This special issue of Fire Ecology is dedicated to furthering scientific understanding of the rol... more This special issue of Fire Ecology is dedicated to furthering scientific understanding of the role fire plays in the development and functioning of wetland ecosystems. While not initially intuitive, the concept of fire exerting significant influence on how wetland environments function has only recently become a prominent topic of discussion among researchers, although it has been recognized by the management community for some time. This new interest in determining how large scale disturbances modulate ecological processes in wetlands led to a series of invited talks at a Fire in Wetlands session during the 9 th International Association for Ecology (INTECOL) meeting in Orlando, Florida, USA, in 2012. The collection of work presented here is the product of that special session, and includes research covering diverse topics such as fire effects on wetland biogeochemistry, vegetation community structure, and wildlife dynamics. Managers' perspectives, while presented in multiple talks during the INTECOL session, are captured here in discussions of the management implications of the research presented. This introduction summarizes each of the papers included in this special issue and is organized into topics of biogeochemistry, vegetation, community dynamics, and wildlife dynamics. The summarizing comments include key messages for management and future directions for research on fire in wetlands.
Extreme-temperature events have consequences for human health and mortality, forest disturbance p... more Extreme-temperature events have consequences for human health and mortality, forest disturbance patterns, agricultural productivity, and the economic repercussions of these consequences combined. To gain insight into whether extreme-temperature events are changing in light of global climate dynamics, the annual numbers of high-temperature days (those with temperatures higher than 20, 22.5, and 25 • C at 850 hPa) were analyzed across southern Europe from the years 1978 to 2012. A significant increase in the frequency of these days was found in many areas over the time period analyzed, and patterns in the spatial distribution of these changes were identified. We discuss the potential consequences of the increases in high-temperature days with regards to forest fire risk, human health, agriculture, energy demands, and some potential economic repercussions.
Study Site A grid of plots 250m x 250m was drawn over the length of the island in ArcView. The ce... more Study Site A grid of plots 250m x 250m was drawn over the length of the island in ArcView. The center of each plot was determined and GPS coordinates recorded. From each plot center, 2 nested plots of radii 40m and 80m were established. Two Increment cores per tree were collected from two trees within the 40m radius nested plots. We selected the largest slash pine trees in the plot in an attempt to obtain the longest possible chronology. Within the 80m plots, partial cross sections were extracted from fire scars as close to the ground as possible (Fig. 2). When possible, two trees were sampled within each plot. In order to increase sample size, trees were also opportunistically sampled between plots when trees with scars were found. Fire Scars We collected partial cross sections (Fig. 6&7) from 55 trees at the south end of the island. Of these, 19 were not usable due to high levels of decomposition. The remaining samples were compared with fire history records maintained by USFWS si...
1. The imperiled frosted elfin butterfly, Callophrys irus Godart, is restricted to frequently dis... more 1. The imperiled frosted elfin butterfly, Callophrys irus Godart, is restricted to frequently disturbed habitats where its larval host plants, Lupinus perennis L. and Baptisia tinctoria (L.) R. Br. reside. C. irus pupae are noted to reside in the leaf litter and soil, which may allow them to escape direct mortality by fire, a major force of disturbance in many areas they inhabit. The ability (or lack of an ability) to cope with prescribed fire is a critical factor to consider in developing land management and conservation strategies in the few areas that this species remains. 2. C. irus pupa location was sampled from a well-known population at a Florida state forest with an active history of prescribed fire management. Survival of experimental surrogate butterfly pupae to the heat pulse radiated into the soil as a result of prescribed fire was tested using controlled water bath experiments and a series of prescribed fire field experiments. 3. 12 C. irus pupae were excavated from 201...
Soil CO2 efflux (Rs) is a significant flux of carbon dioxide from ecosystem soils to the atmosphe... more Soil CO2 efflux (Rs) is a significant flux of carbon dioxide from ecosystem soils to the atmosphere and is a critical component of the total ecosystem carbon budget. Rs fluxes are comprised of autotrophic (Ra) sources of CO2 produced by plant roots and associated rhizosphere fungi and heterotrophic (Rh) sources of CO2 produced by aerobic soil microbes. A variety of forest management activities, including prescribed fire and mechanical fuels mastication treatments have been shown to significantly influence Rs rates in forests of the Western United States (US), yet these relationships are not well known for southeastern US forests. Prescribed fire is one of the most prevalent forest management tools employed in the southeastern US, and mechanical fuels treatments are becoming more common in the region as efforts to mitigate potential wildfire behavior in the wildland urban interface grow. Given that many of these forests provide habitat for endangered species, understanding the implic...
Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone u... more Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone uplands. Rare occurrence and difficulty of access have limited efforts to understand impacts of wildfires fires in wetlands. Following a 2009 wildfire, we measured tree mortality and structural changes in wetland forest patches. Centers of these circular landscape features experienced lower fire severity, although no continuous patch-size or edge effect was evident. Initial survival of the dominant tree, pondcypress (Taxodium distichum var. imbricarium), was high (>99%), but within one year of the fire approximately 23% of trees died. Delayed mortality was correlated with fire severity, but unrelated to other hypothesized factors such as patch size or edge distance. Tree diameter and soil elevation were important predictors of mortality, with smaller trees and those in areas with lower elevation more likely to die following severe fire. Depressional cypress forests typically exhibit increasing tree size towards their interiors, and differential mortality patterns were related to edge distance. These patterns result in the exaggeration of a dome-shaped profile. Our observations quantify roles of fire and hydrology in determining cypress mortality in these swamps, and imply the existence of feedbacks that maintain the characteristic shape of cypress domes.
