Fire Years Research Articles

A 700-year record of large fire years in northern Scandinavia shows large variability and increased frequency during the 1800 s

Years with climatically mediated increases in boreal forest fire activity, referred to as large fire years (LFYs), contribute to a disproportionally large portion of the burned area over centuries, and are important drivers of ecosystem processes by affecting forest structure, biodiversity, and carbon balance at regional and continental scales. We analysed changes in LFY return intervals in northern Sweden (the area above 60 °N) over 1273–1960 using a network of 29 sites with dendrochronologically reconstructed fires, complemented by documentary records of fires available from forestry statistics. We observed large variability in return intervals of LFYs, an increase in LFY frequency during the 1800 s, and consistent associations between LFY occurrence and 500-hPa pressure anomalies over the European sub-continent over 1800xps2#1960. An increase in LFY frequency during the 1800 s might be climatically driven, and would thus long precede the period of likely human-induced climatic changes of the 1900 s. Long-term variability in climatically driven LFYs may present a challenge in partitioning the effects of human-related and human-independent components of climatic forcing upon forest fire activity.

Area burned in the western United States is unaffected by recent mountain pine beetle outbreaks

In the western United States, mountain pine beetles (MPBs) have killed pine trees across 71,000 km(2) of forest since the mid-1990s, leading to widespread concern that abundant dead fuels may increase area burned and exacerbate fire behavior. Although stand-level fire behavior models suggest that bark beetle-induced tree mortality increases flammability of stands by changing canopy and forest floor fuels, the actual effect of an MPB outbreak on subsequent wildfire activity remains widely debated. To address this knowledge gap, we superimposed areas burned on areas infested by MPBs for the three peak years of wildfire activity since 2002 across the western United States. Here, we show that the observed effect of MPB infestation on the area burned in years of extreme fire appears negligible at broad spatial extents. Contrary to the expectation of increased wildfire activity in recently infested red-stage stands, we found no difference between observed area and expected area burned in red-stage or subsequent gray-stage stands during three peak years of wildfire activity, which account for 46% of area burned during the 2002-2013 period. Although MPB infestation and fire activity both independently increased in conjunction with recent warming, our results demonstrate that the annual area burned in the western United States has not increased in direct response to bark beetle activity. Therefore, policy discussions should focus on societal adaptation to the effects of recent increases in wildfire activity related to increased drought severity.

Comparison of Two Approaches for Determining Fire Dates From Tree Scars

Knowledge regarding the historic role of fire in forest ecosystems is often derived by dating fire scars. Fire history studies in boreal and western coniferous forests have used either complete or partial cross sections cut from fire-scarred trees. The occurrence of missing or false rings presents an obstacle to the accurate dating of individual fires. Two different techniques of dating partial cross sections of fire-scarred ponderosa pine (Pinus ponderosa Laws) were compared using the same samples. Method I involves the tabulation of raw dates followed by a subsequent adjustment based on synchronization with fire dates from adjacent trees. Method II uses correlations with master chronologies based on analysis of increment cores taken in the same region as the sampled fire scar sections. Method I is prone to error since the assumption that fire dates differing by a few years may actually be from the same year cannot be independently verified. Method II provides a higher degree of certainty with regard to the accuracy of individual dates because the cross dating of local patterns of ring widths circumvents the problem of absent or false rings. Eight samples from the Horse Pasture Plateau in Zion National Park, Utah, were dated by both methods. Agreement on dates derived by the two methods for 39 separate fire years was limited to only 26 percent. The average error of Method I was 1.0 year. Fire history studies using Method I are accurate enough for most managerial recommendations and some ecological interpretations, but they may lack the precision necessary to correctly identify fire years or differentiate small changes in fire frequency. The dendrochronological approach of Method II is preferable because of its greater reliability, especially in ecosystems where short fire intervals are common or where fires occur in consecutive years. FORESX SCI. 28:856861. ADDITIONAL

Climate change and land management impact rangeland condition and sage-grouse habitat in southeastern Oregon

