Dormant Season Fires Research Articles

Dormant Season Prescribed Fire as a Management Tool for the Control of Salix caroliniana Michx. in a Floodplain Marsh

Expansion of woody species into herbaceous wetlands is a serious concern in wetland management. Prescribed fire is often used as a tool to manage woody species, although many species resprout after fire making control problematic. In this study, we assessed the usefulness of repeated dormant season fires for controlling Salix caroliniana (Michx.) in a floodplain marsh in Florida. Salix is a common shrub in southeastern marshes that resprouts prolifically after fire. We compared stem basal area, stem density, and cover of Salix in three adjacent sites in a floodplain marsh in east central Florida. One site was burned once in February 1997, another site was burned in February 1997 and then again in March 1999 and one site was left unburned. At the unburned site, Salix stem basal area, stem density, and cover increased over the course of the study. In the two burned sites, the first fire destroyed large diameter stems and stimulated production of sprouts. As a result, stem basal area and cover decreased but stem density remained unchanged. The second fire caused a decline in stem density and a further decline in cover. Changes in understory species composition and cover could not be attributed to the fires. Our results suggest that dormant season fires are effective in reducing Salix cover and basal area, and that repeated fires have greater effects than a single fire.

Effects of understory prescribed burning on shortleaf pine (Pinus echinata Mill.)/mixed-hardwood forests

Abstract Elliott, K. J. and J. M. Vose (Coweeta Hydrologic Laboratory, Southern Research Station, USDA Forest Service, Otto, NC 28763). Effects of prescribed burning on shortleaf pine (Pinus echinata Mill.)/mixed-hardwood forests. J. Torrey Bot. Soc. 132: 236–251. 2005.—We examined the effects of a single dormant season fire on overstory and understory species diversity and composition and tree seedling regeneration patterns the first and second years following a prescribed burn in the Conasauga River Watershed of southeastern Tennessee and northern Georgia. We asked: Can a single dormant season fire initiate a trajectory of overstory and understory species change consistent with restoring Pinus echinata/mixed-oak/bluestem (Andropogon gyrans and Schizachyrium scoparium)-grass community types? Six sub-watersheds (similar in vegetation, soil type, stream size, and disturbance history) were located within the Conasauga River Watershed; four of the sites were burned in March 2001, and two sites were designate...

Glomalin content of forest soils in relation to fire frequency and landscape position.

Low-intensity, dormant season fires were frequent and widespread in oak-hickory ( Quercus-Carya) forests of eastern North America until widespread fire suppression began in the mid-1900s. To assess how reintroduction of fire into such ecosystems might affect the activity of arbuscular mycorrhizal (AM) fungi and, thereby, predict the long-term responses of plants and soils to fire, we analyzed the content of the immunoreactive fractions of the AM-fungus-specific glycoprotein glomalin in soils taken in 1994 and 2000 from three forested watersheds in southern Ohio, USA. One watershed remained unburned, one was burned annually from 1996-1999 and one was burned twice, in 1996 and 1999. In addition, to account for the strong landscape-scale gradients of microclimate and soil that typify these watersheds, we stratified each watershed-scale treatment area into three microclimatic zones (=landscape positions) using a GIS-based integrated moisture index (IMI). In the unburned control, the concentrations of immunoreactive, easily-extractable glomalin (IREEG) and immunoreactive total glomalin (IRTG) did not change significantly over the 6-year interval between sampling times, either overall or within any of the three IMI classes. IRTG content was greatest in the mesic landscape positions and lowest in the relatively xeric landscape positions, but IREEG did not vary among landscape positions. Neither IREEG nor IRTG contents were affected by fire, nor were there significant interactions between fire and landscape position in glomalin content. Both correlation and regression analyses demonstrated significant linkages between soil glomalin content, the density/diversity of herbaceous plants, and soil N availability. Despite significant effects of fires on soil N availability and root growth, we resolved no effect of fire on AM fungal activity at this spatial scale.