The southern region of the U.S. uses prescribed fire as a management tool on more of its burnable... more The southern region of the U.S. uses prescribed fire as a management tool on more of its burnable land than anywhere in the U.S., with ecosystem restoration, wildlife habitat enhancement, and reduction of hazardous fuel loads as typical goals. Although the region performs more than 50,000 prescribed fire treatments each year, evaluation of their effects on wildfire suppression resources or behavior/effects is limited. To better understand trends in the use and effectiveness of prescribed fire, we conducted a region-wide survey of 523 fire use practitioners, working on both public and private lands. A 1-2 year prescribed fire interval was consistently viewed as effective in decreasing wildfire ignitions, behavior, and severity, as well as reducing suppression resources needed where wildfire occurred. Yet fewer than 15% of practitioners viewed burn intervals of 3-4 years as effective in reducing ignitions, underscoring the importance of high-frequency burning in vegetation communities where fuel recovery is rapid. Public lands managers identified limited budget and staffing as major institutional impediments to prescribed fire, in contrast to private individuals, more of whom chose liability as a key challenge. Differences in responses across ownership type, state, and vegetation type call for a broader perspective on how fire managers in the southern U.S. view prescribed fire.
Patterned landscapes are often evidence of biotic control on geomorphic processes, emerging in re... more Patterned landscapes are often evidence of biotic control on geomorphic processes, emerging in response to coupled ecosystem processes acting at different spatial scales. Self-reinforcing processes at local scales expand patches, while self-inhibiting processes, operating at a distance, impose limits to expansion. In Big Cypress National Preserve (BICY) in southwest Florida, isolated forested wetland depressions (cypress domes) appear to be evenly distributed within a mosaic of short-hydroperiod marshes and pine uplands. To test the hypothesis that the apparent patterning is regular, we characterized frequency distributions and spatial patterns of vegetation communities, surface and bedrock elevation, and soil properties (thickness and phosphorus content). Nearest neighbor distances indicate strongly significant wetland spatial overdispersion, and bedrock elevations exhibited periodic spatial autocorrelation; both observations are consistent with regular patterning. Bedrock elevations and soil P were clearly bimodal, suggesting strong positive feedbacks on wetland patch development. Soil-surface elevations exhibited weaker bimodality, indicating smoothing of surface morphology by some combination of sediment transport, mineral reprecipitation, and organic matter production. Significant negative autocorrelation of bedrock elevations at scales similar to wetland spacing suggest the presence of distal negative feedbacks on patch expansion. These findings support the inference of regular patterning, and are consistent with the presence of local positive feedbacks among hydroperiod, vegetation productivity and bedrock dissolution. These processes are ultimately constrained by distal negative feedbacks, potentially induced by landscape scale limitations on the water volume required to enable this biogeomorphic mechanism.
Pine flatwoods forests in the southeastern US have experienced severe wildfires over the past few... more Pine flatwoods forests in the southeastern US have experienced severe wildfires over the past few decades, often attributed to fuel load build-up. These forest communities are fire dependent and require regular burning for ecosystem maintenance and health. Although prescribed fire has been used to reduce wildfire risk and maintain ecosystem integrity, managers are still working to reintroduce fire to long unburned areas. Common perception holds that reintroduction of fire in long unburned forests will produce severe fire effects, resulting in a reluctance to prescribe fire without first using expensive mechanical fuels reduction techniques. To inform prioritization and timing of future fire use, we apply remote sensing analysis to examine the set of conditions most likely to result in high burn severity effects, in relation to vegetation, years since the previous fire, and historical fire frequency. We analyze Landsat imagery-based differenced Normalized Burn Ratios (dNBR) to model the relationships between previous and future burn severity to better predict areas of potential high severity. Our results show that remote sensing techniques are useful for modeling the relationship between elevated risk of high burn severity and the amount of time between fires, the type of fire (wildfire or prescribed burn), and the historical frequency of fires in pine flatwoods forests.
Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone u... more Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone uplands. Rare occurrence and difficulty of access have limited efforts to understand impacts of wildfires fires in wetlands. Following a 2009 wildfire, we measured tree mortality and structural changes in wetland forest patches. Centers of these circular landscape features experienced lower fire severity, although no continuous patch-size or edge effect was evident. Initial survival of the dominant tree, pondcypress (Taxodium distichum var. imbricarium), was high (>99%), but within one year of the fire approximately 23% of trees died. Delayed mortality was correlated with fire severity, but unrelated to other hypothesized factors such as patch size or edge distance. Tree diameter and soil elevation were important predictors of mortality, with smaller trees and those in areas with lower elevation more likely to die following severe fire. Depressional cypress forests typically exhibit increasing tree size towards their interiors, and differential mortality patterns were related to edge distance. These patterns result in the exaggeration of a dome-shaped profile. Our observations quantify roles of fire and hydrology in determining cypress mortality in these swamps, and imply the existence of feedbacks that maintain the characteristic shape of cypress domes.
