Search

Abstract: Background: Prairie–forest ecotones are ecologically important for biodiversity and ecological processes. While these ecotones cover small areas, their sharp gradients in land cover promote rich ecological interaction and high conservation value. Our objective was to understand how historical and current fire occurrences and human development influenced the Palouse Prairie–forest ecotone. We used General Land Office survey field notes about the occurrence of bearing trees to locate historical (1870s to 1880s) prairie, pine savanna, and forest at the eastern edge of the bioregion. We combined LANDFIRE Existing Vegetation classes to contrast historical land cover with current land cover. We reconstructed historical fire occurrence (1650 to 1900) from fire-scarred trees. We used fire and lightning records from 1992 to 2015 to interpret the role of people and lightning. Results: Historically, the ecotone was a matrix of prairie with extensive savanna and some forest. More than half of the ecotone area was prairie, which is now dominated by agriculture, with some residential development. The 16% of the landscape that was pine savanna is now forest or shrubs, agriculture, perennial vegetation under the Conservation Reserve Program, or developed; no savanna now exists. Forests covered 12% of the ecotone and these are still mostly forest. Fires were historically frequent, occurring on average every 5 to 8 years at most sites. Lightning was not frequent but could likely have been sufficient to ignite fires that could spread readily given the rolling terrain and long fire season. Conclusions: Fire was far more frequent historically than currently. Conservation, restoration, and other ongoing land-use changes will likely result in more continuous vegetation and hence fuel for fires. Lightning and people may ignite fires that therefore spread readily in the future. Understanding the past and potential future of fire in the Palouse Prairie bioregion may help us live with fire while conserving ecological values here and in similar prairie–forest ecotones.

© 2015 The Author(s) Context: More than a century of forest and fire management of Inland Pacific landscapes has transformed their successional and disturbance dynamics. Regional connectivity of many terrestrial and aquatic habitats is fragmented, flows of some ecological and physical processes have been altered in space and time, and the frequency, size and intensity of many disturbances that configure these habitats have been altered. Current efforts to address these impacts yield a small footprint in comparison to wildfires and insect outbreaks. Moreover, many current projects emphasize thinning and fuels reduction within individual forest stands, while overlooking large-scale habitat connectivity and disturbance flow issues. Methods: We provide a framework for landscape restoration, offering seven principles. We discuss their implication for management, and illustrate their application with examples. Results: Historical forests were spatially heterogeneous at multiple scales. Heterogeneity was the result of variability and interactions among native ecological patterns and processes, including successional and disturbance processes regulated by climatic and topographic drivers. Native flora and fauna were adapted to these conditions, which conferred a measure of resilience to variability in climate and recurrent contagious disturbances. Conclusions: To restore key characteristics of this resilience to current landscapes, planning and management are needed at ecoregion, local landscape, successional patch, and tree neighborhood scales. Restoration that works effectively across ownerships and allocations will require active thinking about landscapes as socio-ecological systems that provide services to people within the finite capacities of ecosystems. We focus attention on landscape-level prescriptions as foundational to restoration planning and execution.

Time-varying fire-climate relationships may represent an important component of fire-regime variability, relevant for understanding the controls of fire and projecting fire activity under global-change scenarios. We used time-varying statistical models to evaluate if and how fire-climate relationships varied from 1902-2008, in one of the most flammable forested regions of the western U.S.A. Fire-danger and water-balance metrics yielded the best combination of calibration accuracy and predictive skill in modeling annual area burned. The strength of fire-climate relationships varied markedly at multi-decadal scales, with models explaining < 40% to 88% of the variation in annual area burned. The early 20th century (1902-1942) and the most recent two decades (1985-2008) exhibited strong fire-climate relationships, with weaker relationships for much of the mid 20th century (1943-1984), coincident with diminished burning, less fire-conducive climate, and the initiation of modern fire fighting. Area burned and the strength of fire-climate relationships increased sharply in the mid 1980s, associated with increased temperatures and longer potential fire seasons. Unlike decades with high burning in the early 20th century, models developed using fire-climate relationships from recent decades overpredicted area burned when applied to earlier periods. This amplified response of fire to climate is a signature of altered fire-climate-relationships, and it implicates non-climatic factors in this recent shift. Changes in fuel structure and availability following 40+ yr of unusually low fire activity, and possibly land use, may have resulted in increased fire vulnerability beyond expectations from climatic factors alone. Our results highlight the potential for non-climatic factors to alter fire-climate relationships, and the need to account for such dynamics, through adaptable statistical or processes-based models, for accurately predicting future fire activity.

With longer and more severe fire seasons predicted, the incidence and extent of fires are expected to increase in western North America. As more area is burned, past wildfires may influence the spread and burn severity of subsequent fires, with implications for ecosystem resilience and fire management. We examined how previous burn severity, topography, vegetation, and weather influenced burn severity on four wildfires, two in Idaho, one in Washington, and one in British Columbia. These were large fire events, together burning 330 000 ha and cost $165 million USD in fire suppression expenditures. Collectively, these four study fires reburned over 50 000 ha previously burned between 1984 and 2006. We used sequential autoregression to analyze how past fires, topography, vegetation, and weather influenced burn severity. We found that areas burned in the last three decades, at any severity, had significantly lower severity in the subsequent fire. Final models included maximum temperature, vegetation cover type, slope, and elevation as common predictors. Across all study fires and burning conditions within them, burn severity was reduced in previously burned areas, suggesting that burned landscapes mitigate subsequent fire effects even with the extreme fire weather under which these fires burned. Key words: fire weather, reburn, repeated wildfires, sequential autoregression, self-regulation. Prevoyant que la saison des feux sera plus longue et plus severe, on anticipe une augmentation de l'incidence et de l'etendue des feux dans l'ouest de l'Amerique du Nord. A mesure que davantage de superficie est brulee, les feux de foret passes peuvent influencer la propagation et la severite des feux subsequents, ce qui a des implications pour la resilience des ecosystemes et la gestion du feu. Nous avons etudie de quelle facon la severite des feux passes, la topographie, la vegetation et les conditions meteorologiques ont influence la severite de quatre feux de foret : deux en Idaho, un dans l'Etat de Washington et un en Colombie-Britannique. Il s'agit de feux majeurs qui ensemble ont brule 330 000 ha et engendre des couts de suppression de 165 millions de dollars US. Collectivement, les quatre feux a l'etude ont brule a nouveau 50 000 ha deja brules entre 1984 et 2006. Nous avons utilise l'autoregression sequentielle pour analyser comment les feux passes, la topographie, la vegetation et les conditions meteorologiques ont influence la severite des feux plus recents. Nous avons trouve que les zones brulees au cours des trois dernieres decennies, peu importe la severite, avaient une severite significativement plus faible lors de feux subsequents. Les modeles finaux incluaient la temperature maximum, le type de couvert vegetal, la pente et l'altitude en tant que predicteurs communs. Parmi tous les feux etudies et les conditions de brulage associees a ces feux, la severite du feu etait reduite dans les endroits qui avaient brule anterieurement, indiquant que les paysages ayant deja brules attenuent les effets des feux subsequents, meme si ces feux surviennent dans des conditions meteorologiques extremes. [Traduit par la Redaction] Mots-cles : conditions meteorologiques propices aux feux de foret, rebrulage, feux de foret repetes, autoregression sequentielle, autoregulation., Introduction As a self-regulating process, the pattern of previous fires may limit the progression and burn severity of subsequent wildfires for some time due to limited burnable fuels and changes [...]