Quercus agrifolia

Abstract: Sudden oak death is a new disease affecting tanoak (Lithocarpus densiflora) and oaks (Quercus spp) in California and Oregon, caused by the recently described pathogen Phytophthora ramorum. It has reached epidemic proportions in several counties in central California, leading to the death of tens of thousands of trees. In addition to oaks and tanoak, P ramorum has been found in nearly all woody plant species in mixed evergreen and redwood forests from central California to southern Oregon. Plant species that are not killed appear to serve as a reservoir for the pathogen. The high susceptibility of tanoak to infection and death suggests that P ramorum is an exotic pathogen, but its origins, and most details of its biology and ecology, remain unknown. Our limited knowledge only compounds our concern over the long-term implications of this epidemic for the ecology of coastal forests.

Abstract: Plant roots may be linked by shared or common mycorrhizal networks (CMNs) that constitute pathways for the transfer of resources among plants. The potential for water transfer by such networks was examined by manipulating CMNs independently of plant roots in order to isolate the role(s) of ectomycorrhizal (EM) and arbuscular mycorrhizal fungal (AMF) networks in the plant water balance during drought (soil water potential -5.9 MPa). Fluorescent tracer dyes and deuterium-enriched water were used to follow the pathways of water transfer from coastal live oak seedlings (Quercus agrifolia Nee; colonized by EM and AMF) conducting hydraulic lift (HL) into the roots of water-stressed seedlings connected only by EM (Q. agrifolia) or AMF networks (Q. agrifolia, Eriogonum fasciculatum Benth., Salvia mellifera Greene, Keckiella antirrhinoides Benth). When connected to donor plants by hyphal linkages, deuterium was detected in the transpiration flux of receiver oak plants, and dye-labelled extraradical hyphae, rhizomorphs, mantles, and Hartig nets were observed in receiver EM oak roots, and in AMF hyphae of Salvia. Hyphal labelling was scarce in Eriogonum and Keckiella since these species are less dependent on AMF. The observed patterns of dye distribution also indicated that only a small percentage of mycorrhizal roots and extraradical hyphae were involved with water transfer among plants. Our results suggest that the movement of water by CMNs is potentially important to plant survival during drought, and that the functional ecophysiological traits of individual mycorrhizal fungi may be a component of this mechanism.

Abstract: A total of 139 reflectance spectra (between 350 and 2500 nm) from coast live oak (Quercus agrifolia) leaves were measured in the laboratory with a spectrometer FieldSpecAPro FR. Correlation analysis was conducted between absorption features, three-band ratio indices derived from the spectra and corres- ponding relative water content (RWC, %) of oak leaves. The experimental results indicate that there exist linear relationships between the RWC of oak leaves and absorption feature parameters: wavelength position (WAVE), absorption feature depth (DEP), width (WID) and the multiplication of DEP and WID (AREA) at the 975 nm, 1200 nm and 1750 nm positions and two three-band ratio indices: RATIO 975 and RATIO 1200 , derived at 975 nm and 1200 nm. AREA has a higher and more stable correlation with RWC compared to other features. It is worthy of noting that the two three-band ratio indices, RATIO 975 and RATIO 1200 ,m ay have potential application in assessing water status in vegetation.

Abstract: Using a geographic information system (GIS), digital maps of environmental variables including geology, topography and calculated clear-sky solar radiation, were weighted and overlaid to,predict the distribution of coast live oak (Quercus agrifolia) forest in a 72 km2 region near Lompoc, California. The predicted distribution of oak forest was overlaid on a map of actual oak forest distribution produced from remotely sensed data, and residuals were analyzed to distinguish prediction errors dueto alteration of the vegetation cover from those due to defects of the statistical predictive model and due to cartographic errors. Vegetation pattern in the study area was associated most strongly with geologic substrate. Vegetation pattern was also significantly associated with slope, exposure and calculated monthly solar radiation. The proportion of observed oak forest occurring on predicted oak forest sites was 4O(rlo overall, but varied substantially between substrates and also depended strongly on forest patch size, with a much higher rate of success for larger forest patches. Only 21% of predicted oak forest sites supported oak forest, and proportions of observed vegetation on predicted oak forest sites varied significantly between substrates. The non-random patterns of disagreement between maps of predicted and observed forest indicated additional variables that could be included to improve the predictive model, as well as the possible magnitude of forest loss due to disturbances in different parts of the landscape.