Stand-replacing Fire Research Articles

Variability and dynamics of old-growth forests in the circumboreal zone: implications for conservation, restoration and management

Due to the unprecedented loss of old-growth forests to harvesting throughout circumboreal regions an understanding of similarities and differences in old-growth dynamics is needed to design effective restoration, management and conservation efforts. This paper reviews concepts, prevalence and variability of old-growth forests across landscapes, and evaluates different stand scale dynamics at the old-growth stage across the circumboreal zone. Old-growth historically dominated many boreal forest landscapes in both Eurasia and North America. Throughout much of North America, and to some extent in western Siberia, the natural prevalence and development of old-growth forests are regulated by the occurrence of stand-replacing fires. In eastern North America and Siberia, insect outbreaks may, however, be more important. Insect outbreaks as well as recurrent non-stand replacing surface fires and windthrows, when occurring at the old-growth stage, often form stands characterized by several tree age-class cohorts. This multi age-class forest development type is common in Europe and eastern Siberia but its prevalence and importance in boreal North-America is not well documented. Similarities in successional dynamics across the circumboreal region are found in the development of mono-dominant even-aged stands, the replacement of shade intolerant tree species by shade tolerant species, as well as in all-aged stands driven by small-scale gap dynamics. The message to land managers is that the focus should not only be on setting aside remaining old-growth forests or in restoring static old-growth attributes, but also in emulating natural disturbances and successional dynamics at landscape and regional scales to maintain natural variability in old-growth attributes through time.

Bats of Mesa Verde National Park, Colorado: Composition, Reproduction, and Roosting Habits

We determined the bat fauna at Mesa Verde National Park (Mesa Verde) in 2006 and 2007, characterized bat elevational distribution and reproduction, and investigated roosting habits of selected species. We captured 1996 bats of 15 species in mist nets set over water during 120 nights of sampling and recorded echolocation calls of an additional species. The bat fauna at Mesa Verde included every species of bat known west of the Great Plains in Colorado, except the little brown bat (Myotis lucifugus). Some species showed skewed sex ratios, primarily due to a preponderance of males. Thirteen species of bats reproduced at Mesa Verde. Major differences in spring precipitation between the 2 years of our study were associated with differences in reproductive rates and, in some species, with numbers of juveniles captured. Reduced reproductive effort during spring drought will have a greater impact on bat populations with the forecasted increase in aridity in much of western North America by models of global climate change. We radiotracked 46 bats of 5 species to roosts and describe the first-known maternity colonies of spotted bats (Euderma maculatum) in Colorado. All 5 species that we tracked to diurnal roosts relied almost exclusively on rock crevices rather than trees or snags, despite the presence of mature forests at Mesa Verde and the use of trees for roosts in similar forests elsewhere by some of these species. Comparisons with past bat surveys at Mesa Verde and in surrounding areas suggest no dramatic evidence for effects of recent stand-replacing fires on the composition of the bat community.

Effects of fire on spotted owl site occupancy in a late-successional forest

The spotted owl ( Strix occidentalis) is a late-successional forest dependent species that is sensitive to forest management practices throughout its range. An increase in the frequency and spatial extent of stand-replacing fires in western North America has prompted concern for the persistence of spotted owls and other sensitive late-successional forest associated species. However, there is sparse information on the effects of fire on spotted owls to guide conservation policies. In 2004–2005, we surveyed for California spotted owls during the breeding season at 32 random sites (16 burned, 16 unburned) throughout late-successional montane forest in Yosemite National Park, California. Our burned areas burned at all severities, but predominately involved low to moderate fire severity. Based on an information theoretic approach, spotted owl detection and occupancy rates were similar between burned and unburned sites. Nest and roost site occupancy was best explained by a model that combined total tree basal area (positive effect) with cover by coarse woody debris (negative effect). The density estimates of California spotted owl pairs were similar in burned and unburned forests, and the overall mean density estimate for Yosemite was higher than previously reported for montane forests. Our results indicate that low to moderate severity fires, historically common within montane forests of the Sierra Nevada, California, maintain habitat characteristics essential for spotted owl site occupancy. These results suggest that managed fires that emulate the historic fire regime of these forests may maintain spotted owl habitat and protect this species from the effects of future catastrophic fires.

