Wildfires devastated communities in Oregon and Washington in September 2020, burning almost as much forest west of the Cascade Mountain crest (“the westside”) in 2 weeks (~340,000 ha) as in the previous five decades (~406,00 ha). Unlike dry forests of the interior western United States, temperate rain forests of the Pacific Northwest have experienced limited recent fire activity, and debates surrounding what drove the 2020 fires, and management strategies to adapt to similar future events, necessitate a scientific evaluation of the fires. We evaluate five questions regarding the 2020 Labor Day fires: (1) How do the 2020 fires compare with historical fires? (2) How did the roles of weather and antecedent climate differ geographically and from the recent past (1979–2019)? (3) How do fire size and severity compare to other recent fires (1985–2019), and how did forest management and prefire forest structure influence burn severity? (4) What impact will these fires have on westside landscapes? and (5) How can we adapt to similar fires in the future? Although 5 of the 2020 fires were much larger than any others in the recent past and burned ~10 times the area in high‐severity patches >10,000 ha, the 2020 fires were remarkably consistent with historical fires. Reports from the early 1900s, along with paleo‐ and dendro‐ecological records, indicate similar and potentially even larger wildfires over the past millennium, many of which shared similar seasonality (late August/early September), weather conditions, and even geographic locations. Consistent with the largest historical fires, strong east winds and anomalously dry conditions drove the rapid spread of high‐severity wildfire in 2020. We found minimal difference in burn severity among stand structural types related to previous management in the 2020 fires. Adaptation strategies for similar fires in the future could benefit by focusing on ignition prevention, fire suppression, and community preparedness, as opposed to fuel treatments that are unlikely to mitigate fire severity during extreme weather. While scientific uncertainties remain regarding the nature of infrequent, high‐severity fires in westside forests, particularly under climate change, adapting to their future occurrence will require different strategies than those in interior, dry forests.

Our objectives were to examine the relationship between contemporary vegetation and surface soil phytolith assemblages, and use phytoliths and d13C of soil organic matter (SOM) to explore forest-grassland vegetation dynamics. We established plots within three canopy types (open, old-growth, and dense young pine) with different grass species compositions in a Pinus ponderosa forest in northern Arizona and collected vegetation data and surface (0-2 cm) and subsurface (2-7 cm) mineral soil samples. Surface soil phytolith assemblages strongly reflected vegetation at the site scale (within several km2). Local vegetation patterns (< 50 m²) associated with overstory canopy types were weakly detected. Significantly fewer C4 grass and ponderosa pine phytoliths were found in subsurface compared to surface soils. Surface d13C values showed no difference among canopy types. Subsurface d13C values were significantly (+ 0.83 ‰) more enriched in 13C than surface values. Phytolith assemblages and d13C of SOM reflect long-term accumulation of organic matter in soils and may not mirror contemporary vegetation for many reasons, including spatial shifts in species distribution and productivity. Considering all our phytolith and d13C evidence, we suggest that C4 grasses were more widely distributed but less abundant, grasses were more spatially continuous, total grass productivity was greater, and species in the genus Koeleria and Bromus were more common in the past.

We investigated herbaceous richness and cover in relation to fire season and severity, and other variables, five growing seasons following prescribed fires. Data were collected from six stands consisting of three randomly applied treatments: no burn, spring burn, and fall burn. Fall burns had significantly more exotic/native annual/biennial (an/bi) species and greater cover of these species (6.5% exotic; 1.7% native) compared to spring and unburned areas. These patterns are likely related to indirect fire effects associated with fire severity and resource availability, rather than direct fire effects due to burn timing. CART models indicated that high native and exotic an/bi richness and cover were associated with overstory gaps and higher fire severity areas, conditions common to fall burns. Exotics may be more successful at exploiting these environments. No treatment differences were found for native perennials. Location was important for explaining native perennial patterns, but richness and c... Résumé Nous avons examiné la richesse et la couverture en herbacées en relation avec la saison et la sévérité des feux, cinq saisons de croissance après des brûlages dirigés. Les données ont été récoltées dans six peuplements forestiers auxquels ont été appliqués au hasard trois traitements : pas de feu, un feu printanier et un feu automnal. Les feux d'automne comportaient significativement plus d'espèces exotiques et indigènes annuelles/bisannuelles (an/bi) et une plus grande couverture de cellesci (6,5 % d'exotiques; 1,7 % d'indigènes) que les feux d'automne ou que les aires n'ayant pas été brûlées. Ces patrons sont probablement dus aux effets indirects associés à la sévérité du feu et à la disponibilité de la ressource plus qu'à l'effet direct du feu associé à la période de brûlage. Les modèles CART ont indiqués que la richesse et la couverture élevées des espèces exotiques et indigènes an/bi étaient associées à des trouées dans l'étage dominant et à des aires brûlées sévèrement, des conditions courant...

