Search

Increasing fire severity and warmer, drier postfire conditions are making forests in the western United States (West) vulnerable to ecological transformation. Yet, the relative importance of and interactions between these drivers of forest change remain unresolved, particularly over upcoming decades. Here, we assess how the interactive impacts of changing climate and wildfire activity influenced conifer regeneration after 334 wildfires, using a dataset of postfire conifer regeneration from 10,230 field plots. Our findings highlight declining regeneration capacity across the West over the past four decades for the eight dominant conifer species studied. Postfire regeneration is sensitive to high-severity fire, which limits seed availability, and postfire climate, which influences seedling establishment. In the near-term, projected differences in recruitment probability between low- and high-severity fire scenarios were larger than projected climate change impacts for most species, suggesting that reductions in fire severity, and resultant impacts on seed availability, could partially offset expected climate-driven declines in postfire regeneration. Across 40 to 42% of the study area, we project postfire conifer regeneration to be likely following low-severity but not high-severity fire under future climate scenarios (2031 to 2050). However, increasingly warm, dry climate conditions are projected to eventually outweigh the influence of fire severity and seed availability. The percent of the study area considered unlikely to experience conifer regeneration, regardless of fire severity, increased from 5% in 1981 to 2000 to 26 to 31% by mid-century, highlighting a limited time window over which management actions that reduce fire severity may effectively support postfire conifer regeneration.

Uncharacteristic disturbances exacerbated by climate change are challenging forests and social systems of North America. To improve efficiency and effectiveness of forest management to address these challenges, we demonstrated structured decision-making in the collaborative development of a novel 20-year dry forest management strategy for southwestern Oregon, USA. We framed priorities and evaluated options with a wildfire risk assessment, then modeled stand-scale prescriptions to estimate management outputs (e.g., area treated, fuels reduced, and timber volume). We mapped landscape-scale objectives and used optimization software to prioritize treatment placement constrained by realistic access considerations and robust habitat protections. The resulting prioritization integrated proactive forest adaptation and fire management (ecological forest thinning, prescribed fire) with protection of imperiled species. To evaluate tradeoffs, we tested three 20-year scenarios, finding that the All-Lands scenario best mitigated wildfire risk; it reduced risk overall by 70%, to homes by 50%, and to core northern spotted owl habitat by 47%. This scenario treated 25% of the 1.9 million ha landscape, including 31% of federal land and 40% of the community at risk. Clear articulation of collaborative objectives and evaluation of scenarios have expanded partnerships and co-investment in actions supporting a shared vision of resilient southwestern Oregon forests applicable to other landscapes. Key words: climate adaptation, forest restoration, wildfire risk, ecological forestry, prescribed fire. Des perturbations inhabituelles accentuees par le changement climatique menacent les forets et les systemes sociaux de l'Amerique du Nord. Dans le but d'ameliorer l'efficience et l'efficacite de l'amenagement forestier pour faire face a ces menaces, nous presentons un processus de prise de decision structure dans le cadre du developpement collaboratif d'une nouvelle strategie d'amenagement de la foret seche sur une periode de 20 ans pour le sud-ouest de l'Oregon, aux Etats-Unis. Nous avons formule des priorites et evalue des options accompagnees d'une evaluation des risques de feu de foret. Nous avons ensuite modelise des prescriptions a l'echelle du peuplement pour estimer les resultats de l'amenagement (p. ex., superficie traitee, reduction des combustibles et volume de bois). Nous avons cartographie des objectifs a l'echelle du paysage et utilise un logiciel d'optimisation pour prioriser l'emplacement des traitements avec comme contraintes des considerations realistes d'accessibilite et des mesures robustes de protection de l'habitat. L'etablissement consecutif des priorites integrait l'adaptation proactive de la foret et la gestion du feu (eclaircie ecologique de la foret, brulage dirige) avec la protection des especes menacees. Pour evaluer les compromis, nous avons teste trois scenarios d'une duree de 20 ans. Nous avons trouve que le scenario qui incluait tous les terrains reduisait le plus les risques de feu de foret; il reduisait les risques de 70 % globalement, de 50 % dans le cas des habitations et de 47 % dans le cas de l'habitat principal de la chouette tachetee nordique. Ce scenario traitait 25 % du paysage de 1,9 millions d'hectares, incluant 31% de terrain federal et 40% de communautes a risque. Une articulation claire des objectifs collaboratifs et l'evaluation des scenarios ont permis de developper des partenariats et un coinvestissement dans des actions supportant une vision partagee des forets resilientes du sud-ouest de l'Oregon applicables a d'autres paysages. [Traduit par la Redaction] Mots-cles : adaptation au climat, restauration des forets, risques de feu de foret, foresterie ecologique, brulage dirige., Introduction Globally, land managers are challenged to integrate diverse societal goals with fire and forest management (Bowman et al. 2011). In the western United States, climate change is increasing fire [...]