Contemporary pressures on sagebrush steppe from climate change, exotic species, wildfire, and land use change threaten rangeland species such as the greater sage-grouse ( Centrocercus urophasianus ). To effectively manage sagebrush steppe landscapes for long-term goals, managers need information about the potential impacts of climate change, disturbances, and management activities. We integrated information from a dynamic global vegetation model, a sage-grouse habitat climate envelope model, and a state-and-transition simulation model to project broad-scale vegetation dynamics and potential sage-grouse habitat across 23.5 million acres in southeastern Oregon. We evaluated four climate scenarios, including continuing current climate and three scenarios of global climate change, and three management scenarios, including no management, current management and a sage-grouse habitat restoration scenario. All climate change scenarios projected expansion of moist shrub steppe and contraction of dry shrub steppe, but climate scenarios varied widely in the projected extent of xeric shrub steppe, where hot, dry summer conditions are unfavorable for sage-grouse. Wildfire increased by 26% over the century under current climate due to exotic grass encroachment, and by two- to four-fold across all climate change scenarios as extreme fire years became more frequent. Exotic grasses rapidly expanded in all scenarios as large areas of the landscape initially in semi-degraded condition converted to exotic-dominated systems. Due to the combination of exotic grass invasion, juniper encroachment, and climatic unsuitability for sage-grouse, projected sage-grouse habitat declined in the first several decades, but increased in area under the three climate change scenarios later in the century, as moist shrub steppe increased and rangeland condition improved. Management activities in the model were generally unsuccessful in controlling exotic grass invasion but were effective in slowing woodland expansion. Current levels of restoration treatments were insufficient to prevent some juniper expansion, but increased treatment rates under the restoration scenario maintained juniper near initial levels in priority treatment areas. Our simulations indicate that climate change may have both positive and negative implications for maintaining sage-grouse habitat.

Climate change and land management in the rangelands of central Oregon.

Climate change, along with exotic species, disturbances, and land use change, will likely have major impacts on sagebrush steppe ecosystems in the western U.S. over the next century. To effectively manage sagebrush steppe landscapes for long-term goals, managers need information about the interacting impacts of climate change, disturbances and land management on vegetation condition. Using a climate-informed state-and-transition model, we evaluated the potential impacts of climate change on rangeland condition in central Oregon and the effectiveness of multiple management strategies. Under three scenarios of climate change, we projected widespread shifts in potential vegetation types over the twenty-first century, with declining sagebrush steppe and expanding salt desert shrub likely by the end of the century. Many extreme fire years occurred under all climate change scenarios, triggering rapid vegetation shifts. Increasing wildfire under climate change resulted in expansion of exotic grasses but also decreased juniper encroachment relative to projections without climate change. Restoration treatments in warm-dry sagebrush steppe were ineffective in containing exotic grass, but juniper treatments in cool-moist sagebrush steppe substantially reduced the rate of juniper encroachment, particularly when prioritized early in the century. Overall, climate-related shifts dominated future vegetation patterns, making management for improved rangeland condition more difficult. Our approach allows researchers and managers to examine long-term trends and uncertainty in rangeland vegetation condition and test the effectiveness of alternative management actions under projected climate change.

Millennial disturbance-driven forest stand dynamics in the Eastern Canadian taiga reconstructed from subfossil logs

1. Although wildfire is the main natural disturbance factor driving changes in the North American boreal forest, understanding how the fire history of the last millennium shaped the present-day landscape diversity is a difficult task due to the lack of palaeoecological reconstructions with high spatial (few hundreds of square metres) and temporal (annual) resolutions. 2. We combined a detailed inventory of the present-day lakeshore forest of two lakes of the Eastern Canadian taiga with the dendrochronological dating of the subfossil logs that accumulated in the lit-toral zones facing these shores. Our objective was to compare the millennial impact of wildfires among stands of various structures and compositions. Past stem densities and fire years were reconstructed from log recruitment rates and dating of charred logs. 3. Multivariate analysis of the present-day lakeshore forest revealed three and two homogeneous shore segments per site (i.e. clusters). Cluster 1 at both sites exhibited denser forest, higher dead wood values and a higher percentage of balsam fir, a fire-sensitive species. 4. In total, 426 and 611 subfossil logs (mostly black spruce) were crossdated over the last ~1400 years. Their dendrochronological analysis confirmed that each lakeshore cluster, identified from the traits of the present-day forest, experienced a specific fire history over the last millennium (i.e. 0–5 fires of variable severity) that locally influenced forest composition, tree density and growth. Each fire triggered a specific forest structure trajectory characterized by a different stem density and rate of recovery. 5. Synthesis. This study provides a long-term perspective that helps explain how the present-day landscape diversity in the Eastern Canadian taiga reflects the site-specific fire history over the last millennium. Fires have caused persistent and cumulative impacts resulting in a progressive opening of the forest cover along with balsam fir exclusion. Present-day landscapes are mosaics of forest stands characterized by different times since fire and different post-fire forest structure trajectories.

