Yr Postfire Research Articles

Effects of Anthropogenic and Climate-Induced Habitat Changes on Adult Female Mule Deer Survival

Increased wildfire size and frequency, invasion of non-native annual grasses, extensive fire suppression, climate change, and widespread juniper expansion have led to dramatic changes in sagebrush ecosystems, which provide habitat for a suite of wildlife species, including mule deer (Odocoileus hemionus). These landscape-level disturbances can cause habitat loss and degradation, which influence the quantity and quality of available forage and can negatively influence adult female mule deer survival. We used Program MARK to estimate survival rates using a known-fate model. Our dataset included 111 radio-collared female mule deer to estimate monthly survival rates and to investigate factors that may affect these rates, including movement behavior (migratory or resident) and habitat characteristics (wildfire and juniper canopy cover) in mule deer habitats supporting sagebrush potential vegetation types (PVTs). The dataset included 116 421 Global Positioning System (GPS) location points from 2015 to 2017 in the John Day Basin, Oregon, United States. Survival averaged 0.78 (95% confidence interval = 0.61–0.82) across the study period but was 0.69 (95% confidence interval = 0.59–0.77) in 2015. Our results indicated survival was positively influenced by the presence of small amounts of recent fire (< 15% of total winter range burned; 1−20 yr postfire) within an individual's winter range. Annual survival (0.78) was low compared with survival rates for adult female mule deer in other parts of their geographic range. These findings demonstrate how postfire vegetation response can have a positive effect on mule deer survival, regardless of their migration strategy. Our findings also indicate how climate change poses a growing threat to mule deer populations as prolonged periods of drought increase the spread of fatal diseases.

Wildfire-Grazing Impact on Forage Quality Assessed with Near-Infrared Spectroscopy and Generalized Partial Least Squares Regression

Fire and grazing are key drivers of plant community structure in the Great Plains ecoregion, with critical impacts on the quantity and quality of forage. While the impact of fire on forage quality is well understood in many ecosystems, few studies have examined this question in the northern mixed-grass prairie. We investigated the postburn nutrient content of forbs and graminoids over a 4-yr timeframe, asking 1) how forage quality changed over the 4 yr post fire and 2) whether the effect of fire on quality was impacted by the resumption of grazing. We used near-infrared spectroscopy and generalized partial least squares regression (plsRglm) methods to assess crude protein. We show that the use of generalized models provides improved estimates of percent nitrogen than the standard partial least squares approach. Both crude protein and fiber varied annually after the wildfires, with no effect of grazing on forage quality. In the first and second years, burned sites displayed higher protein than unburned locations. Fire did not affect crude protein between plant functional groups; however, forbs showed higher nutrient values than grasses throughout the 4 yr. Fire affected fiber content with grasses showing higher fiber than forbs. There was a positive relationship between neutral and acid detergent fiber and litter in burned sites. These results indicate no long-term effect of wildfire on protein content, which stabilizes in the third year post burn. The improvement of forb digestibility and retention of protein under dry conditions could modify the grazing capacity of the prairies at large scales. This may also change the foraging behavior of large ungulate grazers through mechanisms such as increasing patch reselection (i.e., intensified grazing cycles) and broadening feeding preferences to forbs when grasses are limited or have high fiber content.

Wildfire-dependent changes in soil microbiome diversity and function

Forest soil microbiomes have crucial roles in carbon storage, biogeochemical cycling and rhizosphere processes. Wildfire season length, and the frequency and size of severe fires have increased owing to climate change. Fires affect ecosystem recovery and modify soil microbiomes and microbially mediated biogeochemical processes. To study wildfire-dependent changes in soil microbiomes, we characterized functional shifts in the soil microbiota (bacteria, fungi and viruses) across burn severity gradients (low, moderate and high severity) 1 yr post fire in coniferous forests in Colorado and Wyoming, USA. We found severity-dependent increases of Actinobacteria encoding genes for heat resistance, fast growth, and pyrogenic carbon utilization that might enhance post-fire survival. We report that increased burn severity led to the loss of ectomycorrhizal fungi and less tolerant microbial taxa. Viruses remained active in post-fire soils and probably influenced carbon cycling and biogeochemistry via turnover of biomass and ecosystem-relevant auxiliary metabolic genes. Our genome-resolved analyses link post-fire soil microbial taxonomy to functions and reveal the complexity of post-fire soil microbiome activity.

