Transitioning western U.S. dry forests to limited committed warming with bet‐hedging and natural disturbances

Baker, William L.

doi:10.1002/ecs2.2288

Cited by 17 publications

(30 citation statements)

References 138 publications

(276 reference statements)

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“…High-severity fires also burned historically in dry mixed-conifer forests, where ponderosa pine was dominant; about 18,000 ha of high-severity fire was documented by the atlases during 1850-1909 (Table 1). Evidence of high-severity fire has been found in nearly all other ponderosa pine and dry mixed-conifer landscapes where probabilistic landscape-level historical evidence has been studied [6,40,41]. Large high-severity fires in ponderosa pine and dry mixed-conifer forests had not been documented by tree-ring studies in the San Juan Mountains, likely because tree-ring fire studies often cannot reach sufficiently large landscape scales.…”

Section: Moderate To High-severity Fires From Forest Atlases and Othementioning

confidence: 99%

“…The resulting landscape heterogeneity of old forests, younger forests, and openings conferred bet-hedging resistance and resilience to unpredictable subsequent disturbances by fires, insects, and droughts, especially important as we enter a period of climate change with expected natural disturbances and tree mortality [41,44]. Bet-hedging at the landscape scale means that the landscape is not uniformly resistant or resilient to any one type of disturbance, but instead provides resistance and resilience to a diversity of disturbances in different parts of the landscape [41,44].…”

Section: Managing Low- Moderate- and High-severity Fires In Montanementioning

confidence: 99%

“…Natural recovery favored shade-tolerant trees (Abies concolor, Pseudotsuga menziesii, and Picea pungens), in the middle-to later-stages of succession in mixed-conifer forests [26]; these trees were even dominant in older dry mixed-conifer forests [10]. Where mixed-conifer forests are recovering, restored fires and other disturbances can readjust the abundance of shade-tolerant trees, and in the meantime recovering forests provide a key component of bet-hedging resilience at the stand scale [41,44]. For example, recovering forests, which already have small trees, are increasingly valuable because post-fire tree regeneration has been lower with warmer and drier conditions since 2000 [45].…”

Section: Managing Low- Moderate- and High-severity Fires In Montanementioning

confidence: 99%

“…If mechanical treatment is undertaken anyway in these areas, I suggest now retaining all older trees and sufficient trees <65 years old, of as many species as possible, so that after-treatment stand-structure is numerically dominated by small trees of maximum available species diversity and variable density. These provide bet-hedging against impending future beetle outbreaks, droughts, and fires [41,44].…”

Section: Managing Low- Moderate- and High-severity Fires In Montanementioning

confidence: 99%

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Historical Fire Regimes in Ponderosa Pine and Mixed-Conifer Landscapes of the San Juan Mountains, Colorado, USA, from Multiple Sources

Baker

2018

Fire

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Reconstructing historical fire regimes is difficult at the landscape scale, but essential to determine whether modern fires are unnaturally severe. I synthesized evidence across 725,000 ha of montane forests in the San Juan Mountains, Colorado, from forest atlases, forest-reserve reports, fire-scar studies, early reports, and newspaper accounts. Atlases mapped moderate-to high-severity fires during 1850-1909 (~60 years), and 86% of atlas area was attributable to 24 fire years. 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. Moderate-to high-severity fire rotations were long enough to enable old-growth forests, but short enough to foster heterogeneous landscapes with expanses of recovering forests and openings. About 38-39% is still recovering from the 1850-1909 fires. Large, infrequent severe fires historically enhanced resilience to subsequent beetle outbreaks, droughts, and fires, but have burned at lower rates in the last few decades.

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Section: Moderate To High-severity Fires From Forest Atlases and Othementioning

confidence: 99%

Section: Managing Low- Moderate- and High-severity Fires In Montanementioning

confidence: 99%

Section: Managing Low- Moderate- and High-severity Fires In Montanementioning

confidence: 99%

Section: Managing Low- Moderate- and High-severity Fires In Montanementioning

confidence: 99%

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Historical Fire Regimes in Ponderosa Pine and Mixed-Conifer Landscapes of the San Juan Mountains, Colorado, USA, from Multiple Sources

