Leda N. Kobziar

The efficacy of fire and fuels reduction treatments in a Sierra Nevada pine plantation.

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.

Effects of fuel load and moisture content on fire behaviour and heating in masticated litter-dominated fuels

Mechanical fuels treatments are being used in fire-prone ecosystems where fuel loading poses a hazard, yet little research elucidating subsequent fire behaviour exists, especially in litter-dominated fuelbeds. To address this deficiency, we burned constructed fuelbeds from masticated sites in pine flatwoods forests in northern Florida with palmetto-dominated understoreys and examined the effects of fuel load and fuel moisture content (FMC) on fire behaviour.Flamelengths(49-140cm)andfirelineintensity(183-773kJm � 1 s � 1 )increasedwithloading(10-30Mgha � 1 ) and were reduced by 40 and 47% with increasing FMC from 9 to 13%. Rate of spread was not influenced by fuel load, but doubledunderdrierFMC.Fuel consumptionwas.90% forallburns.Soiltemperatures wereinfluenced bybothfuelload and FMC, but never reached lethal temperatures (608C). However, temperatures of thermocouple probes placed at the fuelbed surface reached 274-5038C. Probe maximum temperature and duration at temperatures

Fire Reinforces Structure of Pondcypress (Taxodium distichum var. imbricarium) Domes in a Wetland Landscape

608C (9.5-20.08Cmin) both increased with fuel load, but were unaffected by FMC. The fire behaviour observed in these unique litter-dominated fuelbeds provides additional insight into the burning characteristics of masticated fuels in general. Additional keywords: fire hazard reduction, flammability, mechanical fuel treatment, pine flatwoods, saw palmetto.

The Historical Dendroarchaeology Of The Ximénez-Fatio House, St. Augustine, Florida, U.S.A.

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.

Modeling Relationships among 217 Fires Using Remote Sensing of Burn Severity in Southern Pine Forests

Abstract 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. Augustines 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.

Tracking postfire successional trajectories in a plant community adapted to high-severity fire.

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 ignition patterns affect production of charcoal in southern forests

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 Floridas 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.

The effect of mastication on surface fire behaviour, fuels consumption and tree mortality in pine flatwoods of Florida, USA

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 = 34) or a backing fire (n = 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.

Can butterflies evade fire? Pupa location and heat tolerance in fire prone habitats of Florida.

Mastication of understorey shrubs and small trees to reduce fire hazard has become a widespread forest management practice, but few empirical studies have quantified the effects of this mechanical treatment on actual fire behaviour and fire effects at the stand scale. We conducted experimental burns in masticated pine flatwoods with palmetto/gallberry understories, a common ecosystem of the Southern US Coastal Plain. Fire behaviour (flame height, rate of spread) and fire effects were compared between treated and untreated sites burned in the typical winter prescribed burning season. Mastication effectively reduced flame heights by 66%, but recovering shrubs (cover, height) influenced fire behaviour within six months following treatment, suggesting time-limited effectiveness. Trees had less crown scorch and bole char in masticated sites, but tree mortality was minimal on both treated and untreated sites. Consumption of masticated fuel was substantial across both treatments, but little duff was consumed under the moist soil conditions. When burning is conducted soon after treatment, mastication may effectively reduce fire behaviour in pine flatwoods sites, but the duration of treatment efficacy remains unclear.

Problems and Needs for Restorationists of Longleaf Pine Ecosystems: A Survey

Butterflies such as the atala hairstreak, Eumaeus atala Poey, and the frosted elfin, Callophrys irus Godart, are restricted to frequently disturbed habitats where their larval host plants occur. Pupae of these butterflies are noted to reside at the base of host plants or in the leaf litter and soil, which may allow them to escape direct mortality by fire, a prominent disturbance in many areas they inhabit. The capacity of these species to cope with fire is a critical consideration for land management and conservation strategies in the locations where they are found. Survival of E. atala pupae in relation to temperature and duration of heat pulse was tested using controlled water bath experiments and a series of prescribed fire field experiments. Survival of E. atala pupae was correlated to peak temperature and heat exposure in both laboratory and field trials. In addition, E. atala survival following field trials was correlated to depth of burial; complete mortality was observed for pupae at the soil surface. Fifty percent of E. atala survived the heat generated by prescribed fire when experimentally placed at depths ≥ 1.75cm, suggesting that pupation of butterflies in the soil at depth can protect from fatal temperatures caused by fire. For a species such as E. atala that pupates above ground, a population reduction from a burn event is a significant loss, and so decreasing the impact of prescribed fire on populations is critical.