Acorn Dispersal of California Black Oak after a Stand-Replacing Fire

We investigated California black oak (Quercus kelloggii Newberry) acorn dispersal by rodents and birds in the months after a stand-replacing fire in a mixed conifer forest in the San Bernardino Mountains of southern California, USA. The objective of this study was to compare scatter-hoarding in a high-severity burn to that in an unburned forest. In the fall of 2007, we placed 600 magnet-bearing acorns under trees in the unburned area. Of the 600, we recovered 77 (13%). Dispersers moved acorns an average distance of 5 m and buried them to an average depth of 30 mm. By spring of 2008, 90% of the cached acorns were missing. In the high-severity burn, we recovered 59 (9.8%) of the 600 acorns placed under top-killed oaks; these had been scatter-hoarded an average of 5.27 m from the source plots and buried an average of 22 mm. By spring of 2008, 55% these acorns were missing, and many of those that we relocated had been re-cached in new locations. Our results suggest that scatter-hoarding of acorns may be a common phenomenon after fire, and likely plays an important role in seedling recruitment.

Disturbance history influences downed woody debris and soil respiration

In boreal forests, disturbances such as stand-replacing fires and clearcut harvesting create large amounts of downed woody debris (DWD), which release considerable amounts of CO2 to the atmosphere during decomposition. Harvesting and fire differ with respect to DWD characteristics (e.g., size), decomposition environment (temperature and moisture), and abundance; hence, differences in piece- and stand-level DWD respiration rates between stands of different disturbance at origin can be expected. From July to September 2008 (every 5–9 days), we measured temperatures, moisture content, weight, and respiration of 45 standardized black spruce logs placed in three old-growth (>140 years), three clearcut harvested (3 years prior), and three burned (23 years prior) black spruce forest stands in Labrador, Canada. Concurrently, soil temperatures, soil moisture potential, and soil respiration were measured next to each log. Moisture content was the dominant environmental control of DWD respiration, followed by temperature. Within-log differences in moisture and temperature resulted from drying of the log surface and water transfer from the live moss layer to the lower log parts. Downed woody debris temperatures and respiration rates were higher in harvested and burned stands compared to old-growth stands, and piece-level DWD respiration rates were highest in harvested stands. Downed woody debris moisture levels were lower in disturbed stands, particularly in burned stands, where respiration was limited by low moisture content. Compared to soil respiration, stand-level DWD respiration (based on estimated DWD surface area per hectare) reached similar (83%; following fire) or equal (100%; following harvest) rates. Disturbance-induced changes in forest temperature and moisture regimes are reflected by DWD respiration rates; hence, for purposes of forest C modeling, decomposition rates of DWD should be differentiated by the decomposition environment created by different disturbance types.

Estimating annual carbon dioxide eddy fluxes using open-path analysers for cold forest sites

Annual net ecosystem production (NEP) was estimated at three boreal forest sites where open-path infrared gas analysers were used in eddy covariance systems. The analysers showed apparent ecosystem uptake of carbon dioxide during frozen conditions where small net respiration was expected. Previous studies have shown this to be largely caused by instrument heating creating an additional heat flux that is not used in density corrections. A set of meteorological conditions where good data could be extracted in cold temperatures was not evident. Annual NEP was evaluated based on estimates that used a heating correction of Burba et al. (2008) or removal of data when air temperature <0 °C, with replacement using a regression function based on soil temperature. The methods agreed within ±0.5 t C ha −1 y −1 which is similar to the potential bias that could be caused by density corrections if accounting for energy balance closure at some sites. Annual NEP (±0.5 t C ha −1 y −1) for boreal forest sites that had experienced stand-replacing fire was: a 6-year-old site was losing 0.6, a 15-year-old site was gaining 0.9, and a 27-year-old site was losing 0.8, for 2–3-year averages. It is difficult to reduce the uncertainty in annual NEP estimates at these boreal sites because of the long cold periods. Cold-weather anomalies have been observed by other researchers, but this has not been a universal problem.

