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Study area. a Geographic features of our 130 × 130 km study in ID, USA. b Location of our study area in relation to the Rocky Mountains (shaded area), in western North America. c Representative vegetation includes rangelands at lower elevations and mixed conifer forest at higher elevations
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Introduction
Climate change is expected to impose significant tension on the geographic distribution of tree species. Yet, tree species range shifts may be delayed by their long life spans, capacity to withstand long periods of physiological stress, and dispersal limitations. Wildfire could theoretically break this biological inertia by killing for...
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Context 1
... study area includes ~17,000 km 2 of mountainous terrain in the southern Idaho Batholith (Fig. 1). Eleva- tions range from ~900 to 3600 m, with low elevations characterized by hot summers and cool winters and high elevations characterized by short growing seasons and cold winters. Precipitation ranges from 220 to 1440 mm annually, most of it arriving as snow, especially at higher elevations. Natural plant communities are ...
Citations
... Abies lasiocarpa increased after the period of thinning (i.e. after 2020;Figure 4). By decreasing the occurrences of high-severity fire, mid-elevation treatments favoured the maintenance of subalpine species populations, which became older and minimized their replacement by Populus tremuloides, an early-successional speciesCampbell & Shinneman, 2017). This aligns with prior research suggesting that the combination of thinning and prescribed fire may reduce the occurrence of high-severity fires that spread from mid-elevation dry pine forests to historically less flammable high-elevation mixed-conifer forests(O'Donnell et al., 2018). ...
In southwestern US forests, the combined impact of climate change and increased fuel loads due to more than a century of human‐caused fire exclusion is leading to larger and more severe wildfires. Restoring frequent fire to dry conifer forests can mitigate high‐severity fire risk, but the effects of these treatments on the vegetation composition and structure under projected climate change remain uncertain.
We used a forest landscape model to assess the impact of thinning and prescribed burns in dry conifer forests across an elevation gradient, encompassing low‐elevation pinyon‐juniper woodlands, mid‐elevation ponderosa pine and high‐elevation mixed‐conifer forests.
Our results demonstrated that the treatments decreased the probability of high‐severity fires by 42% in the study area. At low elevation, the treatments did not prevent loss in forest cover and biomass with decreases in Pinus edulis and Juniperus monosperma abundances. At mid‐elevation, changes in fire effects maintained a greater diversity of tree species by favouring the maintenance of cohorts of old trees, in particular Pinus ponderosa which accumulated 5.41 Mg ha⁻¹ more above‐ground biomass than without treatments by late‐century. Treatments in dry conifer forests modified fire effects beyond the treated area, resulting in increased cover and biomass of old Picea englemannii and Abies lasiocarpa cohorts.
Synthesis and applications: Our findings indicate that thinning and prescribed burning can enhance tree species diversity in dry conifer forests by protecting old cohorts from stand‐replacing fires. Moreover, our results suggest that treatments mainly implemented in dry pine forests with high risk of high‐severity fires can be beneficial for subalpine species conservation by reducing the chance that high‐severity fire at mid‐elevation is transmitted into high‐elevation forest.
... Evidence for fire as a catalyst of tree species range shifts is mixed. Simulation modeling is the most common approach to obtaining such evidence and, while some models support disturbance as a facilitator of climateinduced range expansion (Moran & Ormond, 2015;Stralberg et al., 2018), others find only weak evidence (Campbell & Shinneman, 2017;Liang et al., 2018) or stress that the influence of disturbance may depend on its frequency (Moran & Ormond, 2015) or severity (Brice et al., 2020). Empirical studies often describe the negative impacts of fire on tree regeneration at the warmer, more arid trailing edges of species distributions (Davis et al., 2019;Renwick et al., 2016), but empirical evidence for fireinduced movement at the leading edges of species distributions is less clear perhaps due to the lack of robust datasets across species range limits (Brice et al., 2020;Hill & Field, 2021). ...