Virtual Fencing Effectively Excludes Cattle from Burned Sagebrush Steppe

On public lands grazing allotments in the western US sagebrush steppe, cattle are generally excluded from burned pastures for 2 yr post fire. If only a portion of a pasture burns, the burned area may be fenced, allowing for cattle grazing to resume in the unburned portion. However, traditional wire-based fencing is often not an option due to expense, conflicts with wildlife management objectives, and extensive procedural logistics. We evaluated the use of a “virtual fence” (VF) for excluding cattle from burned areas within small pastures in the sagebrush steppe of southeast Oregon. VF technology (Vence Corporation, San Francisco, CA) uses satellite-controlled collars that direct animal movement within user-defined polygons using auditory and electrical cues. We fall-burned a 0.6-ha area in each of six adjacent 2.1-ha pastures in a Wyoming big sagebrush plant community in 2019. In June 2020, each pasture was stocked with 3 mature dry cows for 14 d. All cows were fitted with VF collars; collars were programed to create a virtual fence around the burned area within three of the pastures (VF treatment), and remaining pastures had electrical and auditory cues turned off (control treatment). Collars recorded animal location every 5 min. Cows in the control treatment initially spent up to 40% of their time within the burned area, and forage utilization of the burned area was nearly 70%. Cows in the VF treatment spent approximately 4% of their time in the burned area on day 1 and were recorded in the burn only incidentally thereafter; forage utilization in the burn was < 3%. Our trial suggests VF technology is effective in controlling rangeland cattle movements and can severely curtail use of burned areas. Additional work is needed to evaluate VF technology in larger rangeland settings.

Prescribed Summer Fire and Seeding Applied to Restore Juniper-Encroached and Exotic Annual Grass-Invaded Sagebrush Steppe

Western juniper (Juniperus occidentalis Hook.) encroachment and exotic annual grass (medusahead [Taeniatherum caput-medusae L. Nevski] and cheatgrass [Bromus tectorum L.]) invasion of sagebrush (Artemisia L.) communities decrease ecosystem services and degrade ecosystem function. Traditionally, these compositional changes were largely confined to separate areas, but more sagebrush communities are now simultaneously being altered by juniper and exotic annual grasses. Few efforts have evaluated attempts to restore these sagebrush communities. The Crooked River National Grassland initiated a project to restore juniper-encroached and annual grass-invaded sagebrush steppe using summer (mid-July) applied prescribed fires and postfire seeding. Treatments were unburned, burned, burned and seeded with a native seed mix, and burned and seeded with an introduced seed mix. Prescribed burning removed all juniper and initially reduced medusahead cover but did not influence cheatgrass cover. Neither the native nor introduced seed mix were successful at increasing large bunchgrass cover, and 6 yr post fire, medusahead cover was greater in burned treatments compared with the unburned treatment. Large bunchgrass cover and biological soil crusts were less in treatments that included burning. Exotic forbs and bulbous bluegrass (Poa bulbosa L.), an exotic grass, were greater in burned treatments compared with the unburned treatment. Sagebrush communities that are both juniper encroached and exotic annual grass invaded will need specific management of both juniper and annual grasses. We suggest that additional treatments, such as pre-emergent herbicide control of annuals and possibly multiple seeding events, are necessary to restore these communities. We recommend an adaptive management approach in which additional treatments are applied on the basis of monitoring data.

Feast not famine: Nitrogen pools recover rapidly in 25-yr-old postfire lodgepole pine.

