California Oak Woodland Research Articles

Habitat Relationships of Amphibians and Reptiles in California Oak Woodlands

We used pitfall traps and time-constrained searches to sample amphibians and reptiles and to describe their habitats in oak woodlands at three areas in California. We captured 766 individuals rep- resenting 15 species during pitfall trapping and 333 animals representing 15 species during the time-con- strained searches. A total of 19 species were sampled. Across all study areas, several positive relationships were found between animal abundance and the cover of specific tree species. At Tejon Ranch, two salaman- ders-Batrachoseps nigriventris and Ensatina eschscholtzii croceater-were associated with canyon live oak (Quercus chrysolepis) and two lizards-Sceloporus occidentalis and Eumeces gilberti-were associated with California black oak (Q. kelloggii). At San Joaquin, B. nigriventris was associated with foothill pine (Pinus sabiniana), as was B. attenuatus at Sierra Foothill. Generally, salamanders were found in live oak woodlands on north-facing slopes at Tejon Ranch, or on north-facing woodlands dominated by foothill pine and interior live oak (Q. wislizenii) at Sierra Foothill and San Joaquin. In contrast, lizards used more xeric and open habitats dominated by California black oak, blue oak (Q. douglasii), and valley oak (Q. lobata). As would be expected for terrestrial and fossorial animals, litter depth, the development of grasses and forbs, and cover by downed woody debris and rocks were important in the habitat models. At Sierra Foothill and San Joaquin, these latter variables, in addition to slope, were of primary importance in the habitat models.

Oak tree and grazing impacts on soil properties and nutrients in a California oak woodland

There is great interest in understanding how rangeland management practices affect the long-term sustainability of California oak woodland ecosystems through their influence on nutrient cycling. This study examines the effects of oak trees and low to moderate intensity grazing on soil properties and nutrient pools in a blue oak (Quercus douglasii H.&A.) woodland in the Sierra Nevada foothills of northern California. Four combinations of vegetation and management were investigated: oak with grazing, oak without grazing, open grasslands with grazing, and open grasslands without grazing. Results indicate that oak trees create islands of enhanced fertility through organic matter incorporation and nutrient cycling. Compared to adjacent grasslands, soils beneath the oak canopy have a lower bulk density, higher pH, and greater concentrations of organic carbon, nitrogen, total and available P, and exchangeable Ca, Mg, and K, especially in the upper soil horizons (0-35 cm). In contrast, the light grazing utilized at this site had minimal effects on soil properties which included an increase in the bulk density of the surface horizon and an increase in available P throughout the entire soil profile. While low to moderate intensity grazing has little effect at this study site, there could be much larger impacts under the more intensive grazing practices utilized on many rangelands. The lack of oak regeneration and oak tree removal to enhance forage production may eventually lead to large losses of nutrients and soil fertility from these ecosystems. Results of this study have important implications for predicting how management practices may potentially affect oak regeneration, water quality, and ecosystem sustainability.

Blue-Oak Regeneration and Seedling Water Relations in Four Sites within a California Oak Savanna

Water relations of transplanted and naturally occurring blue-oak seedlings (Quercus douglasii Hook. & Arn.) were studied to examine the effects of site differences with regard to the rates of progressing drought on the current lack of blue-oak establishment in California oak savannas. Seedling water relations were compared from May to September 1987 at four sites, differing in terms of canopy structure, grazing history, and grass density. During the dry season, water status of transplanted seedlings was more favorable at a grazed open site where grass density was minimal but soil and atmospheric drought were most pronounced. In contrast, transplanted seedlings experienced the highest rates of water deficit and senesced earliest at a grazed canopy site that had the highest density of grasses. Naturally occurring seedlings were present only in the grazed canopy and ungrazed canopy sites, and their water relations were similar at both sites. Naturally occurring seedlings were 3-4 yr old, and thus their roots might have already extended to deeper soil layers where competition from grass roots was low. We conclude that blue-oak seedlings resist drought by osmotic adjustment, particularly when seedling water stress progresses slowly because of lack of severe belowground competition from grasses. The process of osmotic adjustment was perhaps more critical for seedling survival than for seedling growth. Seedling stomatal conductances responded primarily to seedling water status rather than to soil or atmospheric drought. It seemed that the density of grasses was more important in explaining patterns of seedling water stress than was either microclimate or the change in dominance from perennial to annual grasses during the past century.