... Alongside an average predicted 34% increase in climatic suitability at our study sites by 2030 (compared with 5% for red fir), our results suggest that Jeffrey pine may be the species most likely to colonize future subalpine forests under predicted increases in fire and temperature (Alizadeh et al., 2021;Remy et al., 2021;Thorne et al., 2018). Our findings align with recent modeling studies from across the western USA showing that Ponderosa pine (Pinus ponderosa)-an ecologically close relative of Jeffrey pine in the "yellow pine" group (McCune, 1988)-was one of only two species that expanded to higher elevations under future climate and disturbance scenarios (Remy et al., 2021) or was the most likely to do so (Bell et al., 2014b;Campbell & Shinneman, 2017). Ponderosa pine was adapted to warmer and drier conditions than the subalpine fir and spruce that it replaced in the simulation (Remy et al., 2021). ...
Wildfires may facilitate climate tracking of forest species moving upslope or north in latitude. For subalpine tree species, for which higher elevation habitat is limited, accelerated replacement by lower elevation montane tree species following fire may hasten extinction risk. We used a dataset of postfire tree regeneration spanning a broad geographic range to ask whether the fire facilitated upslope movement of montane tree species at the montane‐to‐subalpine ecotone. We sampled tree seedling occurrence in 248 plots across a fire severity gradient (unburned to >90% basal area mortality) and spanning ~500 km of latitude in Mediterranean‐type subalpine forest in California, USA. We used logistic regression to quantify differences in postfire regeneration between resident subalpine species and the seedling‐only range (interpreted as climate‐induced range extension) of montane species. We tested our assumption of increasing climatic suitability for montane species in subalpine forest using the predicted difference in habitat suitability at study plots between 1990 and 2030. We found that postfire regeneration of resident subalpine species was uncorrelated or weakly positively correlated with fire severity. Regeneration of montane species, however, was roughly four times greater in unburned relative to burned subalpine forest. Although our overall results contrast with theoretical predictions of disturbance‐facilitated range shifts, we found opposing postfire regeneration responses for montane species with distinct regeneration niches. Recruitment of shade‐tolerant red fir declined with fire severity and recruitment of shade‐intolerant Jeffrey pine increased with fire severity. Predicted climatic suitability increased by 5% for red fir and 34% for Jeffrey pine. Differing postfire responses in newly climatically available habitats indicate that wildfire disturbance may only facilitate range extensions for species whose preferred regeneration conditions align with increased light and/or other postfire landscape characteristics.
... First, those growing on the West and East Coasts are adapted to humid conditions and snowpacks (Mori, Mizumachi, & Sprugel, 2008). Second, the specific conditions of the Rocky Mountains (snowfalls, high drought, and topographic variability) strongly influence the conifer distribution and fire regimes (Campbell & Shinneman, 2017). In contrast, Mexican Abies species experience moderate or absent snowfalls, less diurnal temperature, and seasonal variations compared to forests of higher latitudes (Rzedowski, 2006). ...
Fir forests (Abies, Pinaceae) are dominant in temperate regions of North America; however, they have experienced high degradation rates that can threaten their long-term continuity. This study aimed to identify the priority areas for the conservation of the genus Abies in North America. First, we modeled the species distribution of the 17 native species through ecological niche modeling, considering 21 environmental variables. Then, we defined the priority areas through multi-criteria analysis, considering the species richness, geographic rareness, irreplaceability, habitat degradation, and risk extinction. We also built six scenarios, giving more priority to each criterion. Finally, we identified the proportion of the extent of the priority areas covered by protected areas. Elevation, precipitation seasonality, and winter precipitation influenced the distribution of most of the Abies species. When considering equal weights to each criterion, the priority areas summed up 6% of the total extent covered by the Abies species in North America. Most priority areas were located on the West Coast of the United States, the Eastern Sierra Madre, Southern Sierra Madre, Sierras of Chiapas and Central America, and the Trans-Mexican Volcanic Belt ecoregions. In these ecoregions, the Abies species are restricted to small areas facing high degradation levels. Only 16% of the area covered by the Abies species in North America is protected, mainly under restrictive schemes such as National Parks and Wilderness Areas. The priority areas identified could be the basis for establishing or enlarging protected areas. The preservation of the genus Abies could also maintain other ecological features and processes such as biodiversity, forest resources, and environmental services.