The extent of young postfire conifer forests is growing throughout western North America as the frequency and size of high-severity fires increase, making it important to understand ecosystem structure and function in early seral forests. Understanding nitrogen (N) dynamics during postfire stand development is especially important because northern conifers are often N limited. We resampled lodgepole pine (Pinus contorta var. latifolia) stands that regenerated naturally after the 1988 fires in Yellowstone National Park (Wyoming, USA) to ask (1) How have N pools and fluxes changed over a decade (15 to 25yr postfire) of very rapid forest growth? (2) At postfire year 25, how do N pools and fluxes vary with lodgepole pine density and productivity? Lodgepole pine foliage, litter (annual litterfall, forest-floor litter), and mineral soils were sampled in 14 plots (0.25 ha) that varied in postfire lodgepole pine density (1,500 to 344,000stems/ha) and aboveground net primary production (ANPP; 1.4 to 16.1Mg·ha-1 ·yr-1 ). Counter to expectation, foliar N concentrations in lodgepole pine current-year and composite needles (1.33 and 1.11% N, respectively) had not changed over time. Further, all measured ecosystem N pools increased substantially: foliar N increased to 89kg N/ha (+93%), O-horizon N increased to 39kg N/ha (+38%), and mineral soil percent total N (0-15cm) increased to 0.08% (+33%). Inorganic N availability also increased to 0.69μg N·[g resin]-1 ·d-1 (+165%). Thus, soil N did not decline as live biomass N pools increased. Among stands, biomass N pools at postfire year 25 remained strongly influenced by early postfire tree density: foliar and litterfall N concentrations declined with lodgepole pine density and ANPP, but the foliar N pool increased. Lodgepole pine ANPP correlated negatively with annual resin-sorbed N, and we found no indication of widespread N limitation. The large increases in N pools cannot be explained by atmospheric N deposition or presence of known N fixers. These results suggest an unmeasured N source and are consistent with recent reports of N fixation in young lodgepole pine.

Factors Affecting Efficacy of Prescribed Fire for Western Juniper Control

Western juniper (Juniperus occidentalis Hook.) is a tree species occurring on 3.6 million ha in the northern Great Basin. This native species can be quite invasive, encroaching into sagebrush-grassland vegetation, forming woodlands, and dominating extensive landscapes. Control of encroaching juniper is often necessary and important. Efficacy of prescribed fire for western juniper control depends on many factors for which our understanding is still quite incomplete. This knowledge gap makes fire management planning for western juniper control more difficult and imprecise. Natural resource managers require a fire efficacy model that accurately predicts juniper mortality rates and is based entirely on predictors that are measurable prefire. We evaluated efficacy models using data from a fall prescribed fire conducted during 2002 in southwestern Idaho on mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) rangelands with early to midsuccessional juniper encroachment. A logistic regression model, which included vegetation cover type, tree height, fire type, and bare ground as predictors, accurately predicted (area under the receiver operating characteristic [ROC] curve [AUC] = 0.881 ± 0.128 standard deviation [SD]) the mortality rate for a random sample of western juniper trees marked and assessed prefire and 5 yr post fire. Trees occurring in an antelope bitterbrush (Purshia tridentata [Pursh] DC.) type, which had a heavy fuel load, were 8 times more likely to be killed by fire than trees in a mountain big sagebrush type, where loading was typically lighter. Probability of mortality decreased by 28.8% for each 1-meter increase in tree height. Trees exposed to head fire were 3 times as likely to be killed as those exposed to backing fire. Findings from this case study suggest that with just four factors which are readily quantifiable prefire, managers can accurately predict juniper mortality rate and thus make better informed decisions when planning prescribed fire treatments.

Dynamics of gaps, vegetation, and plant species with and without fire

Areas lacking dominant plants, or gaps, can support high diversity and specialist species. Previous chronosequence research in Florida rosemary scrub showed indistinct gap area patterns with fire and the dependence of certain species on gaps. We hypothesized that fire and gap size would affect extinction, colonization, diversity, and vegetation composition. In 2011-12, we revisited gaps first sampled in 2003, recording vascular plant and ground lichen occurrence by species, gap area, and burn history. We analyzed gap, vegetation, and species dynamics using linear mixed models, with Florida rosemary scrub patch as a random factor. Gap areas declined quickly during the first 10 yr postfire and then stabilized. Between 2003 and 2011-12, unburned gaps usually remained extant or split, whereas burned gaps usually merged. Unburned gaps tended to shrink, whereas burned gaps became larger. Species richness was positively related to gap area, fire, and their interaction. Over time, richness declined in unburned gaps and increased in burned gaps. Local extinction and colonization of individual species were related to fire between 2003 and 2011-12. In burned gaps, ground lichens disappeared, but many herbaceous species, including those killed by fire, increased occupancy. Colonization of most species was favored by burning, large gaps, or both. In Florida rosemary scrub, fire and increasing gap size increased species richness and many individual species occurrences, reduced local extinctions, and increased colonizations. Therefore, land management activities that encourage the creation and maintenance of large gaps will promote biodiversity in this system.

