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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.

Climate-change adaptation focuses on conducting and translating research to minimize the dire impacts of anthropogenic climate change, including threats to biodiversity and human welfare. One adaptation strategy is to focus conservation on climate-change refugia (that is, areas relatively buffered from contemporary climate change over time that enable persistence of valued physical, ecological, and sociocultural resources). In this Special Issue, recent methodological and conceptual advances in refugia science will be highlighted. Advances in this emerging subdiscipline are improving scientific understanding and conservation in the face of climate change by considering scale and ecosystem dynamics, and looking beyond climate exposure to sensitivity and adaptive capacity. We propose considering refugia in the context of a multifaceted, long-term, network-based approach, as temporal and spatial gradients of ecological persistence that can act as "slow lanes" rather than areas of stasis. After years of discussion confined primarily to the scientific literature, researchers and resource managers are now working together to put refugia conservation into practice.

Fire refugia--locations that burn less severely or less frequently than surrounding areas--support late-successional and old-growth forest structure and function. This study investigates the influence of topography and fuels on the probability of forest fire refugia under varying fire weather conditions. We focused on recent large fires in Oregon and Washington, United States (n = 39 fires > 400 ha, 2004-2014). Our objectives were to (1) map fire refugia as a component of the burn severity gradient, (2) quantify the predictability of fire refugia as a function of prefire fuels and topography under moderate and high fire weather conditions, and (3) map the conditional probability of fire refugia to illustrate their spatial patterns in old-growth forests. Fire refugia exhibited higher predictability under relatively moderate fire weather conditions. Prefire live fuels were strong predictors of fire refugia, with higher refugia probability in forests with higher prefire biomass. In addition, fire refugia probability was higher in topographic settings with relatively northern aspects, steep catchment slopes, and concave topographic positions. Conditional probability maps revealed consistently higher fire refugia probability under moderate versus high fire weather scenarios. Results from this study inform conservation planning by determining late-successional forests most likely to persist as fire refugia despite increasing regional fire activity. Key words: biological legacies, burn severity, fire refugia, late-successional forests, Pacific Northwest. Les refuges de feu (endroits ou la foret brule moins severement ou moins frequemment que dans le territoire environnant) maintiennent la structure et la fonction des forets en fin de succession et des forets anciennes. Cette etude examine l'influence de la topographie et des combustibles sur la probabilite de la presence d'un refuge de feu en tenant compte de differentes conditions meteorologiques propices aux incendies. Nous avons mis l'accent sur les grands feux recents dans les Etats de l'Oregon et de Washington, aux Etats-Unis (n = 39 feux > 400 ha, 2004-2014). Nos objectifs consistaient a (1) cartographier les refuges de feu en tant que composantes d'un gradient de severite du feu, (2) quantifier la previsibilite des refuges de feu en fonction des combustibles presents avant que survienne un feu et de la topographie en tenant compte de conditions meteorologiques moderement et tres propices aux incendies et (3) cartographier la probabilite conditionnelle de la presence des refuges de feu pour illustrer leur configuration spatiale dans les forets anciennes. Les refuges de feu etaient plus previsibles lorsque les conditions meteorologiques propices aux incendies etaient relativement moderees. Les combustibles vivants presents avant que survienne un feu etaient de bons predicteurs de la presence des refuges de feu et la probabilite de la presence d'un refuge de feu etait plus elevee dans les forets contenant une plus grande biomasse avant que survienne un feu. De plus, la probabilite de la presence d'un refuge de feu etait plus elevee dans des contextes topographiques caracterises par des expositions relativement septentrionales, des deniveles de bassin abrupts et des positions topographiques concaves. Les cartes de probabilite conditionnelle revelent que la probabilite de la presence des refuges de feu est constamment plus elevee avec les scenarios de conditions meteorologiques moderement plutot que tres favorables aux incendies. Les resultats de cette etude contribuent a la planification de la conservation en determinant les forets en fin de succession qui ont le plus de chances de persister en tant que refuges de feu malgre l'augmentation regionale des incendies. [Traduit par la Redaction] Mots-cles: legs biologiques, severite du feu, refuges de feu, forets en fin de succession, Pacific Northwest., Introduction The spatiotemporal patterns of wildfires have important implications for biodiversity conservation throughout the world. In forest ecosystems of western North America, following decades of fire exclusion, wildfire activity has [...]

