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

Knight, Clarke A.; Anderson, L.; Bunting, M. Jane; Champagne, Marie; Clayburn, Rosie M.; Crawford, Jeffrey N.; Klimaszewski-Patterson, Anna; Knapp, Eric E.; Lake, Frank K.; Mensing, Scott; Wahl, David B.; Wanket, James A.; Watts-Tobin, Alex; Potts, Matthew D.; Battles, John J.

doi:10.1073/pnas.2116264119

Cited by 53 publications

(42 citation statements)

References 46 publications

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“…The combined records of hydroclimatic change, wildfire, and vegetation community from WMC support the link between precipitation volatility and fire activity in western North America that has been observed in tree-ring records in the late Holocene, inferred from mid-Holocene lake records, and predicted for future warming scenarios 7 , 8 . Our record provides evidence for this climate-fire relationship under early Holocene boundary conditions prior to substantial forcing from anthropogenic greenhouse gas emissions and land use changes such as fire suppression 54 . Furthermore, our records suggest enhanced volatility and fire activity during the 8.2 kyr event, an interval of freshwater forcing and abrupt cooling in the North Atlantic.…”

Section: Discussionmentioning

confidence: 65%

Linked fire activity and climate whiplash in California during the early Holocene

et al. 2022

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Recent wildfire activity in semi-arid regions like western North America exceeds the range of historical records. High-resolution paleoclimate archives such as stalagmites could illuminate the link between hydroclimate, vegetation change, and fire activity in pre-anthropogenic climate states beyond the timescale of existing tree-ring records. Here we present an analysis of levoglucosan, a combustion-sensitive anhydrosugar, and lignin oxidation products (LOPs) in a stalagmite, reconstructing fire activity and vegetation composition in the California Coast Range across the 8.2 kyr event. Elevated levoglucosan concentrations suggest increased fire activity while altered LOP compositions indicate a shift toward more woody vegetation during the event. These changes are concurrent with increased hydroclimate volatility as shown by carbon and calcium isotope proxies. Together, these records suggest that climate whiplash (oscillations between extreme wetness and aridity) and fire activity in California, both projected to increase with anthropogenic climate change, were tightly coupled during the early Holocene.

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Section: Discussionmentioning

confidence: 65%

Linked fire activity and climate whiplash in California during the early Holocene

et al. 2022

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“…Peak biomass varied at each site from early 20th century to early 21st century. While the overall trend in increased biomass following Euro-American colonization is due to effective landscape-level fire suppression starting in 1905 (Taylor and Skinner, 2003;Knight et al, 2020;Knight et al, 2022), variation in the timing of peak biomass depends on site-specific management histories.…”

Section: Results From Seven Lake Sitesmentioning

confidence: 99%

“…Uncertainty analysis identifies where error matters most Accounting for the error in PAR estimates more than doubled the estimate of uncertainty in the reconstructions of aboveground live tree biomass. The coefficient of variation (cov) reported for contemporary to colonial-era biomass at Lake Ogaromtoc and Fish Lake ranged from 0.16 to 0.20 when only accounting for error in the PAR-to-biomass transfer function (Knight et al, 2022). Including uncertainty in PAR increased the range of observed cov from 0.22 to 0.48 (Figure 1).…”

Section: Discussionmentioning

confidence: 98%

“…These quantitative reconstructions are also relevant to policy and management (Davies and Bunting, 2010). For example, reconstructed forest biomass records can inform current debates about the viability of long-term carbon sequestration in forestlands given increasing threats from biotic and abiotic disturbances (Morris et al, 2015;Knight et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

“…This paper expands our earlier work and more fully considers errors associated with biomass reconstructions. Knight et al (2022) concluded that the contemporary increase in tree biomass for two lake sites in the Klamath bioregion of California was largely attributed to the change in land stewardship from Indigenous to Euro-American. To test the generality of this trend, we reconstruct tree biomass from five additional lake sites in the region.…”

