Mean Fire Interval Research Articles

How do intervals between fires influence canopy seed production and viability?

Abstract Canopy storage of seed (serotiny) is an important persistence strategy in fire‐prone environments. Serotinous populations can be threatened when fire intervals are shorter than the time needed to accumulate seed, or when longer than plant lifespans. Understanding how fire regimes influence canopy seedbanks requires study of the timing of plant maturity, seed output and germination traits. Research that spans plant functional types, such as resprouters or obligate seeders, helps to understand the mechanisms through which fire has influence. Using field data collected at 57 sites in a Mediterranean shrubland of southeastern Australia, we modelled how time since fire and mean fire interval influenced infructescence (hereby cone) production. Additionally, seed output, viability and germination speed were assessed in the laboratory. Reproductively mature resprouters were first observed 2 to 4 years post‐fire in the field, and reproductively mature obligate seeders 6 years post‐fire, depending on the species. Reproductively mature plants were not observed at short mean fire intervals: until 3 and 9 years for resprouters and nine and 18 years for obligate seeders, again, varying by species. When resprouter species reached maturity, we observed a decline in cone production as time since fire increased. This decline was not observed for obligate seeder species. Fire influenced the number of viable seeds produced within cones for one resprouter species, Allocasuarina paludosa, but we did not detect a relationship for other species. Germination speed was faster for species that produce few seeds per cone, and slower for species that produce many seeds, indicating a trade‐off between fire‐related seed traits. For example, Hakea rostrata, which holds two seeds per cone, germinated mostly within the first few weeks, while Callitris rhomboidea, which holds many seeds per cone, germinated asynchronously over 9 months. Short intervals between fires reduce canopy seed production for the serotinous species studied. Obligate seeders were more sensitive to frequent fire than resprouters. In the context of expected increases in wildfire frequency and droughts in Mediterranean ecosystems, our findings suggest that serotinous species' reproduction and recruitment will be differentially impacted depending on a suite of functional traits. Read the free Plain Language Summary for this article on the Journal blog.

Temporal and spatial patterns of fire regime disruption in conifer forests of western North America

ABSTRACT Temporal and spatial patterns of fire regime disruption were reconstructed in conifer forests of western North America from information on pre-disruption and disrupted mean fire intervals (MFIs) of 498 dendrochronology-based fire chronologies. We identified the conifer forest types most affected by MFI shift and the influence of land category designation on MFI change. We also mapped the years of the MFI shift, the last fire recorded, and disrupted/pre-disruption MFI ratios. Fire cessation and longer MFIs predominated in most fire chronologies and conifer forest types. MFI was significantly higher in most conifer forest types, with most differences in dry conifer forests. MFI shift occurred mainly before the designation of protected, federal, social-property, and private areas. MFI shift began in 1829 in the United States of America Southwest, a region subjected to prolonged fire exclusion and with the highest disrupted/pre-disruption MFI ratios. Fire regime disruption moved gradually into the Pacific Northwest and the Sierra Nevada until reaching the northern conifer forests of Canada and Alaska. In contrast, one-third of fire chronologies in Mexican conifer forests retained pre-disruption MFIs. Our findings allowed us to identify areas with MFIs outside of their natural variability, with prolonged fire exclusion, or with intact fire regimes.