The Potential for a California Oak Wilt Epidemic

The relative disease susceptibilities of 14 Quercus species from Texas and California were tested in three inoculation studies with different isolates of the oak wilt pathogen, Ceratocystis fagacearum. Ten of the oaks were evergreen or semi-evergreen live oaks while the remaining four were deciduous species. The species represented 3 different Quercus sub-genera. All species were susceptible to the pathogen, but there was significant variability in disease response. In the first study, there was variability among different selections of live oak from Texas, and there were distinct differences in disease response among the California oaks in the other two experiments. In two of the studies, the most susceptible species was the exotic cork oak, Q. suber. Q. kelloggii, the only deciduous red oak inoculated, responded similarly to Q. suber, an evergreen white oak. The two evergreen red oaks, Q. agrifolia and Q. wislizenii, were the least susceptible in one of the studies while the two evergreen "intermediate" oaks, Q. chrysolepisand Q. tomentella, were the least susceptible in another. Significant differences in pathogenicity were observed between two Texas isolates of C. fagacearum. The implications of these results forthe California oak woodlands is discussed.

Composition and Production of California Oak Savanna Seasonally Grazed by Sheep

Seasonal grazing trials, conducted over 3 years at the Hopland Field Station in Mendocino County, Calif., tested the effects of 2 seasonal grazing strategies on within- and between-year production and composition in blue oak (Quercus douglasii H.A.) savanna understory and adjacent open annual grassland. Moderate intensity summer-fall-winter and spring-summer sheep use had few within-year effects. In contrast, production and composition varied considerably between years in both treatments. Forbs (especially legumes) decreased in open grassland and oak understory between years within both seasonal grazing regimes. This change could not have been caused by selective grazing because there were no corresponding within-year patterns. Instead, between-year changes are more likely related to nonselective effects of stocking rate and/or weather. Results from this study suggest that seasonal grazing systems offer little potential for improvement of annual range composition.

Mineral Cycling and Epiphytic Lichens: Implications at the Ecosystem Level

AbstractThe nutrient contribution of lichens as litterfall in forests is discussed for a number of different ecosystems and it is hypothesized that lichens are important in capturing nutrients from wet deposition, occult precipitation, sedimentation, impaction and gaseous uptake. Most nutrients captured by these processes represent new nutrient inputs that would otherwise not be intercepted by the ecosystem. Part of these nutrients will be incorporated into lichen biomass and only become available upon death and decomposition, but a portion will be leached by precipitation and become deposited on the soil surface. Although quantifying nutrient sources, fluxes and pool sizes is a potentially complex task, we describe a simplified approach for determining whether lichens significantly affect the mineral cycling of a forest. Preliminary results for an oak woodland in California document that epiphytic lichens may reduce throughfall and alter throughfall chemistry.

California Oak-Woodland Overstory Species Affect Herbage Understory: Management Implications

Concerns for the future of California's oak-woodlands have intensified the need to better understand how different overstory species affect herbage standing crops and species frequencies. Data from over 8,000 plots harvested between 1961 and 1968 at the San Joaquin Experimental Range in the Sierra Nevada foothills of central California show that peak standing crops averaged 2,795 kg/ha in the open; 3,086 kg/ha under blue oak (Quercus douglasii); 1,840 kg/ha under interior live oak (Quercus wislizenii); 1,696 kg/ha under digger pine (Pinus sabiniana), and 1,917 kg/ha under buck brush (Ceanothus cuneatus). Overstory species affected standing crops differently on different range sites. On swales, standing crops were less under live oak and digger pine than in open areas. On open-rolling uplands, standing crops were less in the open and under live oak than under blue oak. On rocky-brush uplands, standing crops were less under all other overstory species than under blue oak. Data on species frequency suggest that herbage species of inter successional stages are more common under trees. The frequency of plant species varied with the species of overstory, and a diversity of overstory species may help to maintain adequate species diversity among understory species.

