Reid A.M.,Tall United |
Robertson K.M.,Tall United |
Hmielowski T.L.,Louisiana State University
Canadian Journal of Forest Research | Year: 2012
The ability to predict fuel consumption during fires is essential for a wide range of applications, including estimation of fire effects and fire emissions. This project identified predictors of fuel consumption for the dominant fuel bed components (litter (<0.6-cm diameter dead material) and live herbs) during 217 prescribed fires in native longleaf pine (Pinus palustris Mill.) and old-field loblolly pine (Pinus taeda L.) - shortleaf pine (Pinus echinata Mill.) communities in the southeastern United States. Additionally, these data were used to validate the First Order Fire Effects Model (FOFEM) fuel consumption computer model using custom and default fuel loads. Regression models using empirical data suggested that litter and live herb fuel consumption can be predicted by prefire litter and live herb fuel loads, litter and live herb fuel moisture, litter fuel bed bulk density, season of burn, years since fire, days since last rain ≥0.64 cm, relative humidity, energy release component, community type, pine and hardwood basal areas, and the Keetch-Byram drought index. FOFEM's prediction of fuel consumption for litter, live herbs, and duff combined using default fuel loads was 1.5 times the measured fuel consumption (where duff fuel load was zero). Refinement of FOFEM's fuel load and consumption calculations in the studied community types using the newly collected data and suggestions for model improvement would provide more accurate air quality inventories and assist in guiding appropriate regulation of prescribed fire.
Robertson K.M.,Tall United |
Hmielowski T.L.,Louisiana State University
Oecologia | Year: 2014
Past studies suggest that rates of woody plant resprouting following a "topkilling" disturbance relate to timing of disturbance because of temporal patterns of below-ground carbohydrate storage. Accordingly, we hypothesized that fire-return interval (1 or 2 years) and season of burn (late dormant or early growing season) would influence the change in resprout growth rate from one fire-free interval to the next (Δ growth rate) for broadleaf woody plants in a pine-grassland in Georgia, USA. Resprout growth rate during one fire-free interval strongly predicted growth rate during the following fire-free interval, presumably reflecting root biomass. Length of fire-free interval did not have a significant effect on mean Δ growth rate. Plants burned in the late dormant season (February-March) had a greater positive Δ growth rate than those burned in the early growing season (April-June), consistent with the presumption that root carbohydrates are depleted and thus limiting during spring growth. Plants with resprout growth rates above a certain level had zero or negative Δ growth rates, indicating an equilibrium of maximum resprout size under a given fire-return interval. This equilibrium, as well as relatively reduced resprout growth rate following growing season fires, provide insight into how historic lightning-initiated fires in the early growing season limited woody plant dominance and maintained the herb-dominated structure of pine-grassland communities. Results also indicate tradeoffs between applying prescribed fire at 1- versus 2-year intervals and in the dormant versus growing seasons with the goal of limiting woody vegetation. © 2013 Springer-Verlag Berlin Heidelberg.
Cox J.A.,Tall United |
Jones C.D.,University of Georgia
Condor | Year: 2010
Bachman's Sparrow (Peucaea aestivalis) is listed as a species of conservation concern throughout its range and therefore an important candidate for demographic studies. We estimated probabilities of males' annual survival by monitoring a large color-marked population for 4 years by using a combination of (1) mark-resighting within a primary study area and (2) surveys outside the primary area to document emigration. We used multi-strata models to assess probabilities of survival, detection, and movement between the primary study area and the surrounding landscape. In the top models included in our confidence set, probabilities of annual survival were ≥0.68. Probabilities of detection and dispersal varied among the top models but averaged ≥0.86 and ≤0.14, respectively, for individuals in the primary study area. We used a survival probability of 0.68 in combination with published information on the species' productivity to construct a two-stage Leslie matrix. Survival of adult males had the greatest proportional influence on population projections (elasticity = 0.52), while survival of juveniles and annual productivity had equal influence (elasticities = 0.24). Our results suggest that off-plot surveys and multistrata models provide an efficient method for estimating probabilities of survival of Bachman's Sparrow. © 2010 The Cooper Ornithological Society.
Picotte J.J.,U.S. Geological Survey |
Robertson K.,Tall United
Remote Sensing | Year: 2011
Remote sensing using Landsat Thematic Mapper (TM) satellite imagery is increasingly used for mapping wildland fire burned area and burn severity, owing to its frequency of collection, relatively high resolution, and availability free of charge. However, rapid response of vegetation following fire and frequent cloud cover pose challenges to this approach in the southeastern US. We assessed these timing constraints by using a series of Landsat TM images to determine how rapidly the remotely sensed burn scar signature fades following prescribed burns in wet flatwoods and depression swamp community types in the Apalachicola National Forest, Florida, USA during 2006. We used both the Normalized Burn Ratio (NBR) of reflectance bands sensitive to vegetation and exposed soil cover, as well as the change in NBR from before to after fire (dNBR), to estimate burned area. We also determined the average and maximum amount of time following fire required to obtain a cloud-free image for burns in each month of the year, as well as the predicted effect of this time lag on percent accuracy of burn scar estimates. Using both NBR and dNBR, the detectable area decreased linearly 9% per month on average over the first four months following fire. Our findings suggest that the NBR and dNBR methods for monitoring burned area in common southeastern US vegetation community types are limited to an average of 78-90% accuracy among months of the year, with individual burns having values as low as 38%, if restricted to use of Landsat 5 TM imagery. However, the majority of burns can still be mapped at accuracies similar to those in other regions of the US, and access to additional sources of satellite imagery would improve overall accuracy. © 2011 by the authors.