In recent decades, agencies charged with managing historic structures and sites have found dendro... more In recent decades, agencies charged with managing historic structures and sites have found dendroarchaeological studies increasingly valuable, given the ability of such studies to verify (or refute) accepted dates of construction. The Ximénez-Fatio House has well-documented historical and cultural significance for the state of Florida, as it is one of St. Augustine's oldest, best-preserved, and most studied historic properties. According to documentary sources, the two-story coquina-stone main house was reportedly built around 1797-1798, and included a one-story wing of warehouses, giving the house a distinctive ''L'' shape. Documentary evidence also suggests that a second story was added above the wing sometime between 1830 and 1842. However, after studying the building fabric itself, historical architects now believe the entire wing of the house was remodeled two decades later in the 1850s. Our goals were to: (1) determine the probable construction years for the original house and wing using tree-ring dating techniques, and (2) verify the probable construction year for the remodeling that occurred in the wing section of the house. A total of 74 core samples were extracted from longleaf pine (Pinus palustris P. Miller) timbers used to construct the house. Twenty-six were confidently crossdated both visually and statistically against each other to produce a 185-year floating tree-ring chronology. A statistically significant (p , 0.0001) correlation between our chronology and a longleaf pine chronology from Lake Louise, Georgia, anchors our chronology between 1673 and 1857. No cutting dates were obtained from the main house, but the lack of any tree rings that post-date 1798 supports the 1797 construction date. Furthermore, cutting dates obtained from beams in the first-floor wing revealed that the extensive remodeling of the wing likely occurred in the period 1856 to 1858 soon after the house had been purchased by Louisa Fatio in 1855.
... Mark J. Hainds is the Research Coordinator for The Longleaf Alliance and a Research Associate... more ... Mark J. Hainds is the Research Coordinator for The Longleaf Alliance and a Research Associate with Auburn University. ... Pp. 948 in S. Jose, EJ Jokela, and DL Miller, eds., The Longleaf Pine Ecosystem: Ecology, Silviculture, and Restoration. ...
Plantations are the most common means of reforestation following stand-replacing wildfires. As wi... more Plantations are the most common means of reforestation following stand-replacing wildfires. As wildfires continue to increase in size and severity as a result of fire suppression or climate change, establishment of plantations will likely also increase. Plantations' structural characteristics, including dense, uniform spacing and abundant ladder fuels, present significant wildfire hazards. Large-scale fuels reduction techniques may be necessary to reduce potential fire behavior in plantations and to protect surrounding forests. In the present study, four different manipulations aimed at reducing potential fire behavior in a Sierra Nevada pine plantation are compared. The treatments include: mechanical shredding, or mastication, of understorey vegetation and small trees; mastication followed by prescribed fire; fire alone; and controls. Fire behavior modeling shows that mastication is detrimental whereas prescribed fire is effective in reducing potential fire behavior at moderate to extreme weather conditions. Predicted fire behavior was compared with actual values from the prescribed burns in an effort to explore the limitations of fire modeling. Fire behavior predictions were similar to field observations in the more structurally homogeneous stands, but differed greatly where mastication created forest openings and patchy fuels distributions. In contrast to natural stands, the homogeneity of pine plantations make the results of the present work applicable to other regions such as the south-eastern US, where similar fuels reduction techniques are used to increase fire-resistance and stand resilience.
Although charcoal represents a relatively minor portion of available biomass burned in wildfires ... more Although charcoal represents a relatively minor portion of available biomass burned in wildfires and prescribed burns, its recalcitrant properties confer residence times ranging from centuries to millennia, with significance for carbon sequestration in frequently burned forests. Here, we determined whether charcoal formation differed between the two most common prescribed fire spread patterns in southern forests: head (with the wind) and backing (against the wind). Pine wood samples were distributed randomly within a mesic flatwoods burn unit in north-central Florida, and subjected either to a head fire (n ¼ 34) or a backing fire (n ¼ 34). Backing fires formed more than twice as much charcoal as head fires (1.53 v. 0.38% of available biomass), presumably because of differences in residence times, oxygen availability and fire intensity between the two fire spread patterns. These results suggest that the contribution of charcoal to ecosystem carbon sequestration is greater when flatwoods forests are burned against the prevailing wind direction, and that further investigation of these trends is warranted.
Mechanical fuel hazard reduction treatments are widely implemented in fire-prone ecosystems, but ... more Mechanical fuel hazard reduction treatments are widely implemented in fire-prone ecosystems, but research evaluating their effects on fuel dynamics has focused only on woody-dominated post-treatment fuels. In the southeastern US, one of the most fire-prone regions of the world, mechanical fuels reduction is being increasingly used, yet the resulting fuelbeds have yet to be fully characterized for their fire risk. In order to broaden our understanding of the longevity and effectiveness of these treatments, mechanical mastication (''mowing'') was examined in a common pine ecosystem of the southeastern US Coastal Plain, where the post-mastication fuel environment was dominated by non-woody fuels. Fuel dynamics differed between recently burned mature stands, mature stands that had not burned for several years, and younger pine plantations. Foliar litter dominated (46-69%) the 17.1-23.1 Mg ha À1 of post-mastication surface fuels across these ecosystems, where pre-treatment understories were dominated by palmetto and gallberry shrubs. Although surface fuels compacted over time, the shrub layer recovered quickly, contributing to the result that stand-alone mechanical treatments did not reduce overall fuel loads. Increases in surface fuels followed by rapid shrub recovery may indicate short-term treatment efficacy, with narrow windows of opportunity for post-treatment fuel reduction burns. The fuelbed characteristics and fuel dynamics observed in these treated sites broaden our understanding of mechanical fuels reduction treatments in general, and provide the critical data for fuel model development.