Immediate and Long-Term Fire Effects on Total Mercury in Forests Soils of Northeastern Minnesota

Within the Boundary Waters Canoe Area Wilderness in northeastern Minnesota, soils were collected from 116 sites in areas of primarily virgin forest with fire-origin stand years (year of last recognizable stand-killing wildfire) that range from the 1759 to 1976. Median concentrations for total mercury in soils for this span of 217 years range from 0.28 +/- 0.088 ppm (1759) to 0.09 +/- 0.047 ppm (1976) for A-horizon soils and from 0.23 +/- 0.062 ppm (1759) to 0.09 +/- 0.018 ppm (1976) for O-horizon soils. A separate study of soils collected from 30 sites within an area that burned in a 2004 wildfire at Voyageurs National Park, northern Minnesota, suggested that high soil burn severity resulted in significant mercury loss from both organic and mineral soils. Integrated data from these two studies and additional regional soil data demonstrate that older forests have progressively higher mercury concentrations in O-horizon soils (r(2) = 0.423) and A-horizon soils (r(2) = 0.456). These results support the hypotheses that an important factor for mercury concentrations in forest soils is time since stand-replacing fire and that high soil burn severity has the potential to reduce the concentration of mercury in burned soils for tens to hundreds of years.

Age and growth of a fire prone Tasmanian temperate old-growth forest stand dominated by Eucalyptus regnans, the world's tallest angiosperm

Forests are key components of the global carbon cycle, with deforestation being an important driver of increased atmospheric carbon dioxide. Temperate old-growth forests have some of the highest above ground stores of carbon of any forest types on Earth. Unlike tropical forests, the ecology of many temperate forests is dominated by episodic disturbance, such as high intensity fire. An exemplar of a particularly carbon dense temperate forest system adapted to infrequent catastrophic fires is the Eucalyptus regnans forests of south eastern Australia. Knowledge of the growth and longevity of old-growth trees is crucial to understanding the carbon balance and fire regimes of these forest systems. In an old-growth E. regnans stand in the Styx Valley in southern Tasmania we used dendrochronological techniques and radiocarbon dating to determine the age and stem growth of E. regnans and Phyllocladus aspleniifolius, an understorey rainforest conifer. Our analysis revealed that an even-aged cohort of E. regnans and P. aspleniifolius established in 1490–1510AD, apparently after a stand-replacing fire. The stem growth rates of E. regnans in the first 100 years were very rapid compared to the co-occurring P. aspleniifolius. That the longevity of E. regnans is >500 years challenges the suggested 350–450 year timeframe proposed for the widely held model of succession from eucalypt to rainforest. These forests not only have the potential to store vast amounts of carbon, but can also maintain these high carbon densities for a long period of time. Estimates of the capacity of these forests to sequester and store carbon should explicitly consider past harvesting and fire regimes and the potential increases in the risk of fire associated with climate change.

El Niño–Southern Oscillation effect on a fire regime in northeastern Mexico has changed over time

The El Niño Southern Oscillation (ENSO) is a climate-forcing mechanism that has been shown to affect precipitation and the occurrence of wildfires in many parts of the world. In the southern United States and northern Mexico, warm events (El Niño) are associated with moist winter conditions and fewer fires, while cool events (La Niñia) tend to favor dry winters and more fires. We tested this relationship in a region of northeastern Mexico by characterizing the historical fire regime and climatic influences: Fire regimes were reconstructed from fire-scar samples collected from 100 trees in three high-elevation sites on Peña Nevada in southern Nuevo Le6n. The sites were approximately 25 ha each, and the site centers were approximately 1 km apart. The earliest recorded fire occurred in 1521 and the time period we used for analysis was 1645-1929. The sites were characterized by frequent surface fires before the 1920s. In the three sites, mean fire intervals ranged from 8.6 to 9.6 years (all fires) and 11.9 to 18.6 years (fires that scarred > or = 25% of recording trees). The per-tree mean fire return interval was 17 years, and all three sites burned in the same year seven times between 1774 and 1929. After 1929, fires were nearly eliminated in all sites, likely due to human causes. We found a temporal change in the association between ENSO events and fires; before the 1830s La Niña events were significantly associated with fire years, while after the 1830s this association was not significant. In 1998, when the most severe El Niño event of the past century occurred, the three sites experienced severe, stand-replacing fires that killed many trees that had survived multiple surface fires in the past. Prior to the 1830s, fires tended to occur during dry La Niña years, but since then both La Niña and El Niño have been associated with dry years in this region, especially during the last three decades. This result suggests that ENSO effects have changed over time in this location and that phases of ENSO are not consistent indicators of precipitation, fire occurrence, or fire behavior in this area of northeastern Mexico.

