Dormant-season Burns Research Articles

Season of burn has minimal effect on groundlayer community structure and composition in an Appalachian mixed‐oak forest

The groundlayer flora has a disproportionate influence on ecosystem function and contributes to the biodiversity in temperate Quercus forests of eastern North America. Historically open understory conditions perpetuated, in part by fire, have become closed and homogenized by long‐term fire exclusion, likely impacting the groundlayer community. We explored the effects of burn season (unburned = CON, dormant season = DSB, growing season = GSB) on groundlayer (<1 m) vegetation attributes pre‐ and post‐burn. The difference (post‐burn – pre‐burn) in tree cover was greater in GSB (+8.22%) than DSB (+1.24%) and CON (+0.15%), while the change in forb cover was greater in GSB (+1.17%) than CON (−0.15%). Minor effects of burning were observed in diversity metrics, with the change in forb richness greater in GSB (+0.11 species/m2) than CON (−0.78 species/m2), while the change in tree richness was greater in GSB (+1.11 species/m2) than DSB (−1.11 species/m2) and CON (−1.67 species/m2). Nonmetric multi‐dimensional scaling provided evidence that between pre‐ and post‐burn, modest composition shifts in DSB and GSB were associated with more open conditions and lower litter depth. Understory composition did not vary among burn treatments pre‐burn, while post‐burn, composition differed significantly between CON and DSB and DSB and GSB. However, overall, a growing season burn had relatively minor effects on the groundlayer community compared to a dormant season burn. A better understanding of multiple factors affecting groundlayer response to burning is critical to the effective use of prescribed burning in attaining restoration goals.

Changes in canopy cover and forest structure following dormant season and early growing season prescribed burns in the Southern Appalachians, USA

BackgroundFire seasonality is important for forest managers to consider when restoring historical disturbance regimes and recovering native ecosystem structure and composition, but it is less understood and less frequently studied than other aspects of fire ecology. In the Southern Appalachians, historical fires likely occurred most often in late spring and early summer when fuels were dry and canopy conditions were conducive to fire; however, most prescribed fires today occur during the dormant season (January–March). Because fire behavior can vary seasonally, it is important for forest managers to understand the practical applications of fire season in order to burn at a time that meets management objectives. Therefore, we investigated the effect of fire seasonality on forest structure and land cover diversity in the Southern Appalachians.ResultsUsing a complete randomized block design, we analyzed leaf-on canopy cover imagery with ArcGIS Pro to compare canopy cover and forest structure between growing and dormant season burns. We compared imagery between three blocks, each with an unburned control unit, dormant season burn, and growing season burn, and found an average of 8.84% (SE = ± 1.46) reduction in canopy cover in growing season treatment units from pre-burn (2017) to post-burn (2019) compared to 5.21% (SE = ± 1.51) reduction in dormant season treatment units and 0.01% (SE = ± 0.009) reduction in unburned controls. Canopy cover reductions corresponded with substantial increases in early- and mid-successional habitat, edge length, and land cover diversity — especially in growing season burn treatment units.ConclusionsOur results indicate that early growing season burns are more effective than dormant season burns at enhancing forest structural heterogeneity. Early growing season burns, therefore, may be a viable option for forest managers looking to expand their burn season and achieve restoration and management goals faster than traditional dormant season burns.

Effects of burn season on fire-excluded plant communities in the southern Appalachian Mountains, USA

Following decades of fire exclusion, managers are increasingly implementing prescribed fire in southern Appalachian forests. To date, the use of prescribed fire in the region has often been focused on reducing hazardous fuel loads and has typically occurred in the dormant season. Understanding the effects of burning in different periods of plant growth may reveal how burn season influences patterns of vegetative succession. In this study, we compared the effects of prescribed burn treatments conducted in the dormant season (January-early April) vs. the early growing season (mid-late April) on changes in plant abundance by understory, midstory, and overstory forest strata. Plant groups were distinguished by growth habit, stem origin, functional characteristics, and species of management interest (red maple (Acer rubrum L.) and mountain laurel (Kalmia latifolia L.)). Burn season had minimal effect on understory cover, density, richness, or diversity. In the midstory, early growing season burns were more effective in reducing shrub density than dormant season burns (−1,585 ± 188 ha−1 vs. −813 ± 240 ha−1, respectively), with greater differences among smaller stems. Early growing season burns also reduced midstory red maple density to a greater degree than dormant season burns (−356 ± 57 ha−1 vs. −219 ± 69 ha−1), a response that was not observed among other mesophytic hardwood species. Burning slightly reduced canopy cover, but neither canopy cover nor overstory density response varied by burn season. Our results demonstrate that managers may find increased opportunities to promote forest restoration objectives in the southern Appalachians by extending the use of prescribed fire into the early growing season.

