1,721,006 research outputs found
Fuel loading and vegetation response to mechanical mastication fuels treatments
No full textThesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 2007Mechanical mastication is a fuels management tool that is increasingly utilized to treat\ud
small trees and shrubs in fire-prone ecosystems throughout the western United States.\ud
This study characterized fuel loading in masticated fuelbeds across ten sites in northern California and southwestern Oregon. In addition, the vegetation response to mechanical mastication and supplemental fuels treatments was investigated at one study site. Total woody fuel loading of masticated fuelbeds significantly differed by site (P < 0.001) ranging between 15.3 and 63.4 Mg ha-1. Over 50% of the woody fuel loading across all sites occurred within the 10-hr timelag class. Additionally, mechanically masticated fuelbeds were distinct compared to existing fuel models, warranting the future development of fuel models specific to masticated fuelbeds. The vegetation response to mechanical mastication treatments varied by treatment type and vegetation measure.\ud
Plant cover did not significantly differ across treatment type (P = 0.062) but non-native forb density (P = 0.010) and diversity (P = 0.002) measures did. Mastication only treatments resulted in the highest non-native forb densities (0.8 stems m-2) while mastication followed by prescribed fire resulted in the highest species richness (11.3 species m-2)
Moisture dynamics and fire behavior in mechanically masticated fuelbeds
No full textThesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 2008Changing 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.McIntire-Stennis Forestry Research Program\ud
Joint Fire Science Progra
Assessing the impact of sudden oak death on crown fire potential in Tanoak forests of California
Get PDFThe introduction of non-native pathogens can have profound effects on forest ecosystems resulting in tree mortality, changes in species composition, and altered fuel structure. The 1990's introduction of Phytophthora ramorum, the pathogen recognized as causing the tree and plant disease known as sudden oak death, has caused rapid decline and mortality of tanoak (Lithocarpus densiflorus) in forests of coastal California, USA. To understand the potential effect that mortality could have on fuel structure and fire behavior, foliar moisture content of uninfected tanoaks, sudden oak death-infected tanoaks, sudden oak death-killed (dead) tanoaks, and surface litter was tracked for 12 months. Foliar moisture content of uninfected tanoaks averaged 82.3% for the year whereas foliar moisture content of infected tanoaks had a lower average of 77.8%. Dead tanoaks had significantly lower foliar moisture content than uninfected and infected trees, averaging 12.3% for the year. During fire season (June through September), dead tanoak foliar moisture content reached a low of 5.8%, with no significant difference between dead canopy fuels and surface litter. Remote automated weather station (RAWS) 10-hour timelag fuel moisture data corresponded to foliar moisture content of dead leaves, holding promise as a predictor of seasonal crown fire hazard. Decision support tools, based on Van Wagner's (1977) crown ignition equation, can predict canopy base height values to escape crown ignition, however the Van Wagner equation was developed for conifers, not broadleaf trees (such as tanoak). No empirical data exist to corroborate ignition thresholds for extremely low foliar moistures found in dead foliage. To quantify crown base height ignition thresholds, a laboratory experiment was employed to measure foliar ignition and consumption at crown base heights from 0.5 m to 1.5 m across the range of foliar moistures found in healthy, sudden oak death-infected, and sudden oak death-killed tanoaks. Results from laboratory burning showed all foliage was consumed at the lowest simulated crown base heights in the laboratory, however consumption of live foliage dropped off quickly with increasing crown base height, with minimal consumption occurring at 1 m and above. Consumption of dead foliage declined with increasing simulated crown base heights, with some consumption still occurring at the highest crown base height tested (1.5 m). Using logistic regression, variables of crown base height, temperature, and duration of temperatures above 320 ºC or 410 ºC were used to predict crown ignition probabilities for all foliar moisture treatments tested (80%, 70%, 9%, and 5% foliar moisture content). Crown base height performed well as a predictor of crown ignition with correct predictions 87% to 91% of the time. Minimizing the probability of live tanoak foliage ignition results in a crown base ignition threshold lower than the Van Wagner model, while the dead tanoak foliage ignition threshold is considerably lower than an extrapolated Van Wagner equation. This suggests that tanoak will resist crown ignition at a lower threshold than conifers across the crown base heights tested. Results from this study will help refine the decision support tools for fire managers in sudden oak death-affected areas as well as serve as a model for other forests where diseases and insect epidemics have altered forest crown fuels.Thesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 201
