Fall Burn Research Articles

The effects of burning season and severity on the mortality over time of Pinus nigra spp. salzmannii (Dunal) Franco and P. sylvestris L.

Abstract Understanding tree mortality after fires can be used to improve planning of prescribed burning and post-burning salvage logging. This study aims to assess the effects of burning season, fire severity and tree size on the evolution of post-burning mortality of pine species with different fire resistance traits. In 2013, two paired plots (1 ha each) were burned, one in spring and the other in fall, in two mixed-stands of P. sylvestris and P. nigra, and the fire severity and tree size variables were measured. Mortality was assessed individually in a total of 933 pines during the following 3 years post-burning. We modeled the initial (1 year post-burning) and delayed (3 years post-burning) tree mortality using Firth logistic regression and Conditional Inference trees. The probability of dying after burning was lower in P. nigra than in P. sylvestris confirming that P. nigra has higher fire-resistance compared to the moderate fire-resistance of P. sylvestris . Initial mortality was slightly higher for pines burned in spring than for those burned in fall; however, after 3 years the proportion of pines that had died after the fall burns was higher than that after the spring burns. Nevertheless, for the two periods modeled, the likelihood of a pine dying was significantly higher in spring than in fall given a certain level of crown scorch. This suggests that pines with damaged crowns were more likely to die when burning occurred during periods of active growth. However, the higher fire severities at the base of the trees that occurred during the fall burns compared to the spring burns are probably the cause of the higher rates of delayed tree mortality. Higher likelihood of mortality in trees burned in fall, with higher percentages of white ashes in the stem base suggest basal stem girdling as a cause of delayed pine mortality. We can conclude that crown damage is more detrimental when burning occurs during the growth season, while longer combustion times during fall burns may have caused the higher delayed pine mortality in comparison with spring burns.

Plant community response to prescribed fire varies by pre-fire condition and season of burn in mountain big sagebrush ecosystems

Artemisia tridentata ssp. vaseyana ecosystems evolved with periodic fire, but invasive grasses, conifer encroachment, fire suppression, and climate change have resulted in altered fire regimes and plant communities. Post-fire increases in invasive annual grasses such as Bromus tectorum and reductions in native vegetation are common across the sagebrush steppe. Where fire has been excluded though, there are increases in the native tree Juniperus occidentalis, which outcompetes the native understory. We applied prescribed fire in spring and fall at three sites (native-dominated, B. tectorum-dominated, and J. occidentalis-dominated). We documented 65% survival of A. tridentata following fall burns and 33% survival following spring burns in native-dominated plots, with evidence of post-fire sprouting in Purshia tridentata and Tetradymia canescens. At the B. tectorum-dominated site, shrub cover was reduced to <1%. Fires at the J. occidentalis site were discontinuous, resulting in ∼50% mortality of trees and shrubs, with little resprouting. Native herbaceous vegetation persisted following fires, with no increases in B. tectorum. There were higher plant survival rates following fall fires and native-dominated sites than in spring burns or where exotics dominated. These results show that burn season and prefire condition are important considerations when evaluating management alternatives in A. tridentata ssp. vaseyana ecosystems.

Prescribed Burning in Ponderosa Pine: Fuel Reductions and Redistributing Fuels near Boles to Prevent Injury