Influence of Season and Frequency of Fire on Henslow's Sparrows (Ammodramus Henslowii) Wintering on Gulf Coast Pitcher Plant Bogs

Abstract Henslow's Sparrow (Ammodramus henslowii) is a grassland bird that has suffered drastic population declines for over 30 years. Declining populations can be largely attributed to loss of breeding habitat, but loss of wintering habitat associated with longleaf pine (Pinus palustris) communities, especially pitcher plant (Sarracenia spp.) bogs, along the Gulf Coast also may be a contributing factor. Fire is critical for restoration and conservation of remaining longleaf pine communities, but the influence of fire on wintering Henslow's Sparrows has not been evaluated. We examined the influence of season and frequency (time since burning) of fire on use of pitcher plant bogs by Henslow's Sparrows wintering in the Conecuh National Forest, Alabama, and Blackwater River State Forest, Florida, during winters of 1999–2000 and 2000–2001. Density of Henslow's Sparrows was greatest on bogs the first winter after burning. Although significant effects for season of burning were not found, bogs burned during winter typically hosted Henslow's Sparrows for only one winter, whereas bogs burned during the growing season hosted sparrows for at least three winters. Growing-season fires may be more beneficial than dormant-season fires and will prevent forced abandonment of bogs burned during winter. Frequency of seed stalks of grasses and density of forbs were the most influential vegetation parameters affecting occurrence of Henslow's Sparrows at pitcher plant bogs. Henslow's Sparrows were found on bogs as small as 0.06 ha, but were found on bogs >0.25 ha more frequently than on smaller bogs. We conclude that burning pitcher plant bogs on an annual or biennial basis during the growing season will maximize the benefits to both wintering Henslow's Sparrows and the host of other organisms associated with those unique communities.

Season of Burn Influences Fire Behavior and Fuel Consumption in Restored Shortleaf Pine–Grassland Communities

AbstractPine forests of southeastern United States have been burned primarily in the dormant season to accomplish silvicultural objectives, but with increased emphasis on ecosystem restoration fires are now prescribed in other seasons. We observed fire behavior during both growing season and dormant season prescribed fires in shortleaf pine (Pinus echinata) stands managed as pine–grassland communities for the endangered Red‐cockaded Woodpecker (Picoides borealis). Fuel beds for dormant season fires were characterized by lower amounts of live fuels, higher amounts of 1‐hr time lag fuel and a greater total fuel load than growing season fires. Fuel consumption and percent of the total fuels consumed was greater in dormant season fires than in growing season fires. Fireline intensity, heat per unit area, reaction intensity, and rate of spread were greater in dormant season fires than in growing season fires. Lower fire intensity in growing season fires was possibly a function of lower amounts of 1‐hr time lag fuels, higher amounts of live herbaceous fuels, and possibly a less porous fuel bed. Additionally, growing season fires had lower heat per unit area and reaction intensity and slower rates of spread. The Keetch‐Byram drought index (KBDI) did not provide a good index for potential fire behavior on our drought‐prone sandy loam soils. KBDI during growing season fires averaged over four times greater than during dormant season fires, but fire intensity was greater in dormant season fires. Low KBDI values may be misleading and give a false sense of security for dormant season fire prescriptions on sandy loam soils because the duff layer may dry more quickly as a result of inherent low water holding capacity. High KBDI values may result in prescribed burns being canceled because of conditions that are erroneously perceived to be outside the prescription window. We caution against over‐reliance on KBDI as a determining factor for conducting prescribed burns on areas with sandy or sandy loam soils.

