Influence of fire refugia spatial pattern on post-fire forest recovery in Oregon’s Blue Mountains

Downing, William M.; Krawchuk, Meg A.; Meigs, Garrett W.; Haire, Sandra L.; Walker, Ryan B.; Whitman, Ellen; Chong, Geneva W.; Miller, Carol

doi:10.1007/s10980-019-00802-1

Cited by 44 publications

(35 citation statements)

References 64 publications

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“…Field counts of branch internodes of ponderosa pine seedlings, which correlated strongly with counts of tree rings, indicated ongoing regeneration throughout the interval between fire and our sampling (Downing et al. )—a finding consistent with studies examining even longer intervals (Savage and Mast , Shatford et al. , Haire and McGarigal ).…”

Section: Discussionsupporting

confidence: 89%

“…, Haire and McGarigal , Landesmann and Morales , Downing et al. ). Our D 2 WD term that integrated potential seed rain from multiple sources was generally a much stronger predictor of tree regeneration than linear distance (Tables , ).…”

Section: Discussionmentioning

confidence: 99%

“…A broader description of these sites is available in Downing et al. (). The Southern Rockies comprise numerous, large mountain ranges in Colorado and northern New Mexico encompassing steep elevational and climatic gradients.…”

Section: Methodsmentioning

confidence: 99%

“…Such that findings could be generalized across ponderosa pine and dry mixed-conifer forest types in the western United States, sampled burns occurred across a broad range of environmental conditions (Table 1) Hijmans et al 2005). A broader description of these sites is available in Downing et al (2019). The Southern Rockies comprise numerous, large mountain ranges in Colorado and northern New Mexico encompassing steep elevational and climatic gradients.…”

Section: Study Areamentioning

confidence: 99%

“…Fire refugia that retain mature trees through disturbance may serve importantly as seed sources for post‐fire landscape reforestation (Landesmann and Morales , Downing et al. ), thus serving as elements of spatial resilience. Within contemporary high‐severity burn interiors in ponderosa pine and dry mixed‐conifer forests western North America, numerous prior studies have demonstrated that regeneration by obligate‐seeding tree species is limited by distance from surviving seed sources (Bonnet et al.…”

Section: Introductionmentioning

confidence: 99%

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Contributions of fire refugia to resilient ponderosa pine and dry mixed‐conifer forest landscapes

et al. 2019

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Altered fire regimes can drive major and enduring compositional shifts or losses of forest ecosystems. In western North America, ponderosa pine and dry mixed‐conifer forest types appear increasingly vulnerable to uncharacteristically extensive, high‐severity wildfire. However, unburned or only lightly impacted forest stands that persist within burn mosaics—termed fire refugia—may serve as tree seed sources and promote landscape recovery. We sampled tree regeneration along gradients of fire refugia proximity and density at 686 sites within the perimeters of 12 large wildfires that occurred between 2000 and 2005 in the interior western United States. We used generalized linear mixed‐effects models to elucidate statistical relationships between tree regeneration and refugia pattern, including a new metric that incorporates patch proximity and proportional abundance. These relationships were then used to develop a spatially explicit landscape simulation model. We found that regeneration by ponderosa pine and obligate‐seeding mixed‐conifer tree species assemblages was strongly and positively predicted by refugia proximity and density. Simulation models revealed that for any given proportion of the landscape occupied by refugia, small patches produced greater landscape recovery than large patches. These results highlight the disproportionate importance of small, isolated islands of surviving trees, which may not be detectable with coarse‐scale satellite imagery. Findings also illustrate the interplay between patch‐scale resistance and landscape‐scale resilience: Disturbance‐resistant settings (fire refugia) can entrain resilience (forest regeneration) across the burn matrix. Implications and applications for land managers and conservation practitioners include strategies for the promotion and maintenance of fire refugia as components of resilient forest landscapes.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Study Areamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Contributions of fire refugia to resilient ponderosa pine and dry mixed‐conifer forest landscapes

et al. 2019

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Nucleation sites and forest recovery under high shrub competition

Ursell

Safford

2022

Ecological Applications

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Forests currently face numerous stressors, raising questions about processes of forest recovery as well as the role of humans in stimulating recovery by planting trees that might not otherwise regenerate. Theoretically, planted trees can also provide a seed source for further recruitment once the planted trees become reproductive, acting as "nucleation" sites; however, it is unclear whether changing site conditions over time (e.g., through the growth of competitors like woody shrubs) influences establishment in the long term, even if seed availability increases. We tested the nucleation concept in a system where shrub competition is known to influence tree establishment and growth, performing an observational study of sites within and close to newly reproductive planted stands in yellow-pine (YP) and mixed-conifer ecosystems in the Sierra Nevada, California. We surveyed and then modeled both seedling occurrence and density as a function of distance to seed sources, competing woody vegetation, and other environmental characteristics. We found that proximity to a planted stand was associated with an increase in the probability of YP seedlings (species more likely to originate from the planted stand) from 0.33 at 35 m from the planted stand to 0.56 directly adjacent to the stand and 0.65 within the stand. However, we found no significant effect of proximity on YP seedling density. This proximity effect suggests that seed availability continues to be a driver of recruitment several decades postwildfire, though other processes may influence the expected density of recruits. Proxies for competitive pressure (shrub volume and shrub cover) were not significant, suggesting that competing vegetation did not have a major influence on recruitment. Though

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Postfire futures in southwestern forests: Climate and landscape influences on trajectories of recovery and conversion

Coop

2022

Ecological Applications

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Southwestern ponderosa pine forests are vulnerable to fire‐driven conversion in a warming and drying climate, yet little is known about what kinds of ecological communities may replace them. To characterize postfire vegetation trajectories and their environmental determinants, plant assemblages (361 sample plots including 229 vascular plant species, surveyed in 2017) were sampled within eight burns that occurred between 2000 and 2003. I used nonmetric multidimensional scaling, k‐means clustering, principal component analysis, and random forest models to assess relationships between vegetation pattern, topographic and landscape factors, and gridded climate data. I describe seven postfire community types, including regenerating forests of ponderosa pine, aspen, and mixed conifers, shrub‐dominated communities of Gambel oak and mixed species, and herb‐dominated communities of native bunchgrasses and mixtures of ruderal, native, and nonnative species. Forest recovery was generally associated with cooler, mesic sites in proximity to forested refugia; shifts toward scrub and grassland types were most common in warmer, dryer locations distant from forested refugia. Under future climate scenarios, models project decreases in postfire forest recovery and increases in nonforest vegetation. However, forest to nonforest conversion was partially offset under a scenario of reduced burn severity and increased retention of forested refugia, highlighting important management opportunities. Burning trends in the southwestern United States suggest that postfire vegetation will occupy a growing landscape fraction, compelling renewed management focus on these areas and paradigm shifts that accommodate ecological change. I illustrate how management decisions around resisting, accepting, or directing change could be informed by an understanding of processes and patterns of postfire community variation and likely future trajectories.

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Influence of fire refugia spatial pattern on post-fire forest recovery in Oregon’s Blue Mountains

Cited by 44 publications

References 64 publications

Contributions of fire refugia to resilient ponderosa pine and dry mixed‐conifer forest landscapes

Contributions of fire refugia to resilient ponderosa pine and dry mixed‐conifer forest landscapes

Nucleation sites and forest recovery under high shrub competition

Postfire futures in southwestern forests: Climate and landscape influences on trajectories of recovery and conversion

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