How do fire behavior and fuel consumption vary between dormant and early growing season prescribed burns in the southern Appalachian Mountains?

BackgroundDespite the widespread use of prescribed fire throughout much of the southeastern USA, temporal considerations of fire behavior and its effects often remain unclear. Opportunities to burn within prescriptive meteorological windows vary seasonally and along biogeographical gradients, particularly in mountainous terrain where topography can alter fire behavior. Managers often seek to expand the number of burn days available to accomplish their management objectives, such as hazardous fuel reduction, control of less desired vegetation, and wildlife habitat establishment and maintenance. For this study, we compared prescribed burns conducted in the dormant and early growing seasons in the southern Appalachian Mountains to evaluate how burn outcomes may be affected by environmental factors related to season of burn. The early growing season was defined as the narrow phenological window between bud break and full leaf-out. Proportion of plot area burned, surface fuel consumption, and time-integrated thermocouple heating were quantified and evaluated to determine potential relationships with fuel moisture and topographic and meteorological variables.ResultsOur results suggested that both time-integrated thermocouple heating and its variability were greater in early growing season burns than in dormant season burns. These differences were noted even though fuel consumption did not vary by season of burn. The variability of litter consumption and woody fuelbed height reduction were greater in dormant season burns than in early growing season burns. Warmer air temperatures and lower fuel moisture, interacting with topography, likely contributed to these seasonal differences and resulted in more burn coverage in early growing season burns than in dormant season burns.ConclusionsDormant season and early growing season burns in southern Appalachian forests consumed similar amounts of fuel where fire spread. Notwithstanding, warmer conditions in early growing season burns are likely to result in fire spread to parts of the landscape left unburnt in dormant season burns. We conclude that early growing season burns may offer a viable option for furthering the pace and scale of prescribed fire to achieve management objectives.

Seasonality of Biennial Burning Has No Adverse Effects on Mature Longleaf Pine Survival or Productivity

Emulating natural disturbance has become an increasingly important restoration strategy. In the fire-maintained woodlands of the southeastern United States, contemporary restoration efforts have focused on approximating the historical fire regime by burning at short intervals. Due to concerns over escape and damage to mature trees, most prescribed burning has occurred in the dormant season, which is inconsistent with the historical prevalence of lightning-initiated fire in the region. This discordance between contemporary prescribed burning and what is thought to be the historical fire regime has led some to question whether dormant season burning should remain the most common management practice; however, little is known about the long-term effects of repeated growing season burning on the health and productivity of desirable tree species. To address this question, we report on a long-term experiment comparing the effects of seasonal biennial burning (winter, spring, and summer) and no burning on the final survival status, height, diameter, and volume growth of 892 mature longleaf pine (Pinus palustris) over 23 years in three mature even-aged stands in southern Alabama, United States. Overall, longleaf pine survival across all treatments averaged 81 ± 2% [s.e]. Among seasonal burn treatments, survival was highest in the spring burns (82 ± 4%) but did not vary significantly from any other treatment (summer – 79 ± 4%, winter – 81 ± 4%, unburned – 84 ± 4%). However, survival was statistically influenced by initial diameter at breast height, as survival of trees in the largest size class (30 cm) was 40% higher than trees in the smallest size class (5 cm). Productivity of longleaf pine was not significantly different among treatment averages in terms of volume (38.9–44.1 ± 6.0 m3 ha–1), diameter (6.0–6.7 ± 0.3 cm), and height (2.5–3.4 ± 0.4 m) growth. Collectively, our results demonstrate that burning outside the dormant season will have little impact on mature longleaf pine survival and growth. This finding has important implications for the maintenance of restored southeastern woodlands, as interest in burning outside the dormant season continues to grow.