Fire history of coniferous riparian forests in the Sierra Nevada

Fire is an important ecological process in many western U.S. coniferous forests, yet high fuel loads, rural home construction and other factors have encouraged the suppression of most wildfires. Using mechanical thinning and prescribed burning, land managers often try to reduce fuels in strategic areas with the highest fuel loads. Riparian forests, however, are often designated as areas where only limited management action can take place within a fixed-width zone. These highly productive forests have developed heavy fuel loads capable of supporting stand-replacing crown fires that can alter wildlife habitat and ecosystem function, and contribute to stream channel erosion. Objectives of this study were to determine whether adjacent coniferous riparian and upland forests burned historically with different frequencies and seasonalities, and whether these relationships varied by forest, site, and stream characteristics. We measured dendrochronological fire records in adjacent riparian and upland areas across a variety of forest, site and stream conditions at 36 sites in three sampling areas in the northern Sierra Nevada. Riparian fire return intervals (FRI) ranged from 8.4 to 42.3 years under a liberal filter (mean 16.6), and 10.0 to 86.5 years under a conservative filter (mean 30.0). Upland FRI ranged from 6.1 to 58.0 years under a liberal filter (mean 16.9), and 10.0 to 56.3 years under a conservative filter (mean 27.8). Riparian and upland fire return intervals were significantly different in only one quarter of the sites we sampled. Riparian and upland areas did not burn with different seasonalities, and fire events occurred primarily during the late summer-early fall dormant season in both riparian and upland areas (88% and 79% of scars, respectively). FRI was shorter in forests with a higher proportion (>22.7–37.6%) of fire-tolerant pine ( Pinus spp.), sites east of the Sierra crest, lower elevation sites (<1944 m), and riparian zones bordering narrower, more incised streams (width/depth ratio <6.2). Upland areas exhibited a greater degree of fire–climate synchrony than riparian areas. Our study suggests that Sierra Nevada coniferous riparian forests bordering many montane streams might be managed for fuel loads and fire return intervals similar to adjacent upland forests.

Fuel buildup and potential fire behavior after stand-replacing fires, logging fire-killed trees and herbicide shrub removal in Sierra Nevada forests

Abstract Typically, after large stand-replacing fires in mid-elevation Sierra Nevada forests, dense shrub fields occupy sites formerly occupied by mature conifers, until eventually conifers overtop and shade out shrubs. Attempting to reduce fuel loads and expedite forest regeneration in these areas, the USDA Forest Service often disrupts this cycle by the logging of fire-killed trees, replanting of conifers and killing of shrubs. We measured the effects of these treatments on live and dead fuel loads and alien species and modeled potential fire behavior and fire effects on regenerating forests. Sampling occurred in untreated, logged and herbicide-treated stands throughout the Sierra Nevada in four large fire areas 4–21 years after stand-replacing fires. Logging fire-killed trees significantly increased total available dead fuel loads in the short term but did not affect shrub cover, grass and forb cover, alien species cover or alien species richness. Despite the greater available dead fuel loads, fire behavior was not modeled to be different between logged and untreated stands, due to abundant shrub fuels in both logged and untreated stands. In contrast, the herbicide treatment directed at shrubs resulted in extremely low shrub cover, significantly greater alien species richness and significantly greater alien grass and forb cover. Grass and forb cover was strongly correlated with solar radiation on the ground, which may be the primary reason that grass and forb cover was higher in herbicide treated stands with low shrub and tree cover. Repeat burning exacerbated the alien grass problem in some stands. Although modeled surface fire flame lengths and rates of spread were found to be greater in stands dominated by shrubs, compared to low shrub cover conifer plantations, surface fire would still be intense enough to kill most trees, given their small size and low crown heights in the first two decades after planting.