... More frequent surface fire in mixed-conifer forests may promote fire-resistant species over others. In the Central RCKS, simulated increases in fire frequency accelerated declines in predicted area occupied by the less fire-resistant species lodgepole pine, subalpine fir, and Douglas-fir due to climate change, but maintained the area occupied by the more resistant species ponderosa pine (Campbell and Shinneman 2017). More frequent low-severity fire may favor the establishment of faster-growing ponderosa pine over Douglas-fir, as it develops thicker bark at a younger age (Rodman et al. 2020b). ...
... Other studies found that increased temperatures led to lower recruitment of lodgepole pine and Engelmann spruce establishment across an elevation gradient (Kueppers et al. 2017;Conlisk et al. 2018). A recent modeling study in central Idaho suggested that there may be a decline in area occupied by lodgepole pine, Douglasfir, and subalpine fir due to the combined effects of climate change and increased fire frequency (Campbell and Shinneman 2017). Fire in subalpine areas may provide an opportunity for recruitment of montane or lower elevation species at higher elevations, within constraints of dispersal distances (Campbell and Shinneman 2017). ...
... A recent modeling study in central Idaho suggested that there may be a decline in area occupied by lodgepole pine, Douglasfir, and subalpine fir due to the combined effects of climate change and increased fire frequency (Campbell and Shinneman 2017). Fire in subalpine areas may provide an opportunity for recruitment of montane or lower elevation species at higher elevations, within constraints of dispersal distances (Campbell and Shinneman 2017). Aspen may increase in areas previously dominated by conifers because it is less sensitive to many climatically-sensitive disturbances (e.g., fire, insect outbreaks; Gill et al. 2017). ...
Fire is a dominant driver of ecosystem patterns and processes across the Rocky Mountains. This chapter describes fire ecology and fire-related management for the major forest types in the Rocky Mountains. Major forest types included are ponderosa pine, Douglas-fir, mixed-conifer, lodgepole pine, spruce-fir, five-needle pines, and aspen. For each forest type we describe historical fire regimes, interactions between fire and other disturbances, departures from historical patterns, and projected future patterns. We explain fire resistance and postfire recovery patterns. We also include projected alterations to fire regimes and ecological implications due to climate change, with common silvicultural and fuel treatment options for restoration and wildfire mitigation. This information provides a comprehensive examination of contemporary fire ecology and management options in the Rocky Mountains, couched in a historical perspective.
... Homogeneous Western landscapes generally have low resilience to disturbance (Keane et al. 2002 and may have little ability to buffer potential climate impacts because of the high tree densities and an abundance of shadetolerant trees (Vanderwel and Purves 2014). Wildfires and harvest activities over the last decade have returned some heterogeneity to forest landscapes, especially in wilderness areas (Campbell and Shinneman 2017;Hessburg et al. 2019). However, most are well outside of the historical range of variability in landscape structure. ...
Higher temperatures, lower snowpacks, drought, and extended dry periods have contributed to increased wildfire activity in recent decades. Climate change is expected to increase the frequency of large fires, the cumulative area burned, and fire suppression costs and risks in many areas of the USA. Fire regimes are likely to change due to interactions among climate, fire, and other stressors and disturbances; resulting in persistent changes in forest structure and function. The remainder of the twenty-first century will present substantial challenges, as natural resource managers are faced with higher fire risk and the difficult task of maintaining ecological function in a rapidly changing biophysical and social landscape. Fuel treatments will continue to be important for minimizing the undesirable ecological effects of fire, and for enhancing firefighter safety; however, treatments must be implemented strategically across large areas. Collaboration among agencies, private landowners, and other organizations will be critical for ensuring resilience and sustainable forest management.