202 years of changes in Mediterranean fire regime in Pinus nigra forest, Corsica

Wildfires are critical socio-ecological features in the Mediterranean basin. In a context of global changes (climate, land use), we questioned whether the wildfire regime was altered in the mountains of Corsica, France. Using tree-ring analysis of fire-scarred trees, we tested for changes in frequency, seasonality, and area. We hypothesized that the fire regime changed during the middle-20th century due to human activities, as observed elsewhere in the Mediterranean. We sampled fire-scarred trees, geolocated for mapping fire areas, in a forest of black pine (Pinus nigra laricio). The oldest fire was in 1684 but the fire chronology with adequate sample depth for analysis covered 202 years [1820–1921]. Between 1820–2012, 15 fires were recorded, 8 of which scarred at least 25% of the sampled trees. The mean fire interval was 14 years, corresponding to a high fire frequency with 4 major fires per century. Most fires occurred between 1931–1970. On average, about 50% of trees were scarred by fires before 1931, but this percentage decreased thereafter. The exception was the 2000 fire that impacted 100% of living trees. Mapping showed spatially heterogenous fire areas. These results match other Mediterranean studies showing longer fire intervals since the late-20th century, and wildfires generally occurred during the period of late-earlywood or latewood formation, i.e., summer or early autumn, which is the season of contemporary fires. Although fires were recurrent for more than 200 years with no change in the fire season, the regime changed twice in frequency. These changes likely result from a combination of land use and warmer summer conditions. While pines survived most past fires of low intensity through the last large fire in the 1970’s, the severe fire of 2000, following ca 30 years of fire suppression, killed large patches of mature trees. Such chronology provides rational arguments for black pine ecosystem management, notably to consider seeking to recover the sustainable fire regime of the 19th century, for instance by using prescribed fires to manage surface fuel.

Fire regimes over a 1070-m elevational gradient, San Francisco Peaks/Dook’o’oosłííd, Arizona, USA

BackgroundSteep elevational gradients bring multiple forest types and fire regimes together in close proximity. The San Francisco Peaks/Dook’o’oosłííd in northern Arizona rise to 3851 m elevation with slopes that span many of the major forest types of the southwestern US mountains. To reconstruct past fire regimes across this broad elevational gradient, we sampled fire-scarred trees across the south face of the Peaks, complementing previous research on forest structure, composition, and origin of aspen stands.ResultsAt the highest elevations, Rocky Mountain bristlecone pine forests had a mean fire interval (MFI) of 19.7 years prior to a modern fire exclusion period beginning after 1879. Other high-elevation (> 2800 m) mixed conifer forests had MFI = 5.7 years and low-elevation (< 2,800 m) pine forests had MFI = 4.0 years. After 1879, there were no large fires through the end of the twentieth century. Before 1879, fires occurred in the early to middle growing season, and fire event years were linked to climate across all elevations, with a stronger association to drought (i.e., the Palmer Drought Severity Index) than to El Niño-Southern Oscillation phase. Pulses of forest regeneration were associated with the fire regime, with the largest pulse occurring shortly after fire exclusion. In addition to fire exclusion, other factors such as post-fire sprouting and regeneration after tree harvesting likely contributed to the current dense forest structure on the Peaks.ConclusionsFollowing over a century of fire exclusion, fire activity has increased on the Peaks over the past two decades, with large recent fires of uncharacteristic severity raising concerns about tree mortality, erosion, flooding, and infrastructure damage in surrounding human communities. Past fire regimes provide useful insight into fire-climate-forest interactions and the conditions under which existing forest communities were well adapted, but adaption to future conditions is likely to be challenging due to the rapid pace of projected environmental changes.

Historical fire regimes and contemporary fire effects within sagebrush habitats of Gunnison Sage‐grouse

