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Changing disturbance regimes and climate can overcome forest ecosystem resilience. Following high-severity fire, forest recovery may be compromised by lack of tree seed sources, warmer and drier postfire climate, or short-interval reburning. A potential outcome of the loss of resilience is the conversion of the prefire forest to a different forest type or nonforest vegetation. Conversion implies major, extensive, and enduring changes in dominant species, life forms, or functions, with impacts on ecosystem services. In the present article, we synthesize a growing body of evidence of fire-driven conversion and our understanding of its causes across western North America. We assess our capacity to predict conversion and highlight important uncertainties. Increasing forest vulnerability to changing fire activity and climate compels shifts in management approaches, and we propose key themes for applied research coproduced by scientists and managers to support decision-making in an era when the prefire forest may not return.

Background Site-specific data about fire regimes and ecosystem attributes is valuable for developing conservation strategies. Aims We determined fire history linked to forest attributes in Talassemtane National Park, Morocco, which conserves rare species at the northern tip of Africa. Methods We sampled fire-scarred conifers at three high-elevation forest sites, along with forest measurements. Key results Surface fires recurred frequently at all sites (mean fire intervals 15–23 years) over the period 1879–2018, burning primarily in the late summer. Fires were not highly synchronous among sites and were not climate-driven, suggesting a pattern of human ignitions at times when burning was safe. Stands were dominated by large and old Pinus and Abies trees that had survived numerous surface fires. Sites where fires continued to the present had relatively open structure with few ladder fuels. The site where 36 years had passed since the last fire had a dense mid-storey of sprouting Quercus trees. Conclusions Fire regimes and forest attributes were linked with fire-quiescent periods associated with high tree density, creating ladder fuels that could support crown fire. Implications Maintaining frequent-fire regimes in these forests could provide benefits for reducing fuels, avoiding undesired fires under extreme conditions, and supporting adaptation to warmer climate.

Current U.S. forest fire policy emphasizes short‐term outcomes versus long‐term goals. This perspective drives managers to focus on the protection of high‐valued resources, whether ecosystem‐based or developed infrastructure, at the expense of forest resilience. Given these current and future challenges posed by wildland fire and because the U.S. Forest Service spent >50% of its budget on fire suppression in 2015, a review and reexamination of existing policy is warranted. One of the most difficult challenges to revising forest fire policy is that agency organizations and decision making processes are not structured in ways to ensure that fire management is thoroughly considered in management decisions. Current resource‐specific policies are so focused on individual concerns that they may be missing the fact that there are “endangered landscapes” that are threatened by changing climate and fire. We propose that forest restoration should be at least equal to other land management priorities because large‐scale restoration is necessary for the sake of forest ecosystem integrity now and into the future. Another proposal is to switch the “default” rule in federal planning documents that currently have to “justify” managed wildland fire; instead, U.S. federal agencies should be required to disclose the long‐term ecological impacts of continued fire suppression. Proposed legislation that identifies the most expensive 2% of wildfires annually to be funded from emergency funding instead of by the federal land management agencies. If increases in forest restoration fail to accompany the change in how large wildfires are funded, then U.S. fire suppression costs will remain high while resilience will continue to decline. Expansion of the wildland–urban interface will continue to drive suppression costs higher; new federal partnerships with States and local governments are needed to address this problem. Given the legacy of fire suppression and a future of climate change, management for other values in forests will be, in the long run, futile without also managing for long‐term forest resilience.

Anticipating future forest-fire regimes under changing climate requires that scientists and natural resource managers understand the factors that control fire across space and time. Fire scars - proxy records of fires, formed in the growth rings of long-lived trees - provide an annually accurate window into past low-severity fire regimes. In western North America, networks of the fire-scar records spanning centuries to millennia now include hundreds to thousands of trees sampled across hundreds to many thousands of hectares. Development of these local and regional fire-scar networks has created a new data type for ecologists interested in landscape and climate regulation of ecosystem processes - which, for example, may help to explain why forest fires are widespread during certain years but not others. These data also offer crucial reference information on fire as a dynamic landscape process for use in ecosystem management, especially when managing for forest structure and resilience to climate change.