Did the 2002 Hayman Fire, Colorado, USA, Burn with Uncharacteristic Severity?

There is considerable interest in evaluating whether recent wildfires in dry conifer forests of western North America are burning with uncharacteristic severity—that is, with a severity outside the historical range of variability. In 2002, the Hayman Fire burned an unlogged 3400 ha dry conifer forest landscape in the Colorado Front Range, USA, that had been the subject of previous fire history and forest age structure research. We opportunistically leveraged pre-existing data from this research, in combination with post-fire aerial imagery, to provide insight into whether the Hayman Fire’s patterns of high-severity, stand-replacing fire effects were uncharacteristic. Living old overstory trees were well distributed and abundant in the landscape before the Hayman Fire, despite the fact that some stand-replacing burning had been a component of the landscape’s historical mixed-severity fire regime. Of 106 randomly selected stand polygons that were sampled for the age of the oldest living overstory tree prior to the fire, 30% contained only trees ≤200 yr, while 70% contained at least one tree >200 yr and 29% contained at least one tree >400 yr. Following the Hayman Fire, only 5% of the polygons contained any living trees; these polygons were all immediately adjacent to the reservoir in the center of the landscape. At most, 4% of the polygons contained one or more trees >200 yr post fire, and 3% contained one or more trees >400 yr. The nearly complete loss of old trees, most of which were located in areas with evidence of past non-stand-replacing burning, leads us to conclude that the amount and extent of stand-replacing burning within the Hayman Fire were uncharacteristic for this landscape over at least the last two to four centuries.

Disturbance gradient shows logging affects plant functional groups more than fire.

Understanding the impacts of natural and human disturbances on forest biota is critical for improving forest management. Many studies have examined the separate impacts on fauna and flora of wildfire, conventional logging, and salvage logging, but empirical comparisons across a broad gradient of simultaneous disturbances are lacking. We quantified species richness and frequency of occurrence of vascular plants, and functional group responses, across a gradient of disturbances that occurred concurrently in 2009 in the mountain ash forests of southeastern Australia. Our study encompassed replicated sites in undisturbed forest (~70yr post fire), forest burned at low severity, forest burned at high severity, unburned forest that was clearcut logged, and forest burned at high severity that was clearcut salvage logged post-fire. All sites were sampled 2 and 3yr post fire. Mean species richness decreased across the disturbance gradient from 30.1 species/site on low-severity burned sites and 28.9 species/site on high-severity burned sites, to 25.1 species/site on clearcut sites and 21.7 species/site on salvage logged sites. Low-severity burned sites were significantly more species-rich than clearcut sites and salvage logged sites; high-severity burned sites supported greater species richness than salvage logged sites. Specific traits influenced species' sensitivity to disturbance. Resprouting species dominated undisturbed mountain ash forests, but declined significantly across the gradient. Fern and midstory trees decreased significantly in frequency of occurrence across the gradient. Ferns (excluding bracken) decreased from 34% of plants in undisturbed forest to 3% on salvage logged sites. High-severity burned sites supported a greater frequency of occurrence and species richness of midstory trees compared to clearcut and salvage logged sites. Salvage logging supported fewer midstory trees than any other disturbance category, and were distinctly different from clearcut sites. Plant life form groups, including midstory trees, shrubs, and ferns, were dominated by very few species on logged sites. The differences in biotic response across the gradient of natural and human disturbances have significant management implications, particularly the need to reduce mechanical disturbance overall and to leave specific areas with no mechanical disturbance across the cut area during logging operations, to ensure the persistence of resprouting taxa.

Regeneration of montane forests 24 years after the 1988 Yellowstone fires: A fire‐catalyzed shift in lower treelines?