AbstractThe historical role of fire in sagebrush (Artemisia tridentata) landscapes remains poorly understood, yet is important to inform management and conservation of obligate species such as the threatened Gunnison Sage‐grouse (GUSG; Centrocercus minimus). We reconstructed fire histories from tree‐ring fire scars at sagebrush–forest ecotones (10 sites, 111 trees) to better understand the role of fire in sagebrush landscapes of the Upper Gunnison Basin (UGB), Colorado, and how fire may have changed following Euro‐American settlement. We assessed likely influences of historical fire by surveying plant composition and structure at 100 sagebrush sites with and without recent (2001–2020) fires. Tree‐ring fire scars revealed a history of repeated low‐severity fire at sagebrush–forest ecotones until 1892, followed by over a century without fire. Between 1684 and 1892, the mean fire interval (MFI) among sites averaged 49.6 years (ranging from 18.2 to 119 years). Fire over this period occurred synchronously at two or more sites on average every 23.6 years, potentially indicative of spread between sites. Most (70%) of the historical fires burned in the early growing season, consistent with times of strong wind. Recent burns exhibited reductions in sagebrush cover (5% vs. 25% in unburned sites) and concomitant increases in herbaceous cover (55% vs. 40%). These differences declined over time but persisted for at least two decades. Burned sites were dominated by native perennial grasses, forbs, and resprouting shrub species. Historically, such openings may have served as seasonal GUSG habitat. Our results indicate that parts of the UGB sagebrush landscapes were characterized historically by frequent fire and dynamic vegetation mosaics that included open, grassy patches. These findings support the use of prescribed fire to restore and maintain this ecological process and vegetation heterogeneity. However, the contemporary context for fire has changed and now includes substantially reduced, Endangered Species Act (ESA)‐listed GUSG populations, increased risk of non‐native plant invasion, and climate warming. These circumstances highlight new risks, information needs, and opportunities for key knowledge co‐production via management–research partnerships.

Climate, landscape, and human influences on fire in southern Patagonia: A basin-scale approach

Human activities and how they interact with climate and landscape to influence fire regimes is complex and still remains a major research challenge in most Patagonian forests. Recent studies on the fire history in Patagonia covered large areas, making it difficult to model fire occurrence and burned patch size. The main objective of this work was to evaluate the influence of climatic variability, landscape variations and human activities on the occurrence and size of fire at the basin scale. We aimed to update previous fire history of the Río de las Vueltas – Río Túnel basin, in southern Patagonian Andes, with the specific aims to (1) reconstruct in detail the spatio-temporal patterns of fire, (2) model fire variability as a function of climate variability, landscape and human activities, and (3) determine the influence of regional climate on fire occurrence at the basin scale. We used dendrochronological techniques to update the fire history of the study basin. At the basin scale, we used (1) maximum entropy models to estimate the influence of climate, landscape, and humans on fire probability, (2) general linear models to assess how these factors modulate fire size, and (3) superposed epoch analysis to assess the influence of regional water deficit on fire occurrence. We found that fire occurrence increased sharply with the arrival of settlers in the early 20th century and decreased in the early 21st century due to the shift in recognition of the ecosystem services provided by forests. Additionally, the mean fire interval, the number of fires during drier years, and fire size, increased along the northwest-southeast gradient of decreasing precipitation. Our results support that fire regimes are largely human driven, and conditioned by climate and landscape characteristics. The analysis at the basin scale facilitated the understanding of how these factors regulate fire regimes, and consequently, our comprehension at larger spatial scales.

Impact of Fire History on the Structure of a Temperate Forest in Northern Mexico

Understanding the ecological role of fire in forests is essential for proper management and conservation programs. The objectives of this study were: (1) to reconstruct the history of fires in a temperate forest in Sierra Madre Occidental; and (2) to interpret the impacts of fire and climate on forest structure. Sixty tree cross-sections with fire scars were analyzed, and descriptive statistics of fire history were generated. Additionally, growth cores were analyzed, and the ages of trees of different diameter categories were calculated. The synchrony between fire history and tree establishment was determined, and precipitation and Palmer Drought Severity Index (PDSI) values were correlated with the number of trees established per year. The presence of 137 fire scars was determined, which allowed the reconstruction of 41 fire events over the period 1855–2019; however, only the period 1940–2015 was used to compare tree recruitment, as tree establishment was detected in this period. The mean fire interval (MFI) was 2.28 years in general, and 12.17 years for extensive fires. As regards vegetation, a continuous recruitment pattern was observed, typical of a frequent low-intensity fire regime, although peak regeneration occurred after extensive fires. The correlation analysis showed that the number of trees established per year was influenced by the wet conditions that occurred in December of the previous year and the dry conditions in September and October of the previous year. This finding demonstrates the historical influence of fire and climate on the structure of the current stand in the study area. Therefore, the present study highlights the importance of including fire in forest management programs, considering the natural fire regime to which the species in this ecosystem are already adapted.

