Treesearch

Frost heaving is a major cause of mortality in naturally and artificially regenerated ponderosa pine on basaltic soils in the Southwest. The effect of prescribed burning and mechanical removal of forest floor material on seedling size, soil nutrients, and subsequent susceptibility to frost heaving was observed in this study. A lower percentage of seedlings frost heaved on the burned treatment (3 percent) compared to scraped treatment (6 percent). The average seedling size that frost heaved was about the same for both treatments. Seedlings that survived the first winter were larger on the...

Heavy grazing and timbering during settlement by Europeans, and a policy of fire exclusion shortly after caused extensive structural and compositional changes to the southwestern ponderosa pine ecosystem. These changes have resulted in forest health problems, such as increased insect and disease epidemics, reduced wildlife habitat, and a serious wildfire hazard. Prescribed burning can reduce heavy fuel accumulations, provide adequate sites for natural regeneration, thin dense stagnated thickets, and create an edaphic and stand environment conducive to better forest health and productivity....

This paper is directed to the policy-makers who are responsible for urban design and its climatological consequences. It summarizes our current knowledge on the structure, energetics, and mitigation of the urban heat island. Special attention is given to physical features of the environment that can be easily manipulated, particularly vegetation. Prototypical designs illustrate how concepts of sustainable landscapes and urban climatology can be applied to counteract urban warming in street canyons, parking lots, urban parks, and residential streets. In a previous study (McPherson 1990a),...

A high-density genetic map based on restriction fragment length polymorphisms (RFLPs) is being constructed for loblolly pine (Pinus taeda L.). Consequently, a large number of DNA probes from loblolly pine are potentially available for use in other species. We have used some of these DNA probes to detect RFLPs in 12 conifers and an angiosperm. Thirty complementary DNA and two genomic DNA probes from loblolly pine were hybridized to Southern blots containing DNA from five species of Pinus (P. elliottii, P. lambertiana, P. radiata, P. sylvestris, and P. taeda), one species from each of four...

A total of 225 new genetic loci [151 restriction fragment length polymorphisms (RFLP) and 74 random amplified polymorphic DNAs (RAPD)] in coastal Douglas- fir [Pseudotsuga menziesii (Mirb.) Franco var. menziesii] have been identified using a three-generation outbred pedigree. The Mendelian inheritance of 16 RFLP loci and 29 RAPD loci was demonstrated based on single-locus segregation in a sample of F 2 progeny. One RFLP locus, PtIFG2025, showed segregation distortion. Probe pPtIFG2025 is a loblolly pine cDNA probe encoding for rbcS. The 16 RFLP loci and 23 allozyme loci were also assayed...

San Dimas Canyon seems a wild place beyond the reach of civilization. It is home to black bears, gray foxes, Anna's hummingbirds, scrub jays, and in early summer, a multitude of biting insects. Along the steep, northfacing hillsides, the chaparral has the appearance of an ancient forest. From within the canyon it is difficult to remember that one is less than 7 km from metropolitan Los Angeles. It is also difficult to conceive of the landscape swept by flames 30- or 40-m high, or to visualize San Dimas Creek afterwards scoured by debris flows. Our difficulty in perceiving these catastrophic...

Effects of wind velocity and slope on fire spread rate and flame length were examined. Fuel beds of vertical sticks (13.97 cm x 0.455 cm x 0.1 10 cm) and coarse excelsior were burned in an open-topped tilting wind tunnel. Mean fuel moisture content of sticks and excelsior was 11% and 12%, respectively. Mean surface area to volume ratio was 23 cm-! Five slopes (negative, positive, none) were combined with five wind velocities (heading, backing, none). Spread rate was measured with thermocouples; flame length was estimated from video imagery. Mean spread rate ranged from 0.001 to 0.06 m/s....

The combined effects of wind velocity and slope on wildland fire behavior can be studied in the laboratory using a tilting wind tunnel. The tilting wind tunnel requires a commercially available fan to induce wind and can be positioned to simulate heading and backing fires spreading up and down slope. The tunnel is portable and can be disassembled for transport using a full-size pickup truck. Vertical velocity profiles indicate that the average turbulence level is about 15 percent of mean wind velocity.

Severe fires in chaparral watersheds subject to air pollution from metropolitan Los Angeles mobilized accumulated nitrogen and caused streamwater to be polluted with nitrate at concentrations exceeding the Federal Water Quality Standard. Streamwater NO3- concentrations were elevated during peak flows, the largest of which was a debris flow that transported NO3- at concentrations as high as 1.12 mequiv/L. Annual NO3- loss from severely burned watersheds, averaging 1.2 kequiv/ha, was 40 times greater than that from areas that remained unburned. Fires of moderate intensity produced a more...

The Marbled Murrelet (Brachyramphus marmoratus) occurs along the coasts of the North Pacific. It is unique among the Alcidae in its tree nesting habits. Recent research has revealed that in forested areas it is closely associated with old-growth coniferous forests, most of which have been harvested over the past 100 years. All historical accounts, although fragmentary, indicate a previously higher population of the bird throughout its North American range. Several reasons for the decline have been advanced, including habitat removal, mortality due to capture in fishing nets, and increased...