Riparian vegetation plays an integral role in the ecology of the streams it borders, and in many ... more Riparian vegetation plays an integral role in the ecology of the streams it borders, and in many western US forests, is subjected to frequent wildfire disturbances. Many questions concerning the role of natural fire in the dynamics of riparian zone vegetation remain unanswered. This case study explores the relationships between wildfire burn patterns, stream channel topography, and the short-term response of riparian vegetation to fire along two creeks in the northern Sierra Nevada mixed-conifer forest. Post-fire sampling along 60, 3 m wide transects across riparian zones was used to document the topography, species distribution, sprouting response, and seedling recruitment 1 year after the Lookout fire in the Plumas National Forest, CA. Our results indicate that larger riparian zones acted as natural fire breaks, limiting the progression of the predominantly backing fire downhill toward the stream. On Fourth Water creek's steeper first terraces, where crown fires occurred, the percentage of burned plants that sprouted was higher than in the less-severely burned and more extensive first terraces of Third Water creek (93% versus 33%, P < 0.05). Total seedling recruitment was higher along Fourth Water creek (69 versus 35 seedlings, P < 0.05), while plant regeneration along Third Water creek was primarily vegetative. Along Fourth Water creek, the percent of burned hardwoods that sprouted increased with proximity to the water's edge from 33% on the slope above the riparian zone to 95% on the gravel bar, suggesting that moisture content plays a role in riparian species response to fire. An influx of white fir (Abies concolor Gordon & Glend. (Lindl.)) seedlings on the second terraces of Third Water creek may indicate a shift in species composition if future fires are suppressed and regeneration trends do not change significantly in the next few years. These results contribute to the limited research on natural fire in riparian zones, and can inform management strategies designed to restore and maintain riparian vegetation in the fire-prone forests of the Sierra Nevada. #
Remotely sensed imagery has been used extensively in the western US to evaluate patterns of burn ... more Remotely sensed imagery has been used extensively in the western US to evaluate patterns of burn severity and vegetation recovery following wildland fires. Its application in southern US ecosystems, however, has been limited. Challenges in southern areas include very high rates of vegetation recovery following fire, frequent cloud cover, and the presence of standing water. Use of remote sensing in southern forests should therefore be coupled with concurrent ground-based assessments, at least until the methods are tested for different ecosystems. Here, we assessed burn severity using remote sensing in a sand pine scrub ecosystem, which occurs on the central ridge of the Florida peninsula and is characterized by infrequent (>40 years on average) high severity fire. Two overlapping fires that burned in 2006 and 2009 provided a unique opportunity to explore compounded fire severity patterns. Landsat-based imagery analysis matched ground-based severity measures roughly half of the time. In general, higher severity fire led to lower severity or unburned conditions, while low severity fire had a less pronounced impact on either preventing or reducing fire severity in the subsequent fire. The unusually frequent fires both occurred during drought conditions. As the region's climate is predicted to be drier and hotter in the future, this work has implications for potential climate change effects on sand pine scrub fire regimes and, hence, ecosystem perpetuity.
In order to develop management strategies that maintain native biodiversity in plant communities ... more In order to develop management strategies that maintain native biodiversity in plant communities adapted to high-severity fire, an understanding of natural postfire succession in the target ecosystem is essential. Detailed information on fire effects is lacking for the sand pine (Pinus clausa [Chapm. ex Engelm.] Vasey ex Sarg.) scrub of the southeastern United States, limiting our ability to decide how and when to apply prescribed fire in this ecosystem. We studied the effects of fire-severity heterogeneity on sand pine scrub following a 4700-ha wildfire in Florida&amp;amp;amp;amp;#39;s Juniper Prairie Wilderness Area (USA). We identified four levels of fire severity (unburned, low, moderate, and high) and three pre-burn stand conditions (sapling, mature, and senescent). Study plots were established in each severity-stand-class combination, and were sampled at one and two years following fire. Nonmetric multidimensional scaling (NMS) ordination was applied in order to identify differences in community composition and successional trajectories in each of the stand-class-fire-severity combinations. NMS analyses indicated a shift in dominance between the dominant understory oak species, from Quercus myrtifolia Willd. to Quercus geminata Small, as sand pine basal area increases. Our ordination and regression results showed that Q. myrtifolia was the most aggressive colonizer of postfire open space, which is an important structural and habitat component of a sand pine scrub. Successional trajectories were heavily influenced by Quercus myrtifolia Willd. and were more uniform in the mature class than in the senescent class, probably due to more consistent overstory basal area. In both mature and sapling stands, herbaceous species cover was highest in moderate-severity plots. Woody-debris load varied significantly with stand age, fire severity level, and time. Sand pine seedling recruitment was highest in mature stands burned at high severity, while sapling and senescent stands exhibited much lower sand pine seedling recruitment rates at all levels of fire severity. The observed differences in seedling recruitment are expected to influence the progressive development of vertical structure and composition in the sand pine forest, leading to community differences that will persist and influence the effects of subsequent disturbances.