Clewell A.,Tall United
Castanea | Year: 2011
Forest vegetation near Tallahassee, Florida was inventoried on a former cultivated field, called NB66h, which had been abandoned 43 yr earlier. Subsequently, the site suffered no disturbance and no colonization by alien invasive species. The canopy consisted of pines (Pinus taeda, P. echinata) and hardwoods, primarily Liquidambar styraciflua, Quercus nigra. Most tree species were characteristic of plant communities that historically occurred at lower slope positions in the landscape and not of presettlement upland shortleaf pine-oak-hickory woodland. Offsite species colonized surrounding uplands following abandonment of cotton plantations towards the end of the 19th century. Presettlement vegetation was represented by few species and individuals, and offsite species were abundant in every size class. Plant succession was arrested with little sign of directional development towards a predictable seral endpoint. Hypothesized seral trends towards proposed "climax" forests of magnolia-beech and southern mixed hardwoods were not supported. © 2011 Southern Appalachian Botanical Society.
Clewell A.F.,Tall United
Castanea | Year: 2013
Shortleaf pine-oak-hickory woodlands provided the principal vegetation cover in the Tallahassee Red Hills prior to land clearing for plantation agriculture in the 19th century. Ample historical documentation and extant remnants of that community, including old-growth, support this conclusion. This woodland was maintained by surface fires and consisted principally of open stands of shortleaf pine, post oak, Spanish oak, black oak, mockernut hickory, and dogwood. The species-diverse and predominantly herbaceous ground cover was dominated by grasses, legumes, and composites. Coppice sprouting of trees and shrubs after fires was common. In the absence of fire, shortleaf pine-oak-hickory woodlands convert to oak-hickory forest with similar tree species composition and loss of herbaceous species. Within the past 130 years, nearly all stands of shortleaf pine-oak-hickory woodlands and oak-hickory forests have been extirpated or compromised beyond recognition by intrusions of offsite tree species that are typical of moist soils at less elevated landscape positions. © 2013 Southern Appalachian Botanical Society.
Engstrom R.T.,Tall United
Fire Ecology | Year: 2010
Models of first-order fire effects are designed to predict tree mortality, soil heating, fuel consumption, and smoke production. Some of these models can be used to predict first- order fire effects on animals (e.g., soil-dwelling organisms as a result of soil heating), but they are also relevant to second-order fire effects on animals, such as habitat change. In this paper, I review a sample of studies of first-order fire effects on animals that use aquatic, subterranean, and terrestrial habitats; use an envirogram as a graphical approach to organize first- and second-order fire effects for a single animal species; recommend how one could obtain better data using Species-Centered Environmental Analysis; and begin to model these effects.
Picotte J.J.,Tall United |
Robertson K.M.,Tall United
International Journal of Wildland Fire | Year: 2011
We assessed an existing method of remote sensing of wildland fire burn severity for its applicability in south-eastern USA vegetation types. This method uses Landsat satellite imagery to calculate the Normalised Burn Ratio (NBR) of reflectance bands sensitive to fire effects, and the change in NBR from pre- to post fire (dNBR) to estimate burn severity. To ground-truth ranges of NBR and dNBR that correspond to levels of burn severity, we measured severity using the Composite Burn Index at 731 locations stratified by plant community type, season of measurement, and time since fire. Best-fit curves relating Composite Burn Index to NBR or dNBR were used to determine reflectance value breakpoints that delimit levels of burn severity. Remotely estimated levels of burn severity within 3 months following fire had an average of 78% agreement with ground measurements using NBR and 75% agreement using dNBR. However, percentage agreement varied among habitat types and season of measurement, with either NBR or dNBR being advantageous under specific combinations of conditions. The results suggest this method will be useful for monitoring burned area and burn severity in south-eastern USA vegetation types if the provided recommendations and limitations are considered. © IAWF 2011.
Reid A.M.,Tall United |
Robertson K.M.,Tall United
International Journal of Wildland Fire | Year: 2012
Knowing the energy content of wildland fire fuels is important for predicting fire behaviour and for interpreting the pyrogenicity of plant communities. Energy content was determined for fuel categories characteristic of south-eastern US pine savannas, specifically live herbs, 10-h fuels, broadleaf litter, fine dead surface fuels, needle litter from three pine species, and other 1-h fuels combined. Pine needles had higher energy content than the other fuels, fine litter had lower energy content than the other fuels, and all other categories did not differ from each other. Longleaf pine (Pinus palustris) needle litter had lower energy content than loblolly (P. taeda) and shortleaf (P. echinata) pines, which did not differ from each other. Measured energy contents were used to estimate energy content for total fuel loads in native and old-field pine savannas of southern Georgia and northern Florida based on data from a previous study that provided fuel loads in each fuel category. Fire behaviour was predicted using the BehavePlus 5.0.0 default and newly estimated energy contents. This comparison revealed that fire behaviour parameters in the studied native and old-field pine savannas are overpredicted using the default energy content. In savannas, energy content estimates should take into consideration the proportion of fuel types, especially tree leaf litter relative to other fine fuels, for accurately predicting fire behaviour. © IAWF 2012.