Jesse K. Kreye

Effects of particle fracturing and moisture content on fire behaviour in masticated fuelbeds burned in a laboratory

Mechanicalmasticationisafuelstreatmentthatconvertsshrubsandsmalltreesintodensefuelbedscomposed of fractured woody particles. Although compaction is thought to reduce fireline intensity, the added particle surface area due to fracturing could also influence fire behaviour. We evaluated effects of particle fracturing and moisture content (ranging from 2.5 to 13%) on fire behaviour in fuelbeds composed of masticated Arctostaphylos manzanita Parry and Ceanothus velutinus Dougl. shrubs in the laboratory. Fuelbeds composed of fractured particles did not burn with greater intensity than fuelbeds composed of intact particles, as hypothesised. Flame heights ranged from 54 to 95cm and fireline intensityfrom50to140kJs � 1 m � 1 ,approximatingvaluesobservedinfieldexperiments.Masticatedfuelbedsburnedwith shorter flame heights and longer flaming duration under higher fuel moistures, but duration of lethal heating (4608C) above fuelbeds did not differ across the range of fuel moistures, averaging 12min over a 0.1-m 2 area. Our results suggest that expected fire behaviour increases due to particle fracturing may be overwhelmed by fuelbed bulk density. The long-duration heating of burning masticated fuels may require managers to mitigate effects to trees and soils when fuel loads are high.

The Flammability of Forest and Woodland Litter: a Synthesis

Fire behavior and effects in forests and woodlands are influenced by surface fuels and senesced leaf litter in particular. We have known that species exhibit differential flammability for some time, but isolated efforts have often attributed differences to disparate mechanisms. Recent research has expanded the diversity of species evaluated, clarified patterns at the fuelbed level, and provided evidence that the physical and chemical traits of litter or fuelbeds drive flammability. To date, little effort has focused on uniting methods, clarifying the awkward terminology, or, perhaps most importantly, comparing laboratory findings to field observations of fire behavior. Here, we review recent literature and synthesize findings on what we know about the flammability of litter and propose future research directions.

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

Moisture desorption in mechanically masticated fuels: effects of particle fracturing and fuelbed compaction

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

Mechanical mastication is increasingly used as a wildland fuel treatment, reducing standing trees and shrubs to compacted fuelbeds of fractured woody fuels. One major shortcoming in our understanding of these fuelbeds is how particle fracturing influences moisture gain or loss, a primary determinant of fire behaviour. To better understand fuel moisture dynamics, we measured particle and fuelbed drying rates of masticated Arctostaphylos manzanita and Ceanothus velutinus shrubs, common targets of mastication in fire-prone western USA ecosystems. Drying rates of intact and fractured particles did not differ when desorbing at the fuelbed surface, but these particles did dry more rapidly than underlying fuelbeds. Average response times of 10-h woody particles at the fuelbed surfaces ranged from 16 to 21 h, whereas response times of fuelbeds (composed of 1-h and 10-h particles) were 40 to 69 h. Response times did not differ between fuelbeds composed of fractured woody particles and fuelbeds composed of intact particles (P¼0.258). Particle fracturing as a result of mastication does not affect the drying rate, but the longer-than-expected response times of particles within fuelbeds underscores the needs to better understand fuel moisture dynamics in these increasingly common fuels.

The impact of aging on laboratory fire behaviour in masticated shrub fuelbeds of California and Oregon, USA

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.

Toward a mechanism for eastern North American forest mesophication: differential litter drying across 17 species.

Mastication of shrubs and small trees to reduce fire hazard has become a widespread management practice, yet many aspects of the fire behaviour of these unique woody fuelbeds remain poorly understood. To examine the effects of fuelbed aging on fire behaviour, we conducted laboratory burns with masticated Arctostaphylos spp. and Ceanothus spp. woody debris that ranged from 2 to 16 years since treatment. Masticated fuels that were 10 years or older burned with 18 to 29% shorter flame heights and 19% lower fireline intensities compared with the younger fuelbeds across three different fuel loads (25, 50 and 75 Mg ha–1). Older fuelbeds smouldered for almost 50% longer than the younger masticated fuelbeds. Fuel consumption was 96% in the two higher fuel load categories regardless of fuelbed age, whereas consumption was 77% in the lighter fuel load. Fire intensity in masticated fuels may decrease over time owing to particle degradation, but in dry environments where decomposition is slow, combustion of the remaining fuels may still pose risks for tree mortality and smoke production associated with protracted smouldering.