Fire suppression and other factors have resulted in high wildfire risk in the western US, and prescribed burning can be an effective tool for thinning forests and reducing fuels to lessen wildfire risks. However, prescribed burning sometimes fails to substantially reduce fuels and sometimes damages and kills valuable, large trees. This study compared fuel reductions between spring and fall prescribed burns and tested whether removing (i.e., raking) fuels within 1 m of boles reduced fire damage to ponderosa pine (Pinus ponderosa Douglas ex Lawson & C. Lawson). In 2007 and 2008, raking was applied to alternating trees along 18 transects in central Oregon, USA. Fuels surrounding 292 trees were burned in fall 2010, and fuels surrounding 216 trees were burned in spring 2012. Both seasons of burn affected most fuel size classes similarly, with one exception being duff, which was more fully consumed in fall than in spring. Where fall burning occurred, raking reduced the percentage of dead cambium samples from 24.3 ±4.9 % to 6.4 ±3.0 % (point estimates ±95 % confidence intervals), in addition to reducing bole scorch. Conversely, where spring burning occurred, injury of not-raked trees was milder, so raking did not have the potential to greatly reduce damage. Redistributing fuels away from boles would be more beneficial under relatively dry conditions when duff is prone to extensive smoldering. Our study and most other studies suggest that duff is, on average, drier in fall than in spring, so raking would tend to afford more protection from fall burns than from spring burns. The little tree mortality that occurred was split nearly evenly between raked trees (25) and not-raked trees (30), so raking did not appreciably increase survival in this study. However, the finding that raking reduced injury suggests that it may reduce mortality from more intense burns.

Oriental bittersweet (Celastrus orbiculatus): Spreading by fire

In many forest ecosystems, fire is critical in maintaining indigenous plant communities, but can either promote or arrest the spread of invasive species depending on their regeneration niche and resprouting ability. We examined the effects of cutting and burning treatments on the vegetative response (cover, stem density) and root resources of Oriental bittersweet (Celastrus orbiculatus), a liana invasive to North America that was introduced from East Asia. Treatments were control, spring cut, spring burn, spring cut & burn, summer cut, fall cut, fall burn, fall cut & burn, and fall herbicide. Cover was reduced the greatest by herbicide and summer cutting treatments, but increased more in the second year on moraine soils than on sandy soils. Burning and cutting & burning combined resulted in a resprout density four times greater than stem density prior to treatment for stems <2.5mm diameter than cutting alone. For stems, across all diameter classes, there was a more than 100% increase in stem density with burning and almost a 300% increase in stem density with cutting & burning in the spring. Density of resprouts and root-suckers, and survival increased with increasing stem size. While cutting of C. orbiculatus during the growing season (summer) reduced total nonstructural carbohydrates by 50% below early growing season levels and 75% below dormant season levels, burning did not significantly reduce total nonstructural carbohydrates. Thus, Oriental bittersweet is quite responsive to burning as a disturbance and resprouting and root-suckering creates additional opportunities for growth and attainment of the forest canopy. The positive response of Oriental bittersweet to burning has important implications for management of invasive lianas in fire-dependent forest landscapes.

Synergistic interactions between leaf beetle herbivory and fire enhance tamarisk (Tamarix spp.) mortality

The combined effects of herbivory and fire on plant mortality were investigated using prescribed burns of tamarisk (Tamarix ramosissima Lebed) exposed to herbivory by the saltcedar leaf beetle (Chrysomelidae: Diorhabda carinulata Desbrocher). Tamarix stands in the Humboldt Sink (NV, USA) were divided into three treatments: summer burn (August 2006), fall burn (October 2006) and control (unburned), and litter depth was manipulated to vary fire intensity within burn seasons. A gradient of existing herbivory impact was described with three plant condition metrics prior to fire: reduced proportions of green canopy, percent root crown starch sampled at the height of the growing season (August 2006), and percent root crown starch measured during dormancy (December 2006). August root crown starch concentration and proportion green canopy were strongly correlated, although the proportion green canopy predicted mortality better than August root crown starch. December root crown starch concentration was more depleted in unburned trees and in trees burned during the summer than in fall burn trees. Mortality in summer burned trees was higher than fall burned trees due to higher fire intensity, but December root crown starch available for resprouting in the spring was also lower in summer burned trees. The greatest mortality was observed in trees with the lowest December root crown starch concentration which were exposed to high fire intensity. Disproportionate changes in the slope and curvature of prediction traces as fire intensity and December starch reach reciprocal maximum and minimum levels indicate that beetle herbivory and fire intensity are synergistic.

