Moisture dynamics and fire behavior in mechanically masticated fuelbeds
Graduation Date
2008
Document Type
Thesis
Program
Other
Program
Thesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 2008
Committee Chair Name
J. Morgan Varner
Committee Chair Affiliation
HSU Faculty or Staff
Keywords
Fuel moisture, Fuels treatments, Fuels management, Fire, Humboldt State University -- Theses -- Forestry
Abstract
Changing fuel complexes, increases in the wildland/urban interface, and potential climatic change have made the threat of catastrophic wildfire in the western United States a great concern. One method used to mitigate potential wildfire hazard is mechanical mastication, a treatment that reduces vertical fuel continuity in forest and shrub ecosystems. Mastication results in densely compacted fuelbeds composed of highly fractured fuel particles. Despite the widescale adoption of mastication treatments, it is unknown how the fracturing of particles or the highly compacted nature of these treatments affects future fire behavior. Masticated fuels have been observed to burn with intensities not predicted by fire modeling software. Moisture desorption and fire behavior were both studied here in order to understand the role of particle fracturing and high fuelbed bulk density on drying rates and the role of particle fracturing on fire behavior. Experiments were conducted with Arctostaphylos manzanita (common manzanita) and Ceanothus velutinus (snowbrush) under laboratory conditions. Drying rates (response time) did not differ between intact and fractured particles or pine dowels (control) when desorbing at the fuelbed surface, but these particles did respond much faster than did the entire fuelbeds in which they were drying. Average response times of 10-h particles (0.635 to 2.54 cm) at the surface of fuelbeds ranged from 17 to 21 h, while response time of entire fuelbeds was 240 to 440 percent slower. Also, response time of fuelbeds composed exclusively of fractured particles did not differ from fuelbeds composed exclusively of intact particles. Laboratory burning of masticated A. manzanita fuelbeds under four fuel moisture content treatments (2.5, 7, 9, and 11 percent) resulted in lower fire intensity and longer duration of flaming combustion under higher fuel moisture content, but duration of lethal heating at fixed positions above fuelbeds did not differ across fuel moisture content. In addressing the effect of particle fracturing, fuelbeds composed exclusively of fractured particles did not burn with greater intensity than fuelbeds composed exclusively of intact particles across both shrub species and two fuel moisture content treatments (5 and 13 percent). A. manzanita burned with greater intensity compared with C. velutinus and drier (5 percent fuel moisture content) treatments burned with greater intensity than wetter (13 percent fuel moisture content) treatments regardless of particle fracturing. This thesis provides empirical evidence that the physical shape of fractured particles from mechanical mastication does not affect moisture dynamics or increase fire intensity. The longer than expected response times of particles within fuelbeds and substantially longer response times of fuelbeds suggests that moisture dynamics is being controlled not exclusively at the particle level, but also by fuelbed properties. The compact nature of masticated fuelbeds may mitigate any influence of particle level fracturing on moisture dynamics that could potentially affect the availability of these fuels for combustion. This thesis also supports that intensity and flaming time both influence heating duration and that masticated fuelbeds burn with sufficient fire behavior to induce long duration heating that, while serving to reduce local fire behavior, may ultimately lead to undesired fire effects.
Recommended Citation
Kreye, Jesse K., "Moisture dynamics and fire behavior in mechanically masticated fuelbeds" (2008). Cal Poly Humboldt theses and projects. 2130.
https://digitalcommons.humboldt.edu/etd/2130
https://scholarworks.calstate.edu/concern/theses/0v8382895