... Our results from early in the simulation period approximate this historic condition well, with high interannual variability in area burned and a mix of low-and moderate-severity coupled with high-severity fire (Fig. 2). These high-severity fire patches create larger canopy openings favoring the regeneration of early seral species that are capable resprouting or wind dispersal, such as P. tremuloides (Campbell and Shinneman 2017;Shive et al. 2018). As the climate continued to warm, the proportion of area burned at high-severity increased, causing declines in the dominant species P. engelmannii and A. lasiocarpa, which are not fire resistant (Bigler et al. 2005;Stevens et al. 2020). ...
Over the twenty-first century, the combined effects of increased fire activity and climate change are expected to alter forest composition and structure in many ecosystems by changing postfire successional trajectories and recovery. Southwestern US mountain ecosystems contain a variety of vegetation communities organized along an elevation gradient that will respond uniquely to changes in climate and fire regime. Moreover, the twentieth-century fire exclusion has altered forest structure and fuel loads compared to their natural states (i.e., without fire suppression). Consequently, uncertainties persist about future vegetation shifts along the elevation gradient. In this study, we simulated future vegetation dynamics along an elevation gradient in the southwestern US comprising pinyon-juniper woodlands, ponderosa pine forests, and mixed-conifer forests for the period 2000-2099, to quantify the effects of future climate conditions and projected wildfires on species productivity and distribution. While we expected to find larger changes in aboveground biomass, species diversity and species-specific abundance at low elevation due to warmer and drier conditions, the largest changes occurred at high elevation in mixed-conifer forests and were caused by wildfire. The largest increase in high-severity and large fires were recorded in this vegetation type, leading to high mortality of the dominant species, Picea engelmannii and Abies lasiocarpa, which are not adapted to fire. The decline of these two species reduced biomass productivity at high elevation. In ponderosa pine forests and pinyon-juniper woodlands, fewer vegetation changes occurred due to higher abundance of well-adapted species to fire and the lower fuel loads mitigating projected fire activity, respectively. Thus, future research should prioritize understanding of the processes involved in future vegetation shifts in mixed-conifer forests in order to mitigate both loss of diversity specific to high-elevation forests and the decrease in biomass productivity, and thus carbon storage capacity, of these ecosystems due to wildfires.
... This discrepancy in climate tolerance between juveniles and adults, combined with the long lifespan of many tree species, can result in plantclimate disequilibrium (Svenning and Sandel 2013), where the dominant mature trees on a landscape do not reflect current climate conditions (e.g. Campbell andShinneman 2017, Serra-Diaz et al 2018). ...
... Our results are indicative of the potential for fire-catalyzed range contraction at the warm dry margins of the current distribution of ponderosa pine and Douglas-fir; importantly, they do not capture the potential for fire to catalyze range expansion along the cooler and wetter range margins of these species (e.g. by reducing competition with existing vegetation). Some models predict fire will catalyze range expansion due to climate change (Stralberg et al 2018), while others suggest that dispersal may limit expansion into burned areas (Campbell and Shinneman 2017). ...
... This discrepancy in climate tolerance between juveniles and adults, combined with the long lifespan of many tree species, can result in plantclimate disequilibrium (Svenning and Sandel 2013), where the dominant mature trees on a landscape do not reflect current climate conditions (e.g. Campbell andShinneman 2017, Serra-Diaz et al 2018). ...
... Our results are indicative of the potential for fire-catalyzed range contraction at the warm dry margins of the current distribution of ponderosa pine and Douglas-fir; importantly, they do not capture the potential for fire to catalyze range expansion along the cooler and wetter range margins of these species (e.g. by reducing competition with existing vegetation). Some models predict fire will catalyze range expansion due to climate change (Stralberg et al 2018), while others suggest that dispersal may limit expansion into burned areas (Campbell and Shinneman 2017). ...
