When Active Management of high conservation value forests may erode biodiversity and damage ecosystems by David Lindenmayer, et al., Biological Conservation, 2025
“[T]he scale and intensity of some kinds of AM [Active Management] (e.g. such as over-burning and excessive thinning in western North America and south-eastern Australia appears likely to be well beyond the kinds of activities practiced by Indigenous peoples before colonization.”
“A fire deficit persists across diverse North American forests despite recent increases in area burned” by Sean A. Parks, et al., Nature Communications, 2025
“Our study of 1851 tree-ring fire-scar sites and contemporary fire perimeters across the United States and Canada reveals a substantial, persistent fire deficit from 1984–2022 in many forest and woodland ecosystems, despite recent increases in burning. Contemporary fire occurrence is still far below historical (1600–1880) levels at NAFSN [North American tree-ring fire-scar network] sites despite multiple large and ‘record-breaking’ recent fire years, such as 2020 in the western United States. Individual years with particularly widespread fire during the 1984–2022 period were not unprecedented in comparison with the active fire regimes of the historical period across most of the study region.”
“Long-term tree population growth can predict woody encroachment patterns” by Robert K Shriver, et al., PNAS, 2025
“Removing pinyon and juniper trees and promoting ecosystem services provided by grasslands and shrublands has become an increasingly high priority for land management agencies, often based on the assumption that greater woodland density and extent over the last 200 y represent an unnatural phenomenon.
“We suggest that the processes driving much of the recent increases in woodland density may not be historically unprecedented, but rather a continuation of population recovery and expansion that initiated at least 400 y ago, possibly following major changes in western North American forests caused by drought, wildfire, and shifts in Indigenous land use.
“As a result, management practices that counter woody encroachment by removing trees or other policies that focus on local scales likely cannot address the underlying regional drivers of increasing tree density in these ecosystems.”
“Setting the Stage for Mixed- and High-Severity Fire” by Chad T. Hanson, Dominick A. DellaSala, Rosemary L. Sherriff, Richard L. Hutto, Thomas T. Veblen, William L. Baker, Elsevier, 2024
“Drier montane forest ecosystems and some shrub habitats are assumed to have been maintained historically by lower-severity fires that created open and park-like structures in western North America. High-severity fires—especially larger patches—are often assumed to be unnatural and ecologically damaging. These assumptions drive current land management policies where fires burn in higher severities. However, evidence indicates that montane forests, including ponderosa pine and mixed-conifer forests, were historically far more variable in tree densities and fire regimes and were maintained by a mixed-severity fire regime.”
“Contemporary Wildfires Not More Severe Than Historically: More Fire of All Severities Needed to Sustain and Adapt Western US Dry Forests as Climate Changes” by William L. Baker, Sustainability, 2024
“I compared government fire-severity data from 2000–2020 with corresponding government Landfire historical data, representing the last few centuries. The fire rotation (expected time to burn across an area of interest) for high-severity fire was 477 years recently versus 255 years historically, a deficit, not a surplus. High-severity fire would need to increase 1.9 times to equal historical rates.”
“Countering Omitted Evidence of Variable Historical Forests and Fire Regime in Western USA Dry Forests: The Low-Severity-Fire Model Rejected” by W.L. Baker, et al., Fire, 2023.
“The “low-severity” model is that dry forests were relatively uniform, low in tree density, and dominated by low- to moderate-severity fires; the “mixed-severity” model is that dry forests were heterogeneous, with both low and high tree densities and a mixture of fire severities. Here, we simply rebut evidence in the low-severity model’s latest review, including its 37 critiques of the mixed-severity model. A central finding of high-severity fire recently exceeding its historical rates was not supported by evidence in the review itself. A large body of published evidence supporting the mixed-severity model was omitted. These included numerous direct observations by early scientists, early forest atlases, early newspaper accounts, early oblique and aerial photographs, seven paleo-charcoal reconstructions, ≥18 tree-ring reconstructions, 15 land survey reconstructions, and analysis of forest inventory data. Our rebuttal shows that evidence omitted in the review left a falsification of the scientific record, with significant land management implications.”
“Historical Fire Regimes in Ponderosa Pine and Mixed-Conifer Landscapes of the San Juan Mountains, Colorado, USA, from Multiple Sources” by William L. Baker, Fire, 2018
“Historical fire rotations from atlases were mostly 225–360 years for high-severity fires and 133–185 years for moderate- to high-severity fires. Historical low-severity fire from tree-ring data at 33 sites revealed a median fire rotation of 31 years in ponderosa pine, 78 years in dry mixed-conifer, and 113 years in moist mixed-conifer forests. Only 15% of montane sites had “frequent-fire” forests with fire rotations <25 years that kept understory fuels at low levels.”