The effects of native conifer encroachment and importance of high-severity wildfire in fire-excluded California black oak ecosystems of northern California
No full textThesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 2011The absence of fire in many oak woodlands that historically experienced frequent fire has resulted in invasion and subsequent overtopping of oaks by fast-growing conifers. Little is known about the effects of these structural and compositional changes occurring in California black oak (Quercus kelloggii) woodlands. This study addresses two broad questions: 1) How will conifer-encroached California black oaks respond to re-introduced fire in areas that have gone unburned for many decades? And 2) what actions can forest managers take toward California black oak woodland restoration and maintenance over time? Tree competition around individual California black oaks, tree age, and California black oak post-fire responses were investigated in Klamath and Lassen National Forests in northern California. Plots were established around focal oaks where attributes of neighboring encroaching trees, tree regeneration, and fire effects were measured. At both sites woodland overstory was heavily dominated by relatively fire-intolerant conifers, particularly Douglas-fir (Pseudotsuga menziesii) and white fir (Abies concolor). At the Klamath site, trees that pierced California black oak crowns were younger than paired oaks. The probability of California black oak mortality from fire was correlated with neighboring Douglas-fir height, indicating a compromising effect of encroachment on oak survival. At the Lassen site 90% of killed California black oak stems sprouted following fire. Oak recovery was strongest in severely burned areas; linear modeling revealed significant negative relationships between overstory tree survival and both California black oak sprout height and basal area. A conceptual model for the formation and persistence of these specific stand structures is proposed in which fire severity and encroachment pressure affect compositional change over time. Unless specific management actions are taken to protect California black oak woodlands, many encroached stands may be converted to conifer forest.United States Department of Agriculture - Forest Service, Pacific Southwest Research Statio
Fuelbed heterogeneity, flammability, and restoration of historically fire frequent oak woodlands with fire
Get PDFThe role of fire in the maintenance of Quercus-dominated ecosystems is widely recognized. Variability in surface fuels is a mechanism rooted in the maintenance of stand structure. This study examined fuelbed heterogeneity, fire behavior, and young conifer mortality within Quercus garryana woodlands and grasslands in the Bald Hills of Redwood National Park, California, USA. Woodlands were stratified into five structural communities: grassland; oak savanna; oak cluster; oak woodland; and woodland invaded by Pseudotsuga menziesii (invaded woodland). Live and dead fuel moisture and fuel mass (Mg ha-1) in three fuel strata (herbaceous, litter, woody) were sampled in the summers of 2008 and 2009. Fire temperature maxima during prescribed burns were measured with pyrometers. Across woodland structural communities, results reveal herbaceous mass decreases markedly from a high in grassland (3.38 ± 0.19 Mg ha-1) to a low in invaded woodland (0.03 ± 0.03 Mg ha-1) (p 0.001), whereas leaf litter and woody fuel mass increase significantly along this gradient (p 0.001). Mean fire temperatures ranged from 74.7 °C in invaded woodland up to 207.9 °C in grassland, but did not differ significantly across structural communities. P. menziesii invasion ultimately dampens flammability through increased fuel moisture, replacement of herbaceous with woody fuels, and altered understory micro-climate. To prevent invasion by P. menziesii, managers use prescribed fire to kill fire-sensitive saplings. Post-fire mortality was monitored for 100 P. menziesii saplings following a prescribed burn. The fire resulted in 50 percent mortality of conifer seedlings and saplings, with strong patterns in the drivers of individual tree injury. Percent crown volume scorched was the most important factor affecting initial mortality status, and was related to cambium injury (r = 0.67). Prescribed fire is a valuable tool for the maintenance of oak woodlands and grasslands, but the achievement of desired fire effects in these ecosystems may depend on site-specific burning strategies to account for alterations in fuelbeds and flammability across structural communities.Thesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 201
Natural tree regeneration dynamics a decade after the Storrie Fire in the Lassen National Forest