Climate change and wildfire are interacting to drive vegetation change and potentially reduce water quantity and quality in the southwestern United States, Forest restoration is a management approach that could mitigate some of these negative outcomes. However, little information exists on how restoration combined with climate change might influence hydrology across large forest landscapes that incorporate multiple vegetation types and complex fire regimes. We combined spatially explicit vegetation and fire modeling with statistical water and sediment yield models for a large forested landscape (335,000 ha) on the Kaibab Plateau in northern Arizona, USA. Our objective was to assess the impacts of climate change and forest restoration on the future fire regime, forest vegetation, and watershed outputs. Our model results predict that the combination of climate change and high-severity fire will drive forest turnover, biomass declines, and compositional change in future forests. Restoration treatments may reduce the area burned in high-severity fires and reduce conversions from forested to non-forested conditions. Even though mid-elevation forests are the targets of restoration, the treatments are expected to delay the decline of high-elevation spruce–fir, aspen, and mixed conifer forests by reducing the occurrence of high-severity fires that may spread across ecoregions. We estimate that climate-induced vegetation changes will result in annual runoff declines of up to 10%, while restoration reduced or reversed this decline. The hydrologic model suggests that mid-elevation forests, which are the targets of restoration treatments, provide around 80% of runoff in this system and the conservation of mid- to high-elevation forests types provides the greatest benefit in terms of water conservation. We also predict that restoration treatments will conserve water quality by reducing patches of high-severity fire that are associated with high sediment yield. Restoration treatments are a management strategy that may reduce undesirable outcomes for multiple ecosystem services.

Quantifying historical fire regimes provides important information for managing contemporary forests. Historical fire frequency and severity can be estimated using several methods; each method has strengths and weaknesses and presents challenges for interpretation and verification. Recent efforts to quantify the timing of historical high-severity fire events in forests of western North America have assumed that the \"stand age\" variable from the US Forest Service Forest Inventory and Analysis (FIA) program reflects the timing of historical high-severity (i.e. stand-replacing) fire in ponderosa pine and mixed-conifer forests. To test this assumption, we re-analyze the dataset used in a previous analysis, and compare information from fire history records with information from co-located FIA plots. We demonstrate that 1) the FIA stand age variable does not reflect the large range of individual tree ages in the FIA plots: older trees comprised more than 10% of pre-stand age basal area in 58% of plots analyzed and more than 30% of pre-stand age basal area in 32% of plots, and 2) recruitment events are not necessarily related to high-severity fire occurrence. Because the FIA stand age variable is estimated from a sample of tree ages within the tree size class containing a plurality of canopy trees in the plot, it does not necessarily include the oldest trees, especially in uneven-aged stands. Thus, the FIA stand age variable does not indicate whether the trees in the predominant size class established in response to severe fire, or established during the absence of fire. FIA stand age was not designed to measure the time since a stand-replacing disturbance. Quantification of historical \"mixed-severity\" fire regimes must be explicit about the spatial scale of high-severity fire effects, which is not possible using FIA stand age data.

The US Endangered Species Act has enabled species conservation but has differentially impacted fire management and rare bird conservation in the southern and western US. In the South, prescribed fire and restoration-based forest thinning are commonly used to conserve the endangered red-cockaded woodpecker (Picoides borealis; RCW), whereas in the West, land managers continue to suppress fire across the diverse habitats of the northern, Californian, and Mexican spotted owls (Strix occidentalis subspecies; SO). Although the habitat needs of the RCW and SO are not identical, substantial portions of both species’ ranges have historically been exposed to relatively frequent, low-to moderate-intensity fires. Active management with fire and thinning has benefited the RCW but proves challenging in the western US. We suggest the western US could benefit from the adoption of a similar innovative approach through policy, public–private partnerships, and complementarity of endangered species management with multiple objectives. These changes would likely balance long-term goals of SO conservation and enhance forest resilience.

