Treesearch

Mortality and resprouting of shrubs and trees were assessed in one recent fire and 11 older burns in blue oak woodland in the southern Sierra Nevada foothills. This poster reported results for blue oak. Survival following fire was high; with a 93 percent two year postfire survival rate after one intensively studied fire, despite a large number of trees with 100 percent crown scorch. Differences between sites accounted for most of the variability in mortality. Tree diameter was a minor component in mortality variability. Diameter was more important in resprouting, with most resprouting...

One wildfire and two prescription burns were monitored at 15 oak seedling/sapling regeneration sites and at four non-burned comparison sites to study the effect of fire on seedlings and saplings of Quercus engelmannii (Engelmann oak) and Q. agrifolia (coast live oak). The number of initial topkilled seedlings and saplings, initial survivors, postburn resprouts and total survivors at the end of the study were compared between fire study sites and the non-burned comparison sites. The initial top-kill rate was higher in the burn sites than in comparison sites. Although top-killed seedlings...

The influence of oak trees and grazing on nutrient cycling in oak woodland-grass ecosystems was examined at the Sierra Foothill Range Field Station in the northern-Sierra Nevada foothills of California. Nutrient concentrations in ecosystem waterflows (precipitation, canopy throughfall, and soil solutions) were monitored in a non-managed natural area and in an adjacent grazed area. Grazing increased soil solution concentrations of chloride (Cl) and sodium (Na), but had no effect on major nutrient levels. When comparing between oak and nonoak sites, the oak sites had enhanced soil solution...

A logical framework is required to provide a focus for the implementation of a variety of landowner incentive techniques in accordance with existing goals to protect and enhance hardwood resources. A system is presented for identifying and prioritizing critical hardwood resources for site specific conservation purposes. Flexibility is built into this system so that various sources of information can be utilized, the scope can vary from state-wide to local perspectives, and additional criteria can be added within specified system parameters.

Field measurements of oxygen concentration and oxygen diffusion rate (ODR) indicate that ODR is a more reliable indicator of problem sites. In a landscaped area where oak trees are declining, ODR in the upper part of the soil profile ranged between 0.1-0.2 µg O2cm2/minute (where µg = micrograms, and O2 = oxygen) for weeks at a time. In laboratory experiments, we have found low oxygen levels to inhibit oak root growth, and to predispose cork oak roots to extensive colonization by Phytophthora cinnamomi. Work is continuing to better define stress thresholds, and the effectiveness of aeration...

We studied the impacts of diseases and arthropods on acorns and naturally occurring seedlings of blue oak, Quercus douglasii, in northern California. Damage levels were always significantly higher in acorns collected from the ground than those picked from the tree. Accurate assessments of damage levels could only be made by dissecting acorns, since external symptoms were frequently absent from acorns with severe damage to the embryo. Levels of insect and disease damage to acorns varied significantly between locations and between trees. Foliar feeding by several types of insects had no...

Lack of blue oak (Quercus douglasii) saplings and seedlings throughout much of its range has prompted research into the regeneration status of the species. Our ability to assess whether the current lack of regeneration is a natural pattern or a response to human induced environmental change is limited by lack of data on the history of blue oak establishment. This study presents data on blue oak age stand structure collected from three sites on the Tejon Ranch, in the Tehachapi Mountains. Over half of the trees aged became established during the 1850s, whereas almost no new trees have come...

Changes in the availability, productivity and cost of hardwood rangeland affects the production and location of range-fed livestock. The California Range Livestock Model (CRLM) was developed to determine the effect of proposed policies and alternative economic conditions on the range-fed livestock industry generally and hardwood rangeland in particular. Three possible changes in range conditions were analyzed with the CRLM. Eliminating grazing on 9.7 million acres of Federally owned rangeland in California reduced annual livestock production by $80 million and producer's incomes by $9.3...

The oak woodlands of San Diego County are below their potential productivity due to the low levels of the most needed plant nutrient, nitrogen, associated with the common soils of this zone. Atmospheric nitrogen fixing legumes could address this deficiency. However, because of limiting environmental constraints, adapted commercial legume cultivars have not been available. By the early 1980's, a modest plant exploration program was begun to identify annual legumes with potential for adaptation to this region, locate them in their native or naturalized habitat, collect and reproduce an...

Two-hundred shoots contained within randomly selected locations from each of thirty-six coast live oak, Quercus agrifolia, trees were sampled to determine the abundance and spatial distribution of acorns infested by the filbert weevil, Curculio occidentis in northern California during 1989. The seasonal abundance of infested acorns was highest at 30 percent during mid-September. Overall, 25 percent of all acorns observed on sample trees revealed signs of boring insect activity. Slightly higher infestation rate of 38 percent was obtained from laboratory dissections of field collected acorns...