Latitudinal gradient of fire return interval in conifer forests of western North America

ABSTRACT Mean fire interval (MFI) is the average time between successive fires, influenced by environmental factors such as latitude, elevation, and vegetation type. This study evaluated the relationship between MFI and latitude in conifer forests of western North America. First, we obtained pre-fire-disruption MFI data from dendrochronology-based fire history studies in western Canada, the United States, and Mexico montane ranges. Then, we used generalized additive models (GAMs) to evaluate the relationship between MFI and latitude, considering elevation and conifer forest type as covariables. In addition, we mapped the spatial mean fire intervals (SMFIs) through inverse distance weighting (IDW). MFI increased significantly at higher latitudes, influenced by elevation and conifer forest type (R2 = 0.7). Furthermore, we found longer MFI in high elevations of the Madrean Archipelago, the Rocky Mountains, and the Alaska Range. Fire frequency also decreased in the boreal, Douglas-fir, and subalpine forests, with MFI longer than 20 yr. Moreover, the shortest SMFIs were found in the Mexican sierras and the Madrean Archipelago, with fire intervals between 4.1 and 5.6 yr. Our results showed a latitudinal gradient of MFI in conifer forests of western North America, which provides valuable information for fire management and the restoration of natural fire regimes.

Working toward a fire-scar network for the Cumberland Plateau—Fire history results from Bridgestone Nature Reserve at Chestnut Mountain, Tennessee1

We reconstructed historical fire regime characteristics at the Bridgestone Nature Reserve at Chestnut Mountain using tree-ring dated fire scars on live and dead shortleaf pine (Pinus echinata Mill.) trees. Fire-scar records described the historical fire frequency and seasonality from the mid-18th century to present. Overall, we found historical fires occurred relatively frequently, predominantly in the dormant season, and were likely low-severity events. Mean fire intervals (MFIs) were slightly longer in the pre-Euro-American period (1744–1834; MFI = 9.6 yrs) versus the post-Euro-American period (1834–1935; MFI = 5.6 yrs). No fires were recorded after 1940, which in combination with past logging and land uses, is likely a major contributor to the ongoing decline of shortleaf pine and pyrophytic oak species observed here. Surprisingly, the majority of fire event years after 1834 were also recorded at Savage Gulf State Natural Area (52 km to the south), raising questions about potential historical fire sizes, patterns, and driving factors across the Cumberland Plateau landscape. In a landscape where fire-scarred remnants are present but relatively scarce and rapidly disappearing, these data are important for evidencing historical fire regimes and developing a more comprehensive regional network of fire history sites that could reveal valuable historical ecological information for the Cumberland Plateau.

Frequent burning in chir pine forests, Uttarakhand, India

BackgroundSubtropical coniferous forests of the lesser Himalaya provide critical ecosystem services but fire regimes have received limited scientific attention. We reconstructed fire regimes using tree-ring methods in a chir pine (Pinus roxburghii Sarg.) forest of Uttarakhand, India. We cross-dated tree-ring samples with fire scars from 36 trees at three sites near rural villages between 1535 and 1848 m elevation.ResultsFires were highly frequent (mean fire intervals all <6 yr) but of low severity, so most mature trees of this thick-barked species survived numerous burns. Fire scars occurred primarily in the dormant period to the middle of early wood formation in tree-rings, consistent with fire season records. Despite the high fire frequency, fires were mostly asynchronous among the three sites, indicating a bottom-up pattern of local ignitions. We observed that resin tapping of the pines interacted with surface fire by allowing fire to burn into the wood of some tapped trees and weaken their structural integrity to the point of breakage.ConclusionsOngoing frequent surface fire regimes linked to human land use are prominent disturbance factors in chir pine forests. Given that these forests support substantial human populations and form part of the watershed for many more people, the effects of anthropogenic fire and interactions with resin-tapping merit further investigation at landscape to regional scales. We suggest developing a research network in Himalayan forests as well as more broadly across southeast Asian pine forests to track interacting disturbances and their ecological and social implications.