Climate change and the compounding effects of drought and wildfire are catalyzing rapid ecosystem changes throughout the world. Relatively dry, trailing edge (TE) forests are especially vulnerable to ecological transformation when tree regeneration is moisture-limited following high-severity fire. Here, we illustrate the potential landscape-scale impacts of changing disturbance regimes by focusing on TE forests in the eastern Cascades of Washington, USA. Our specific objectives were to: (1) map TE forests based on climatic water deficit and forest cover; (2) characterize the composition, structure, and ownership of TE and non-TE forests; (3) quantify recent fire activity in TE and non-TE forests; (4) identify locations of potential forest loss where recent fires have burned severely in TE forests. Across the study area, TE forests encompassed 387 000 ha, representing a substantial portion (21 per cent) of the total forested landscape. TE forests generally were characterized by dry, mixed-conifer forest types with more open structure and less biomass than non-TE forests. The structural and compositional conditions within TE forests make them ideal locations for management strategies designed to enhance landscape resilience and sustain fire-resistant trees. TE forestland ownership is diverse (35 per cent federal, 19 per cent Tribal, 16 per cent Washington State, 14 per cent private non-industrial and 13 per cent private industrial), indicating that successful land management will require collaboration among numerous partners. Recent wildfires (1984–2020) cumulatively covered 84 300 ha (22 per cent) of TE forests and 363 500 ha (25 per cent) of non-TE forests. TE forests experienced less high-severity fire than non-TE forests (39 per cent vs. 46 per cent, respectively). Recent high-severity fire effects in TE forests occurred primarily in the northern portion of the study region, reflecting the distribution of individual large fires. By quantifying the variability of TE forests and their recent fire activity, this study supports adaptive management strategies for landscape restoration, post-disturbance reforestation and climate adaptation. [ABSTRACT FROM AUTHOR]

Aims: Wildfires in dry forest ecosystems in western North America are producing fire effects that are more severe than historical estimates, raising concerns about the resilience of these landscapes to contemporary disturbances. Despite increasing fire activity, relatively little is known about the structure and composition of fire refugia — unburned or low‐severity burned patches where trees survived fire — or the degree to which their understory composition differs from fire‐generated early‐seral forests. Locations: Four recent large fires in dry mixed‐conifer forest in eastern Oregon, USA. Methods: We sampled vegetation and environmental factors in 187 plots (100‐m2) in fire refugia (n = 52) and stand‐replacement patches (SRPs) (n = 135). We used non‐metric multidimensional scaling, indicator species analysis, and randomization tests to compare understory plant communities and diversity in fire refugia and SRPs 12–17 years post‐fire. Results: Understory plant communities in fire refugia and SRPs showed strong compositional affinities, but exhibited shifts in reproductive trait prevalence and differences in landscape‐scale species richness. There were no differences in plot‐scale species richness or the occurrence of two prominent invasive annual grasses (Bromus tectorum, Ventenata dubia). The abundance of common obligate seeding species was similar between plot types, but resprouting and seed‐banking species became substantially more abundant in SRPs. Significantly more plant species occurred only in fire refugia, and significantly fewer in SRPs, than expected by chance. Conclusions: Similarities in understory plant communities between fire refugia and early‐seral forest in SRPs provide evidence for the resilience of historically frequent‐fire forest understory communities to contemporary fire effects. However, fire refugia may serve an ecologically important role as patches with relatively intact forest structure, seed sources that contribute to post‐fire forest recovery, and as reservoirs of species and age structure that may be absent from the higher‐severity burned matrix. [ABSTRACT FROM AUTHOR]