Environmental and Management Effects on Demographic Processes in the U.S. Threatened Platanthera leucophaea (Nutt.) Lindl. (Orchidaceae).

Populations of the U.S. threatened orchid, Platanthera leucophaea, are restricted to fragmented grassland and wetland habitats. We address the long-term (1998–2020) interactive effects of habitat (upland prairie vs. wetland), fire management (burned vs. unburned) and climatic variation, as well as pollination crossing effects, on population demography in 42 populations. Our analysis revealed the consistent interactive effects of habitat, dormant season burning, and climatic variation on flowering, reproduction, and survival. Burning increased flowering and population size under normal or greater than normal precipitation but may have a negative effect during drought years apparently if soil moisture stress reduces flowering and increases mortality. Trends in the number of flowering plants in populations also correspond to precipitation cycles. As with flowering and fecundity, survival is significantly affected by the interactive effects of habitat, fire, and climate. This study supports previous studies finding that P. leucophaea relies on a facultative outcrossing breeding system. Demographic modeling indicated that fire, normal precipitation, and outcrossing yielded greater population growth, and that greater fire frequency increased population persistence. It also revealed an ecologically driven demographic switch, with wetlands more dependent upon survivorship than fecundity, and uplands more dependent on fecundity than survivorship. Our results facilitate an understanding of environmental and management effects on the population demography of P. leucophaea in the prairie region of its distribution. Parallel studies are needed in the other habitats such as wetlands, especially in the eastern part of the range of the species, to provide a more complete picture.

Buried but unsafe – Defoliation depletes the underground storage organ (USO) of the mesic grassland geophyte, Hypoxis hemerocallidea

Mesic grasslands in South Africa (> 650 mm a − 1 MAP) are rich in herbaceous forbs, which outnumber grass species by more than 5 to 1. Many of these forbs are geophytes with underground storage units (USOs), such as thickened rootstocks, rhizomes, bulbs, or corms, that provide resources (non-structural carbohydrates, minerals, and water) enabling them to resprout after dry, frosty winters, and fire. However, despite their extensive biomass and reserves ostensibly protected underground, mesic grassland geophytes can be severely depleted or extirpated by chronic trampling and grazing of their aerial parts by livestock. This study examined a possible explanation for the demise of grassland geophytes in overgrazed grassland by investigating, in a pot trial, whether the growth of a geophyte and the size of its USOs are negatively affected by simulated green leaf loss. In a 2 × 2 factorial (clipped vs. unclipped x spring regrowth in the dark vs. light), five replicate plants of Hypoxis hemerocallidea, a common mesic grassland geophyte that resprouts from a corm, were subject to six severe (clipped to 80 mm) defoliations during the growing season and regrown in spring under full or restricted light to measure stored reserve contribution to regrowth. Defoliated plants were resilient to defoliation during the growing season, matching the total biomass production of unclipped plants, though cutting reduced the number of leaves by ¬60% and flowers by almost 85%. Spring regrowth on stored reserves equalled that from reserves plus concurrent photosynthesis, indicating the value of USOs for regrowth. However, there was a marked carry-over effect of previous season defoliation, resulting in a one-third reduction in shoot growth and 40% fewer inflorescence in spring. Crucially, corm mass was more than halved by clipping, which resulted in lower spring biomass and inflorescence production. It was concluded that buried stored reserves are not protected from recurrent defoliation and mechanical damage to aerial plant parts and that continued diminishment of USOs under chronic disturbance by overgrazing or frequent mowing would weaken and likely eventually kill plants, reducing overall forb species richness. Lenient management by infrequent summer mowing or grazing at moderate stocking rates combined with periodic rotational full season resting and dormant-season burning is recommend to maintain the USOs and vigour of grassland geophytes in mesic grassland.