Fire History (1896–2013) in an Abies religiosa Forest in the Sierra Norte of Puebla, Mexico

The oyamel forests, as Abies dominated forests are commonly known as, register their largest distribution (95% of their population) along the Trans-Mexican Volcanic Belt (TMVB). Although efforts have been made to study these forests with various approaches, dendrochronology-based studies have been limited, particularly in pure Abies forests in this region. The objective of this study was to reconstruct fire regimes in an Abies religiosa forest in the Sierra Norte in the state of Puebla, Mexico. Within an area of 50-ha, we collected 40 fire-scar samples, which were processed and analyzed using dendrochronological techniques to identify 153 fire scars. The fire history was reconstructed for a period of 118 years (1896–2013), with low severity surface fires occurring mainly during in the spring (92.8%) and summer (7.2%). Over the past century, fires were frequent, with an mean fire interval (MFI) and Weibull median probability of (WMPI) of five years when considering all fire scars and less than 10 years for fires covering larger areas (fires recorded by ≥25% of samples). Extensive fires were synchronized with drought conditions based on Ring Width Indexes, Palmer Drought Severity Index (PDSI) and El Niño Southern Oscillation (ENSO). After 1983, we observed a change in fire frequencies attributed to regulated management. Longer fire intervals within the last several decades are likely leading to increased fuel accumulations and could potentially result in more severe fires in the future, threatening the sustainability of these forests. Based on our finding, we recommend management actions (silvicultural or prescribed fire) to reduce fuels and the risk of severe fires, particularly in the face of climatic changes.

Red pine (Pinus resinosa Ait.) fire history and management implications in the Mississippi River headwaters, Minnesota, USA

We used dendrochronological methods and remnant fire-scarred red pines (Pinus resinosa Ait.) to reconstruct historical fire regime characteristics and relate these findings to past climate, human land use changes, and vegetation for a landscape in northern Minnesota, USA. A total of 314 fire scars were dated, representing 56 unique fire events from 1565 to 1967. In the period prior to fire exclusion (1535–1935), fire intervals ranged from 1 to 40 years across the landscape and the mean fire interval was 6.6 years. The majority of fire scars (74%) occurred in the dormant season. Climate analyses showed that conditions two years before fire events were significantly wet and, in the year of fires, conditions were significantly dry. Overall, our study reveals complex interactions among climate, humans, and physiographic factors and how these have varied through time. For fire and forest management of red pine specifically, the results point to the use of silvicultural systems with high levels of retention, including non-stand replacing disturbances.

WEB-BASED GIS FOR MAPPING FIRE REGIMES OF PECHORO-ILYCH RESERVE AND ITS ENVIRONS

The article is devoted to the description of the web-GIS for mapping fire regimes in the Pechora-Ilych reserve and its environs. The main purpose of the resource is to provide the results of mapping fire regimes in the designated area to a wide range of researchers in an accessible form. Web-GIS allows organizing and storing the received thematic spatial data. The resource performs research and educational functions. The structure of the web-GIS includes the following sections: the study area, fire frequency indicators, fire regimes, fire regime condition class, and fire cycles. The web GIS was created using the ArcGIS StoryMaps tool on the ArcGIS Online platform. All sections use data from the ArcGIS Living Atlas of the World. Web-GIS allows receiving reference information about the indicators of fire frequency, fire cycles and regimes, as well as their deviations within the boundaries of the Pechora-Ilych nature reserve, district forestries, and spatial units. In particular, the results of a retrospective statistical analysis of forest fire indicators within spatial units (fire frequency, mean fire interval, etc.) are available for users.