The Effect of Experimental Prescribed Fire on White Pine Regeneration

We examined the effects of prescribed fire on white pine (Pinus strobus) advance regeneration in small experimental plots in mixed hardwood-pine forests in southwestern Virginia during the fall and spring. Fires killed all newly germinated seedlings in both spring and fall. Saplings (ranging from 0.7 - 3.4 m in height) all suffered some degree of crown scorch, but sapling survival was higher on plots burned in the fall (54%) compared to those burned in the spring (20%). After one growing season following the fires, seedling density had recovered to a level similar to that of control plots for fall burns, but was still significantly lower than control plots for spring burns. After one growing season, the amount of crown mortality for saplings was reduced with increasing height and root collar diameter. Height growth of saplings after one growing season following fires was not different between burned and control plots. Fall burns may be less detrimental to white pine regeneration because of reduced mortality to saplings and by providing microsite conditions during the period of seed rain that are conducive to recover seedling regeneration.

The effects of indigenous prescribed fire on riparian vegetation in central California

Introduction: Fire has a long history, but little documented role, as a process in riparian ecosystems. For millennia California Indians have applied fire to riparian ecosystems for a variety of purposes, but the effects of such fires on riparian vegetation are poorly known outside of traditional knowledge structures of indigenous communities. Methods: This study involved the seasonal application of fire based on traditional ecological knowledge versus alternate burn methods to assess fire effects on riparian vegetation in central California. Results: While the annual variation amongst treatments was not significant, the results of this study suggest that fall burns support higher overall richness and native species richness; spring burns yield a decrease in overall richness, but an increase in native species richness; and summer burns contribute to an initial decline in overall and native species richness. The evenness indices of treatments increase most with spring and summer burning. Conclusion: These findings are key to understanding the seasonal role of fire in managing native species in areas prone to non-native or other invasive species. This research demonstrates the application of traditional ecological knowledge to facilitate an understanding of how prescribed fire could aid in the management and conservation of riparian ecosystems.

Restoring habitat for the northern Idaho ground squirrel (Urocitellus brunneus brunneus): Effects of prescribed burning on dwindling habitat

Land use and fire exclusion have contributed to an increase in ponderosa pine (Pinus ponderosa) forest extent and density in west-central Idaho. Open areas within ponderosa pine forests are decreasing, thus reducing habitat for the endemic northern Idaho ground squirrel (NIDGS; Urocitellus brunneus brunneus). In 2000, the NIDGS was listed on the Endangered Species Act as threatened in part due to habitat loss. Therefore, recovery plans encourage the use of burning to expand meadows and open corridors. We gathered data on habitat attributes altered by prescribed fall burning at three sites selected for habitat restoration. Each site was divided into two units: a CONTROL unit occupied by the NIDGS and a BURN unit not occupied by the NIDGS. We sought to assess whether the prescribed fall burning fulfilled management goals and generated habitat features similar to CONTROL conditions that are suitable for the NIDGS. Data were collected before the fall prescribed burn and one and two years post-burn. Before the prescribed burn, BURN units had higher tree densities and canopy cover than CONTROL units; however, the prescribed fall burn did not reduce tree density or canopy cover one year later. Understory height in the BURN unit decreased slightly post-burn, approaching CONTROL conditions. Majority of understory characteristics were similar between CONTROL and BURN units before, one, and two years after the burn, but understory community structure remained strongly dissimilar. This study preliminarily examines NIDGS habitat and is the first paper to evaluate the effects of prescribed burning as restoration practices to create NIDGS habitat. Key habitat attributes associated with NIDGS presence include tree canopy cover, understory height and community structure, and litter depth. Management goals were not attained within the stated timeline, one year post-burn, or even two years after prescribed burn was implemented. Based on our results, managers should consider extending the timeframe for restoration goal achievement and perhaps modifying goals to include changes in tree canopy cover, understory height and community structure, and litter depth. Future efforts should monitor beyond two years post-fire, focus on long-term effects of prescribed burning, and examine how repeat burns may help attain habitat restoration goals.