Overstory Longleaf Pines and Hardwoods Create Diverse Patterns of Energy Release and Fire Effects During Prescribed Fire

Litter from pine trees in open woodlands is an important fuel for surface fires, but litter from hardwood species may quell fire behavior. Lower intensity fires favor hardwood over longleaf pine regeneration, and while overstory hardwoods are important sources of food and shelter for many wildlife species, too many could result in canopy closure and a loss of ground layer diversity. Although some researchers have found synergies in fire effects when leaves of different species are combined, field tests of effects of tree guild diversity on fire behavior are lacking from the literature. We used neighborhood modeling to understand how diverse overstory trees in longleaf pine forests affect fire radiative energy density (FRED), and to determine the effect on top-kill of shrub-form hardwood trees. We measured the effects of three guilds of overstory trees (longleaf pine, upland oaks, and mesic oaks) on FRED, and related FRED to post-fire damage in four guilds of understory hardwoods (sandhill oaks, upland oaks, mesic oaks, and fleshy-fruited hardwoods). We found that FRED increased 33–56% near overstory longleaf pine but decreased 23–37% near overstory mesic oaks. Additive models of FRED performed well and no synergies or antagonisms were present. Seventy percent of stems of understory hardwoods survived fire with energy release typical of dormant-season fires in canopy gaps and near overstory mesic oaks. We also found that among understory trees >2 m tall, upland and sandhill oaks were more likely than mesic oaks or fleshy-fruited hardwoods to avoid top-kill. We conclude that neighborhood models provide a method to predict longleaf pine forest structure and composition that allows for the ecological benefits of overstory hardwoods while maintaining ground-layer diversity. To maintain hardwood control, fire practitioners may need to select fire weather conditions to increase fire behavior especially during dormant-season burns.

Winter roost selection of Lasiurine tree bats in a pyric landscape.

Day-roost selection by Lasiurine tree bats during winter and their response to dormant season fires is unknown in the southeastern United States where dormant season burning is widely applied. Although fires historically were predominantly growing season, they now occur in the dormant season in this part of the Coastal Plain to support a myriad of stewardship activities, including habitat management for game species. To examine the response of bats to landscape condition and the application of prescribed fire, in the winter of 2019, we mist-netted and affixed radio-transmitters to 16 Lasiurine bats, primarily Seminole bats (Lasiurus seminolus) at Camp Blanding Joint Training Center in northern Florida. We then located day-roost sites to describe roost attributes. For five Seminole bats, one eastern red bat (Lasiurus borealis), and one hoary bat (Lasiurus cinereus), we applied prescribed burns in the roost area to observe bat response in real-time. Generally, Seminole bats selected day-roosts in mesic forest stands with high mean fire return intervals. At the roost tree scale, Seminole day-roosts tended to be larger, taller and in higher canopy dominance classes than surrounding trees. Seminole bats roosted in longleaf (Pinus palustris), slash (Pinus elliotii) and loblolly pine (Pinus taeda) more than expected based on availability, whereas sweetbay (Magnolia virginiana), water oak (Quercus nigra) and turkey oak (Quercus laevis), were roosted in less than expected based on availability. Of the seven roosts subjected to prescribed burns, only one male Seminole bat and one male eastern red bat evacuated during or immediately following burning. In both cases, these bats had day-roosted at heights lower than the majority of other day-roosts observed during our study. Our results suggest Seminole bats choose winter day-roosts that both maximize solar exposure and minimize risks associated with fire. Nonetheless, because selected day-roosts largely were fire-dependent or tolerant tree species, application of fire does need to periodically occur to promote recruitment and retention of suitable roost sites.

Frequent burning maintained a stable grassland over four decades in the Drakensberg, South Africa

The mesic montane grasslands of the uKhahlamba-Drakensberg, which produce cured flammable fuel, have evolved under and are sustained by recurrent fires. The Brotherton burning trial (12 replicated treatments) was established at Cathedral Peak (1 890 m asl) in 1980 to understand how burn season and frequency control the composition and diversity of the montane catchment grassland. Multivariate methods were used to examine the long-term (almost 40 years). compositional stability under different burning regimes. The species composition deviated steadily and markedly from the initial state (Bray–Curtis dissimilarity) by 43.4 ± 9.32% with quinquennial burning (alternating autumn/spring) and by 64.6 ± 2.24% with attempted fire exclusion (three unplanned burns). Composition was rapidly transformed (by 53.1 ± 4.6%) by biennial summer burning (discontinued in 1991). Dominance shifted from Themeda triandra to other grasses (Stiburus alopecuroides, Tristachya leucothrix, Harpochloa falx) with biennial summer and infrequent burning. In contrast, regular dormant season burning annually or biennially (in autumn, winter, or spring) maintained a stable grassland close to the original composition (mean deviation 23.08%). Burning homogenised the composition, overriding the initial extant small-scale spatial variation. Results support the current practice to burn biennially in the dormant season to maintain stable grassland in the Drakensberg catchments.