Wildlife diversity of the central Sierra foothills

A 3-year study of wildlife-habitat relationships in the oak woodlands of California's Sierra foothills found a wide range of species. This was directly related to the diversity of habitats provided by oak woodlands.

A Field Study of Parasitism of Larval Black Flies (Diptera: Simuliidae) by Neomesomermis flumenalis (Nematoda: Mermithidae) in Southern California

The prevalence of Neomesomermis flumenalis (Welch) parasitism in late-instar larvae of black fly populations was investigated in two California oak woodland streams in the foothills of the San Gabriel Mountains. A permanent stream in San Dimas Canyon was sampled from July 1982 through January 1984. The age-specific attack rate was documented in Simulium aureum Fries and Simulium piperi Dyar & Shannon populations during an epizootic in the fall of 1982. Sporadic infections of larvae were found throughout the year; however, high rates of parasitism developed only in association with substantial S. aureum populations. Mermithid infections were also documented in S. argus Williston, S. arcticum Malloch, S. vittatum Zetterstedt, and S. virgatum Coquillett. Study of an intermittently dry stream in Lodi Canyon suggests that free living N. flumenalis survive periods of summer drought in the stream bed and infect invading Simulium larvae when fall rains flood the channel.

Seasonal Change in Guild Structure: Oak Woodland Insectivorous Birds

The use of foraging sites by a foilage— and bark—gleaning guild of insectivorous birds was studied for 2 yr in a California oak woodland. Choices of plant types, perch size, and foraging height are presented for both residents and migrants in two contrasting seasons (fall/winter and spring). Seasonal differences were fewer than differences between years at the same season. Niche breadths and overlaps of residents in the 2nd yr of the study were mostly larger in spring than in fall/winter, although the contrasts were not statistically significant. The niche breadth findings are viewed as consistent with a prediction of optimal foraging theory that a broader range of patch types will be used when food is abundant. Dendrograms based on niche overlaps for fall/winter and spring showed that three resident species (Chestnut—backed Chickadee, Plain Titmouse, and Hutton's Vireo) constituted the core of the guild, together with two migrants in fall/winter (Ruby—crowned Kinglet and Yellow—rumped Warbler) and one in spring (Blue—gray Gnatcatcher). The foraging of residents was not influenced by the presence of different migrants at different seasons. Species most similar in foraging sites were distinct in bill size or behavior, except for the chickadee and the vireo. These two species are viewed as potential competitors.

Ecological Complementarity of Three Sympatric Parids in a California Oak Woodland

Journal Article Ecological Complementarity of Three Sympatric Parids in a California Oak Woodland Get access Paul E. Hertz, Paul E. Hertz Museum of Comparative Zoology and Department of Biology, Harvard University, Cambridge, Massachusetts 02138 Search for other works by this author on: Oxford Academic Google Scholar J. V. Remsen, Jr, J. V. Remsen, Jr Museum of Comparative Zoology and Department of Biology, Harvard University, Cambridge, Massachusetts 02138 Present address for second author: Department of Zoology and Museum of Vertebrate Zoology, University of California, Berkeley, California 94720. Present address for third author: Department of Chemistry, University of California at San Diego, La Jolla, California 92037 Search for other works by this author on: Oxford Academic Google Scholar Stacey I. Zones Stacey I. Zones Museum of Comparative Zoology and Department of Biology, Harvard University, Cambridge, Massachusetts 02138 Present address for second author: Department of Zoology and Museum of Vertebrate Zoology, University of California, Berkeley, California 94720. Present address for third author: Department of Chemistry, University of California at San Diego, La Jolla, California 92037 Search for other works by this author on: Oxford Academic Google Scholar The Condor, Volume 78, Issue 3, 1 July 1976, Pages 307–316, https://doi.org/10.2307/1367689 Published: 01 July 1976 Article history Accepted: 17 April 1975 Published: 01 July 1976