Get PDFLarge scale, high-severity fires are increasing in the western United States. Despite this trend, there have been few studies investigating post-fire tree regeneration, even fewer have focused on tree regeneration after large wildfires in the southern Cascades-northern Sierra Nevada. We established a study in the 2000 Storrie Fire, a 23,000 ha wildfire that occurred in the Lassen and Plumas National Forests in northern California. We used a stratified sampling design to quantify post-fire vegetation dynamics across four levels of burn-severity (unchanged, low-severity, medium-severity, high-severity) and three vegetation types (mixed conifer, low-elevation fir, high-elevation fir) on the Lassen during the summers of 2009 and 2010. Conifer seedlings were measured within five replicates of clustered 3.59 m radius plots. Within each plot we recorded biotic and abiotic factors that we hypothesized to influence seedling growth and establishment. We found abundant mature conifer seedlings across much of the landscape. Oaks were prevalent in the lower elevation strata and responded to fire with heavy sprouting. Median conifer seedling densities varied substantially by burn severity, ranging from 1,918 seedlings ha-1 in the unchanged units; 4,838 seedlings ha-1 in the low-severity units; 6,484 seedlings ha-1 in the medium-severity units; and 710 seedlings ha-1 in the high-severity units. The majority (80%) of high-severity units sampled were "understocked" according to regional density thresholds. We fitted a Zero-Inflated Negative Binomial (ZINB) linear model to determine significant predictors of mature conifer seedling density. The developed model best accounted for the high level of residual variance inherent to seedling densities across the landscape. In addition to the strata blocking (burn severity × vegetation type), significant positive predictors included the topographic index (a transform of slope and aspect), slope position (lower-, mid- and upper-slope), available growing space (a transform of free above-ground growing space and shrub cover), average shrub height and the stand perimeter-to-area ratio. A linear model was also developed to better understand seedling stocking across the landscape. Interpretation of model coefficients is useful in aiding land management decisions and better understanding regeneration dynamics in response to large wildfires that are increasingly common in fire-prone western landscapes.Thesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 2011
Plant community responses to fire exclusion, species invasions, and restoration in California woodlands and grasslands
Get PDFQuercus garryana woodlands and coastal grasslands in the Pacific Northwest are fire-dependent communities, threatened by encroachment from the native conifer Pseudotsuga menziesii in the absence of fire. In the Bald Hills of Redwood National Park in California, prescribed fire and conifer removal are used to restore and maintain woodlands. Understory vegetation was compared in four categories: encroached woodlands; formerly encroached woodlands treated with conifer removal; formerly encroached woodlands treated with conifer removal and prescribed fire; and never encroached and burned woodlands. At the site level no difference was found in mean native species richness (p = 0.155). When sites were combined by treatment category, the two categories that included fire had the greatest number of unique native species. Encroached woodlands had significantly lower richness (p 0.001), and lower Shannon Diversity (p 0.01), compared to the three other categories. The two categories that included fire also had a significantly greater number of mean non-native species compared to encroached woodlands (p 0.001). These results suggest prescribed fire and conifer removal have benefits to understory plant communities and the maintenance of this ecosystem; however, the abundance of exotic species and their adaption to fire in the Bald Hills complicates the restoration of native flora. Fuel moisture content of four native and four non-native grass species were sampled in a coastal grassland during the 2012 fire season. Differences in mean moisture content were compared between native and non-native groups using a linear mixed effects model with species as a random effect nested in group. No significant difference was found between natives and non-native groups (p = 0.337). Differences in moisture content among species, across dates, and for the species × date interaction were compared with a two-way analysis of variance. Across all dates, moisture content of the eight grasses differed significantly (p 0.001). Harding grass, Phalaris aquatica, an aggressive non-native, had the highest mean moisture content for all months and differed significantly from all species for all dates (p 0.05). The non-native dogtail, Cynosurus echinatus, had the lowest moisture content in August (21%), and fell well below the moisture of extinction before most species studied. Our results suggest that some non-native species have the capacity to alter fire behavior by either increasing or decreasing fire intensity and rate of spread. These findings reveal another way non-native species complicate restoration in this fire-dependent ecosystem.Thesis (M.S.)--Humboldt State University, Natural Resources: Forest, Watershed, and Wildland Sciences, 201
Carbon distribution in managed upland redwood stands using the California Climate Action Registry Forest Project Protocol