Restoring fire as an ecological process in shortgrass prairie ecosystems: initial effects of prescribed burning during the dormant and growing seasons

Prior to Anglo-European settlement, fire was a major ecological process influencing the structure, composition and productivity of shortgrass prairie ecosystems on the Great Plains. However during the past 125 years, the frequency and extent of grassland fire has dramatically declined as a result of the systematic heavy grazing by large herds of domestic cattle and sheep which reduced the available levels of fine fuel and organized fire suppression efforts that succeeded in altering the natural fire regime. The greatly diminished role of recurrent fire in these ecosystems is thought to be responsible for ecologically adverse shifts in the composition, structure and diversity of these grasslands, leading specifically to the rise of ruderal species and invasion by less fire-tolerant species. The purpose of this study was to evaluate the ecological effects of fire season and frequency on the shortgrass prairie and to determine the means by which prescribed fire can best be restored in this ecosystem to provide the greatest benefit for numerous resource values. Plant cover, diversity, biomass and nutrient status, litter cover and soil chemistry were measured prior to and following fire treatments on a buffalograss-blue grama shortgrass prairie in northeastern New Mexico. Dormant-season fire was followed by increases in grass cover, forb cover, species richness and concentrations of foliar P, K, Ca, Mg and Mn. Growing-season fire produced declines in the cover of buffalograss, graminoids and forbs and increases in litter cover and levels of foliar P, K, Ca and Mn. Although no changes in soil chemistry were observed, both fire treatments caused decreases in herbaceous production, with standing biomass resulting from growing-season fire ∼ 600 kg/ha and dormant-season fire ∼1200 kg/ha, compared with controls ∼1800 kg/ha. The initial findings of this long-term experiment suggest that dormant-season burning may be the preferable method for restoring fire in shortgrass prairie ecosystems where fire has been excluded for a prolonged time period.

Influence of season of fire on flowering of wet prairie grasses in south Florida, USA

We measured the effects of prescribed fire during January (dormant season) and May (growing season) on flowering of three perennial grasses, muhly (Muhlenbergia capillaris), gulfdune paspalum (Paspalum monostachyum), and south Florida bluestem (Schizachyrium rhizomatum), which are dominant grasses in wet prairies of south Florida, USA. Flowering was promoted by growing season fire but not by dormant season fire. Flowering was significantly greater for all species following prescribed fire conducted during May compared with areas burned during January of the same calendar year. The strong positive effect of growing season fire on flowering of all three species decreased after the first growing season. We rejected the hypothesis that season of fire did not influence flowering. Our results indicated that flowering by these dominant, wet prairie grasses is promoted by early growing season fire, which corresponds to historical patterns of lightning-ignited fire in south Florida.

Influence of long-term dormant-season burning and fire exclusion on ground-dwelling arthropod populations in longleaf pine flatwoods ecosystems

Frequent dormant-season prescribed burns were applied at 1-, 2- and 4-year intervals to longleaf pine stands, Pinus palustris, for over 40 years on the Osceola National Forest in Baker County, Florida. Control plots were unburned for the same period of time. Pitfall traps were operated from November 1994 to October 1999 to measure the short- and long-term effects of prescribed burning frequency on the relative abundance and diversity of ground-dwelling macroarthropods. We also measured dead and live plant biomass to determine how long-term frequent fires affected the structure of the forest floor. The average total dead plus live plant biomass was significantly higher on plots where fire had been excluded. Annual and biennial burning resulted in about the same amount of total plant biomass (dead and live plant material combined) which was significantly less than the quadrennially burned plots. Shannon diversity ( H′) and evenness of ground-dwelling arthropods were reduced by burning. Annually burned plots had the lowest diversity and evenness while biennially and quadrennially burned plots also were significantly lower than unburned control plots. Dormant-season burning did not increase the number of rare genera regardless of frequency. Percent similarity of arthropod communities was highest for comparisons between plots that had been burned (60–68%) and lowest for the comparison of annually burned plots to unburned controls (37%). Examination of diversity and similarity through time showed that changes were due to short-term effects caused by the application of fire and not long-term changes in the ground-dwelling arthropod community. Burning significantly reduced the numbers of predators regardless of fire frequency and resulted in an increased number of detritivores. A total of 42 genera were reduced by prescribed burning; 32 genera were captured in greater numbers on annually burned plots, and 11 genera had higher numbers in one or both of the intermediate burn frequencies (biennial or quadrennial). Twenty-six genera were captured in equal numbers on quadrennially and annually burned plots, but in significantly lower numbers than on unburned plots, demonstrating that 4 years was insufficient time for their populations to recover from mild dormant-season fires. Arthropod response to burning appeared to be species specific so attempts to generalize how arthropods will respond based on a few species or groups should be avoided. The slow recovery rate of so many species suggests that management oriented toward conservation of biodiversity in longleaf pine flatwoods should include areas of fire exclusion.