AbstractForests near the lower limit of montane tree cover are expected to be particularly vulnerable to warming climate, potentially converting to non‐forest for prolonged periods if affected by canopy‐removing disturbances. Such disturbance‐catalyzed shifts are by nature stochastic, offering few opportunities to test these predictions. We capitalized on a landmark event exemplary of recent large disturbances—the 1988 wildfires in Yellowstone National Park (USA)—to investigate long‐term (24‐yr) regeneration dynamics in Douglas‐fir (Pseudotsuga menziesiivar.glauca) forests, which compose the lower treeline yet have received little study. We tested the hypothesis that, under current conditions (warmest decades in last 6000 yr), dry lower‐margin stands are less apt to attain self‐replacement than adjacent, but more mesic, stands farther from the ecotone. Mesic sites characterized by dense forests prefire regenerated robustly regardless of burn severity, even in large high‐severity patches, whereas dry sites did so only if nearby seed sources survived (i.e., small patch size or moderate burn severity). Regeneration continued over two decades, peaking between ~5 and 15 yr, with mesic stands continuing regenerating beyond 15 yr to a greater degree than dry stands. Self‐replacement of stands by 24 yr postfire was nearly universal in mesic stands, variable but common in dry stands not adjacent to the lower ecotone, and uncommon in dry stands near the ecotone—particularly if burned at high severity. Whether the lack of regeneration in ecotonal stands is categorically directional with warming climate or part of a long‐term cycle is unresolved, but we estimate that the 1988 fires converted &gt; 4000 ha of lower‐montane forest to grass/sage steppe for at least several decades, possibly indefinitely given current trends in climate. These data support the notion that climate‐driven shifts in vegetation cover are likely to occur in punctuated fashion with disturbances, with relatively abrupt implications for montane forest cover, biogeography, and ecosystem function.

Postfire Seeding and Plant Community Recovery in the Great Basin

As wildland fire frequency increases around the globe, a better understanding of the patterns of plant community recovery in burned landscapes is needed to improve rehabilitation efforts. We measured establishment of seeded species, colonization of Bromus tectorum and other nonnative annual plants, and recovery of nonseeded native species in topographically distinct areas within five fires that burned Great Basin shrub-steppe communities in Elko County, Nevada. Plant density, frequency, and cover data were collected annually for 4 yr postfire. Vegetation composition varied among flat areas and north- and south-facing aspects, and changed over the course of the sampling period; recovery varied among sites. In general, B. tectorum densities were higher on south aspects, particularly 3 and 4 yr after fire, when densities increased dramatically relative to prefire conditions. Nonseeded native perennial grasses, forbs, and shrubs were abundant in three of the five fire sites, and were more likely to be present on north aspects and flat areas. Over time, nonseeded perennial grass densities remained relatively constant, and nonseeded forbs and shrubs increased. Seeded species were most likely to establish in flat areas, and the density of seeded perennial grasses, forbs, and shrubs decreased over time. Frequency and density measurements were highly correlated, especially for perennial species. Our results emphasize the value of considering site aspect and the potential for native regrowth when planning and monitoring restorations. For example, effective rehabilitation of south aspects may require the development of new restoration methods, whereas north aspects and flat areas in sites with a strong native component were not improved by the addition of seeded species, and may require weed control treatments, rather than reseeding, to improve recovery. Tailoring revegetation objectives, seed mixes, seeding rates, and monitoring efforts to conditions that vary within sites may lead to more cost effective and successful restoration.