Fire history and dendroecology of Catoctin Mountain, Maryland, USA, with newspaper corroboration

BackgroundOur study was designed to reveal a detailed forest fire history at Catoctin Mountain Park, Maryland, USA. We compared the ages of living trees to known fire dates in the dendrochronological record. Seasonality and years of fires in the dendrochronological record were juxtaposed with specific dates of fires recorded in newspapers.ResultsTwenty-seven pines (Pinus L.) captured 122 fire scars representing 58 distinct fire years between 1702 and 1951. Climate was significantly hotter and drier in the years of burns that affected at least two trees and was wetter two years prior. Thirty-three fires described in local newspapers were reported largely in the spring and fall months (68% between March and June, 32% between September and December). Ninety-one percent of fire scars in our tree-ring chronology had dormant seasonality. The mean fire interval was 5.47 ± 10.14 (SD; standard deviation) yr, and the Weibull median fire interval was 3.22 yr during the entire chronology. The longest fire-free interval was from 1952 to 2018.The size structure of living trees was biased toward smaller black gums (Nyssa sylvatica Marshall) and oaks (Quercus L.) that recruited in the 1930s and 1940s. Most living pitch pines (Pinus rigida Mill) recruited between 1890 and 1910, but a few individuals recruited before the 1850s. Diversity of tree stems smaller than 10 cm diameter at breast height (DBH) was generally lacking; the youngest tree >10 cm DBH in our study area had recruited by 1967.ConclusionsThe Catoctin Mountains experienced frequent fire during the 1800s and early 1900s. The causes of fires were diverse, including accidental ignitions and purposeful cultural burning for berry (Vaccinium L.) production. The current forest developed during a period of low deer density and after the demise of the charcoal iron industry ended an era of logging. The lack of fire since the 1950s has encouraged the development of a black gum dominated mid- and understory. Management with frequent fire would facilitate pine and oak regeneration.

Wood anatomy, fire wounds and dendrochronological potential of Prosopis pugionata Burkart (Fabaceae) in arid Argentine Chaco

Abstract Prosopis pugionata (Fabaceae) is a halophyte tree species that grows exclusively in Argentina’s arid environments, whose woodlands are mainly affected by fires and overgrazing. Here, we describe the wood anatomy and fire wounds of P. pugionata and their relationship with plant size and bark thickness. Besides, we attempt to determine the potential of P. pugionata for dendrochronological studies in order to date fire events throughout time. We tested the hypothesis that P. pugionataforms datable fire wounds, allowing its use for dendrochronological studies. The study area is located in the arid Argentine Chaco region. Seventeen individuals, varying from 15 to 65 years of age, were randomly sampled and bole disks were taken at 0.3, 1.3 and 2.3 m high. P. pugionatais a diffuse and semi-ring-porous hardwood species with growth rings delimited by marginal parenchyma bands. The bark is longitudinally fissured, with an average thickness of 0.19 cm, and a scarce increase with age. Seventy-seven percent of the samples showed fire wounds (). We identified fire scars (70%) and marks (30%), and differentiated them by wood growth interruption in the former. Sixty-one percent of fire wounds affected less than 20% of the cambial perimeter and there were no significant effects of age, bole diameter, bole height and bark thickness on the cambial damage percentage. After cross-dating, P. pugionata showed a mean correlation value between series of 0.5, which represents an accurate potential for dendrochronological studies. Twenty wildfires were dated from 1943 to 2007 in the study area with a fire frequency of 0.40 fires/year and a mean fire interval of 2.5 years. Wildfires frequency increased from 1980 to 0.48 fires/year and a mean fire interval of 2 years. Our results indicate that P. pugionata has the potential to date fires, considering its potential for dendrochronological studies, its ability to survive recurrent fires and forms identifiable wound scars in the wood.