“Restoring and managing low-severity fire in dry-forest landscapes of the western USA” by William L. Baker, PLoS ONE, 2017
“Long (> 55 years) mean PMFI/FRs were mainly from northern New Mexico to South Dakota. Mountain sites often had a large range in PMFI/FR. Nearly all 342 estimates are for old forests with a history of primarily low-severity fire, found across only about 34% of historical dry-forest area. Frequent fire (PMFI/FR < 25 years) was found across only about 14% of historical dry-forest area, with 86% having multidecadal rates of low-severity fire. Historical fuels (e.g., understory shrubs and small trees) could fully recover between multidecadal fires, allowing some denser forests and some ecosystem processes and wildlife habitat to be less limited by fire.”
“Improving the use of early timber inventories in reconstructing historical dry forests and fire in the western United States” by William L. Baker, Chad T. Hanson, Ecosphere, 2017
“Published uses of two-chain timber inventories are generally invalid, since they have these documented and uncorrected large errors in estimating historical tree density and basal area, or lacked or omitted significant evidence about historical forests or fire severity.”
“Our review also documented biased placement of inventories in merchantable timber, often excluding younger forests, chaparral, and other indicators of preceding mixed/high-severity fires. We found added significant bias introduced by omitting areas burned in mixed/high-severity fires, or by missing evidence of these fires on parts of forms or associated archival materials.”
“Areas of Agreement and Disagreement Regarding Ponderosa Pine and Mixed Conifer Forest Fire Regimes: A Dialogue with Stevens et al.” by Dennis C. Odion Chad T. Hanson, William L. Baker, Dominick A. DellaSala, Mark A. Williams, PLoS ONE, 2016
“We found a major problem with a calculation they used to conclude that the FIA data were not useful for evaluating fire regimes. Their calculation, as well as a narrowing of the definition of high-severity fire from the one we used, leads to a large underestimate of conditions consistent with historical high-severity fire.”
“Are High-Severity Fires Burning at a Much Higher Rates Recently Than Historically in Dry-Forest Landscapes?” by William L. Baker, PLoS ONE, 2015
“I used new reference data and records of high-severity fire from 1984–2012 across all dry forests (25.5 million ha) of the western USA to test these hypotheses. I also approximated projected effects of climatic change on high-severity fire in dry forests by applying existing projections. This analysis showed the rate of recent high-severity fire in dry forests is within the range of historical rates, or is too low, overall across dry forests and individually in 42 of 43 analysis regions.”
“Examining Historical and Current Mixed-Severity Fire Regimes in Ponderosa Pine and Mixed-Conifer Forests of Western North America” by Dennis C. Odion, Chad T. Hanson, Andre Arsenault, William L. Baker, Dominick A. DellaSala, Richard L. Hutto, Walt Klenner, Max A. Moritz, Rosemary L. Sherriff, Thomas T. Veblen, Mark A. Williams, PLoS ONE, 2014
“Our results illustrate broad evidence of mixed-severity fire regimes in ponderosa pine and mixed-conifer forests of western North America. Prior to settlement and fire exclusion, these forests historically exhibited much greater structural and successional diversity than implied by the low/moderate-severity model.”
“Of 54 sites sampled [in Colorado Front Range] to test the validity of the spatial reconstruction, 81% showed mixed- and high-severity fire effects, rather than low-severity effects, prior to fire suppression.” [Table S1]
“Historical, Observed, and Modeled Wildfire Severity in Montane Forests in the Colorado Front Range” by Rosemary L. Sherriff, Rutherford V. Platt, Thomas T. Veblen, Tania L. Schoennagel, Meredith H. Gartner, PLOS One, 2014
“This study compares historical (i.e. pre-1920) fire severity with observed modern fire severity and modeled potential fire behavior across 564,413 ha of montane forests of the Colorado Front Range. We used forest structure and tree-ring fire history to characterize fire severity at 232 sites and then modeled historical fire-severity across the entire study area using biophysical variables. Eighteen (7.8%) sites were characterized by low-severity fires and 214 (92.2%) by mixed-severity fires (i.e. including moderate- or high-severity fires).”
“Thinning treatments at higher elevations of the montane zone will not return the fire regime to an historic low-severity regime, and are of questionable effectiveness in preventing severe wildfires. Based on present-day fuels, predicted fire behavior under extreme fire weather continues to indicate a mixed-severity fire regime throughout most of the montane forest zone. Recent large wildfires in the Front Range are not fundamentally different from similar events that occurred historically under extreme weather conditions.”