Seedbank responses to spring and fall prescribed fire in mountain big sagebrush ecosystems of differing ecological condition at Lava Beds National Monument, California

Land use change in the American West has altered sagebrush dominated ecosystems, facilitating exotic grass invasion, increased woody species, altered fire regimes, and native species losses. Restoring fire regimes may be integral to the restoration of sagebrush ecosystems. However, little is known about how the timing of prescribed fire differentially impacts the soil seedbank. Further, sites of different ecological condition may variably respond to fire. To address these uncertainties, we quantified germination of invasive cheatgrass and plant functional groups (native dicots, exotic dicots, native bunchgrasses, and native shrubs) following spring and fall prescribed burns in three mountain big sagebrush communities at Lava Beds National Monument, California. At cheatgrass and native-dominated sites, there were fewer cheatgrass seedlings (91% and 86%, respectively) immediately following spring fire than in unburned controls, but this reduction did not persist one year later. Fall burns did not significantly impact cheatgrass or exotic dicot germination. At a native dominated site, native dicots increased one year following spring (1620%) and fall burns (67%), suggesting adaptation to a natural fire regime. This research shows that the prefire condition of an ecosystem greatly influences the postfire germination response, and that fire-adapted ecosystems can benefit from the natural disturbance regime.

Changes in Soil Structure and Hydraulic Properties in a Wooded‐Shrubland Ecosystem following a Prescribed Fire

Pre‐ and post‐fire measurements were made for a low‐intensity prescribed fire in a semiarid, shrub‐woodland transition zone, and objectives were to: (i) determine changes in near‐saturated hydraulic conductivity (Kf measured with a tension infiltrometer), air permeability (ka measured with an air permeameter), and soil physical properties at shrub undercanopy and interspace microsites immediately before and after a fall burn and for a 13‐mo period; and (ii) quantify the importance and effect of post‐fire soil structure on hydraulic properties using pre‐ and post‐fire measurements. At undercanopy microsites, structure deteriorated from a moderate to a weak subangular blocky structure after the fire that broke down to a structureless soil 10 mo later. At interspace microsites, post‐fire soil structure deteriorated from a moderate‐strong subangular blocky structure with hard dry consistency to a weak subangular blocky structure with soft dry consistency. After 10 mo, the intercanopy maintained a weak‐moderate soil structure that became structureless‐weak after 13 mo. Immediately after the fire, at both microsites, there was incomplete organic combustion, a decrease in bulk density, and an increase in ka; however, at undercanopy microsites, there was no significant change in Kf even though there was a slight to moderate hydrophobicity, whereas at interspace microsites where no water repellency existed, Kf increased. These changes may be a result of expansion of vaporized water through soil pores that broke up aggregates, deteriorating soil structure. Thus, mechanisms that contributed to changes immediately and after the first year post‐fire were different for low‐intensity burns than for higher intensity burns.