Fire, grazing history, lichen abundance, and winter distribution of caribou in Alaska's taiga

AbstractIn the early 1990s the Nelchina Caribou (Rangifer tarandus) Herd (NCH) began a dramatic shift to its current winter range, migrating at least an additional 100 km beyond its historic range. We evaluated the impacts of fire and grazing history on lichen abundance and subsequent use and distribution by the NCH. Historic (prior to 1990) and current (2002) winter ranges of the NCH had similar vascular vegetation, lichen cover (P = 0.491), and fire histories (P = 0.535), but the former range had significantly less forage lichen biomass as a result of grazing by caribou. Biomass of forage lichens was twice as great overall (P = 0.031) and 4 times greater in caribou selected sites on the current range than in the historic range, greatly increasing availability to caribou. Caribou on the current range selected for stands with &gt;20% lichen cover (P &lt; 0.001), greater than 1,250 kg/ha (P &lt; 0.001) forage lichen biomass and stands older than 80 yr postfire (P &lt; 0.001). After fires, forage lichen cover and biomass seldom recovered sufficiently to attract caribou grazing until after ≥60 yr, and, as a group, primary forage lichen species did not reach maximum abundance until 180 yr postfire. Recovery following overgrazing can occur much more quickly because lichen cover, albeit mostly fragments, and organic substrates remain present. Our results provide benchmarks for wildlife managers assessing condition of caribou winter range and predicting effects of fires on lichen abundance and caribou distribution. Of our measurements of cover and biomass by species, densities and heights of trees, elevation, slope and aspect, only percentage cover by Cladonia amaurocraea, Cladina rangiferina, Flavocetraria cuculata, and lowbush cranberry (Vaccinium vitis‐idaea) were necessary for predicting caribou use of winter range. © 2011 The Wildlife Society

Are long-unburnt eucalypt forest patches important for the conservation of plant species diversity?

Question: Are long-unburnt patches of eucalypt forest important for maintaining floristic diversity? Location: Eucalyptus forests of southeastern New South Wales, Australia. Methods: Data from 976 sites representing a range of fire history from three major vegetation formations – shrubby dry sclerophyll forest (SF), grassy dry SF and wet SF – were analysed. Generalized linear models were used to examine changes in species richness with increasing time since wildfire and analysis of similarities to examine changes in community composition. Chi-squared tests were conducted to examine the distribution of individual species across four time since fire categories. Results: Plant species relationships to fire varied between the three formations. Shrubby dry SF supported lower plant species richness with increasing time since wildfire and this was associated with shifts in community composition. Grassy dry SF showed significant shifts in community composition and species richness in relation to time, with a peak in plant species richness 20–30 yr post fire (either prescribed fire or wildfire). Wet SF increased in species richness until 10–20 yr post wildfire then displayed a general declining trend. Species richness in each vegetation type was not related to the fire frequencies and fire intervals observed in this study. Conclusions: Long-unburnt (30–50 yr post wildfire) forests appeared to play a minor role in the maintenance of plant species diversity in dry forest systems, although this was more significant in wet forests. Maintenance of a range of fire ages within each vegetation formation will assist in maintaining floristic diversity within regions.

Integrated Grazing and Prescribed Fire Restoration Strategies in a Mesquite Savanna: I. Vegetation Responses

Abstract This study evaluated the efficacy of prescribed fire applied within landscape-scale rotational grazing treatments to reduce mesquite ( Prosopis glandulosa Torr.) encroachment and restore herbaceous productivity and cover. One-herd, multiple-paddock rotational grazing was used to accumulate herbaceous fine fuel for fires via prefire deferment and to provide periodic postfire deferment for grass recovery. Treatments were an unburned continuous-grazed control, a four-paddock-1 herd system with fire (4:1F), and an eight-paddock-1 herd system with fire (8:1F), with two replicates per treatment (1 294–2 130 ha per replicate). The management plan was to burn 25% of each system (one paddock in the 4:1F; two paddocks in the 8:1F treatments) and defer grazing during all or portions of the 9 mo (May to January) prior to burning. Deferral was “internalized” by grazing on the remaining 75% of each treatment without reducing stocking rate determined for the entire system. Mesquite cover increased on clay-loam soils from 22% to 40% in unburned paddocks over 7 yr (1995–2001). This increase, coupled with extended drought, reduced fine fuel amounts for fire and limited the number and intensity of fires that were applied. It was possible to burn one paddock in the 8:1F treatment (12.5% of total area), but not in the 4:1F treatment (25% of total area) during drought. Fires reduced mesquite and cactus ( Opuntia spp.) cover by 25–79% and 24–56%, respectively, but cover of these species increased to prefire levels within 6 yr. All fires reduced ( P ≤ 0.05) total herbaceous biomass for 1 yr postfire. The 8:1F treatment increased ( P ≤ 0.05) grass biomass on loamy-bottom soils and reduced ( P ≤ 0.05) bare ground on clay-loam and loamy-bottom soils in unburned paddocks compared to the unburned continuously grazed control. The 8:1F treatment, through internalized grazing deferment, facilitated the application of fire to reduce woody cover during extended drought without degrading the herbaceous understory.