“Is Fire Severity Increasing in the Sierra Nevada, California, USA?” by Chad T. Hanson, Dennis C. Odion, International Journal of Wildland Fire, 2013
“Our goal was to investigate whether a trend in fire severity is occurring in Sierra Nevada conifer forests currently, using satellite imagery. We analysed all available fire severity data, 1984–2010, over the whole ecoregion and found no trend in proportion, area or patch size of high-severity fire. The rate of high-severity fire has been lower since 1984 than the estimated historical rate.”
“Fire History, Woodland Structure, and Mortality in a Piñon-Juniper Woodland in the Colorado National Monument” by Deborah K. Kennard, et al., BioOne, 2013
[I]n persistent piñon-juniper woodlands on the Colorado Plateau, which have found long fire-free intervals…The implications of these long fire rotations are that these woodlands have not been substantially changed by fire exclusion in the past century and, therefore, are not outside of their historic range of variation in stand structure, fire frequency, and fire behavior. As such, prescribed underburns or mechanical thinning of these forests do not represent ecological restoration and, in fact, can do long-term damage by removing old-growth trees and opening up sites for invasion by introduced species.”
“Spatially extensive reconstructions show variable-severity fire and heterogeneous structure in historical western United States dry forests” by Mark A. Williams and William L. Baker, Global Ecology and Biogeology, 2012
“Spatially extensive reconstructions from the late 1800s show that these forests were structurally variable, including areas of dense forests and understorey trees and shrubs, and fires varied in severity, including 15–65% highseverity fire. A set of laws, policies and initiatives that aim to uniformly reduce fuels and fire severity is likely to move many of these forests outside their historical range of variability with adverse effects on biological diversity. Macroscale survey-based reconstructions and palaeoecological studies reveal that higher-severity fires were and are a part of the normal dynamics of dry forests.”
Fire, fuels and restoration of ponderosa pine–Douglas fir forests in the Rocky Mountains, USA, by, William L. Baker, Thomas T. Veblen, and Rosemary L. Sherrif, Journal of Biogeography, 2007
“Exclusion of fire has not clearly and uniformly increased fuels or shifted the fire type from low- to high-severity fires.”
“Recent research has concluded that the low-severity model is inappropriate for most ponderosa pine forests in the Colorado Front Range.”
“Based on the ideas and evidence in this research, we make an initial formulation of a variable severity model as a coherent alternative to the low-severity model. In this model, natural fires vary in severity and frequency, sometimes burning at low severity in surface fuels and sometimes burning as high-severity fires in the crowns of trees, or with a mixture of surface and crown fire. In the variable-severity model, most of the landscape historically experienced or is capable of supporting high-severity fire and most stands (i.e. 1–100 ha areas of forest) have evidence of mixed- or high-severity fire over the last few centuries.”
“The central landscape image from this model is of patches of forest varying in tree age and density, including some young, dense patches and some older, lower-density patches. Variability in tree age and density comes in part from variation in environment (dry, south-facing slopes vs. moister, north-facing slopes) but also from variation in fire severity within each environment. As fires vary in severity, the number of surviving trees and density of post-fire regeneration also vary, as do snags and dead wood.”
“Ecological effects of changes in fire regimes in Pinus ponderosa ecosystems in the Colorado Front Range” by Rosemary L. Sherriff, Thomas T Veblen, Journal of Vegetation Science, 2006
“[F]ire severities prior to any effects of fire suppression were sufficient to kill many trees.”
The Colorado Front Range: A Century of Ecological Change, Thomas T. Veblen and Diane C. Lorenz, University of Utah Press, 1991
“There is a striking contrast in stand density on north- as opposed to south- facing slopes. The mesic, north-facing slopes support much denser stands. Ridgetops and gently rolling uplands are usually well forested with ponderosa pine and less commonly with Douglas fir. On south-facing slopes stands are much more open and the proportion of Douglas fir much less.”
“In the foothills where ponderosa pine forms denser stands mixed with Douglas fir on the more mesic sites, pre-Euro- American settlement mean fire-return intervals have been estimated at 39 to 66 years.”
“At higher elevations, in denser stands of ponderosa pine and particularly in mixed stands with Douglas fir, fires are more likely to become crown fires and are very patchy in spatial pattern as a result of the heterogeneous site and fuel conditions. Throughout the montane zone, most fires are light surface fires, but the infrequent crown fires have had a major impact on the landscape.”
“The sparse stand of conifers on the ridge in the left background also indicates recent logging. Their growth form indicates that they grew in a relatively closed stand (i.e., most lack lower limbs)…it is likely that this site was initially codominated by relatively old Douglas fir and ponderosa pine.”
“The open ponderosa pine woodlands of the center and foreground in the old photograph appear to have been logged.”
“Due to its thick bark, ponderosa pine is the most fire-resistant species of the Front Range.”
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