Acorn viability following prescribed fire in upland hardwood forests

Restoration of structure and function of mixed-oak (Quercus spp.) forests is a focal issue of forest land managers in the eastern United States due to widespread regeneration failure and poor overstory recruitment of oaks, particularly on productive sites. Prescribed fire is increasingly used as a tool in oak ecosystem restoration, with the goal of reducing competition, and creating light and seedbed conditions conducive to germination and growth of oak seedlings. Yet, oak seedling establishment is dependent on the presence of viable acorns, which may be vulnerable to prescribed fire. We assessed the effect of prescribed burning and fire temperature on the viability of white oak and northern red oak acorns placed on the leaf litter surface, in the duff, or in the mineral soil during five winter prescribed burns in southern Appalachian upland hardwood forests. Fire temperatures varied among acorn plots, ranging from <79 to <371°C. After the burns, acorns were planted in trays with water-saturated vermiculite, exposed to 14 continuous hours of light daily, and maintained at 27°C on germination beds in a greenhouse. After three weeks we recorded the proportion of acorns germinating and the proportion of germinants with shoots. Our study indicated that patchy, low-intensity dormant season prescribed fire in upland hardwood forests reduced viability of white oak and northern red oak acorns located on the leaf litter surface, but did not generally affect acorns in the duff or mineral soil. Germination rates of both northern red oak and white oak acorns on the leaf litter surface decreased with increasing fire temperature. Shoot production by northern red oak germinants from acorns on the leaf litter surface (and less so in the duff), also decreased with increasing fire temperature. Acorns of both species on the leaf litter surface burned at temperatures ⩾204°C showed high mortality levels, with mortality virtually 100% at temperatures ⩾260°C. Fall burns, especially after a heavy acorn crop, could result in high acorn mortality, potentially impacting oak regeneration from seedlings for many years given erratic acorn production patterns among years and species. Frequent burning that reduces litter and duff depth could compromise availability of ‘safe sites’ where acorns are insulated from high fire temperatures. When oak ecosystem restoration is a goal, land managers should consider the timing and size of acorn crops, as well as the forest floor condition when determining the timing and frequency of prescribed burning.

Role of season and interval of prescribed burning on ponderosa pine growth in relation to soil inorganic N and P and moisture

Fire exclusion over the past 100years has changed the vegetative community and led to an increase in the propensity for large catastrophic wildfires of ponderosa pine forests. Prescribed burning is used to reduce fuel loads and achieve desired stand conditions while the impact caused by this restoration process is primarily dependent on the severity of the fire, which is managed by burning in either fall or spring. The objectives of this study were to assess the effect of season and interval of burn on soil and tree productivity in a ponderosa pine forest in Malheur National Forest of the southern Blue Mountains of eastern Oregon. Prescribed burning was initiated in the spring of 1997 and fall of 1997 at 5- and 15-year intervals. This study was initiated in 2004 so that the 5-year interval plots had burned twice with 1–2years of recovery while the 15-year interval plots had burned only once with 6–7years of recovery since the last fire. Soils were sampled by major genetic horizon and A horizon samples were analyzed for soil available nitrogen (KCl extractable NH4+ and NO3-) and phosphorous (Bray 1 extract). Soil temperature (2cm) and moisture (7.5, 25, 50, and 100cm) were monitored for 24months. Observations and previous studies indicated that fall burns were more severe than spring burns consuming more fuel and leading to higher rates of tree mortality. Extractable NH4+ and phosphate increased with multiple burns relative to the single burn treatments, but were statistically similar to the control. Soil temperatures were found to be highest in the more severe fall burn treatments, particularly the 5-year interval burns. Soil moisture was also slightly higher with the 5-year interval burns, possibly due to reduced transpiration from understory vegetation and/or reduced interception by the O horizon. These changes to the soil did not significantly affect ponderosa pine growth relative to the control and may have caused a slight increase in tree growth with the spring burns applied at a 5-year interval relative to the other burn treatments. We hypothesize that low severity spring burning improved the soil growing environment without injuring trees. Combined with results from previous studies spring burns appear to preserve stand productivity, soil carbon and nitrogen, and understory vegetative communities. However, more research is necessary to examine the long-term consequences of repeated burning in these forest types.