Susceptibility of ectomycorrhizal fungi to soil heating

Ectomycorrhizal (EcM) fungi are an important biotic factor for successful tree recruitment because they enhance plant growth and alleviate drought stress of their hosts. Thus, EcM propagules are expected to be a key factor for forest regeneration after major disturbance events such as stand-replacing forest fires. Yet the susceptibility of soil-borne EcM fungi to heat is unclear. In this study, we investigated the heat tolerance of EcM fungi of Scots pine ( Pinus sylvestris L., Pinaceae). Soil samples of three soil depths were heated to the temperature of 45, 60 and 70 °C, respectively, and surviving EcM fungi were assessed by a bioassay using Scots pine as an experimental host plant. EcM species were identified by a combination of morphotyping and sequencing of the ITS region. We found that mean number of species per sample was reduced by the 60 and 70 °C treatment, but not by the 45 °C treatment. Species composition changed due to heat. While some EcM fungi species did not survive heating, the majority of species was also found in the heated samples. The most frequent species in the heat treatment were Rhizopogon roseolus, Cenococcum geophilum and several unidentified species.

Subalpine vegetation pattern three decades after stand-replacing fire: effects of landscape context and topography on plant community composition, tree regeneration, and diversity

Objective: Our purpose was to characterize vegetation compositional patterns, tree regeneration, and plant diversity, and their relationships to landscape context, topography, and light availability across the margins of four stand-replacing subalpine burns. Location: Four 1977 to 1978 burns east of the Continental Divide in Colorado: the Ouzel burn, a burn near Kenosha Pass, the Badger Mountain burn, and the Maes Creek burn. Methods: Vegetation and environmental factors were sampled in 200 0.01-ha plots on transects crossing burn edges, and stratified by elevation. We utilized dissimilarity indices, mixed-effects models, and randomization tests to assess relationships between vegetation and environment. Results: Three decades after wildfire, plant communities exhibited pronounced compositional shifts across burn edges. Tree regeneration decreased with increasing elevation and distance into burn interiors; concomitant increases in forbs and graminoids were linked to greater light availability. Richness was roughly doubled in high-severity burn interiors due to the persistence of a suite of native species occurring primarily in this habitat. Richness rose with distance into burns, but declined with increasing elevation. Only three of 188 plant species were non-native; these were widespread, naturalized species that comprised <1% total cover. Conclusions: These subalpine wildfires generated considerable, persistent increases in plant species richness at local and landscape scales, and a diversity of plant communities. The findings suggest that fire suppression in such systems must lead to reduced diversity. Concerns about post-fire invasion by exotic plants appear unwarranted in high-elevation wilderness settings.

Effect of fire severity on long-term occupancy of burned boreal conifer forests by saproxylic insects and wood-foraging birds

Fire severity can vary greatly within and among burns, even in the Canadian boreal forest where fire regimes consist mostly of stand-replacing fires. We investigated the effects of fire severity on the long-term occupancy of burns by (i) saproxylic insects and (ii) three wood-foraging birds. Based on observations made 6 to 11 years after fire in burned conifer forests that varied in fire severity in Quebec, Canada, our results indicate that low-severity portions of the burns likely provided snag conditions suitable for the long-term presence of deadwood-associated insects and birds. The black-backed woodpecker, a post-fire forest specialist, was still abundant 6 and 8 years after fire. This pattern was likely explained by the persistence of several saproxylic insect species that are associated with recently dead trees and by the positive effect of lower fire severity on the abundance of Arhopalus foveicollis, a cerambycid with a long life cycle in dead wood. The American three-toed woodpecker and the brown creeper, and their associated prey (Scolytinae beetles), were more abundant in burned stands of lower v. higher severity. We conclude that less severely burned snags and stands within high-severity burns may favour the long-term presence of trophic webs that involve saproxylic insects and wood-foraging birds in burned boreal forests.

Fire History, Stand Origins, and the Persistence of McNab Cypress, Northern California, USA

Despite their substantial contribution to the uniqueness and diversity of the California Floristic Province’s flora and vegetation, surprisingly little is known about the region’s native cypress species (genus Hesperocyparis Bartel & R.A. Price). Current ideas about the fire regimes that maintained these species in the past are based largely or solely on assumptions about the expression and function of life-history characteristics. Empirical studies of fire history are generally lacking. I used a combination of dendrochronological methods, field observations, and contemporary fire records to investigate the history of fire and its role in stand development in McNab cypress (Hesperocyparis macnabiana [A. Murray bis] Bartel), an uncommon serotinous cypress endemic to northern California. Although even-aged stands were present within all 20 populations surveyed, 4 populations also contained stands exhibiting uneven age structure. Fire records and field observations confirmed that even-aged stands originated following stand-replacing fires, but no link between fire and recruitment was found for uneven-aged stands. Rather, trees within uneven-aged stands were generally older, larger, and exhibited higher rates of senescence than those found in even-aged stands, suggesting that inter-fire tree mortality and inter-fire establishment may be linked. When aggregated, the dates of stand-replacing fires (derived from stand recruitment dates and fire records) revealed that relatively few stand-replacing fires occurred in McNab cypress populations during the 50 yr period between 1940 and 1989 (1 fire per decade) compared to either the previous 100 yr period (at least 3 fires per decade) or the subsequent 20 yr period (3.5 fires per decade). This suggests that short fire return intervals do not appear to be a significant threat to McNab cypress persistence at the present time, and there is little ecological justification for fire exclusion.