Valleys of fire: historical fire regimes of forest-grassland ecotones across the montane landscape of the Valles Caldera National Preserve, New Mexico, USA

Montane grasslands and forest-grassland ecotones are unique and dynamic components of many landscapes, but the processes that regulate their dynamics are difficult to observe over ecologically relevant time spans. We aimed to demonstrate the efficacy of using grassland-forest ecotone trees to reconstruct spatial and temporal properties of the historical fire regime in a complex landscape of montane forests and adjacent grasslands. We sampled and crossdated fire-scarred trees along ecotones and compared variations in historical fire occurrence within and among nine adjoining valle basins in a 10,158 ha landscape. We analyzed fire year extensiveness, climate regulation, and the occurrence of consecutive fire years. The resulting tree-ring record covers 1240–2005 AD, with 296 trees recording 125 replicated fire years during the analysis period 1601–1902 AD. Mean fire intervals for all events recorded on two or more trees ranged from 4.7 to 13.6 years in individual valles, and a mean of 2.4 ± 1.7 (SD) years at the landscape scale. Between 1660 and 1902, extensive fires occurring in six or more valles occurred 15 times, on average at ~ 17-year intervals; 29 moderately widespread fires (3–5 valles) occurred during this period, at 8.7 year intervals on average. Widespread events occurred in years with a significantly lower Palmer Drought Severity Index (PDSI) preceded by years of significantly positive PDSI, indicating conditions favorable for fine fuel production. Spatial reconstruction of fire extent revealed multiple occurrences of consecutive-year fires burning non-overlapping areas, associated with persistent low PDSI anomalies preceded by positive conditions in antecedent years. A landscape spatiotemporal approach to reconstructing fire regimes of montane forest-grassland complexes provides a valuable baseline for guiding prescribed and natural fire management at large spatial scales.

A Multi-Century Fire History from the Potomac Highlands of West Virginia

Tree-ring reconstructions of past fire activity provide context for forest management and restoration plans. Our primary objective in this study was to develop a new fire history in the Potomac Highlands of West Virginia where published reconstructions are particularly sparse, but efforts to develop prescribed fire plans are on the rise. We produced a 293-year (1727–2019) post-settlement fire history from 57 yellow pine (P. pungens, P. rigida, and P. virginiana) trees spread across five topographically diverse sites on Short Mountain in Hampshire County. The filtered composite mean fire interval was 7–15 years at individual sites, while a landscape-scale analysis indicates that fire frequency did not change over nearly 160 years (1855–2011). Fires, however, were significantly less extensive during the "exclusion era" (post-1930). No conclusive relationships between drought and fire were identified, although the most extensive fire year (1930) was uniquely dry. These findings complement existing regional fire histories and provide a new context for the application of prescribed fire in the Potomac Highlands.

Effects of climate on historical fire regimes (1451–2013) in Pinus hartwegii forests of Cofre de Perote National Park, Veracruz, Mexico

Cofre de Perote National Park (CPNP) in Veracruz, Mexico is part of the Transmexican Volcanic Belt, and its Pinus hartwegii forests reflect a balance between the various natural factors that represent the region's climatology and hydrology. Like many other areas in this region, the historical fire regimes of these forests and their relationship with climate are unknown, but are needed for sustainable management plans. The main objectives of this study were to reconstruct the historical fire regime in a Pinus hartwegii forest and decipher the influenced of climate. Our investigation focused in two study areas, Valle la Teta (VT) and Barranca Honda (BH). The VT study area was divided into three sites based on humidity and elevation: 1) Humid (VTH), 2) Dry Low (VTDL) and 3) Dry High (VTDH). The approximated area for each site was ​​30, 30, 35 and 50 ha, for VTH, VTDL, VTDH and BH, respectively. We collected 162 fire scarred samples to reconstruct the fire history for the last 550 years (1461−2013). The fire scarred samples contained 1240 fire scars, with most fires occurring in spring (95 %) or summer (5%). Prior to 1973, these sites were characterized by a frequent surface fire regime. In all four sites, the mean fire intervals ranged from 5 to 6 years (for fires that scarred ≥ 10 % of the samples) and 13–23 years (for fires that scarred ≥ 25 % of the samples). Extensive fires (≥ 10 %) coincided with significantly dry conditions based on the Standardized Precipitation Index (SPI), influenced by El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation Index (PDO). We also found a significant relationship between fire occurrence and ENSO, both in its warm phase, El Niño (21 fires ≥ 10 %) and in its cold phase, La Niña (32 fires ≥ 10 %). Synchronization of the cold phase of ENSO (La Niña) with the cold phase of the PDO (negative), facilitated severe drought conditions, resulting in fires with the greatest spatial extent. Since 1973, extensive fires have been absent from the study area most likely due to anthropogenic activities including active fire suppression. These results show a strong climate-fire relationship in these high elevation forests. The lack of fire in the last four decades is concerning and could potentially lead to unnatural stand-replacing fires, unless the historical fire regime is restored to maintain natural processes and increase forest resilience.