Effects of high-severity fire drove the population collapse of the subalpine Tasmanian endemic conifer Athrotaxis cupressoides.

Athrotaxis cupressoides is a slow-growing and long-lived conifer that occurs in the subalpine temperate forests of Tasmania, a continental island to the south of Australia. In 1960-1961, human-ignited wildfires occurred during an extremely dry summer that killed many A. cupressoides stands on the high plateau in the center of Tasmania. That fire year, coupled with subsequent regeneration failure, caused a loss of ca. 10% of the geographic extent of this endemic Tasmanian forest type. To provide historical context for these large-scale fire events, we (i) collected dendroecological, floristic, and structural data, (ii) documented the postfire survival and regeneration of A. cupressoides and co-occurring understory species, and (iii) assessed postfire understory plant community composition and flammability. We found that fire frequency did not vary following the arrival of European settlers, and that A. cupressoides populations were able to persist under a regime of low-to-mid severity fires prior to the 1960 fires. Our data indicate that the 1960 fires were (i) of greater severity than previous fires, (ii) herbivory by native marsupials may limit seedling survival in both burned and unburned A. cupressoides stands, and (iii) the loss of A. cupressoides populations is largely irreversible given the relatively high fuel loads of postfire vegetation communities that are dominated by resprouting shrubs. We suggest that the feedback between regeneration failure and increased flammability will be further exacerbated by a warmer and drier climate causing A. cupressoides to contract to the most fire-proof landscape settings.

Modeling Climate-Fire Connections within the Great Basin and Upper Colorado River Basin, Western United States

AbstractThe specific temporal patterns of antecedent conditions associated with fire occurrence in the Great Basin and Upper Colorado River Basin are poorly understood. Using 25 years of combined fire and climate data, we identified unique antecedent patterns of climate conditions prior to fires in the Great Basin and Upper Colorado River Basin. Five distinct antecedent patterns of climate related to fire were found within the region; with these antecedent patterns we were able to construct models of fire danger. The occurrence of these antecedent patterns varies both spatially and temporally, and appears to be driven by drought severity. We used a Maximum Entropy approach to model the spatial extent and strength of these fire-climate patterns, and the associated fire danger. This approach provides land managers with a practical way to assess fire danger at a relatively fine spatial scale and also gives researchers a tool for assessing future fire danger.

Changes in plant species richness following reduced fire frequency and drought in one of the most species‐rich savannas in North America

AbstractQuestionsHow has plant species richness changed over two decades in one of the most species‐rich savannas in North America? Is an altered disturbance regime, environmental stress, or both, driving these changes? In what ways can observations in this savanna inform management of other species‐rich plant communities?LocationLongleaf pine savannas in southeast North Carolina, USA.MethodsIn 2011–2013, we re‐surveyed permanent plots established in the 1980s and 1990s in a longleaf pine (Pinus palustris) savanna in North Carolina to quantify changes in species richness at multiple spatial scales following 15 yr of reduced fire frequency plus periodic drought. For comparison, we re‐sampled other longleaf pine savannas in the region that had not experienced reduced fire frequency, but had experienced similar drought. In addition, we identified which types of species were lost and gained, and summarized changes in species frequency by growth form, plant height, and habitat affinity.ResultsWe detected substantial declines in small‐scale species richness and species frequency from the 1980s to 2011, representing a loss of 33% to 41% of the flora, depending on the spatial scale. Small herbaceous species had become particularly scarce. Additional re‐sampling in the wetter years of 2012 and 2013 after consecutive years of fire revealed that species richness had increased slightly from 2011, but was still considerably lower than that in the 1980s. Other savannas did not exhibit such dramatic declines in species richness, suggesting reduced fire frequency in addition to drought contributed to species loss in Big Island Savanna over time.ConclusionsOur work suggests that nearly annual fire is necessary for the maintenance of high plant species richness in mesic longleaf pine savannas, and even a modest reduction in fire frequency can have dramatic negative impacts. This study also suggests that drought is an important factor structuring grassland ecosystems in the southeastern US, despite relatively high regional precipitation. We believe these findings can be generalized to other species‐rich grasslands that are sensitive to changes in disturbance regimes and may require frequent disturbance to maintain plant species richness.