Characterizing the Litter in Postfire Environments: Implications for Seedling Recruitment

Litter accumulation after fire influences the magnitude of seed predation and seed germination. How litter accumulation and patchiness influence postfire seedling recruitment is poorly known. Species with persistent seed banks have seeds available for germination in the immediate postfire period. In contrast, plants with transient seed banks must flower after fire to place seeds in the postfire habitat. In southeastern Australian sclerophyll forests, most seedling recruitment occurs within 3 yr after fire. We found that less litter had accumulated in sites <6 mo postfire than in those 2–3 yr postfire. Seedlings of species with persistent seed banks therefore encounter postfire environments with large areas covered by little or no litter. Among these species there is great variation in seed mass, including some species with very light seeds. In contrast, the seed mass of transient seed bank species is less variable, with the lightest species more than 70 times heavier than the lightest persistent seed bank...

RESPONSE TO FIRE OF CEANOTHUS RODERICKII (RHAMNACEAE), A FEDERALLY ENDANGERED CALIFORNIA ENDEMIC SHRUB

Experimental burns involving rare plants can provide important information for managers of those species. This study examined the response to prescribed fire of Ceanothus roderickii, a federally endangered chaparral species endemic to gabbro soils of the Pine Hill Formation in western El Dorado County, California. I conducted a laboratory study of germination cues, a field comparison of germination and survival on burned and unburned plots, and a comparison of seedling survival in burned plot subplots that were protected from vertebrate herbivores by wire exclosures. Seed germination was stimulated by heat (70° or 100° C) followed by a cold treatment. Burned plots contained 22-fold more seedlings than unburned plots, and seedling survival was significantly greater on burned plots. Exclosures significantly increased seedling survival on burned plots by 2 yr postfire. Plants on burned plots began to bloom and to branch layer (root at the nodes) by the sixth year postfire, with larger plants producing more fruits and being more likely to branch layer. I concluded that C. roderickii was similar to other species in the subgenus Cerastes in its obligate-seeding response to fire. However, its ability to branch layer enabled C. roderickii to increase plant density in burned plots, and thus continue postfire population recovery, long after fire-stimulated seedling establishment ceased. Branch layering by C. roderickii allows a postfire recovery pathway that is unique among species of obligate seeding Ceanothus studied to date.

Effects of an Intense Wildfire in a Mexican Oak-Pine Forest

Abstract An oak-pine forest burned by intense wildfire in April, 1996, and a companion unburned area were sampled 1 month and 1 yr postfire in La Michilía Biosphere Reserve, Durango, Mexico. Up to 90% of the trees were killed or top-killed in the burned area, but larger trees tended to survive, so basal area was only reduced by 66%. Top-killing was relatively higher among fire-susceptible oaks and lower among fire-resistant pines. However, oaks were strong resprouters both in the canopy and at the base of top-killed trees. Damage codes based on crown scorch and bole char were highly accurate when predicting that a tree would die but substantially overestimated survivors. Most tree regeneration was top-killed in the fire, but oak sprout density was 700% that of the unburned area by 1 yr postfire. Manzanita shrubs also resprouted vigorously. Herbaceous production and cover were lower after the first postfire growing season in the burned area than the unburned area. Woody fuels and forest floor depth were also reduced. Although short-term fire effects indicate that the forest ecosystem has moved closer toward a savanna condition, remnant seed trees and sprouting trees are expected to maintain forest cover. Future herbaceous production is likely to increase in response to overstory mortality. Quantification of fire effects is helpful for supporting short-term management decisions since oak-pine forests cover millions of hectares in northern Mexico. As a long-term management strategy, however, we suggest that restoring the frequent, low-intensity fire regime may be desirable for ecological and economic reasons. For. Sci. 46(1):52-61.