Increased wildfire activity combined with warm and dry post-fire conditions may undermine the mechanisms maintaining forest resilience to wildfires, potentially causing ecosystem transitions, or fire-catalyzed vegetation shifts. Stand-replacing fire is especially likely to catalyze vegetation shifts expected from climate change, by killing mature trees that are less sensitive to climate than juveniles. To understand the vulnerability of forests to fire-catalyzed vegetation shifts it is critical to identify both where fires will burn with stand-replacing severity and where climate conditions limit seedling recruitment. We used an extensive dendrochronological dataset to model the influence of seasonal climate on post-fire recruitment probability for ponderosa pine and Douglas-fir. We applied this model to project annual recruitment probability in the US intermountain west under contemporary and future climate conditions, which we compared to modeled probability of stand-replacing fire. We categorized areas as "vulnerable to fire-catalyzed vegetation shifts," if they were likely to burn at stand-replacing severity, if a fire were to occur, and had post-fire climate conditions unsuitable for tree recruitment. Climate suitability for recruitment declined over time in all ecoregions: 21% and 15% of the range of ponderosa pine and Douglas-fir, respectively, had climate conditions unsuitable for recruitment in the 1980s, whereas these values increased to 61% (ponderosa pine) and 34% (Douglas-fir) for the future climate scenario. Less area was vulnerable to fire-catalyzed vegetation shifts, but these values also increased over time, from 6% and 4% of the range of ponderosa pine and Douglas-fir in the 1980s, to 16% (ponderosa pine) and 10% (Douglas-fir) under the future climate scenario. Southern ecoregions had considerably higher vulnerability to fire-catalyzed vegetation shifts than northern ecoregions. Overall, our results suggest that the combination of climate warming and an increase in wildfire activity may substantially impact species distributions through fire-catalyzed vegetation shifts
... In the Klamath region of northern California and southern Oregon, approximately one third of conifer-dominated forest could transition to shrub-or hardwood-dominated ecosystems by the latetwenty-first century (Serra-Diaz et al. 2018). In the mountains of central Idaho, climate change and increased fire activity are expected to substantially reduce the prevalence of four common conifer species (Campbell and Shinneman 2017). In Alberta, Canada, wildfire could catalyze conversion of about 50% of upland mixed-wood and conifer forests to more climatically suited mosaics of grassland, shrubland, and deciduous woodland by 2100 (Stralberg et al. 2018). ...
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.
... Local conditions can outweigh broad geographical patterns, as in the Mediterranean where the southernmost P. nigra site in Morocco is more mesic than Spanish sites to the north (Camarero et al., 2013). Disturbance-mediated change associated with interactions between climate and wildfire or insect pathogens is also likely to affect shifting distributions in variable ways (Waring et al., 2009;Campbell and Shinneman, 2017;Parks et al., 2019). ...
Pinus leiophylla, or Chihuahua pine (PILE), and P. ponderosa, or ponderosa pine (PIPO), are two wide-ranging North American species with distributions that overlap in Arizona, USA. We compared the growth of 58 trees from three study sites over an elevation gradient at the northernmost point of PILE occurrence. Because the PILE trees were growing at the extreme edge of the species' range, we expected that PILE sensitivity to climate would be higher and growth performance would be reduced compared to PIPO. From 1918 to 2017, the study area became drier and warmer with precipitation declining by ~9% while temperature rose by ~5%. We found that PILE tree-ring indices were more sensitive in terms of average year-to-year percent variation than those of PIPO and had higher variability in tree-ring variation in the 10 wettest vs. the 10 driest years. But PILE displayed higher absolute diameter growth rates as measured by basal area index (BAI) and was less negatively correlated with warm monthly temperatures. Within species, low-elevation trees of both species tended to have greater sensitivity to climate over all variables assessed, but the differences were not statistically significant. The overall assessment of growth of paired trees of the two species showed the locally rare species PILE to perform approximately equally as well as the dominant species PIPO. Species migration is reshaping global forests but species found predominantly in Mexico with distributions coinciding closely with national boundaries have received insufficient research attention in the USA. We recommend cross-border, climate-focused, comprehensive studies on PILE and other species likely to migrate northward to provide critical information for conservation and management of forest resources.