Modeling silviculture after natural disturbance to sustain biodiversity in the longleaf pine ( Pinus palustris) ecosystem: balancing complexity and implementation

Modeling silviculture after natural disturbance to maintain biodiversity is a popular concept, yet its application remains elusive. We discuss difficulties inherent to this idea, and suggest approaches to facilitate implementation, using longleaf pine ( Pinus palustris) as an example. Natural disturbance regimes are spatially and temporally variable. Variability leads to a range of structural outcomes, or results in different pathways leading to similar structures. In longleaf pine, lightning, hurricanes, surface fires, and windthrow all lead to similar structures, but at different rates. Consequently, a manager can select among various natural disturbance patterns when searching for an appropriate silvicultural model. This facilitates management by providing flexibility to meet a range of objectives. The outcomes of natural disturbances are inherently different from those of silviculture, for example, harvesting always removes boles. It is instructive to think of silvicultural disturbances along a gradient in structural outcomes, reflecting degree of disparity with natural disturbance. In longleaf pine this might involve managing for two-cohort structure, instead of multi-cohort structure characteristic of old growth stands. While two-cohort structure is a simplification over the old growth condition, it is an improvement over single-cohort management. Reducing structural disparity between managed and unmanaged forests is key to sustaining biodiversity because of linkages that exist between structural elements, forest biota, and ecosystem processes. Finally, interactions of frequency, severity, intensity, seasonality, and spatial pattern define a disturbance regime. These components may not have equal weight in affecting biodiversity. Some are easier to emulate with silviculture than are others. For instance, ecologists consider growing-season fire more reflective of the natural fire regime in longleaf pine and critical for maintenance of biodiversity. However, dormant season fire is easier to use and recent work with native plants suggests that seasonality of fire may be less critical to maintenance of species richness, as one component of biodiversity, than is generally believed. Science can advance the goal of modeling silviculture after natural disturbances by better illustrating cause and effect relationships among components of disturbance regimes and the structure and function of ecosystems. Wide application requires approaches that are adaptable to different operational situations and landowner objectives. A key point for managers to remember is that strict adherence to a silvicultural regime that closely parallels a natural disturbance regime may not always be necessary to maintain biodiversity. We outline examples of silvicultural systems for longleaf pine that demonstrates these ideas.

Prescribed burning effects on soil enzyme activity in a southern Ohio hardwood forest: a landscape-scale analysis

We assessed the effect of a single, dormant season prescribed fire on soil enzyme activity in oak-hickory ( Quercus-Carya) forests in southern Ohio, USA. Four enzymes specific for different C sources were chosen for monitoring: acid phosphatase, β-glucosidase, chitinase and phenol oxidase. Postfire acid phosphatase activity was generally reduced by burning and decreased with increasing longterm soil water potential. Postfire β-glucosidase differed little between control and burned plots. Chitinase activity increased after fire in proportion to fire intensity. Phenol oxidase activity was highly variable and did not correlate well with either fire or soil water potential. Enzyme activities tended to vary more between samples taken upslope vs. downslope of a given tree than as the result of fire or landscape position. Overall enzymes whose activities are controlled by microclimatic or edaphic factors were affected more than those controlled primarily by substrate availability. Single, dormant season fires may consume a large proportion of the forest floor and change the apparent character of the surface organic matter complex without having major effects on soil enzyme activity.