Carbon starvation is absent regardless of season of burn in Liquidambar styraciflua L.

In the Southeastern United States, the function and stability of pine ecosystems depends on frequent low intensity fires. One of the critical effects of frequent fire is the inhibition of hardwood competition by removing above-ground stems (top-kill). Previous long-term studies have correlated early growing season burns with higher understory mortality when compared to dormant season burns. Seasonal differences in mortality from insufficient carbon reserves in roots after leaf flush were posited as the mechanism but this was never explicitly tested. In this experiment, we burned two-year-old pot-grown sweetgums (Liquidambar styracifluaL.) in the dormant season (February), growing season (May), and compared their physiological responses to plants that were unburned. By the end of the first post-burn growing season, mortality was higher after the dormant season burn than the growing season burn and unburned trees had nearly twice the mass of either the burned treatments. Tissue starch concentrations were similar across all treatments highlighting the resiliency of sweetgum carbon stocks to recover from above-ground stem removal regardless of season. We showed the critical importance of top-killing stems regardless of season of burn. Our results further suggest that dormant season fires can be more lethal to young sweetgum, possibly due to susceptibility of tender new shoots to freezing damage.

Annual Understory Plant Recovery Dynamics in a Temperate Woodland Mosaic during a Decade of Ecological Restoration

Temperate woodlands are one of the world's ecosystems in greatest need of ecological restoration, but relatively little is known about their floristic recovery dynamics over decadal timescales. From 2000 to 2012, we monitored understory plant communities in a woodland mosaic in Missouri, USA, as it underwent restoration via prescribed, dormant-season burning and mechanical thinning of red cedar (Juniperus virginiana) and exotic shrubs. Native species richness increased linearly by 36% over this time period, driven primarily by an influx of forb species in thin-soiled upland areas where red cedar was removed. Floristic quality also increased with differential dynamics across local communities; forest floristic quality saturated quickly whereas floristic quality increased gradually over the time series in woodlands and red cedar–dominated woodlands. Species that underlay these patterns were mainly ruderal or matrix forbs and grasses with little dependence on intact, undisturbed habitats. In contrast, conservative species were rare or absent. This case study suggests that understory plant recovery dynamics may be slower in harsher and more degraded sites and faster in more mesic sites within a woodland mosaic. Our observations set a benchmark for woodland understory plant recovery dynamics and indicate that a future restoration challenge is to prioritize the managed translocation of dispersal-limited, conservative species.

Short-term response to season of burn by amphibians and reptiles in a Florida longleaf pine – wiregrass sandhill

We investigated how herpetofauna respond to burning and burn season in longleaf pine (Pinus palustris Mill.) sandhills by contrasting preburn species richness, diversity, and evenness and captures of six reptile and six amphibian species to the first (Y+1) or second (Y+2) year after burn or between dormant-season burns (DSB) and growing-season burns (GSB). Responses to burning overall or burn season were inconsistent among species; several showed no response, whereas others responded positively or negatively. Most responses were evident only in Y+1. Reptile species richness, diversity, and evenness responses were not detected. Amphibian richness increased after burning overall; diversity and evenness decreased more in GSB than in DSB in Y+1. Southern toad (Anaxyrus terrestris (Bonnaterre, 1789)) captures increased and Florida crowned snake (Tantilla relicta Telford, 1966) captures decreased following burns overall in Y+1. Ground skink (Scincella lateralis (Say in James, 1823)) captures increased more in DSB than GSB in Y+1. Florida gopher frog (Lithobates capito (LeConte, 1855)) and southeastern five-lined skink (Plestiodon inexpectatus; Taylor, 1932) captures increased, and oak toad (Anaxyrus quercicus (Holbrook, 1840)) decreased more in GSB than DSB in Y+2. Responses were likely due to changes in aboveground activity affecting captures or (for amphibians especially) annual variability in captures unrelated to burns. Our results indicated that reptiles and amphibians of sandhills are resilient to short-term effects of burning overall and burn season.