Isotopic and anatomical signals for interpreting fire-related responses in Pinus halepensis

Our study aims to define isotopic and anatomical responses to fires of P. halepensis . Main results: decrease in tree growth and relative conductivity and increase in water use efficiency. We investigated the ecophysiological responses of a Pinus halepensis Mill. stand surviving two wildfires in southern France. Basal area, isotope composition and anatomical traits were analysed before and after fires, using tree rings to assess the ecological responses of trees to heat-related damage. The years were determined based on the presence of fire scars. Stable isotopes (δ13C and δ18O) were measured in tree rings before and after the “fire years”. Anatomical observations allowed qualitative analysis of the scar region and quantification of tracheid size in tree rings before and after the fire years. Relative and percentage conductivity of earlywood and latewood far from the woundwood were estimated. Results showed a decrease in tree growth after the fire events accompanied by an increase in 13C-derived water use efficiency (WUEi) and a decrease in relative conductivity. The positive relationship between δ13C and δ18O suggested that both isotopic variations are mostly driven by changes in stomatal conductance following fire events. P. halepensis proved to be a strong isohydric species, able to survive frequent fires with temporary ecophysiological modifications and anatomical adaptations. Our findings afford new insights into post-fire survival strategies of this species in an environment where fires are predicted to increase in frequency during the twenty-first century.

산불 후 입지에 따른 소나무 분포와 환경 요인 - 강원도 고성군을 중심으로 -

This study was conducted to evaluate the effect of forest fire on natural distribution and regeneration of Pinus densiflora Sieb. & Zucc. in Goseong, Gangwon province, Korea. After 13 years of the last forest fire in 2000, five investigation plots (<TEX>$10m{\times}10m$</TEX>) in each of rocky land and ridge, the well-known location as a favorite site for natural distribution of P. densiflora, were set to investigate stand characteristic and soil environment including physico-chemical properties and moisture contents of soil. Also, five investigation plots in slope area were set and investigated as well. The concentration of organic matter, total nitrogen, and exchangeable nutrients (<TEX>$K^+$</TEX>, <TEX>$Ca^{2+}$</TEX>, <TEX>$Mg^{2+}$</TEX>) were highest in the slope while the soil in the rocky land showed the lowest concentration of organic matter, total nitrogen, available <TEX>$P_2O_5$</TEX>, and exchangeable nutrients (<TEX>$K^+$</TEX>, <TEX>$Na^+$</TEX>, <TEX>$Ca^{2+}$</TEX>, <TEX>$Mg^{2+}$</TEX>). The soil in the slope only showed higher concentration of total nitrogen, <TEX>$K^+$</TEX> and <TEX>$Ca^{2+}$</TEX> than the unburned area in Goseong. Mean soil moisture contents in the rocky land (5.77%) were lowest while the slope (15.78%) and the ridge (15.27%) showed almost three times as much than the rocky land. P. densiflora was dominant in the rocky land and Quercus spp. were dominant in the ridge and slope. The average proportion of P. densiflora was highest in rocky land (58.4%, 14.6 trees per plot) followed by the ridge (25.2%, 7.8 trees per plot) and the slope (11.3%, 3.4 trees per plot) while the average height of P. densiflora was highest in slope (277cm) followed by the ridge and the rocky land. The height and crown width of Quercus spp. were higher than P. densiflora in the every plot. The results suggest that P. densiflora may be able to naturally regenerate and survive in the rocky land after the fire while P. densiflora in the ridge and the slope are suppressed by Quercus spp.