Influence of late season fire on early successional vegetation of an Oklahoma prairie

Abstract. The study of vegetation dynamics in tallgrass prairie in response to fire has focused on dormant season fire in late successional prairies. Our objective was to determine if late season fire of varying frequency results in divergent successional patterns in an early successional tallgrass prairie disturbed by grazing and cultivation. Specifically, we evaluated the influence of late‐summer fires of varying frequency on community composition and species richness. We collected vegetation and environmental data on two sites burned in the late growing‐season at varying frequencies. These communities differed in composition depending primarily on edaphic factors, time since the last burn, and year‐to‐year variation. We interpret the time effect as related to changes in species composition accompanying plant succession that followed disturbance either from cropping and heavy grazing on the loamy site or heavy grazing on the shallow site. Other unidentified factors also have a role in vegetation dynamics on this prairie. Community composition and species richness were not consistently responsive to frequency of growing‐season fires.

Effects of experimental fire regimes on the population dynamics of Schwalbea americana L.

We studied the effects of experimental fire regimes, (dormant season fire, growing season fire, growing season mowing and control, i.e., no experimental treatment) on populations of the USA federally endangered, Schwalbea americana L. between 1992 and 1996. Although this species occurs in fire-maintained habitat in the Southeastern USA, there is concern about the use of fire for such rare populations. The purpose of the study was to examine how seasonal timing of fire and fire suppression affect population demography, flowering phenology and spatial distribution; to identify modes of persistence associated with fire regimes; and to determine if summer mowing provides a management alternative to fire. Fire-induced flowering was demonstrated in this species. Seasonal timing of burns appears to have relatively little consequence on population structure or spatial extent, but alters flowering phenology. Burning, regardless of season, resulted in increased population density and expansion in areal extent. Two possible mechanisms of persistence between fire events were identified including regression from reproductive stage to vegetative stage in the absence of fire and dormancy of individual plants for one or more seasons. Growing season mowing does not appear to be an adequate substitute for burning.

Long-term effects of dormant-season prescribed fire on plant community diversity, structure and productivity in a longleaf pine wiregrass ecosystem

A flatwoods longleaf pine wiregrass ecosystem, which regenerated naturally following wildfire in 1942, on the Coastal Plain of southern Georgia was treated over a period of four decades with prescribed fire at annual, biennial and triennial intervals during the winter dormant season. Burning caused substantial changes in the understory plant community, with significant reductions in the foliar cover of Ilex glabra in the shrub layer resulting in corresponding increases in the cover of Vaccinium myrsinites, Sporobolus curtissii, Aristida stricta and Andropogon spp. Understory plant species richness, diversity and evenness also increased as a result of periodic fire. Dormant-season burning decreased the cover of litter on the forest floor and significantly increased the standing biomass of A. stricta, S. curtissii, Andropogon spp., all other grasses and all forbs. Recurrent fire also prevented the development of a vigorous midstory, that impedes understory growth and poses a serious fire hazard to the stand. Overstory trees were largely unaffected by burning. Historical light grazing on the site produced no measurable effects on the plant community. Findings suggest that the biennial burning interval results in declines of I. glabra in the shrub layer and litter cover on the forest floor, leading to the largest increases in understory plant species richness and diversity and the biomass productivity of grasses and forbs. Although flatwoods plant communities evolved in environments characterized by growing-season fires of variable frequency, long-term application of dormant-season fire is also recommended as a useful option for sustaining resource values in this and similar longleaf pine wiregrass ecosystems.