Fire regimes and structural changes in oak-pine forests of the Mogollon Highlands ecoregion: Implications for ecological restoration

Ponderosa pine (Pinus ponderosa) forests occur at their warmer, drier environmental limits in the Mogollon Highlands ecoregion (MHE) of the Southwestern United States, and are commonly found in stringers or discrete stands that form ecotones with interior chaparral. These “rear edge” forests are likely to be highly vulnerable to rapid changes in structure and composition with climate warming, drought, and wildfire. There is increasing interest in understanding historical conditions, ecosystem changes, and restoration needs for MHE forests. However, comprehensive reconstruction analysis of fire regimes and stand structure has not been done for these systems, which differ from many montane ponderosa pine forests by having an abundance of understory shrubs. In this study we used demographic data from field plots, fire scar samples, and dendroecology to reconstruct historical fire regimes and landscape structure at ponderosa pine-dominated sites that spanned a range of environmental conditions on the Prescott and Tonto National Forests. We found strong evidence of historical surface fire regimes with mean fire intervals ranging 1.3–15.6 years across the five MHE sites during the period 1700–1879. We found very little evidence of historical high-severity fire at any study site. Historical forest structure was open with tree densities ranging 84.7–136.4 trees ha−1 and stand basal area (BA) ranging 4.5–8.4 m2 ha−1. Historical composition showed codominance of ponderosa pine, Arizona white oak (Quercus arizonica), Emory oak (Q. emoryi), and Gambel oak (Q. gambelii). Thus, oak species and likely other hardwoods were important historical components of these ecosystems. Contemporary forests are greater in stand density and BA by 359–703% and 285–502%, respectively, compared to historical estimates. In addition, we observed contemporary shifts in species composition. Changes related to disruption of historical fire regimes have increased susceptibility of ponderosa pine forests in the MHE to rapid shifts in structure and composition that may come about with climate change and high-intensity wildfire. Meeting fuels reduction and ecological restoration goals will be challenging for land managers due to vigorous regeneration responses of shrubs to tree thinning, prescribed burning, or other management activities. Managers will be required to balance attention to historical reference conditions, conservation of biological diversity, and needs for fuels management.

Dwarf Blackgum (Nyssa sylvatica) Contains Datable Fire Scars that Complement an Existing Fire History

Blackgum (Nyssa sylvatica) is a “consummate subordinate” hardwood tree species consigned to the mid-canopy of many eastern North American forests. Despite its wide distribution and ecological amplitude, blackgum is an underutilized tree species in fire history reconstructions within its range. In this study, I analyzed cross-section samples collected from 19 fire-scarred blackgum trees at a dry, nutrient-poor ridgetop study area in northeastern Pennsylvania. All but two of these samples were successfully crossdated, each containing between one and six fire scars. Fires recorded by blackgum occurred frequently, with site-level mean fire intervals between approximately three and five years. There was an increase in blackgum growth within two years following fire events, but this increase was not statistically significant and it was dependent on local fire regime characteristics. In addition, the blackgum fire-scar data increased the temporal and spatial resolution of an existing local fire history. These results provide evidence for the potential use of blackgum in fire history reconstructions, but applications may be limited by tree age, complacent growth that prevents crossdating, and the degree of rot resistance after scarring.