Climate and land-use effects on wildfire in northern Mexico, 1650–2010

Characterizing climate controls on fire regimes, and disentangling the effects of human relative to climate influences, has been difficult in forests of the western U.S. due to the nearly ubiquitous legacy of fire exclusion that began in the middle to late 19th century. However, the Sierra San Luis of northern Mexico, just across the border from Arizona and New Mexico, offers an opportunity to examine the influence of climate and land-use on fire history largely without the effects of modern fire exclusion. Pine forests in portions of the Sierra San Luis remain ungrazed and unlogged to this day, while other portions of the Sierra were not logged until ca. 1952–1954 or grazed until the early 1930s. Historical and modern fire regimes closely reflect these differences in land-use through time. Fires were relatively frequent in all sites until 1932, but continued at high frequency only in the sites without grazing or logging. Notably, the influence of drought and antecedent conditions for fires changed over time. From 1650 to 1886 (early period), fires occurred during drought years, with little influence of climate in antecedent years. However, from 1887 to 2003 (modern period), drought in the year of fire became generally unimportant and fires instead occurred following wet years. Above-average precipitation promotes accumulation of fine fuels, which apparently has been the primary constraint on fire ignition and spread in this semi-arid ecosystem during the modern period. Percentage of scarring aligned with multi-year fluctuations in Palmer Drought Severity Index (PDSI), with higher percent scarring in wet periods (X‾=19.371) and lower scarring in dry periods (X‾=13.778). Native American burning was not an important driver of past fire frequency, even though the study area lies within the historical homeland of the Chiricahua Apache people. We found no change in frequency of fires when Apaches were effectively removed in 1886. Climatic controls, rather than Apache wartime and peacetime periods, more easily explain changes in frequency over time. Projected increases in climate variability in the Southwest highlight the need to understand antecedent climate conditions conducive to fire occurrence in fuel-limited systems, including comparisons of historical to current climate–fire relationships. The relict forests of the Sierra San Luis, where fires continue to burn today with only minimal human interference, provide a rare look at these relationships.

Exploiting a window in time. Fate of recruiting populations of two rare fire-dependent Geranium species after forest fire

Fire ephemerals are few in the boreal forest despite a long history of recurrent fires, which suggests such a life-history pose problems here. We analysed the fate of recruiting populations of two rare and fire-dependent annual Geranium species at burnt forest sites in South-eastern Sweden, to extract vital information on their life-history. Seedlings emerged from the soil seed bank only in the year of fire but spread over several weeks. At sites that burnt early in the season, some seedlings exhibited a summer-annual life-cycle, but those were less successful than plants at the same sites that delayed reproduction until the following year (winter-annuals). Herbivory was frequent in the fire year and until the following spring, but later almost absent, and thus hit seed production in summer-annuals badly. Winter mortality was highly variable for rosette-stage winter-annuals, with some populations nearly obliterated. Reproductive success varied greatly between populations mainly due to pre-reproductive mortality, with a return of 0.2–395 (average 79) seeds per seedling. The vast majority of seeds (92–100 %) were produced by the primary generation, emerging from the seed bank. Out of this first seed crop, 0.2–2.5 % germinated within the study period, resulting in secondary generations. Plants in these later generations were small and produced few seeds, showing that the opportunity for high reproductive success is essentially restricted to one year only. This makes populations highly vulnerable to local near-complete reproductive failure due to winter mortality and herbivory and may be the ultimate reason why strict fire ephemerals are so few in northern forests.

Climatic influences on fire regimes in ponderosa pine forests of the Zuni Mountains, NM, USA

We characterized fire history and examined climate–fire relationships in dry ponderosa pine (Pinus ponderosa) forests in the Zuni Mountains of northwestern New Mexico. Our findings indicate that the historical wildfire regime for the study area was typified by high-frequency, low-severity surface fires. Climate–wildfire relationships were assessed using both Superposed Epoch Analysis (SEA) and Bivariate Event Analysis (BEA). SEA revealed that interannual variability of the El Niño–Southern Oscillation (ENSO) and the Palmer Drought Severity Index (PDSI) was a strong driver of widespread wildfires; wetter conditions often occurred one to two years prior to fire and were followed by drought during the fire year. BEA revealed statistically significant relationships only in the case of extreme PDSI events and widespread wildfire in the year of fire (t=0). No relationship was found between either the Pacific Decadal Oscillation (PDO) or the Atlantic Multidecadal Oscillation (AMO) and widespread fire occurrence, signifying that shorter-term (i.e. interannual) oscillations between wet and dry conditions, rather than longer-term climatic variability, were historically most conducive to fire. Contextualizing these findings under ongoing climate and land-use change is challenging. Full restoration to historical conditions may be neither possible nor desired, but targeted efforts to promote a frequent, low-severity wildfire regime are generally consistent with our understanding of historical fire activity in this forest type and may foster ecological, economic, and/or societal goals.

Fuel treatments and landform modify landscape patterns of burn severity in an extreme fire event.