No full textThesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 2009In response to global climate change and the resulting need to reduce greenhouse gases, forest carbon sequestration is being investigated as a way to reduce levels of the primary greenhouse gas: carbon dioxide. To determine sequestered carbon in forests, accurately measuring carbon is of increasing importance. Carbon distribution was assessed in a managed redwood (Sequoia sempervirens D. Don) Endl.) forest in Humboldt County, California using methods described in the newly established California Climate Action Registry???s Forest Project Protocol. Stands studied were closed canopy second- and third-growth stands, dominated by redwood. The second-growth stands had 3.35 times more total carbon than the third-growth stands. By far the largest above-ground carbon pool in both stands was trees greater than or equal to 7.62 cm DBH (433,946 kg carbon ha-1 in second-growth and 69,613 kg carbon ha-1 in third-growth). Litter, downed woody debris, duff, snags greater than or equal to 7.62 cm DBH, and stumps represented 11 percent of the total above-ground carbon in the second-growth and 44 percent in the third (52,691 kg carbon ha-1 in the second-growth and 64,123 kg carbon ha-1 in the third). The recently released Forest Project Protocol was developed as a guide for the design, implementation, and registration of forest projects to allow entities to accurately report their greenhouse gas emissions and reductions. Using the field results, I evaluated the Forest Project Protocol and recommended that future iterations: (1) remove roots as a required carbon pool; (2) add litter and duff as required pools; (3) provide detailed forest project examples; (4) provide additional allometric tree biomass equations relevant to the diversity in California forests; and (5) keep minor pools optional (e.g. trees and snags less than 7.62 cm DBH)
Stucture of downed woody and vegetative debris in old-growth Sequoia sempervirens forests
No full textStructural properties of downed woody and vegetative debris populations in unmanaged old-growth forests provide evidence of the reference conditions from which the impact of natural and anthropogenic disturbances may be evaluated. The structure of downed debris populations in five old-growth Sequoia sempervirens stands along the north coast of California was assessed using data collected from an intensive network of line intersect sampling transects. Total mass of woody and vegetative debris ranged between 252 and 619 Mg ha-1 among sites. Volume ranged between 540 and 1400 m3 ha-1. Eighty-six percent of downed woody debris mass consisted of logs greater than 7.62 cm diameter, four percent consisted of particles less than or equal to 7.62 cm diameter, and ten percent of downed woody debris mass was litter (Oi) and duff (Oe and Oa). Forest floor bulk density ranged between 4.9 and 6.3 Mg ha-1 cm-1 and depth between 7.4 and 10.9 cm among sites. Average surface fuel heights ranged between 26.2 and 46.4 cm among sites. These values are among the greatest recorded in any forest ecosystem.Thesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 200
The effects of native conifer encroachment and importance of high-severity wildfire in fire-excluded California black oak ecosystems of northern California
Get PDFThe absence of fire in many oak woodlands that historically experienced frequent fire has resulted in invasion and subsequent overtopping of oaks by fast-growing conifers. Little is known about the effects of these structural and compositional changes occurring in California black oak (Quercus kelloggii) woodlands. This study addresses two broad questions: 1) How will conifer-encroached California black oaks respond to re-introduced fire in areas that have gone unburned for many decades? And 2) what actions can forest managers take toward California black oak woodland restoration and maintenance over time? Tree competition around individual California black oaks, tree age, and California black oak post-fire responses were investigated in Klamath and Lassen National Forests in northern California. Plots were established around focal oaks where attributes of neighboring encroaching trees, tree regeneration, and fire effects were measured. At both sites woodland overstory was heavily dominated by relatively fire-intolerant conifers, particularly Douglas-fir (Pseudotsuga menziesii) and white fir (Abies concolor). At the Klamath site, trees that pierced California black oak crowns were younger than paired oaks. The probability of California black oak mortality from fire was correlated with neighboring Douglas-fir height, indicating a compromising effect of encroachment on oak survival. At the Lassen site 90% of killed California black oak stems sprouted following fire. Oak recovery was strongest in severely burned areas; linear modeling revealed significant negative relationships between overstory tree survival and both California black oak sprout height and basal area. A conceptual model for the formation and persistence of these specific stand structures is proposed in which fire severity and encroachment pressure affect compositional change over time. Unless specific management actions are taken to protect California black oak woodlands, many encroached stands may be converted to conifer forest.Thesis (M.S.)--Humboldt State University, Natural Resources: Forestry, 201
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