Baker

2018

Fire

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“…Due to dispersal limitations, sites in the interior of large, high‐severity patches may take decades or centuries to regain forest cover (Chambers et al. , Baker ). Furthermore, a warm and dry climate can inhibit post‐fire recovery of forests (Stevens‐Rumann et al.…”

Section: Introductionmentioning

confidence: 99%

Wildfire activity and land use drove 20th‐century changes in forest cover in the Colorado front range

et al. 2019

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Recent shifts in global forest area highlight the importance of understanding the causes and consequences of forest change. To examine the influence of several potential drivers of forest cover change, we used supervised classifications of historical (1938–1940) and contemporary (2015) aerial imagery covering a 2932‐km2 study area in the northern Front Range (NFR) of Colorado and we linked observed changes in forest cover with abiotic factors, land use, and fire history. Forest cover in the NFR demonstrated broad‐scale changes 1938–2015 and overall cover increased 7.8%, but there was notable spatial variability and many sites also experienced Forest Loss. Recent (1978–2015) wildfire was the largest single driver of Forest Loss, with fires burning 14.3% of the total study area. Recently burned areas showed net losses of 36.9% forest cover. Reasons for Forest Gain were more complex, with elevation, past mining density, fire history, and topographic heat load index being the strongest predictors of increases in forest cover. Historical mining activity is one of the dominant anthropogenic impacts in ecosystems in the NFR and it had a complex, non‐linear relationship with 20th‐century changes in forest cover. Subalpine stands originating after stand‐replacing fires circa mid‐1800s to early 1900s showed some of the greatest gains in forest cover, indicative of slow and continuous post‐fire recovery through the 20th century. We also investigated factors such as land ownership, road density, forest management activities, and development intensity, which played detectable, but more minor roles in observed change. Twentieth‐century changes in forest cover throughout the NFR are a result of ecological disturbances and anthropogenic influences operating at varying timescales and overlaid upon variability in the abiotic environment.

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Limitations to recovery following wildfire in dry forests of southern Colorado and northern New Mexico, USA

Rodman

Veblen

Chapman

et al. 2019

Ecological Applications

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Climate warming is contributing to increases in wildfire activity throughout the western United States, leading to potentially long‐lasting shifts in vegetation. The response of forest ecosystems to wildfire is thus a crucial indicator of future vegetation trajectories, and these responses are contingent upon factors such as seed availability, interannual climate variability, average climate, and other components of the physical environment. To better understand variation in resilience to wildfire across vulnerable dry forests, we surveyed conifer seedling densities in 15 recent (1988–2010) wildfires and characterized temporal variation in seed cone production and seedling establishment. We then predicted postfire seedling densities at a 30‐m resolution within each fire perimeter using downscaled climate data, monthly water balance models, and maps of surviving forest cover. Widespread ponderosa pine (Pinus ponderosa) seed cone production occurred at least twice following each fire surveyed, and pulses of conifer seedling establishment coincided with years of above‐average moisture availability. Ponderosa pine and Douglas‐fir (Pseudotsuga menziesii) seedling densities were higher on more mesic sites and adjacent to surviving trees, though there were also important interspecific differences, likely attributable to drought and shade tolerance. We estimated that postfire seedling densities in 42% (for ponderosa pine) and 69% (for Douglas‐fir) of the total burned area were below the lowest reported historical tree densities in these forests. Spatial models demonstrated that an absence of mature conifers (particularly in the interior of large, high‐severity patches) limited seedling densities in many areas, but 30‐yr average actual evapotranspiration and climatic water deficit limited densities on marginal sites. A better understanding of the limitations to postfire forest recovery will refine models of vegetation dynamics and will help to improve strategies of adaptation to a warming climate and shifting fire activity.

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Transitioning western U.S. dry forests to limited committed warming with bet‐hedging and natural disturbances

Cited by 17 publications

References 138 publications

Historical Fire Regimes in Ponderosa Pine and Mixed-Conifer Landscapes of the San Juan Mountains, Colorado, USA, from Multiple Sources

Historical Fire Regimes in Ponderosa Pine and Mixed-Conifer Landscapes of the San Juan Mountains, Colorado, USA, from Multiple Sources

Wildfire activity and land use drove 20th‐century changes in forest cover in the Colorado front range

Limitations to recovery following wildfire in dry forests of southern Colorado and northern New Mexico, USA

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