Under a rapidly warming climate, a critical management issue in semiarid forests of western North America is how to increase forest resilience to wildfire. We evaluated relationships between fuel reduction treatments and burn severity in the 2006 Tripod Complex fires, which burned over 70,000 ha of mixed-conifer forests in the North Cascades range of Washington State and involved 387 past harvest and fuel treatment units. A secondary objective was to investigate other drivers of burn severity including landform, weather, vegetation characteristics, and a recent mountain pine beetle outbreak. We used sequential autoregression (SAR) to evaluate drivers of burn severity, represented by the relative differenced Normalized Burn Ratio index, in two study areas that are centered on early progressions of the wildfire complex. Significant predictor variables include treatment type, landform (elevation), fire weather (minimum relative humidity and maximum temperature), and vegetation characteristics, including canopy closure, cover type, and mountain pine beetle attack. Recent mountain pine beetle damage was a statistically significant predictor variable with red and mixed classes of beetle attack associated with higher burn severity. Treatment age and size were only weakly correlated with burn severity and may be partly explained by the lack of treatments older than 30 years and the low rates of fuel succession in these semiarid forests. Even during extreme weather, fuel conditions and landform strongly influenced patterns of burn severity. Fuel treatments that included recent prescribed burning of surface fuels were particularly effective at mitigating burn severity. Although surface and canopy fuel treatments are unlikely to substantially reduce the area burned in regional fire years, recent research, including this study, suggests that they can be an effective management strategy for increasing forest landscape resilience to wildfires.

Multi‐century reconstruction of fire activity in Northern European boreal forest suggests differences in regional fire regimes and their sensitivity to climate

Summary Forest fires are one of the main disturbance agents in boreal and temperate ecosystems. To decipher large‐scale temporal and spatial patterns of past fire activity in Scandinavia, we analysed the synchronicity of dendrochoronologically reconstructed fire events in a large network of sites (n = 62; 3296 samples, 392 individual fire years) covering a wide geographical gradient (56.5–67.0° N and 9.3–20.5° E) over AD 1400–1900. We identified large fire years (LFY) as years with regionally increased forest fire activity and located the geographical centres of climatic anomalies associated with synchronous LFY occurrence across the region, termed LFY centroids. The spatial pattern of LFY centroids indicated the presence of two regions with climatically mediated synchronicity of fire occurrence, located south and north from 60° N. The return intervals of LFYs in Scandinavia followed a Weibull distribution in both regions. Intervals, however, differed: a period of 40 years would carry a 0.93 probability of LFY occurrence in the southern region, but only a 0.48 probability of LFY occurrence in the northern region. Over 1420–1759, the northern region was characterized by significantly higher temporal variability in LFY occurrence than the southern region. Temporal correlation of LFYs with reconstructed average summer temperature and total precipitation was evident mainly for the northern region. LFYs in this region were associated with positive temperature and negative precipitation anomalies over Scandinavia and with colder and wetter conditions in more southern parts of the European subcontinent. Synthesis. Historical patterns of the occurrence of large fire years (LFY) in Scandinavia point towards the presence of two well‐defined zones with characteristic fire activity, with the geographical division at approximately 60° N. The northern and mid‐boreal forests, although exhibiting lower LFY frequencies, appeared to be more sensitive to past summer climate, as compared to the southern boreal forests. This would imply that fire regimes across Scandinavia may show an asynchronous response to future climate changes.

Fire history of Atlas cedar (Cedrus atlantica Manetti) in Mount Chélia, northern Algeria

The first fire history of the Cedrus atlantica forest of Chélia in northern Algeria is reconstructed from samples of 14 and 12 dead fire-scarred trees from lower and upper elevation stands respectively. Superposed epoch analysis is applied to summarize mean climate conditions before, during, and after sets of fire years in both stands. Prior to 1850, C. atlantica forests in both sites were characterized by high frequency and low intensity fire regimes. The sharp decline in the fire frequency after the mid-nineteenth century coincided with the promulgation of the first laws governing land and forest use in Algeria. Most fire events occurred in the summer, during the latter part of the growing season. No significant relationships were found between an October–June precipitation reconstruction and fire events. This could be due to anthropogenic and topographic factors. The findings of this study provide baseline knowledge on the ecological role of fire in the C. atlantica forest. This information is vital to support ongoing ecosystem management efforts in the region.