Can soil phytolith analysis and charcoal be used as indicators of historic fire in the pinyon-juniper and sagebrush steppe ecosystem types of the Great Basin Desert, USA?

Wildland fire intensity and area are increasing across the Intermountain West, USA, in a variety of ecosystem types including the pinyon-juniper woodlands and sagebrush steppe of the Great Basin Desert. Unfortunately, we do not know if there were historic analogues for these high-intensity stand-replacing fires because of the lack of fire scars that record evidence of them. Soil-charcoal and phytolith analyses have been successfully employed in other regions to garner information about fire regimes through the Holocene. We studied the utility of these methodologies and related taphonomic issues in soils in the Great Basin Desert. Our results showed that both microscopic charcoal and burned phytoliths can be found in soils with radiocarbon ages from modern to late Holocene. Microscopic charcoal abundance was more useful than size class as an indicator of recent local fire. Its abundance declined rapidly and remained low at 2.8 to 4.8 km from the edge of the fire. A Burned Phytolith Index shared a similar pattern starting at 0.4 km from the fire edge. Both proxies declined in abundance with depth in the soil at recent burn sites while remaining constant in unburned sites. We were unable to detect a signal for a known historic fire, however, this may have been a result of sample depth. Our results indicate that soil-charcoal and phytolith analysis can be used to examine questions about historical fires in these two ecosystems of the Great Basin Desert.

Influence of wildfire severity on riparian plant community heterogeneity in an Idaho, USA wilderness

Despite the increasing recognition of riparian zones as important ecotones that link terrestrial and aquatic ecosystems and of fire as a critical natural disturbance, much remains unknown regarding the influence of fire on stream-riparian ecosystems. To further this understanding, we evaluated the effects of mixed severity wildfire on riparian plant community structure and composition in headwater streams of the Big Creek Watershed of the Frank Church ‘River of No Return’ Wilderness of central Idaho. Five years after a large stand-replacing fire, we conducted riparian vegetation surveys at sixteen reaches across a range of burn types. Non-metric Multidimensional Scaling (NMS) and Multi-Response Permutation Procedure (MRPP) analyses showed an overall shift in community composition and structure between vegetation at unburned and severely burned reaches. Although total plant cover was significantly less at severely burned areas, recovery of the deciduous understory was apparent. Severely burned reaches were characterized by a marked increase in cheatgrass ( Bromus tectorum). Reaches that were exposed to low-severity fire were indistinguishable from unburned reaches relative to vegetation community composition and structure, pointing to a possible disturbance threshold that may need to be crossed in order to alter riparian plant communities.

Small Parcel Fuel Reduction with a Low-Investment, High-Mobility Operation

Abstract Fuel reduction treatments are especially urgent near homes, where a stand replacement fire would also endanger property and human lives. However, the forested properties associated with homes are often too small for cost-effective mechanized fuel treatment performed with traditional methods and equipment. This project tested a small rubber-tracked skid-steer specially modified for forestry operations that can provide all the functions of a complete harvesting system. The skid-steer can, alternately,carry a hot saw for tree felling, a processor to delimb and buck felled trees, a brush cutting head for mastication, and a log-grapple to transport logs and trees. All of the equipment can be transported on a trailer pulled by a heavy pickup truck, which makes for fast, economical movement between project sites. The study confirmed that this system is well suited to small-parcel conditions around home sites and performs best on even terrain, moderate slopes, and softwood trees with a dbh between 5 and 8 in. It took from 7 to 15 productive machine-hours ac−1 to perform all treatment phases (i.e., mastication, felling, processing, and skidding). The occurrence of delays significantly increased this figures, bringing the average 9.7 productive hours ac−1 to 13.5 worksite hours. Treatment cost was estimated at $480 ac−1 and $1,146 ac−1 for whole-tree and cut-to-length harvesting, respectively. In addition to offering a reasonable treatment cost, the system has the advantage of requiring a low investment, which allows small-scale enterprises to get into the business.