Late-Summer Fire and Follow-Up Herbicide Treatments in Tallgrass Prairie

Research on fire in tallgrass prairie focuses almost exclusively on dormant season fires, primarily in winter and spring. Relatively little is known about the response of tallgrass prairie vegetation to growing-season fiies or follow-up management. We evaluated vegetation response of grazed, high-seral tallgrass prairies to herbicides after late-summer burning. Dry matter yields of little bluestem [Schizachyrium scopuriutn (Michx.) Nash], other perennial grasses, total perennial grasses, and total herbage were sign% cantly reduced by late-summer burning. Tallgrass and annual grass standing crop did not differ between burn treatments. Forb standing crop on burned plots averaged about twice that of unburned plots. Follow-up treatment with 2,4-D[(2,4-dichlorophenoxy)acetic acid] significantly reduced forb standing crop compared to atrazine[6-chloro-N-ethyl-~~l-methylethyl)-1,3,5-t~azine-2,4-~amine]. Standing crop of tallgrasses and total perennial grasses was greater on plots treated with 2,4-D than on plots treated with no herbicide or with atrazine. Because late-summer burning did not severely reduce herbage production nor drastically alter community composition for more than 1 year, late-summer burning may be a viable alternative for brush control and for improving wildlife habitat in high-seral tallgrass prairie. If management objectives require reduced forb production and increased perennial grass production following late-summer burning, application of 2,4-D would be an appropriate management practice.

Predicting Pinus ponderosa Mortality From Dormant Season and Growing-Season Fire Injury

Understory prescribed burning was conducted in an immature Pinus ponderosa (ponderosa pine) stand in southwestern Colorado during three seasons, late spring, midsummer, and autumn. Tree mortality from various levels of crown scorch was compared for the different seasons of injury. A total of 526 trees of different sizes, with crown scorch ranging from 20 to 100%, were monitored annually for 10 years. Over 80% of the 10-year mortality from injury in all three seasons had occurred by year 3, with over 90% occurring by year 4. Mortality of trees scorched in the spring and summer was about 2.5 times greater than that in the autumn for similar crown damage. Most trees larger than 18 cm in diameter survived autumn injury, even with greater than 90% scorching. Following spring and summer injury, trees smaller than 10 cm in diameter died readily with greater than 50% scorching, but about 90% crown scorch was required by large trees to be lethal. A logistic regression model was developed to predict the probability of mortality given tree size, scorch class, and season of injury. Because mortality was similar within scorch classes less than 90%, they were combined into a single class. Scorch thresholds with large increases in mortality occurred at 90% and 100% crown scorch. The season variable includes two groups, dormant (autumn) and growing (spring and summer). Use of this model to predict mortality of immature P. ponderosa is appropriate where stand, fuel, and fire conditions resemble those of this study.

Differential Response of Woody and Herbaceous Species to Summer and Winter Burning in an Oklahoma Grassland

Fire has historically been an important factor in the maintenance of tallgrass prairie vegetation. Summer fires have often been thought to be more effective than dormant season fires in controlling the invasion of woody species into prairies. However, in an Oklahoma grassland, late-winter burning (March) had a more pronounced effect in reducing the density of woody spe- cies than did summer (July) burning. This response was possibly due to both environmental and site conditions. Two woody species increased in density following both summer or late-winter burning while nine species decreased in density or were eliminated by fire. Two additional woody species exhibited varied responses depending on season of burn. Woody species density increased in the smallest seedling size class, but decreased for larger seedling and sapling size classes follow- ing both burning regimes. Finally, numbers of woody and herbaceous species decreased following both summer and late-winter burns. The importance of fire as a means of increasing production, determining community composition, and controlling the invasion of woody species has been documented in many parts of the tallgrass prairie (Gleason, 1913; Daubenmire, 1968; Peet, Anderson, and Adams, 1975; Anderson, 1976; Rice and Parenti, 1978; and others). In the absence of fire, many woody species readily invade native North American grasslands, especially in the eastern tallgrass prairie where environmental conditions are more favorable for trees than in the more arid West (Sauer, 1950; Weaver, 1968; Bragg and Hulbert, 1976). Mechanisms allowing woody species to replace grassland species or to per-