Treesearch

Sudden oak death (SOD) has been shown to be caused by a new species of Phytophthora, P. ramorum. A basic understanding of the genetics of P. ramorum is critical to any management strategy. We have initiated a number of studies to examine species concepts, population biology and mating behavior of the pathogen. Based on a number of morphological features (e.g., a combination of deciduous sporangia and chlamydospores), the P. ramorum does not match any of the currently described species of Phytophthora. Sequences of the internal transcribed spacer (ITS) of nuclear ribosomal DNA were identical...

The black oaks of California include 4 tree species (California black oak, coast live oak, Shreve oak, interior live oak) that are known to hybridize. Complex patterns of population variation within each species are likely to result from these hybrid combinations and from subsequent introgressions. We have been studying population variation using biochemical and molecular markers and report results from the former here. Diversity is much greater in interior live oak and in Shreve oak than in either of the other two species, and is least in coast live oak. Shreve oak has not received...

We conducted a case-control study to examine the role of water stress and various other factors on the development of Phytophthora ramorum cankers in symptomatic (case) and symptomless (control) coast live oak (Quercus agrifolia) and tanoak (Lithocarpus densiflorus). Midday stem water potential (SWP) in Q. agrifolia subject trees ranged from –0.25 to –3.1 megapascals (MPa). SWP was higher (indicating lower water stress) in cases than controls. Other variables significantly associated with disease in Q. agrifolia included tree canopy dieback, the amount of the canopy shaded by other trees,...

This paper describes the oak woodland plant communities of Northwest California and their ecological status using data from 446 ecology plots collected on federal lands in Humboldt, Trinity, Siskiyou, Mendocino, Tehama, Glenn, Colusa and Lake Counties. Geographically, oak woodlands lie between the coastal mixed evergreen forests and the valley grasslands of the Central Valley. They were found in small patches nested within a mosaic of annual grasslands and conifer forests, and hence contain species common to both of these vegetation types. The oak woodlands of northwest California were...

We evaluated county planning policies and procedures to determine what protection is provided to oak woodlands during the land development process. We selected three Sierra Nevada counties to do a pilot assessment: El Dorado, Placer and Madera. The assessment methodology included three components: 1) analysis of county plans, policies, guidelines, and ordinances to determine if oak woodland management is addressed and if so, how; 2) analysis of development case studies to document the planning process used to conserve oak woodland; and 3) field evaluation of typical oak management activitie...

The mandate by the California Board of Forestry in 1993 required each of the 41 counties which have significant oak woodlands to develop programs for the ultimate protection of this resource. As of 2001, a few counties have planned for the sustainability of their oak woodlands, but some counties may not be addressing the key components that will determine the overall future status of oak woodlands across counties and regions. Most counties and cities use the individual tree as the fundamental unit of conservation and neglect entirely the need for policies on oak woodland conservation and...

The contributions of California and Spanish oak woodlands to owners, neighbors, and society are undervalued. Recent Spanish studies have begun to identify the components of value provided by traditional oak woodland agro-sylvo-pastoral systems, including environmental and self-consumption values. Work in California has revealed that self-consumption by owners, benefits to neighboring properties, and benefits to the larger society are important components of the total valuation of traditional low-intensity oak woodland ranching. In Spain, this type of bioeconomic analysis, known as "Total...

In 1989 The Nature Conservancy initiated a riparian horticultural restoration program on the floodplain of the middle Sacramento River, California. At nearly all restoration sites Valley oak (Quercus lobata Nee) comprised a major component of the planting design. Valley oaks are a keystone tree species of lowland floodplain habitats in California's Central Valley, contributing greatly to the structural and biological diversity of riparian forests in the region. Here we present preliminary comparisons of survival and structural development of oaks planted as acorns at six sites from 1990 to...

A study was conducted at five sites throughout California to determine how the sprouting of harvested blue oak (Quercus douglasii) is affected by the date the trees are cut down, the height of the residual stumps, and whether stumps are protected by fencing or not. After 10 years, 34 percent of the stumps had viable sprouts. The greatest effects were from fencing. Four times as many protected stumps survived than those exposed to browsing animals. Most of the mortality in unfenced areas occurred since the last evaluation eight years ago. Twice as many 90-cm-tall stumps had surviving...

In 1995 and 2000, a monitoring program was designed and implemented to track oak regeneration and native grass populations in target management areas in the four Open Space Preserves of the City of Walnut Creek, California. The program resulted from a collaboration of scientists at the University of California, Berkeley, a group of interested citizens known as the Walnut Creek Open Space Foundation, and the city of Walnut Creek. The goals of the monitoring project were determined by the City and the Foundation, as were the study site locations. The Foundation members volunteered and were...