Quantifying restoration effectiveness using multi‐scale habitat models: implications for sage‐grouse in the Great Basin

A recurrent challenge in the conservation of wide‐ranging, imperiled species is understanding which habitats to protect and whether we are capable of restoring degraded landscapes. For Greater Sage‐grouse (Centrocercus urophasianus), a species of conservation concern in the western United States, we approached this problem by developing multi‐scale empirical models of occupancy in 211 randomly located plots within a 40 million ha portion of the species' range. We then used these models to predict sage‐grouse habitat quality at 826 plots associated with 101 post‐wildfire seeding projects implemented from 1990 to 2003. We also compared conditions at restoration sites to published habitat guidelines. Sage‐grouse occupancy was positively related to plot‐ and landscape‐level dwarf sagebrush (Artemisia arbuscula, A. nova, A. tripartita) and big sagebrush steppe prevalence, and negatively associated with non‐native plants and human development. The predicted probability of sage‐grouse occupancy at treated plots was low on average (0.09) and not substantially different from burned areas that had not been treated. Restoration sites with quality habitat tended to occur at higher elevation locations with low annual temperatures, high spring precipitation, and high plant diversity. Of 313 plots seeded after fire, none met all sagebrush guidelines for breeding habitats, but approximately 50% met understory guidelines, particularly for perennial grasses. This pattern was similar for summer habitat. Less than 2% of treated plots met winter habitat guidelines. Restoration actions did not increase the probability of burned areas meeting most guideline criteria. The probability of meeting guidelines was influenced by a latitudinal gradient, climate, and topography. Our results suggest that sage‐grouse are relatively unlikely to use many burned areas within 20 years of fire, regardless of treatment. Understory habitat conditions are more likely to be adequate than overstory conditions, but in most climates, establishing forbs and reducing cheatgrass dominance is unlikely. Reestablishing sagebrush cover will require more than 20 years using past restoration methods. Given current fire frequencies and restoration capabilities, protection of landscapes containing a mix of dwarf sagebrush and big sagebrush steppe, minimal human development, and low non‐native plant cover may provide the best opportunity for conservation of sage‐grouse habitats.

Defining extreme wildland fires using geospatial and ancillary metrics

There is a growing professional and public perception that ‘extreme’ wildland fires are becoming more common due to changing climatic conditions. This concern is heightened in the wildland–urban interface where social and ecological effects converge. ‘Mega-fires’, ‘conflagrations’, ‘extreme’ and ‘catastrophic’ are descriptors interchangeably used increasingly to describe fires in recent decades in the US and globally. It is necessary to have consistent, meaningful and quantitative metrics to define these perceived ‘extreme’ fires, given studies predict an increased frequency of large and intense wildfires in many ecosystems as a response to climate change. Using the Monitoring Trends in Burn Severity dataset, we identified both widespread fire years and individual fires as potentially extreme during the period 1984–2009 across a 91.2×106-ha area in the north-western United States. The metrics included distributions of fire size, fire duration, burn severity and distance to the wildland–urban interface. Widespread fire years for the study region included 1988, 2000, 2006 and 2007. When considering the intersection of all four metrics using distributions at the 90th percentile, less than 1.5% of all fires were identified as potentially extreme fires. At the more stringent 95th and 99th percentiles, the percentage reduced to &lt;0.5% and 0.05%. Correlations between area burnt and climatic measures (Palmer drought severity index, temperature, energy release component, duff moisture code and potential evapotranspiration) were observed. We discuss additional biophysical and social metrics that could be included and recommend both the need for enhanced visualisation approaches and to weigh the relative strength or importance of each metric.

Fire regime shift linked to increased forest density in a piñon–juniper savanna landscape

Piñon–juniper (PJ) fire regimes are generally characterised as infrequent high-severity. However, PJ ecosystems vary across a large geographic and bio-climatic range and little is known about one of the principal PJ functional types, PJ savannas. It is logical that (1) grass in PJ savannas could support frequent, low-severity fire and (2) exclusion of frequent fire could explain increased tree density in PJ savannas. To assess these hypotheses I used dendroecological methods to reconstruct fire history and forest structure in a PJ-dominated savanna. Evidence of high-severity fire was not observed. From 112 fire-scarred trees I reconstructed 87 fire years (1547–1899). Mean fire interval was 7.8 years for fires recorded at ≥2 sites. Tree establishment was negatively correlated with fire frequency (r=–0.74) and peak PJ establishment was synchronous with dry (unfavourable) conditions and a regime shift (decline) in fire frequency in the late 1800s. The collapse of the grass-fuelled, frequent, surface fire regime in this PJ savanna was likely the primary driver of current high tree density (mean=881treesha–1) that is &gt;600% of the historical estimate. Variability in bio-climatic conditions likely drive variability in fire regimes across the wide range of PJ ecosystems.