Promoting Native Vegetation and Diversity in Exotic Annual Grass Infestations

Exotic plant invasions are especially problematic because reestablishment of native perennial vegetation is rarely successful. It may be more appropriate to treat exotic plant infestations that still have some remaining native vegetation. We evaluated this restoration strategy by measuring the effects of spring burning, fall burning, fall applied imazapic, spring burning with fall applied imazapic, and fall burning with fall applied imazapic on the exotic annual grass, medusahead (Taeniatherum caput‐medusae (L.) Nevski), and native vegetation at six sites in Oregon for 2 years post‐treatment. Medusahead infestations included in this study had some residual native perennial bunchgrasses and forbs. Burning followed by imazapic application provided the best control of medusahead and resulted in the greatest increases in native perennial vegetation. However, imazapic application decreased native annual forb cover the first year post‐treatment and density the first and second year post‐treatment. The spring burn followed by imazapic application produced an almost 2‐fold increase in plant species diversity compared to the control. The fall burn followed by imazapic application also increased diversity compared to the control. Results of this study indicate that native plants can be promoted in medusahead invasions; however, responses vary by plant functional group and treatment. Our results compared to previous research suggest that restoration of plant communities invaded by exotic annual grass may be more successful if efforts focus on areas with some residual native perennial vegetation. Thus, invasive plant infestations with some native vegetation remaining should receive priority for restoration efforts over near monocultures of invasive plant species.

Native Bunchgrass Response to Prescribed Fire in Ungrazed Mountain Big Sagebrush Ecosystems

Fire was historically a dominant ecological process throughout mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) ecosystems of western North America, and the native biota have developed many adaptations to persist in a regime typified by frequent fires. Following spring and fall prescribed fires conducted in sites of different ecological conditions at the Lava Beds National Monument, California, USA, we examined the reproductive, density, and cover responses of four native bunchgrasses: bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve), Thurber’s needlegrass (Achnatherum thurberianum [Piper] Barkworth), squirreltail (Elymus elymoides [Raf.] Swezey), and Sandberg bluegrass (Poa secunda J. Presl). High rates of survival and fire-enhanced flowering were measured following fires. Thurber’s needlegrass density decreased following spring burns in sites dominated by cheatgrass (Bromus tectorum L.) (from 3.3 plants m− 2 to 0.8 plants m− 2; P < 0.05). Density of bluebunch wheatgrass decreased following spring fires (from 3.7 plants m− 2 to 1.9 plants m− 2; P = 0.02) and cover was reduced in both spring and fall burn treatments (P = 0.04) in native dominated sites. Fire-enhanced flowering (increases in reproductive efforts) occurred in bluebunch wheat-grass in cheatgrass dominated sites (244% increase in reproductive culms following fire), native dominated sites (350% increase), and woody encroachment sites (500% increase) sites following fall fires. These results show that these native bunchgrasses positively respond to prescribed fire through increases in reproductive efforts and high rates of survival following fires. This suggests that fire can be an important tool for the restoration and conservation of these fire adapted bunchgrasses.

Short-term effects of burn season on flowering phenology of savanna plants

We examined the effect of season of burn on flowering phenology of groundlayer species, in the year following burns, in a mesic-sand Midwestern oak savanna. Burn treatments were fall, early-season, growing-season, late-season, and 1 or 5 years after a prior early-season wildfire. For these treatments, we compared the number of flowering stems and of flowers for species overall, for the 20 most prolifically flowering species, as well as for species grouped by flowering phenoperiods, and by growth form. Growing-season burn had a significant negative effect on number of flowering stems and total number of flowers. This effect occurred when either the burn occurred during the flowering season or during the season prior to the flowering phenoperiod. Tradescantia ohiensis showed expedited flowering and Phlox pilosa showed delayed flowering in response to early-season burning. Flowering of early shrubs was reduced by the previous fall and early-spring fires, while flowering of mid-season blooming shrubs was reduced by the early- and growing-season burns. Vaccinium and Gaylussacia, early-flowering shrubs, produced fewer flowers 1 year after than 5 years after an early-season burn. Arabislyrata showed reduced flowering from the early-season burn. We also found four instances where the early-spring burn effect on flowering was more severe than the fall burn effect, suggesting that many frequent early-season burns may be deleterious to flowering and reproduction of some species. Burns occurring too frequently in the same season could negatively affect future flowering and reproduction of these plant species.