Section: Introductionmentioning

confidence: 99%

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Methods for robust estimates of tree biomass from pollen accumulation rates: Quantifying paleoecological reconstruction uncertainty

et al. 2022

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Pollen accumulation rates (PAR, grains cm–2 year–1) have been shown to be a reliable but methodologically complex bioproxy for quantitative reconstruction of past tree abundance. In a prior study, we found that the PARs of major tree taxa – Pseudotsuga, Pinus, Notholithocarpus, and the pollen group TC (Taxaceae and Cupressaceae families) – were robust and precise estimators of contemporary tree biomass. This paper expands our earlier work. Here, we more fully evaluate the errors associated with biomass reconstructions to identify weaknesses and recommend improvements in PAR-based reconstructions of forest biomass. We account for uncertainty in our biomass proxy in a formal, coherent fashion. The greatest error was introduced by the age models, underscoring the need for improved statistical approaches to age-depth modeling. Documenting the uncertainty in pollen vegetation models should be standard practice in paleoecology. We also share insights gained from the delineation of the relevant source area of pollen, advances in Bayesian 210Pb modeling, the importance of site selection, and the use of independent data to corroborate biomass estimates. Lastly, we demonstrate our workflow with a new dataset of reconstructed tree biomass between 1850 and 2018 AD from lakes in the Klamath Mountains, California. Our biomass records followed a broad trend of low mean biomass in the ∼1850s followed by large contemporary increases, consistent with expectations of forest densification due to twentieth century fire suppression policies in the American West. More recent reconstructed tree biomass estimates also corresponded with silviculture treatments occurring within the relevant source area of pollen of our lake sites.

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Paleoecology provides context for conserving culturally and ecologically important pine forest and barrens communities

Booth,

Schuurman,

Lynch

et al. 2023

Ecological Applications

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In fire‐prone ecosystems, knowledge of vegetation–fire–climate relationships and the history of fire suppression and Indigenous cultural burning can inform discussions of how to use fire as a management tool, particularly as climate continues to change rapidly. On Wiisaakodewan‐minis/Stockton Island in the Apostle Islands National Lakeshore of Wisconsin, USA, structural changes in a pine‐dominated natural area containing a globally rare barrens community occurred after the cessation of cultural burning by the Indigenous Ojibwe people and the imposition of fire‐suppression policies, leading to questions about the historical role of fire in this culturally and ecologically important area. To help understand better the ecological context needed to steward these pine forest and barrens communities, we developed palaeoecological records of vegetation, fire, and hydrological change using pollen, charcoal, and testate amoebae preserved in peat and sediment cores collected from bog and lagoon sediments within the pine‐dominated landscape. Results indicated that fire has been an integral part of Stockton Island ecology for at least 6000 years. Logging in the early 1900s led to persistent changes in island vegetation, and post‐logging fires of the 1920s and 1930s were anomalous in the context of the past millennium, likely reflecting more severe and/or extensive burning than in the past. Before that, the composition and structure of pine forest and barrens had changed little, perhaps due to regular low‐severity surface fires, which may have occurred with a frequency consistent with Indigenous oral histories (~4–8 years). Higher severity fire episodes, indicated by large charcoal peaks above background levels in the records, occurred predominantly during droughts, suggesting that more frequent or more intense droughts in the future may increase fire frequency and severity. The persistence of pine forest and barrens vegetation through past periods of climatic change indicates considerable ecological resistance and resilience. Future persistence in the face of climate changes outside this historical range of variability may depend in part on returning fire to these systems.

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

Cited by 53 publications

References 46 publications

Linked fire activity and climate whiplash in California during the early Holocene

Linked fire activity and climate whiplash in California during the early Holocene

Methods for robust estimates of tree biomass from pollen accumulation rates: Quantifying paleoecological reconstruction uncertainty

Paleoecology provides context for conserving culturally and ecologically important pine forest and barrens communities

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