This special issue of Fire Ecology is dedicated to furthering scientific understanding of the rol... more This special issue of Fire Ecology is dedicated to furthering scientific understanding of the role fire plays in the development and functioning of wetland ecosystems. While not initially intuitive, the concept of fire exerting significant influence on how wetland environments function has only recently become a prominent topic of discussion among researchers, although it has been recognized by the management community for some time. This new interest in determining how large scale disturbances modulate ecological processes in wetlands led to a series of invited talks at a Fire in Wetlands session during the 9 th International Association for Ecology (INTECOL) meeting in Orlando, Florida, USA, in 2012. The collection of work presented here is the product of that special session, and includes research covering diverse topics such as fire effects on wetland biogeochemistry, vegetation community structure, and wildlife dynamics. Managers' perspectives, while presented in multiple talks during the INTECOL session, are captured here in discussions of the management implications of the research presented. This introduction summarizes each of the papers included in this special issue and is organized into topics of biogeochemistry, vegetation, community dynamics, and wildlife dynamics. The summarizing comments include key messages for management and future directions for research on fire in wetlands.
Extreme-temperature events have consequences for human health and mortality, forest disturbance p... more Extreme-temperature events have consequences for human health and mortality, forest disturbance patterns, agricultural productivity, and the economic repercussions of these consequences combined. To gain insight into whether extreme-temperature events are changing in light of global climate dynamics, the annual numbers of high-temperature days (those with temperatures higher than 20, 22.5, and 25 • C at 850 hPa) were analyzed across southern Europe from the years 1978 to 2012. A significant increase in the frequency of these days was found in many areas over the time period analyzed, and patterns in the spatial distribution of these changes were identified. We discuss the potential consequences of the increases in high-temperature days with regards to forest fire risk, human health, agriculture, energy demands, and some potential economic repercussions.
Study Site A grid of plots 250m x 250m was drawn over the length of the island in ArcView. The ce... more Study Site A grid of plots 250m x 250m was drawn over the length of the island in ArcView. The center of each plot was determined and GPS coordinates recorded. From each plot center, 2 nested plots of radii 40m and 80m were established. Two Increment cores per tree were collected from two trees within the 40m radius nested plots. We selected the largest slash pine trees in the plot in an attempt to obtain the longest possible chronology. Within the 80m plots, partial cross sections were extracted from fire scars as close to the ground as possible (Fig. 2). When possible, two trees were sampled within each plot. In order to increase sample size, trees were also opportunistically sampled between plots when trees with scars were found. Fire Scars We collected partial cross sections (Fig. 6&7) from 55 trees at the south end of the island. Of these, 19 were not usable due to high levels of decomposition. The remaining samples were compared with fire history records maintained by USFWS si...
1. The imperiled frosted elfin butterfly, Callophrys irus Godart, is restricted to frequently dis... more 1. The imperiled frosted elfin butterfly, Callophrys irus Godart, is restricted to frequently disturbed habitats where its larval host plants, Lupinus perennis L. and Baptisia tinctoria (L.) R. Br. reside. C. irus pupae are noted to reside in the leaf litter and soil, which may allow them to escape direct mortality by fire, a major force of disturbance in many areas they inhabit. The ability (or lack of an ability) to cope with prescribed fire is a critical factor to consider in developing land management and conservation strategies in the few areas that this species remains. 2. C. irus pupa location was sampled from a well-known population at a Florida state forest with an active history of prescribed fire management. Survival of experimental surrogate butterfly pupae to the heat pulse radiated into the soil as a result of prescribed fire was tested using controlled water bath experiments and a series of prescribed fire field experiments. 3. 12 C. irus pupae were excavated from 201...
Soil CO2 efflux (Rs) is a significant flux of carbon dioxide from ecosystem soils to the atmosphe... more Soil CO2 efflux (Rs) is a significant flux of carbon dioxide from ecosystem soils to the atmosphere and is a critical component of the total ecosystem carbon budget. Rs fluxes are comprised of autotrophic (Ra) sources of CO2 produced by plant roots and associated rhizosphere fungi and heterotrophic (Rh) sources of CO2 produced by aerobic soil microbes. A variety of forest management activities, including prescribed fire and mechanical fuels mastication treatments have been shown to significantly influence Rs rates in forests of the Western United States (US), yet these relationships are not well known for southeastern US forests. Prescribed fire is one of the most prevalent forest management tools employed in the southeastern US, and mechanical fuels treatments are becoming more common in the region as efforts to mitigate potential wildfire behavior in the wildland urban interface grow. Given that many of these forests provide habitat for endangered species, understanding the implic...
Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone u... more Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone uplands. Rare occurrence and difficulty of access have limited efforts to understand impacts of wildfires fires in wetlands. Following a 2009 wildfire, we measured tree mortality and structural changes in wetland forest patches. Centers of these circular landscape features experienced lower fire severity, although no continuous patch-size or edge effect was evident. Initial survival of the dominant tree, pondcypress (Taxodium distichum var. imbricarium), was high (>99%), but within one year of the fire approximately 23% of trees died. Delayed mortality was correlated with fire severity, but unrelated to other hypothesized factors such as patch size or edge distance. Tree diameter and soil elevation were important predictors of mortality, with smaller trees and those in areas with lower elevation more likely to die following severe fire. Depressional cypress forests typically exhibit increasing tree size towards their interiors, and differential mortality patterns were related to edge distance. These patterns result in the exaggeration of a dome-shaped profile. Our observations quantify roles of fire and hydrology in determining cypress mortality in these swamps, and imply the existence of feedbacks that maintain the characteristic shape of cypress domes.
