; accepted January 8, 2022

                Author contributions: C.A.K., D.W., J.W., M.D.P., and J.J.B. designed research; C.A.K., M.J.B., M.C., R.M.C., J.N.C., A.K.-P., E.E.K., S.A.M., D.W., A.W.-T., and J.J.B. performed research; C.A.K., L.A., M.C., E.E.K., and D.W. contributed new reagents/analytic tools; C.A.K., J.N.C., E.E.K., F.K.L., J.W., and J.J.B. analyzed data; C.A.K., M.J.B., F.K.L., M.D.P., and J.J.B. wrote the paper; R.M.C. provided consultation and contributions regarding Native oral history and tribal knowledge; and A.W.-T. provided Karuk tribal heritage consultation and contributions.

                Author information
                https://orcid.org/0000-0003-0002-6959
                https://orcid.org/0000-0002-3152-5745
                https://orcid.org/0000-0001-8236-3910
                https://orcid.org/0000-0002-7018-4154
                https://orcid.org/0000-0001-7442-3944
                https://orcid.org/0000-0001-7124-7893
                Article
                202116264
                10.1073/pnas.2116264119
                8944927
                35286202
                7ce70e94-5634-4353-bddb-69c6bbcaee9f
                Copyright © 2022 the Author(s). Published by PNAS.

                This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY).

                History
                : 08 January 2022
                Page count
                Pages: 11
                Funding
                Funded by: National Science Foundation (NSF) 100000001
                Award ID: 0926732
                Award Recipient : Jeffrey Crawford Award Recipient : Scott A Mensing
                Funded by: National Science Foundation (NSF) 100000001
                Award ID: 0964261
                Award Recipient : Jeffrey Crawford Award Recipient : Scott A Mensing
                Funded by: DOE | LDRD | Lawrence Livermore National Laboratory (LLNL) 100006227
                Award ID: 09ERI003
                Award Recipient : Jeffrey Crawford
                Funded by: California Department of Forestry and Fire Protection
                Award ID: 18-CCI-FH-0007-SHU
                Award Recipient : Clarke Knight Award Recipient : John J. Battles
                Funded by: United States Forest Service
                Award ID: 1020791
                Award Recipient : Clarke Knight Award Recipient : John J. Battles
                Funded by: California Agricultural Research Station
                Award ID: CA-B-ECO-0144-MS
                Award Recipient : Clarke Knight Award Recipient : John J. Battles
                Categories
                417
                9
                Biological Sciences
                Environmental Sciences
                Social Sciences
                Sustainability Science

                indigenous management,forest biomass,restoration,carbon policy,land use

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