Comparative Effects of Elk Herbivory and 1988 Fires on Northern Yellowstone National Park Grasslands

The drought, frequent lightning strikes, and resultant large fires of 1988 in Yellowstone National Park were considered a several‐century event for the area. They presented an unparalleled opportunity to document the effects of large fires on forage production, forage quality, and herbivory for the largest elk (Cervus elaphus) population in a natural area in North America. We documented elk‐grassland dynamics on the Blacktail Plateau on Yellowstone's northern elk winter range following the burning of 25% of the study area in 1988. Contrary to predictions of earlier scientists, grazing of the grasslands by elk prior to the fires did not result in warmer, drier, or less productive bunchgrass communities. Soil moisture was equivalent, soil temperatures were cooler, aboveground grass biomass was equivalent in two of three years, and N, macronutrients (Ca, Mg, P, K), and digestibility concentrations were higher on grazed than ungrazed grasslands. Forb biomass, Poa sandbergii biomass, and litter accumulations, however, were less on grazed sites, and more bare ground occurred on grazed (35%) than on ungrazed (24%) grasslands (P &lt; 0.05). Elk herbivory resulted in more documented ecosystem effects for Blacktail Plateau elk than did burning. Two years postfire, burning had increased aboveground biomass of grasslands by 20%. However, digestibility of only one (Festuca idahoensis) of three grass species (F. idahoensis, Pseudoroegneria spicata, and Koeleria macrantha) was enhanced. N, cellulose, and macronutrient concentrations in grasses, and digestibility in P. spicata, K. macrantha were unaffected by the firest. In grazed vs. ungrazed areas F. idahoensis, P. spicata, and K. macrantha averaged a 21% higher N concentration, and a 7% higher digestibility. Aboveground herbaceous biomass was greater in grazed than ungrazed areas in one of three years, and total aboveground N yield was greater in two of three years. Forage biomass did increase postfire and could have benefited elk foraging efficiency. Elk use of burned grasslands increased following the fires (P &lt; 0.05). Elk avoided burned forests during the first three winters postfire (P &lt; 0.05), but elk obtain few of their forages from forest communities on the northern Yellowstone winter range (&lt;10% of feeding observations prefire). The possibility exists that shrub and herbaceous biomass in forest understories will increase after ≥ 3 yr postfire. Other studies suggest slower recovery, or increases to preburn levels in forests after ≈ 6‐8 yr. Eventually, the elk might benefit from increased quality and biomass of forages in burned forests. Grazing, by reducing fuels, can alter the extent of burning and create a more patchy fire pattern than occurs on ungrazed areas, thus conserving N that would otherwise be volatilized by burning. We observed no such interaction between elk herbivory and burning, in spite of a sixfold reduction in litter on grazed sites. Burning did not affect N concentrations on either grazed or ungrazed study sites, apparently because accumulations of dead aboveground plant material were still very light on both treatments in comparison to, e.g., tallgrass or mixed‐grass prairies in the Great Plains. The relatively minor effects of the fires of 1988 on the grassland study sites were probably a result of the relatively fast front fires, with little residual burning, and the relatively small dead plant accumulations in bunchgrass communities.

Density and Seed Production of a Florida Endemic, Polygonella basiramia, in Relation to Time since Fire and Open Sand

-Density and reproductive output in relation to fire, open sand, and other site factors were determined for Polygonella basiramia. This federally endangered species is endemic to only three ridges in central Florida and found primarily in rosemary (Ceratiola ericoides) dominated sand pine (Pinus clausa) scrub. Twenty-two sites ranging from 5 to >26 yr postfire were sampled. Site factors of openness, time since last fire, dominant species, ground cover, elevation and soil type were examined. Multivariate analyses identified the amount of open sand habitat at a site as the only variable having a significant positive relationship with both plant density and seed production. Seed production actually increased with conspecific density, suggesting that the lack of interspecific competition in open sand gaps helps define P basiramia microhabitat. Open sand habitat is critical in the life history strategy of this obligate-seeding, perennial herb in a community where it must compete with larger, resprouting shrubs and herbs both immediately after fire and during fire-free inter-