The southern region of the U.S. uses prescribed fire as a management tool on more of its burnable... more The southern region of the U.S. uses prescribed fire as a management tool on more of its burnable land than anywhere in the U.S., with ecosystem restoration, wildlife habitat enhancement, and reduction of hazardous fuel loads as typical goals. Although the region performs more than 50,000 prescribed fire treatments each year, evaluation of their effects on wildfire suppression resources or behavior/effects is limited. To better understand trends in the use and effectiveness of prescribed fire, we conducted a region-wide survey of 523 fire use practitioners, working on both public and private lands. A 1-2 year prescribed fire interval was consistently viewed as effective in decreasing wildfire ignitions, behavior, and severity, as well as reducing suppression resources needed where wildfire occurred. Yet fewer than 15% of practitioners viewed burn intervals of 3-4 years as effective in reducing ignitions, underscoring the importance of high-frequency burning in vegetation communities where fuel recovery is rapid. Public lands managers identified limited budget and staffing as major institutional impediments to prescribed fire, in contrast to private individuals, more of whom chose liability as a key challenge. Differences in responses across ownership type, state, and vegetation type call for a broader perspective on how fire managers in the southern U.S. view prescribed fire.
Patterned landscapes are often evidence of biotic control on geomorphic processes, emerging in re... more Patterned landscapes are often evidence of biotic control on geomorphic processes, emerging in response to coupled ecosystem processes acting at different spatial scales. Self-reinforcing processes at local scales expand patches, while self-inhibiting processes, operating at a distance, impose limits to expansion. In Big Cypress National Preserve (BICY) in southwest Florida, isolated forested wetland depressions (cypress domes) appear to be evenly distributed within a mosaic of short-hydroperiod marshes and pine uplands. To test the hypothesis that the apparent patterning is regular, we characterized frequency distributions and spatial patterns of vegetation communities, surface and bedrock elevation, and soil properties (thickness and phosphorus content). Nearest neighbor distances indicate strongly significant wetland spatial overdispersion, and bedrock elevations exhibited periodic spatial autocorrelation; both observations are consistent with regular patterning. Bedrock elevations and soil P were clearly bimodal, suggesting strong positive feedbacks on wetland patch development. Soil-surface elevations exhibited weaker bimodality, indicating smoothing of surface morphology by some combination of sediment transport, mineral reprecipitation, and organic matter production. Significant negative autocorrelation of bedrock elevations at scales similar to wetland spacing suggest the presence of distal negative feedbacks on patch expansion. These findings support the inference of regular patterning, and are consistent with the presence of local positive feedbacks among hydroperiod, vegetation productivity and bedrock dissolution. These processes are ultimately constrained by distal negative feedbacks, potentially induced by landscape scale limitations on the water volume required to enable this biogeomorphic mechanism.
Pine flatwoods forests in the southeastern US have experienced severe wildfires over the past few... more Pine flatwoods forests in the southeastern US have experienced severe wildfires over the past few decades, often attributed to fuel load build-up. These forest communities are fire dependent and require regular burning for ecosystem maintenance and health. Although prescribed fire has been used to reduce wildfire risk and maintain ecosystem integrity, managers are still working to reintroduce fire to long unburned areas. Common perception holds that reintroduction of fire in long unburned forests will produce severe fire effects, resulting in a reluctance to prescribe fire without first using expensive mechanical fuels reduction techniques. To inform prioritization and timing of future fire use, we apply remote sensing analysis to examine the set of conditions most likely to result in high burn severity effects, in relation to vegetation, years since the previous fire, and historical fire frequency. We analyze Landsat imagery-based differenced Normalized Burn Ratios (dNBR) to model the relationships between previous and future burn severity to better predict areas of potential high severity. Our results show that remote sensing techniques are useful for modeling the relationship between elevated risk of high burn severity and the amount of time between fires, the type of fire (wildfire or prescribed burn), and the historical frequency of fires in pine flatwoods forests.
Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone u... more Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone uplands. Rare occurrence and difficulty of access have limited efforts to understand impacts of wildfires fires in wetlands. Following a 2009 wildfire, we measured tree mortality and structural changes in wetland forest patches. Centers of these circular landscape features experienced lower fire severity, although no continuous patch-size or edge effect was evident. Initial survival of the dominant tree, pondcypress (Taxodium distichum var. imbricarium), was high (>99%), but within one year of the fire approximately 23% of trees died. Delayed mortality was correlated with fire severity, but unrelated to other hypothesized factors such as patch size or edge distance. Tree diameter and soil elevation were important predictors of mortality, with smaller trees and those in areas with lower elevation more likely to die following severe fire. Depressional cypress forests typically exhibit increasing tree size towards their interiors, and differential mortality patterns were related to edge distance. These patterns result in the exaggeration of a dome-shaped profile. Our observations quantify roles of fire and hydrology in determining cypress mortality in these swamps, and imply the existence of feedbacks that maintain the characteristic shape of cypress domes.