Fire history and fire–climate relationships along a fire regime gradient in the Santa Fe Municipal Watershed, NM, USA

The Santa Fe municipal watershed provides up to 40% of the city's water and is at high risk of a stand-replacing fire that could threaten the water resource and cause severe ecological damage. Restoration and crown fire hazard reduction in the ponderosa pine (PP) forest is in progress, but the historic role of crown fire in the mixed-conifer/aspen (MC) and spruce-dominated forests is unknown but necessary to guide management here and in similar forests throughout the southwestern United States. The objective of our study was to use dendroecological techniques to reconstruct fire history and fire–climate relationships along an elevation, forest type, and fire regime gradient in the Santa Fe River watershed and provide historical ecological data to guide management. We combined systematic (gridded) sampling of forest age structure with targeted sampling of fire scars, tree-ring growth changes/injuries, and death dates to reconstruct fire occurrence and severity in the 7016 ha study area (elevation 2330–3650 m). Fire scars from 141 trees (at 41 plots) and age structure of 438 trees (from 26 transects) were used to reconstruct 110 unique fire years (1296–2008). The majority (79.0%) of fires burned during the late spring/early summer. Widespread fires that scarred more than 25% of the recording trees were more frequent in PP (mean fire interval (MFI) 25% = 20.8 years) compared to the MC forest (31.6 years). Only 24% of the fires in PP were recorded in the MC forest, but these accounted for a large percent of all MC fires (69%). Fire occurrence was associated with anomalously wet (and usually El Niño) years preceding anomalously dry (and usually La Niña) years both in PP and in the MC forest. Fire in the MC occurred during more severe drought (mean summer Palmer Drought Severity Index; PDSI = −2.59), compared to the adjacent PP forest (PDSI = −1.03). The last fire in the spruce forest (1685) was largely stand-replacing (1200 ha, 93% of sampled area), recorded as fire scars at 68% of plots throughout the MC and PP forests, and burned during a severe, regional drought (PDSI = −6.92). The drought–fire relationship reconstructed in all forest types suggests that if droughts become more frequent and severe, as predicted, the probability of large, severe fire occurrence will increase.

Effect of Fuel Treatments on Fuels and Potential Fire Behavior in California, USA, National Forests

In many parts of California, past timber harvesting, livestock grazing practices, and fire exclusion have changed the fire regime from low to mixed severity to a high severity regime with an increase in active crown fire. Land managers responded by implementing hazardous fuel treatment projects to reduce the risk of such uncharacteristic stand-replacing crown fires. Various fuel treatments have been implemented using either mechanical methods or prescribed fire in forested ecosystems across 14 national forests in California, USA. Mechanical treatments significantly altered forest structure (tree density, 75th percentile quadratic mean diameter, canopy cover, canopy base height, and canopy bulk density) and generally increased surface fuel loads as compared to pre-treatment conditions. Prescribed fire significantly reduced ground and surface fuel loads and increased canopy base height, but did not appreciably alter other forest structure metrics. The changes in forest and fuel structures from prescribed fire reduced predicted fire behavior metrics (fire type, flame length, fireline intensity, and rate of spread); mechanical methods showed mixed effects on resulting fire behavior metrics. Modeled fire type, in addition to predicted flame length, fireline intensity, and rate of spread, is an essential metric for managers when choosing where to implement fuel treatments and for assessing the effectiveness of completed treatments. Under 90th percentile windspeed, out of the five forest treatment combinations, three exhibited some passive crown fire before treatment and only one exhibited passive crown fire after treatment. Using gusting windspeed, four of the five combinations maintain the potential for crown fire (passive or conditional) after treatment. If reducing the potential for uncharacteristic crown fire is the main priority for fuel treatments, it might be beneficial to prioritize areas with elevated risk and to combine both mechanical methods and prescribed fire in order to achieve desired fire behavior under more extreme conditions.