Treesearch

Competition from understory vegetation for water and nutrients can limit productivity of young forest stands. Less is known of the effect of understory vegetation on long-term stand growth or soil organic properties. The effect of understory vegetation on periodic annual increments (PAIs) of basal area, height, and volume for ponderosa pine (Pinus ponderosa Dougl.) in central Oregon at 4- or 5-yr intervals was examined for a 35-yr period. Soil C, N, and microbial biomass C (MBC) were also quantified after 32 and 35 yr with and without understory vegetation on a sandy loam pumice soil...

Since European settlement, the southwestern ponderosa pine ecosystem has experienced large scale alterations brought about by heavy grazing and timbering and a policy of attempted fire exclusion. These alterations are most evident as large increases in tree numbers and in forest floor organic matter. 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 used in ecosystem restoration can reduce heavy fuel accumulations, provide adequate microsites for natural pine...

Natural forest fuel loadings cause extreme fire behavior during dry, windy weather experienced during most fire seasons in the Southwest. Fire severity is also exacerbated from burning heavy fuels, including heavy humus layers on the forest floor. Ponderosa pine and mixed conifer stands possess more than 21.7 and 44.1 tons per acre of total forest floor fuel, respectively, in Southwestern forest ecosystems.

Soils in mountainous terrain are often thin and unable to store sufficient water to support existing vegetation through dry seasons. This observation has led to speculation about the role of bedrock in supporting plant growth in natural ecosystems, since weathered bedrocks often have appreciable porosity and, like soil, can store and transmit water. This study, within a chaparral ecosystem in southern California, was designed to determine the extent of rooting within weathered granitic bedrock and to measure the relative contributions of soil and weathered bedrock to water-use by chaparral...

Variation in cold-hardiness traits, and their extent of genetic control and interrelationships, were investigated among individuals (clones) within a single large full-sib family of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) from Oregon. Cold injury to needle, stem, and bud tissues was evaluated in fall 1996 and spring 1997 following artificial freeze testing of detached shoots collected from 4-year-old ramets (rooted cuttings). Variation among clones in cold-injury scores was significant (p < 0.01) for all shoot tissues in both fall and spring and averaged...

On the island of Maui, the dispersion of air pollutants associated with the field burning of biomass is complicated because the persistent Maui Vortex in the lee of Haleakala tends to trap smoke making pollution concentration worse in the central valley. In the present study we describe the spatially as well as temporally continuous short-term climatology of the airflow in the central valley of Maui during a summer month under trade wind conditions, simulated by a high-resolution mesoscale model initialized and forced by large-scale objective analyses. These simulations are compared with...

Biomass burning is a common force in much of the developing tropical world and has wide-ranging environmental impacts. Fire is an important component in tropical deforestation and is often used to clear broad expanses of land for shifting agriculture, dispose of crop residue, and "clean" pastures for cattle grazing. It is part of a complex social phenomenon driven by human population expansion, national economics, foreign debt, land speculation, tax incentives, colonization, and political forces (Fearnside 1987; Hecht and Cockburn 1990). Biomass burning has an important role in the annual...

Airborne remotely sensed data were collected and analyzed during and following the 1988 Greater Yellowstone Ecosystem (GYE) fires in order to characterize the fire front movements, burn intensities and various vegetative components of selected watersheds. Remotely sensed data were used to categorize the burn intensities as: severely burned, moderately burned, mixed burn, lightly burned, and unburned. Water samples were then collected in six streams, under various burn conditions, for the next five years. Those samples, collected twice a day, for the summer months following snow melt, were...

Fire has been an important ecosystem process in the Sierra Nevada for thousands of years. Before the area was settled in the 1850s, fires were generally frequent throughout much of the range. The frequency and severity of these fires varied spatially and temporally depending upon climate, elevation, topography, vegetation, edaphic conditions, and human cultural practices. Current management strategies and those of the immediate past have contributed to forest conditions that encourage high-severity fires. The policy of excluding all fires has been successful in generally eliminating fires...

As a result largely of human activities during the past 150 years, fires in Sierra Nevada forests occur less frequently and cover much less area than they did historically but are much more likely to be large and severe when they do occur. High-severity wildfires are considered by many to be the greatest single threat to the integrity and sustainability of Sierra Nevada forests. The continuing accumulation of large quantities of forest biomass that fuel wildfires points to a need to develop landscape-level strategies for managing fuels to reduce the area and average size burned by severe...