Mastication of woody shrubs is used increasingly as a management option to reduce fire risk at the wildland–urban interface. Whether the resulting mulch layer leads to extreme soil heating, if burned, is unknown. We measured temperature profiles in a clay loam soil during burning of Arctostaphylos residues. Four mulch depths were burned (0, 2.5, 7.5 and 12.5 cm), spanning typical conditions at forested sites in northern California with dense pre-mastication shrub cover. Two soil moisture contents were compared at each fuel depth to simulate spring prescribed burning (moist soil) and late-season wildfire (dry soil). Maximum temperatures reached 600°C on the surface of dry soils and were 100–200°C lower for moist soil. Heating was extensive in dry soil for the two deepest mulch depths, exceeding the lethal threshold for plants (60°C) for a minimum of 7 h throughout the 10-cm soil profile. Minimal heat pulse was found with less mulch. Moist soil also dampened heat penetration; peak temperatures exceeded 60°C only to 2.5 cm in the soil profile for all but the deepest mulch layer. No adverse effects of burning on water repellency were found in dry or moist soil. The potential for biological damage from soil heating during fire exists following mastication, particularly in dry soil with a mulch depth of 7.5 cm or greater. Field projections indicate that up to one-fourth of treated areas with dense pre-mastication vegetation would surpass lethal soil temperatures during a surface wildfire.

1 In a study site in interior northern California, twenty individual lodgepole pines Pinus contorta were sprayed with a suspension of DISRUPT Micro-Flake ® Verbenone (4,6,6-trimethylbicyclo(3.1)hept-3-en-2-one) Bark Beetle AntiAggregant flakes (Hercon Environmental, Emigsville, Pennsylvania) in water, with sticker and thickener, from ground level to a height of 7 m. Twenty trees sprayed with just water, sticker and thickener served as controls. All trees were baited immediately after spraying with mountain pine beetle Dendroctonus ponderosae aggregation pheromone lures, and lures were refreshed after 4 weeks. 2 Trees treated with verbenone had significantly lower attack density by D. ponderosae than controls at 2, 4, 6 and 8 weeks after application of flakes. 3 None of the treated trees was attacked by red turpentine beetle Dendroctonus valens , whereas control trees averaged nearly two D. valens attacks per tree, 8 weeks after treatment. 4 A dry frass index, used to predict ultimate tree mortality, was significantly higher in control trees than treated trees for all four sampling intervals. This index proved to be a significant predictor of ultimate tree mortality. 5 Ten months after application, treated trees showed significantly lower mortality than control trees.

The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of multiple use management of the Nation's forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry research, cooperation with the States and private forest owners, and management of the National Forests and National Grasslands, it strives-as directed by Congress-to provide increasingly greater service to a growing Nation.The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual's income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.

Escalating controversy on clear-cutting, herbicides, burning, and grazing led to a research program with 40 studies, begun in 1980, that compared most of the vegetation management techniques used for enhancing growth of 1- to 3-year-old conifer seedlings. These include such direct techniques as manual manipulation, mulching, herbicides, and grazing for releasing conifer seedlings from undesirable vegetation, and several silvicultural practices (broadcast burning, group selection, genetically improved seedlings) that serve as indirect methods for reducing or avoiding vegetation problems. Manual release and mulching are effective but expensive. Herbicides are effective, applicable to almost all plant communities, and relatively inexpensive. Grazing is good for cattle and sheep, but does not significantly enhance conifer seedling growth. Utilizing the silvicultural practices noted above and emphasizing replacement vegetation show promise, but lack sufficient testing for us to evaluate feasibility. In most instances, forests cannot be managed economically without herbicides if the goal is to grow seedlings at the potential of the site and the plant community includes sprouting hardwoods and shrubs or rhizomatous forbs and ferns. If the goal is to create a forest with several age-classes and variable structure, but with slower seedling growth, longer time to harvest, and less species diversity in early seral stages, then it is possible to accomplish this without herbicides and other means of vegetation control.

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Thinning and prescribed burning are common management practices for reducing fuel buildup in ponderosa pine forests. However, it is not well understood if their combined use is required to lower wildfire risk and to help restore natural ecological function. We compared 16 treatment combinations of thinning, prescribed fire, and slash retention for two decades across a site quality gradient of second-growth pine stands, measuring changes in forest vegetation growth, structure, and composition. Thinning alone doubled the diameter growth increment of ponderosa pine, moderately stimulated shrub production, and resulted in lower tree mortality compared with unthinned plots. In contrast, repeated fire alone did not substantially alter stand structure or increase tree vigor, herbaceous production, or plant diversity. The combined use of thinning and repeated burning reduced shrub cover, yet produced no changes in herbaceous production, plant diversity, stand structure, or tree vigor compared with thin-only treatments. Additional findings identified (1) inconsequential effects of thinning residues on site productivity, (2) the need for multiple entries of prescribed fire if the abatement of shrubs is required, (3) the ineffectiveness of repeated burning to stimulate plant growth, and (4) that the thinning treatment served as an effective surrogate to fire for managing central Oregon forest vegetation.

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