In recent decades, agencies charged with managing historic structures and sites have found dendro... more In recent decades, agencies charged with managing historic structures and sites have found dendroarchaeological studies increasingly valuable, given the ability of such studies to verify (or refute) accepted dates of construction. The Ximénez-Fatio House has well-documented historical and cultural significance for the state of Florida, as it is one of St. Augustine's oldest, best-preserved, and most studied historic properties. According to documentary sources, the two-story coquina-stone main house was reportedly built around 1797-1798, and included a one-story wing of warehouses, giving the house a distinctive ''L'' shape. Documentary evidence also suggests that a second story was added above the wing sometime between 1830 and 1842. However, after studying the building fabric itself, historical architects now believe the entire wing of the house was remodeled two decades later in the 1850s. Our goals were to: (1) determine the probable construction years for the original house and wing using tree-ring dating techniques, and (2) verify the probable construction year for the remodeling that occurred in the wing section of the house. A total of 74 core samples were extracted from longleaf pine (Pinus palustris P. Miller) timbers used to construct the house. Twenty-six were confidently crossdated both visually and statistically against each other to produce a 185-year floating tree-ring chronology. A statistically significant (p , 0.0001) correlation between our chronology and a longleaf pine chronology from Lake Louise, Georgia, anchors our chronology between 1673 and 1857. No cutting dates were obtained from the main house, but the lack of any tree rings that post-date 1798 supports the 1797 construction date. Furthermore, cutting dates obtained from beams in the first-floor wing revealed that the extensive remodeling of the wing likely occurred in the period 1856 to 1858 soon after the house had been purchased by Louisa Fatio in 1855.
... Mark J. Hainds is the Research Coordinator for The Longleaf Alliance and a Research Associate... more ... Mark J. Hainds is the Research Coordinator for The Longleaf Alliance and a Research Associate with Auburn University. ... Pp. 948 in S. Jose, EJ Jokela, and DL Miller, eds., The Longleaf Pine Ecosystem: Ecology, Silviculture, and Restoration. ...
Plantations are the most common means of reforestation following stand-replacing wildfires. As wi... more Plantations are the most common means of reforestation following stand-replacing wildfires. As wildfires continue to increase in size and severity as a result of fire suppression or climate change, establishment of plantations will likely also increase. Plantations' structural characteristics, including dense, uniform spacing and abundant ladder fuels, present significant wildfire hazards. Large-scale fuels reduction techniques may be necessary to reduce potential fire behavior in plantations and to protect surrounding forests. In the present study, four different manipulations aimed at reducing potential fire behavior in a Sierra Nevada pine plantation are compared. The treatments include: mechanical shredding, or mastication, of understorey vegetation and small trees; mastication followed by prescribed fire; fire alone; and controls. Fire behavior modeling shows that mastication is detrimental whereas prescribed fire is effective in reducing potential fire behavior at moderate to extreme weather conditions. Predicted fire behavior was compared with actual values from the prescribed burns in an effort to explore the limitations of fire modeling. Fire behavior predictions were similar to field observations in the more structurally homogeneous stands, but differed greatly where mastication created forest openings and patchy fuels distributions. In contrast to natural stands, the homogeneity of pine plantations make the results of the present work applicable to other regions such as the south-eastern US, where similar fuels reduction techniques are used to increase fire-resistance and stand resilience.
Although charcoal represents a relatively minor portion of available biomass burned in wildfires ... more Although charcoal represents a relatively minor portion of available biomass burned in wildfires and prescribed burns, its recalcitrant properties confer residence times ranging from centuries to millennia, with significance for carbon sequestration in frequently burned forests. Here, we determined whether charcoal formation differed between the two most common prescribed fire spread patterns in southern forests: head (with the wind) and backing (against the wind). Pine wood samples were distributed randomly within a mesic flatwoods burn unit in north-central Florida, and subjected either to a head fire (n ¼ 34) or a backing fire (n ¼ 34). Backing fires formed more than twice as much charcoal as head fires (1.53 v. 0.38% of available biomass), presumably because of differences in residence times, oxygen availability and fire intensity between the two fire spread patterns. These results suggest that the contribution of charcoal to ecosystem carbon sequestration is greater when flatwoods forests are burned against the prevailing wind direction, and that further investigation of these trends is warranted.
Mechanical fuel hazard reduction treatments are widely implemented in fire-prone ecosystems, but ... more Mechanical fuel hazard reduction treatments are widely implemented in fire-prone ecosystems, but research evaluating their effects on fuel dynamics has focused only on woody-dominated post-treatment fuels. In the southeastern US, one of the most fire-prone regions of the world, mechanical fuels reduction is being increasingly used, yet the resulting fuelbeds have yet to be fully characterized for their fire risk. In order to broaden our understanding of the longevity and effectiveness of these treatments, mechanical mastication (''mowing'') was examined in a common pine ecosystem of the southeastern US Coastal Plain, where the post-mastication fuel environment was dominated by non-woody fuels. Fuel dynamics differed between recently burned mature stands, mature stands that had not burned for several years, and younger pine plantations. Foliar litter dominated (46-69%) the 17.1-23.1 Mg ha À1 of post-mastication surface fuels across these ecosystems, where pre-treatment understories were dominated by palmetto and gallberry shrubs. Although surface fuels compacted over time, the shrub layer recovered quickly, contributing to the result that stand-alone mechanical treatments did not reduce overall fuel loads. Increases in surface fuels followed by rapid shrub recovery may indicate short-term treatment efficacy, with narrow windows of opportunity for post-treatment fuel reduction burns. The fuelbed characteristics and fuel dynamics observed in these treated sites broaden our understanding of mechanical fuels reduction treatments in general, and provide the critical data for fuel model development.