Prescribed Fire and Post-Fire Seeding in Brush Masticated Oak-Chaparral: Consequences for Native and Non-Native Plants

In fire-suppressed oak-chaparral communities, land managers have treated thousands of hectares by mechanical mastication to reduce hazardous fuels in areas of wildland-urban interface. The chipped debris, which decomposes slowly, can be burned to minimize wildfire hazard. The question is whether controlled burning of masticated debris results in loss of native plant species richness and abundance, allowing for gains in non-native species. We examined the response of vegetation to the seasonality of prescribed fire and to postfire seeding in mechanically masticated oak-chaparral communities in the Applegate Valley of southwestern Oregon, USA. At the landscape level, treatments did not differ. At the site level, response of native and non-native species varied by site and treatment. Following prescribed fire, native species decreased in cover and increased in species richness; non-native species increased in cover and in species richness. Seven species that were not observed on pre-treatment plots appeared after burn treatments. Non-native annual grasses and forbs increased following both spring and fall burns. Among native species, annuals declined in cover while perennials increased slightly. Both annual and perennial natives increased in species richness following burn treatments. Community patterns at the site scale changed following all treatments. Seeded bunchgrasses, Lemmon’s needlegrass (Achnatherum lemmonii [Vasey] Barkworth), California brome (Bromus carinatus Hook. and Arn.), blue wildrye (Elymus glaucus Buckley), and Roemer’s fescue (Festuca idahoensis Elmer ssp. roemeri [Pavlick] S. Aiken), successfully established following fall prescribed fires, but not following spring prescribed fires or in unburned controls. Post-fire seeding and subsequent increased bunchgrass cover correlated with decreased non-native species. Prescribed low severity fire followed by post-fire seeding during the wet, cool season is a viable tool for introducing native bunchgrasses while controlling non-native species in mechanically masticated oak-chaparral in southwestern Oregon.

Sequential Burning Effects on the Soil Chemistry of a Grassland Restoration in the Mid-Atlantic Coastal Plain of the United States

Prescribed burning is a common management tool used in grassland restorations to improve conditions for plant growth. At a grassland restoration in Maryland, we studied the impacts of sequential prescribed burning on near-surface soil chemistry of a highly weathered soil. We hypothesized that soil pH and base cations in the surface soil would increase in the nutrient-poor soils after the burning from char hydrolysis and that cations would be retained in the surface soil between the burns. We collected soil cores 12 days and one year after a fall burn and 12 days after a subsequent spring burn. After the fall burn, we observed that soil pH, extractable cations, and organic matter (OM) were elevated in the soil profile in comparison to soil conditions before initiation of any burning, suggesting an impact of the dissolution of char (the mineral-containing carbonaceous residue of burning), increased root productivity since restoration, and leach­ ing of soluble constituents from aboveground litter in the case of soil K. One year after the second burn, only cations remained elevated. After the third burn, soil pH, OM, Ca, and Mg were greater in the depths below 10 cm in comparison to conditions prior to initiation of burning. We conclude that the net change over time in soil pH, extractable cations, and OM of grassland restorations in the first few years of prescribed burning will depend primarily on the input of new char, the presence of residual char, and the timing and magnitude of leaching events. As the grassland restoration ages, belowground productivity will likely contribute more significantly to changes in soil chemistry.

Interactions among Prescribed Fire, Soil Attributes, and Mycorrhizal Community Structure at Crater Lake National Park, Oregon, USA