Growing or dormant season burns: the effects of burn season on bee and plant communities

Habitat management can play a critical role in increasing and maintaining species diversity, but timing of management techniques can have significant effects on biodiversity management. In tallgrass prairie systems, prescribed burns are a common method to promote diversity. Managers prefer winter dormant season burns but this timing differs significantly from the historic growing season burns that helped shape this community, and it is largely unexplored whether changing burn season has significant effects on higher trophic levels. Here we investigate how the timing of such burns affects the bee communities and their resources. Depending on life history traits such as above or below ground nesting, timing of fire management can have differential effects on bee diversity. In 2016 and 2017, bees were collected from prairies in south-central Illinois using active netting, pan traps, and vane traps, and measurements of plant species, flower abundance and ground cover were recorded. While both burns showed significant improvement over unburned areas, growing season burns had the greatest total bare ground area and an increase in overall bee abundances. This may suggest long term benefits of growing season burns. The results suggest that growing season burns are beneficial for bees, and the use of either burn season can be utilized for land management.

Breeding bird response to season of burn in an upland hardwood forest

Upland hardwood forest managers are increasingly burning during the growing-season in hopes of improving wildlife habitat and attaining or accelerating other restoration goals, highlighting the need for research addressing how season of burning affects wildlife, including breeding birds. We used 1-ha strip transects in nine units before (2011) and after (2013–2016) treatments to experimentally assess how breeding birds respond to early growing-season (26 April 2013; GSB) and dormant-season (5 March 2014; DSB) burns, and controls (C). Burn effects on forest structure were minor and transitory, regardless of burn season. Burns did not affect overstory or midstory tree basal area or density; shrub cover did not significantly differ among treatments, but within GSB and DSB it decreased for 1–2 years post-burn. A trend of reduced leaf litter depth immediately following both burn treatments was apparent, and recovery was rapid. Percent canopy cover decreased slightly in GSB within four years post-burn. Total bird species richness and density did not differ among treatments or years, and no treatment × year interaction effects were detected. A treatment effect was detected for one of the 10 species tested; Red-bellied woodpecker density was greater in GSB than C in 2013 and 2015. No treatment × year interaction effect was detected for any tested species. Density of birds within the tree-, cavity-, and shrub and midstory-nesting guilds were not detectably affected by either burn treatment, but ground-nester density was lower in GSB and DSB than C in 2014. Our results indicate that single, low-intensity burns, regardless of burn season, are not an effective tool in creating suitable forest structure for disturbance-dependent breeding bird species, or changing breeding bird community composition. In the short-term, substantial forest overstory reduction by timber harvests or high-severity burns will likely be required to improve forest conditions for disturbance-dependent species, and to increase species richness and abundance of breeding birds.

White Oak (Quercus alba) Response to Thinning and Prescribed Fire in Northcentral Alabama Mixed Pine–Hardwood Forests

AbstractStrong white oak sawtimber markets, partially attributed to the stave and cooperage industries, are encouraging forest managers to re-examine silvicultural practices for white oak (Quercus alba). We examined recruitment and retention of white oak in mixed oak–pine stands on the William B. Bankhead National Forest in northcentral Alabama. Stands were subjected to three thinning levels (residual basal areas of 75 ft2/ac, 50 ft2/ac, and no thinning) and three fire frequencies (dormant season burns of none, one, three fires) in a factorial design. Both thinning treatments reduced overstory white oak tree densities, and fire had no effect on densities. For all reproduction height classes, regardless of thinning treatment, three prescribed burns increased white oak densities; thinned and burned stands had larger white oak seedling sprouts than those thinned with no burn. However, white oak reproduction height was primarily less than 2 ft tall, and seedlings larger than 4 ft tall were reduced. Thinning with one fire resulted in the highest densities of large white oak reproduction (4 ft tall up to 1.5 in. dbh). Red maple reproduction was the dominant competitor in all treatments and is positioned to dominate the reproduction cohort without additional tending treatments.