Highlights • Locally, dry forests historically recorded fire more than once every decade. • Regionally, fires burned in most years with climate synchronizing fires among sites. • Fire regimes were disrupted by 1905, decades sooner near Euro-American settlements. • The proportion of fall and early summer fires was higher historically than now. • Frequent-fire regimes in Rogue River Basin forests paralleled those in California. Abstract Fire regimes structure plant communities worldwide with regional and local factors, including anthropogenic fire management, influencing fire frequency and severity. Forests of the Rogue River Basin in Oregon, USA, are both productive and fire-prone due to ample winter precipitation and summer drought; yet management in this region is strongly influenced by forest practices that depend on fire exclusion. Regionally, climate change is increasing fire frequency, elevating the importance of understanding historically frequent-fire regimes. We use cross-dated fire-scars to characterize historical fire return intervals, seasonality, and relationships with climate beginning in 1650 CE for 13 sites representative of southwestern Oregon dry forests. Using systematic literature review, we link our local fire histories to a regional dataset and evaluate our data relative to more intensively studied conifer/hardwood forest types in California. Fire-scars show that fires in the Rogue Basin were frequent and regular until disrupted in the 1850s through 1910s, corresponding with forced displacement of Native Americans and Euro-American settlement. Median historical fire return intervals were 8 years at the stand-scale (<25 ha), with site medians ranging from five to 14 years and no significant differences between sampled vegetation types. Burn seasonality was broadly distributed with 47% of recorded fires in the latewood (midsummer), 30% at the ring boundary (late summer and fall), and 23% in the earlywood (spring and early summer). The number of sites recording fire each year was associated with Palmer Drought Severity Index (PDSI) and El Niño Southern Oscillation Index (ENSO). Fires were detected in the study area every other year, and synchrony among sites was associated with stronger annual drought. The ENSO synchronization of fire suggests an herbaceous fuel signal, with warm winters/wet summers two years prior to widespread fire-years, a pattern observed globally in fuel-limited systems. Stand-scale fire histories in the Klamath, southern Cascades, and northern Sierra Nevada ecoregions resemble Rogue River Basin stand-scale fire histories. Across dry mixed conifer, yellow pine, and mixed evergreen forests, fire return intervals converged on 8 years. Moist mixed conifer and red fir forests exhibited 13-year fire return intervals. Across ecoregions, fire periodicity was weakly correlated with climatic water deficit, but well-modeled by elevation, precipitation, and temperature. These data highlight the need for decadal fire and burning outside of the contemporary fire season for forest restoration and climate adaptation in the dry forests of the Rogue Basin. [ABSTRACT FROM AUTHOR]

Climate change will likely have significant effects on forest ecosystems worldwide. In Mediterranean regions, such as that in southwestern Oregon, USA, changes will likely be driven mainly by wildfire and drought. To minimize the negative effects of climate change, resource managers require tools and information to assess climate change vulnerabilities and to develop and implement adaptation actions. We developed an approach to facilitate development and implementation of climate change adaptation options in forest management. This approach, applied in a southwestern Oregon study region, involved establishment of a science-manager partnership, a science-based assessment of forest and woodland vulnerabilities to climate change, climate change education in multiple formats, hands-on development of adaptation options, and application of tools to incorporate climate change in planned projects. Through this approach, we improved local manager understanding of the potential effects of climate change in southwestern Oregon, and enabled evaluation of proposed management activities in the context of climatic stressors. Engaging managers throughout the project increased ownership of the process and outcomes, as well as the applicability of the adaptation options to on-the-ground actions. Science-management partnerships can effectively incorporate evolving science, regardless of the socio-political environment, and facilitate timely progress in adaptation to climate change. [ABSTRACT FROM AUTHOR]