We identified relationships between prescribed burn treatments and selected soil and fuel attributes on mycorrhizal fungus fruiting patterns in an old-growth ponderosa pine (Pinus ponderosa) and white fir (Abies concolor) stand in Crater Lake National Park, Oregon, USA. Three prescribed burn treatments (early spring, late spring, and fall burns) plus non-burned controls were applied to 24 ∼3 ha units in 2002. We sampled mycorrhizal fungus sporocarp production in the spring and fall in the ensuing three years, and collected data on surface fuels, soil C and N concentrations, δ13C and δ15N signatures, pH, and mineral soil bulk density. A gradient of C:N ratios and other soil attributes across the study area facilitated separation of the effect of fire from the effects of soil attributes on fungal fruiting patterns. Distinct guilds of fungal indicator species were identified, correlating more closely with soil C:N ratios than prescribed burn treatments. Although other habitat attributes (such as fuel levels) were correlated with C:N ratios, the C:N ratios were the most consistent predictor of fungal fruiting patterns. The fall burn treatment did reduce soil C:N ratios, and most of the fall burned units produced the fungal indicator species associated with lower C:N ratios, but the same fungal indicator species also fruited in the non-burned control units with lower C:N ratios. The spring burn treatments did not differ significantly from non-burned controls in fungal fruiting patterns or C:N ratios. Fall burn treatment units produced significantly fewer fungal species and collections than spring burn units, but did not differ significantly in fungal diversity and abundance from non-burned controls.

Reproductive output of ponderosa pine in response to thinning and prescribed burning in western Montana

Thinning and thinning followed by prescribed fire are common management practices intended to restore historic conditions in low-elevation ponderosa pine ( Pinus ponderosa Dougl. ex P. &amp; C. Laws.) forests of the northern Rocky Mountains. While these treatments generally ameliorate the physiology and growth of residual trees, treatment-specific effects on reproductive output are not known. We examined reproductive output of second-growth ponderosa pine in western Montana 9 years after the application of four treatments: thinning, thinning followed by spring prescribed fire, thinning followed by fall prescribed fire, and unthinned control stands. Field and greenhouse observations indicated that reproductive traits vary depending on the specific management treatment. Cone production was significantly higher in trees from all actively managed stands relative to control trees. Trees subjected to prescribed fire produced cones with higher numbers of filled seeds than trees in unburned treatments. Seed mass, percentage germination, and seedling biomass were significantly lower for seeds from trees in spring burn treatments relative to all others and were generally higher in trees from fall burn treatments. We show for the first time that thinning and prescribed-burning treatments can influence reproductive output in ponderosa pine.

Soil organic matter in a ponderosa pine forest with varying seasons and intervals of prescribed burn

Prescribed burning is used to reduce fuel loads and return ponderosa pine forests of the Western U.S. to their historical structure and function. The impact of prescribed burning on soil is dependent on fire severity which is largely managed by burning in the fall or the spring; frequency of fire will also regulate long-term fire impacts. The objective of this study was to determine if soils and soil organic matter (SOM) were affected by prescribed burning in the fall or the spring using singular or multiple prescribed burns. Prescribed burning was initiated in the spring of 1997 and fall of 1997 at 5-year intervals and once during a 15-year period on a study site located within the Malheur National Forest of the southern Blue Mountains of eastern Oregon. Soils were sampled by major genetic horizon in 2004. The 5-year interval plots had burned twice with 1–2 years of recovery while the 15-year interval plots had burned only once with 6–7 years of recovery. Samples were analyzed for pH, carbon (C), nitrogen (N), C/N ratio, cation exchange capacity, base saturation, water repellency, and humic substance composition by alkali extraction. Fall burning decreased C and N capital of the soil (O horizon +30 cm depth mineral soil) by 22–25%. Prescribed burning did not have an effect on fulvic or humic acid C concentration (FA and HA, respectively) of the mineral soil and only a minor effect on FA and HA concentration of the O horizon. One or two fall burns decreased humin and the alkali non-soluble C (NS) content of O horizon by 15 and 30%, respectively. Initiating fall burning in fire-suppressed stands may not preserve soil C, N, humin, and NS content, but may replicate the natural fire regime. Spring burning using a return interval of 5 or more years reduces the fuel load while having little impact on soil C, N, and SOM composition and may be used to prepare a site for subsequent fall burns.