Reestablishing historical fire regimes is a high priority for North American coniferous forests, particularly ponderosa pine (Pinus ponderosa) ecosystems. These forests are also used extensively for cattle (Bos spp.) grazing. Prescribed fires are being applied on or planned for millions of hectares of these forests to reduce fuel loads, alter forest structure, and maintain and enhance the productivity of native plant communities. However, cattle grazing is ubiquitous in ponderosa pine forests and the consequences of post‐fire cattle grazing on plant communities are not well understood. We evaluated cattle grazing effects (grazing, no grazing) on upland bunchgrass and Carex geyeri dominated ponderosa pine plant communities over five growing seasons after prescribed fires (spring reburn, fall reburn, no burn). Vegetation was measured prior to a 5‐year interval reburn and the subsequent exclusion of cattle, and in the second and fifth growing seasons thereafter. We found no interactions between reburning and grazing for the understory response variables. For all reburn treatments, including unburned areas, five growing seasons of cattle grazing exclusion significantly increased: (1) total vegetative cover, (2) native perennial forb cover, (3) grass stature, (4) grass flowering stem density, and (5) the cover of some shrub species and functional groups. Grazing exclusion did not strongly affect plant compositional patterns, although differences were detected. Compared to unburned areas, neither spring nor fall reburning increased perennial native species cover or richness, and reburning reduced sedge cover. Fall reburning increased cover of native colonizers, and exotic species cover and richness (largely Bromus tectorum and Cirsium vulgare), although overall exotic cover remains low (<1%). We document several potentially chronic impacts of cattle grazing in both burned and unburned areas, and show that the understory release from a long history of cattle grazing caused a greater degree of change than the initial reintroduction of fire. If a goal of ecological restoration in these forests is increased cover of native perennial plants, and the potential for increased native perennial grass reproduction, then cattle grazing exclusion, or a change in cattle management, could provide critically important options in restoration plans.

Prescribed fire is an active management tool used to address wildfire hazard and ecological concerns associated with fire exclusion and suppression over the past century. Despite widespread application in the United States, there is considerable inconsistency and lack of information regarding the extent to which specific outcomes are achieved and under what prescribed fire regimes, particularly in regard to ecological goals related to plant community structure. We quantify differences and patterns in plant functional group abundance, species richness and diversity, and other key forest components through time from a unique long‐term (15‐yr) experiment within the Malheur National Forest of Oregon. Treatments included five fire regimes: fall and spring 5‐yr burning, fall and spring single burn, and no burning. Original burns were conducted in the fall of 1997 and spring of 1998, and plant data were collected every five years starting in 2002. Many perennial plant group responses were neutral, subtle, and ephemeral. Total cover increased marginally in response to the first burn, but this response disappeared within a decade. Three 5‐yr reburns did not increase or decrease total plant cover, richness, or diversity. Some plant groups with fire resistant and resilient traits, such as annual forbs, exotic forbs, open bunchgrasses, and rhizomatous and resprouting perennials, showed some short‐term positive responses to initial burning and 1–2 reburns, but not 3. The moderately more severe fall burns generally impacted plant responses more than spring burning, but many patterns were legacies from the original higher severity burns. Burn frequency was more important for less severe spring burning. Overall, we document that most native perennial plant functional groups were able to resist or recover from burning and reburning, but did not necessarily strongly respond. This may be due to the importance of other overriding forcing factors and ecosystem inertia not easily overcome by very low‐severity prescribed burns. Results from our study are important for practitioners using prescribed fire to achieve biodiversity, conservation, and habitat goals that hinge on a vigorous native perennial plant response, as such outcomes are not certain even with frequent burn regimes.