Optimizing reproductive opportunity for Florida grasshopper sparrows: When to burn?

ABSTRACTThe critically endangered Florida grasshopper sparrow (Ammodramus savannarum floridanus) is dependent on dry prairies managed with prescribed fires that are applied every 1–3 years. Timing of prescribed fires shifted from predominantly the dormant season (Jan–Mar) to the transition (Apr–Jun) and growing (Jul–Aug) seasons starting in the early 2000s to better mimic natural fire regimes. Populations have continued to decline, however, and the presumption that natural fire regimes are beneficial to the small extant Florida grasshopper sparrow populations needs to be evaluated. We monitored 167 Florida grasshopper sparrow nests across 6 fire treatments at Three Lakes Wildlife Management Area, Osceola County, Florida, USA, 2013–2016, and investigated the role of fire season and interval on clutch initiation date, nest site selection, nest survival, productivity, and nestling mass. Clutch initiation was delayed by ≥33 days in prairies burned during the current transition season and we found no nests in prairies burned during the current growing season. Transition season burns also overlapped with the early breeding season, which could result in the destruction of nests. Clutches were larger at the beginning of the breeding season and nestling mass was highest in the middle of the breeding season, indicating that early and mid‐season nests may be more valuable to annual fecundity than late‐season nests. Florida grasshopper sparrows nested in prairies burned in the current dormant season or previous growing season more than expected based on their availability and as expected or less than expected in prairies burned in the current transition season, previous transition season, previous dormant season, or >2 years ago. However, we found no effect of fire treatment on daily nest survival, clutch size, number of fledglings per successful nest, or nestling mass. We recommend dormant season burning in prairies occupied by Florida grasshopper sparrows to increase reproductive potential given the subspecies’ small population and the importance of each nest attempt to population growth. We recommend transition or growing season burns in unoccupied adjacent prairies to maintain high‐quality dry prairie for nesting in future years. Prescribed fire management goals for Florida grasshopper sparrow populations should be guided by demographic responses rather than natural fire regimes. © 2019 The Wildlife Society.

Season of burn effects on vegetation structure and composition in oak-dominated Appalachian hardwood forests

Previous research indicates that low-intensity single or multiple prescribed burns in oak-dominated upland hardwood forest do not substantially change stand structure or species composition of the arborescent regeneration layer, leading managers and ecologists to suggest that burns during the growing-season may better achieve restoration goals. We examined season of burn effects on dry-mesic oak-hickory forests in the southern Appalachian Mountains, North Carolina. Treatments included: (1) control (CON); (2) dormant-season burn (DSB), and (3) growing-season burn (GSB). Prior to burning and again after three growing seasons post-burn, we inventoried the forest overstory (stems ≥ 25 cm dbh), subcanopy (stems ≥ 5 and <25 cm dbh), sapling (stems ≥ 1.2 m and < 5 cm dbh), and seedling (stems < 1.2 m) strata. We found no effect of prescribed fire, regardless of burn season, on stem density or basal area of the overstory and subcanopy strata, leaving the light environment in the forest understory relatively unchanged. In general, treatment effects on the sapling and seedling layers were limited to the mesophytic species group, where seedling density post-burn was greater in GSB than both CON and DSB and sapling density post-burn was lower than pre-burn in DSB and GSB. Mortality of individually-tagged seedlings three growing seasons post-burn did not differ among treatments for the red oak, white oak, red maple, mesophytic, and pyrophilic species groups, and averaged 29.0, 28.5, 31.8, 29.3, and 25%, respectively. This study provides support for the notion that a single fire in a closed-canopy oak-hickory forest has little effect on forest structure or regeneration composition, regardless of the burn season. Prescribed fires should be repeated in subsequent years to assess whether the effects of burn season are amplified under a periodic burning regime.

