Treesearch

Soil water repellency is partularly common in unburned chaparral, and its degree and duration can be influenced by seasonal weather conditions. Water repellency tends to increase in dry soils, whil eit decreases or vanishes following precipitation or extended periods of soil moisture. The 15426 ha Williams Fire provided an opportunity to investigate post-fire fluctuations in water repellency over a 1-year period. Soil water repellency was measured at the surface, and at 2-cm and 4-cm depths along six east-west positioned transects located within the chaparral-dominated San Dimas Experimenta...

Fire exclusion has led to an unnatural accumulation and greater spatial continuity of organic material on the ground in many forests. This material serves both as potential fuel for forest fires and habitat for a large array of forest species. Managers must balance fuel reduction to reduce wildfire hazard with fuel retention targets to maintain other forest functions. This study reports fuel consumption and changes to coarse woody debris attributes with prescribed burns ignited under different fuel moisture conditions. Replicated early season burn, late season burn, and unburned control...

A regional simulation using the regional spectral model (RSM) with 50-km grid space increment over South America is described. NCEP/NCAR 28 vertical levels T62 spectral resolution reanalyses were used to initialize and force the regional model for a two-year period from March 1997 through March 1999. Initially, the RSM had a severe drying trend in the soil moisture that adversely impacted the precipitation. The drying trend was presumably a response to the positive feedback between imperfect model parameterization schemes and the soil moisture module in the model. This drying trend was...

The National Centers for Environmental Prediction regional spectral model and mesoscale spectral model (NCEP RSM/MSM) use a spectral computation on perturbation. The perturbation is defined as a deviation between RSM/MSM forecast value and their outer model or analysis value on model sigma-coordinate surfaces. The horizontal diffusion used in the models applies perturbation diffusion in spectral space on model sigma-coordinate surfaces. However, because of the large difference between RSM/MSM and their outer model or analysis terrains, the perturbation on sigma surfaces could be large over...

To determine the impact of fertilization and thinning on red fir (Abies magnifica) stand growth and development, we established an experiment in a 60-year-old stand using a 2x3 factorial design with nitrogen fertilized and non-fertilized treatments and three stocking levels. Plots were established in 1976 and were measured every 5 years for 26 years. Fertilized trees grew 97%, 51%, 38%, and 33% more PAI basal area than non-fertilized trees during the first, second, third, and fourth 5-year periods, respectively. After that, non-fertilized trees grew more basal area per year. Annual volume...

The crowns of five canopy dominant black cherry ( Prunus serotina Ehrh.), five white ash ( Fraxinus americana L.), and six red maple ( Acer rubrum L.) trees on naturally differing environmental conditions were accessed with scaffold towers within a mixed hardwood forest stand in central Pennsylvania. Ambient ozone concentrations, meteorological parameters, leaf gas exchange and leaf water potential were measured at the sites during the growing seasons of 1998 and 1999. Visible ozone-induced foliar injury was assessed on leaves within the upper and lower crown branches of each tree. Ambient...

The Scripps Experimental Climate Prediction Center has been making experimental, near-real-time, weekly to seasonal fire danger forecasts for the past 5 years. US fire danger forecasts and validations are based on standard indices from the National Fire Danger Rating System (DFDRS), which include the ignition component (IC), energy release component (ER), burning index (BI), spread component (SC), and the Keetch-Byram drought index (DB). The Fosberg fire weather index, which is a simplified form of the BI, has been previously used not only for the USA but also for other global regions and...

The National Centers for Environmental Prediction (NCEP) regional spectral model (RSM) version 97 was used to investigate the regional summertime climate over Taiwan and adjacent areas for June-July-August of 1990 through 2000. The simulated sea-level-pressure and wind fields of RSM1 with 50-km grid space are similar to the reanalysis, but the strength of the simulated subtropical high tends to be too strong, resulting in intensified southeasterlies, instead of southwesterlies, over the region of southern to southeastern China. Generally, the simulated precipitation patterns of RSM1...

An extensive experimental and numerical study was completed to analyze the marginal burning behavior of live chaparral shrub fuels that grow in the mountains of southern California. Laboratory fire spread experiments were carried out to determine the effects of wind, slope, moisture content, and fuel characteristics on marginal burning in fuel beds of common chaparral species. Four species ([Adenostoma*] sp., Ceanothus sp., Quercus sp., and Arctostaphylos sp.), two wind velocities (0 and 2 m/s), two fuel bed depths (20 and 40 cm), and three slope percents (0%, 40%, or 70%) were used....

The Klamath-Siskiyou ecoregion of northern California is one of the most diverse temperate coniferous forests. A network of "late successional reserves" (LSRs) has been established to maintain characteristics of late successional forest and to promote late successional characteristics in younger stands. Also, an important goal of conservation management is the maintenance of genetic diversity of ecologically important species. However, this management strategy has not yet been implemented among the LSRs. This study examined the level of genetic diversity among populations of a soil-inhabiti...