Climate change threatens the provisioning of forest ecosystem services and biodiversity (ESB). The climate sensitivity of ESB may vary with forest development from young to old‐growth conditions as structure and composition shift over time and space. This study addresses knowledge gaps hindering implementation of adaptive forest management strategies to sustain ESB. We focused on a number of ESB indicators to (a) analyze associations among carbon storage, timber growth rate, and species richness along a forest development gradient; (b) test the sensitivity of these associations to climatic changes; and (c) identify hotspots of climate sensitivity across the boreal–temperate forests of eastern North America. From pre‐existing databases and literature, we compiled a unique dataset of 18,507 forest plots. We used a full Bayesian framework to quantify responses of nine ESB indicators. The Bayesian models were used to assess the sensitivity of these indicators and their associations to projected increases in temperature and precipitation. We found the strongest association among the investigated ESB indicators in old forests (>170 years). These forests simultaneously support high levels of carbon storage, timber growth, and species richness. Older forests also exhibit low climate sensitivity of associations among ESB indicators as compared to younger forests. While regions with a currently low combined ESB performance benefitted from climate change, regions with a high ESB performance were particularly vulnerable to climate change. In particular, climate sensitivity was highest east and southeast of the Great Lakes, signaling potential priority areas for adaptive management. Our findings suggest that strategies aimed at enhancing the representation of older forest conditions at landscape scales will help sustain ESB in a changing world. [ABSTRACT FROM AUTHOR]

Locations within forest fires that remain unburned or burn at low severity—known as fire refugia—are important components of contemporary burn mosaics, but their composition and structure at regional scales are poorly understood. Focusing on recent, large wildfires across the US Pacific Northwest (Oregon and Washington), our research objectives are to (1) classify fire refugia and burn severity based on relativized spectral change in Landsat time series; (2) quantify the pre-fire composition and structure of mapped fire refugia; (3) in forested areas, assess the relative abundance of fire refugia and other burn severity classes across forest composition and structure types. We analyzed a random sample of 99 recent fires in forest-dominated landscapes from 2004 to 2015 that collectively encompassed 612,629 ha. Across the region, fire refugia extent was substantial but variable from year to year, with an annual mean of 38% of fire extent and range of 15–60%. Overall, 85% of total fire extent was forested, with the other 15% being non-forest. In comparison, 31% of fire refugia extent was non-forest prior to the most recent fire, highlighting that mapped refugia do not necessarily contain tree-based ecosystem legacies. The most prevalent non-forest cover types in refugia were vegetated: shrub (40%), herbaceous (33%), and crops (18%). In forested areas, the relative abundance of fire refugia varied widely among pre-fire forest types (20–70%) and structural conditions (23–55%). Consistent with fire regime theory, fire refugia and high burn severity areas were inversely proportional. Our findings underscore that researchers, managers, and other stakeholders should interpret burn severity maps through the lens of pre-fire land cover, especially given the increasing importance of fire and fire refugia under global change. [ABSTRACT FROM AUTHOR]

With accelerating environmental change, understanding forest disturbance impacts on trade-offs between biodiversity and carbon dynamics is of high socio-economic importance. Most studies, however, have assessed immediate or short-term effects of disturbance, while long-term impacts remain poorly understood. Using a tree-ring-based approach, we analysed the effect of 250 years of disturbances on present-day biodiversity indicators and carbon dynamics in primary forests. Disturbance legacies spanning centuries shaped contemporary forest co-benefits and trade-offs, with contrasting, local-scale effects. Disturbances enhanced carbon sequestration, reaching maximum rates within a comparatively narrow post-disturbance window (up to 50 years). Concurrently, disturbance diminished aboveground carbon storage, which gradually returned to peak levels over centuries. Temporal patterns in biodiversity potential were bimodal; the first maximum coincided with the short-term post-disturbance carbon sequestration peak, and the second occurred during periods of maximum carbon storage in complex old-growth forest. Despite fluctuating local-scale trade-offs, forest biodiversity and carbon storage remained stable across the broader study region, and our data support a positive relationship between carbon stocks and biodiversity potential. These findings underscore the interdependencies of forest processes, and highlight the necessity of large-scale conservation programmes to effectively promote both biodiversity and long-term carbon storage, particularly given the accelerating global biodiversity and climate crises.