Seasonal prescribed fire variation decreases inhibitory ability of Poa pratensis L. and promotes native plant diversity

Global biodiversity is threatened by invasive plant species. Without a thorough understanding of effective management strategies, minimizing their impacts while improving native species diversity will be challenging. Burning in fire-prone landscapes has been successful for managing invasive species and increasing native biodiversity, but it is unclear how specific fire regimes improve restoration practices in novel ecosystems where invasive plants have a similar growth phenology to native plants. We investigated fire as a restoration practice in the Northern Great Plains to decrease the cover of Kentucky bluegrass Poa pratensis (bluegrass), a perennial cool-season invasive grass phenologically similar to dominant native cool-season grasses, by 1) evaluating season of burn (early-growing season, late-growing season, and dormant season) in a field experiment to test differences in plant community composition and 2) manipulating fine fuels (3000–5000 kg ha−1) in an experimental approach to determine the effects of fire on plant survivability of selected native grasses and bluegrass. Bluegrass cover decreased 27% on all field burned plots the first year post-fire. Three years post-fire, late-growing season and dormant season treatments had 35% less bluegrass, whereas the early-growing season treatment was not significantly different from the control. Overall, fire altered the native plant community, with native plants more associated with burned plots. However, native plant community changes were only evident three years post-fire in late-growing season and dormant season burn treatments. In the experimental approach, native grasses and bluegrass experienced high rates of mortality (40–50%) at fuel loads above 4000 kg ha−1 and heat dosages above 30,000 °C·sec, features commonly associated with early-growing season burns. Therefore, early-growing season burns meant to reduce bluegrass may also impact native plants dominant in the region. Invasive species management is complicated in novel ecosystems when invasive plants have similar growth phenologies to native species. Control efforts should consider how different management strategies impact invasive and native plants alike. We found that late-growing season and dormant season burns, along with higher fuel loads, decreased bluegrass cover. Determining mechanisms of control in fire-prone landscapes is a crucial step to improving invasive plant control and increasing native biodiversity.

Legacy effects of prescribed fire season and frequency on soil properties in a Pinus resinosa forest in northern Minnesota

Abstract Prescribed fire is a widely used ecosystem management approach and the vast majority of burns are conducted during the dormant season; however, these burning conditions (and therefore the type and persistence of fire effects) often differ from those of natural or historical fire regimes. Therefore, we leveraged a historical study (conducted 1959–70) with remeasurements in 2015 to evaluate effects of fire season (dormant, summer), frequency (annual, biennial, periodic), and their interaction on soil physical and chemical properties in a red pine (Pinus resinosa Ait.) forest in northern Minnesota, USA. To protect against across-year differences in sampling and analysis, we used a meta-analysis approach to evaluate treatment effects on soil properties. We also used non-metric multidimensional scaling (NMDS) ordination to investigate legacy (>45 years post-fire) treatment effects. The greatest effects of fire occurred in organic horizons, and decreased with depth. In the short-term, fire decreased organic horizon depths and nitrogen (N) and increased base cations (K, Ca, Mg) and pH in the mineral soil, whereas effects on phosphorus (P) were variable. Prescribed fire treatments had legacy effects on organic horizon and mineral soil properties >45 years post-fire. In general, summer burns decreased nutrient stocks, whereas dormant season burns increased nutrient stocks, and the majority of legacy effects occurred in annual burn treatments, in both seasons. Legacy effects of summer burns decreased organic horizon depths, organic matter, nutrient stocks (N, P, K), and pH, as well as lower (0–15 cm) mineral soil N; whereas, the dormant annual burn increased Ca in the total forest floor and N and P in the upper (15–91 cm) mineral soil. In contrast, the summer annual burn increased P, whereas the dormant annual burn decreased pH in the lower mineral soil. Trends in short- and long-term effect sizes appeared to differ by season of burning and further magnified by increased fire frequency within season. Relative to dormant season burns, summer burns resulted in immediate and long-lasting desirable effects for red pine ecosystems (e.g., decreased forest floor depths and nutrient stocks) without persistent undesirable effects (e.g., increased nutrient stocks or changes in cation exchange capacity, soil texture, and bulk density) in the mineral soil. Our results suggest that summer burns may be a valuable approach to increase the variability in burn schedules representative of historical regional fire regimes in red pine forests, and may help promote soil characteristics that support overall ecosystem health.