Riparian vegetation plays an integral role in the ecology of the streams it borders, and in many ... more Riparian vegetation plays an integral role in the ecology of the streams it borders, and in many western US forests, is subjected to frequent wildfire disturbances. Many questions concerning the role of natural fire in the dynamics of riparian zone vegetation remain unanswered. This case study explores the relationships between wildfire burn patterns, stream channel topography, and the short-term response of riparian vegetation to fire along two creeks in the northern Sierra Nevada mixed-conifer forest. Post-fire sampling along 60, 3 m wide transects across riparian zones was used to document the topography, species distribution, sprouting response, and seedling recruitment 1 year after the Lookout fire in the Plumas National Forest, CA. Our results indicate that larger riparian zones acted as natural fire breaks, limiting the progression of the predominantly backing fire downhill toward the stream. On Fourth Water creek's steeper first terraces, where crown fires occurred, the percentage of burned plants that sprouted was higher than in the less-severely burned and more extensive first terraces of Third Water creek (93% versus 33%, P < 0.05). Total seedling recruitment was higher along Fourth Water creek (69 versus 35 seedlings, P < 0.05), while plant regeneration along Third Water creek was primarily vegetative. Along Fourth Water creek, the percent of burned hardwoods that sprouted increased with proximity to the water's edge from 33% on the slope above the riparian zone to 95% on the gravel bar, suggesting that moisture content plays a role in riparian species response to fire. An influx of white fir (Abies concolor Gordon & Glend. (Lindl.)) seedlings on the second terraces of Third Water creek may indicate a shift in species composition if future fires are suppressed and regeneration trends do not change significantly in the next few years. These results contribute to the limited research on natural fire in riparian zones, and can inform management strategies designed to restore and maintain riparian vegetation in the fire-prone forests of the Sierra Nevada. #
Remotely sensed imagery has been used extensively in the western US to evaluate patterns of burn ... more Remotely sensed imagery has been used extensively in the western US to evaluate patterns of burn severity and vegetation recovery following wildland fires. Its application in southern US ecosystems, however, has been limited. Challenges in southern areas include very high rates of vegetation recovery following fire, frequent cloud cover, and the presence of standing water. Use of remote sensing in southern forests should therefore be coupled with concurrent ground-based assessments, at least until the methods are tested for different ecosystems. Here, we assessed burn severity using remote sensing in a sand pine scrub ecosystem, which occurs on the central ridge of the Florida peninsula and is characterized by infrequent (>40 years on average) high severity fire. Two overlapping fires that burned in 2006 and 2009 provided a unique opportunity to explore compounded fire severity patterns. Landsat-based imagery analysis matched ground-based severity measures roughly half of the time. In general, higher severity fire led to lower severity or unburned conditions, while low severity fire had a less pronounced impact on either preventing or reducing fire severity in the subsequent fire. The unusually frequent fires both occurred during drought conditions. As the region's climate is predicted to be drier and hotter in the future, this work has implications for potential climate change effects on sand pine scrub fire regimes and, hence, ecosystem perpetuity.
In order to develop management strategies that maintain native biodiversity in plant communities ... more In order to develop management strategies that maintain native biodiversity in plant communities adapted to high-severity fire, an understanding of natural postfire succession in the target ecosystem is essential. Detailed information on fire effects is lacking for the sand pine (Pinus clausa [Chapm. ex Engelm.] Vasey ex Sarg.) scrub of the southeastern United States, limiting our ability to decide how and when to apply prescribed fire in this ecosystem. We studied the effects of fire-severity heterogeneity on sand pine scrub following a 4700-ha wildfire in Florida&amp;amp;amp;amp;#39;s Juniper Prairie Wilderness Area (USA). We identified four levels of fire severity (unburned, low, moderate, and high) and three pre-burn stand conditions (sapling, mature, and senescent). Study plots were established in each severity-stand-class combination, and were sampled at one and two years following fire. Nonmetric multidimensional scaling (NMS) ordination was applied in order to identify differences in community composition and successional trajectories in each of the stand-class-fire-severity combinations. NMS analyses indicated a shift in dominance between the dominant understory oak species, from Quercus myrtifolia Willd. to Quercus geminata Small, as sand pine basal area increases. Our ordination and regression results showed that Q. myrtifolia was the most aggressive colonizer of postfire open space, which is an important structural and habitat component of a sand pine scrub. Successional trajectories were heavily influenced by Quercus myrtifolia Willd. and were more uniform in the mature class than in the senescent class, probably due to more consistent overstory basal area. In both mature and sapling stands, herbaceous species cover was highest in moderate-severity plots. Woody-debris load varied significantly with stand age, fire severity level, and time. Sand pine seedling recruitment was highest in mature stands burned at high severity, while sapling and senescent stands exhibited much lower sand pine seedling recruitment rates at all levels of fire severity. The observed differences in seedling recruitment are expected to influence the progressive development of vertical structure and composition in the sand pine forest, leading to community differences that will persist and influence the effects of subsequent disturbances.
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