Climate change affects all ecosystems but despite increasing recognition for the needs to integrate Indigenous knowledge with modern climate science, the epistemological differences between the two make it challenging. In this study, we present how Indigenous belief and knowledge system can frame the application of a modeling tool (Climate-Forest Vegetation Simulator). We focus on managing forest ecosystem services of the Diné (Navajo) Nation as a case study. Most Diné tribal members depend directly on the land for their livelihoods and cultural traditions. The forest plays a vital role in Diné livelihoods through social, cultural, spiritual, subsistence, and economic factors. We simulated forest dynamics over time under alternative climate change scenarios and management strategies to identify forest management strategies that will maintain future ecosystem services. We initialized the Climate-Forest Vegetation Simulator model with data from permanent plots and site-specific growth models under multiple management systems (no-management, thinning, burning, and assisted migration planting) and different climate scenarios (no-climate-change, RCP 4.5, RCP 6.0). Projections of climate change show average losses of basal area by over 65% by 2105, a shift in tree species composition to drier-adapted species, and a decrease in species diversity. While substantial forest loss was inevitable under the warming climate scenarios, the modeling framework allowed us to evaluate the management treatments, including planting, for conserving multiple tree species in mixed conifer forests, thus providing an anchor for biodiversity. We presented the modeling results and management implications and discuss how they can complement Diné kinship concepts. Our approach is a useful step for framing modern science with Indigenous Knowledge and for developing improved strategies to sustain natural resources and livelihoods.

The restoration of historical fire regimes is often a primary objective in the conservation of fire‐adapted forests. However, individual species' responses to future climate change may uncouple historical vegetation–disturbance relationships, producing potentially negative ecological consequences to fire restoration. We used a landscape simulation model to assess how forest pattern will respond to future climate regimes and whether the restoration of historical fire regimes will benefit forest conservation under future climate regimes. Our study landscape was the 335,000‐ha Kaibab Plateau at the North Rim of the Grand Canyon spanning a broad elevation‐vegetation gradient of pinyon‐juniper, ponderosa pine, mixed conifer, and spruce‐fir forests along with a range of associated fire regimes. We employed a novel multimodel landscape simulation approach using the Climate‐Forest Vegetation Simulator to estimate individual tree species climate responses and LANDIS‐II to simulate spatial patterns of fire disturbance, forest growth, regeneration, succession, and dispersal. Model simulations included three climate scenarios (no change, moderate change, and high change) and two fire scenarios (fire exclusion and fire restoration). The climate change scenarios produced declines in mean forest aboveground biomass (AGB) and a compositional turnover equal to one or two vegetation zones, approximating the vegetation displacement that occurred in this location during the Holocene. Fire restoration resulted in earlier, but roughly equivalent, AGB declines and compositional change. Uphill species migration in some elevation zones produced tree species–fire regime mismatches that promoted state changes and increased nonforest area. Regardless of fire management approach, our simulations project that the Kaibab Plateau will eventually be dominated by pinyon–juniper, oak, and ponderosa pine forest types, with a complete loss of mesic conifer species. Our results indicate that fire managers will have to be flexible with the application of historical fire regimes to avoid regeneration failures and abrupt declines in biomass.

After more than a century of low fire activity in the western United States, wildfires are now becoming more common. Reburns, which are areas burned in two or more fires, are also increasing. How fires interact over time is of interest ecologically as well as for management. Wildfires may act as fuel treatments, reducing subsequent fire severity, or they may increase subsequent fire severity by leaving high fuel loads behind. Our goal was to assess whether previous wildfire severity influenced subsequent fire severity across vegetation types and over time in the Southwest U.S. using remotely sensed fire severity data in 2275 fires that burned between 1984 and 2019. Points that reburned tended to be those that burned with lower severity initially. Shrublands burned predominantly at moderate to high severity in initial fires and in reburns. Pinyon-juniper-oak systems burned with mixed severity, and fire severity was consistent from fire to fire. In ponderosa pine and aspen-mixed conifer, fire severity tended to decrease with each fire. Initial and subsequent fire severity was lower in points that reburned after a short interval. These remotely sensed observations of reburn severity need verification through field work to understand specific effects caused by reburns in different ecosystems. However, in ponderosa pine and aspen-mixed conifer forests, it may be beneficial to consider wildfires as fuel treatments and work to maintain the fuel reduction effects they have on forested ecosystems.