Treesearch

Since the mid 1990s, Phytophthora ramorum has been responsible for the widespread mortality of tanoaks, as well as several oak species throughout California and Oregon forests. However, not all trees die, even in areas with high disease pressure, suggesting that some trees may be resistant to the pathogen. The apparent resistance to P. ramorum infection of some individuals within coast live oak populations has been observed in artificial inoculation studies. For example, from artificial branch-cutting inoculation trials, Dodd and others (2005) found significant variation (up to eightfold...

Leaves with lesions caused by Phytophthora ramorum Werres, de Cock & Man in?t Veld often drop off infected plants. Because fallen leaves might serve as sources of inoculum both for the above-ground tissues of host plants and for their roots, this study quantified the inoculum produced by such leaves on the surface of pots when exposed to different watering regimes or different temperatures. In one experiment3, a 6.5 cm2 piece of infected lilac leaf was placed on the surface of potting mix in pots containing healthy lilac plants (Syringa vulgaris L.). The pots were then watered using a leaf...

The aetiology and frequency of Phytophthoras in discoloured xylem tissue beneath phloem lesions was investigated in a range of broadleaved trees infected with P. ramorum, P. kernoviae and several other Phytophthoras. Isolation was attempted from the inner surface of 81, 6 x 4 cm sterilised discoloured wood panels from 53 trees. Discolouration mostly extended 1 to 5 mm into the xylem (75 percent) but incursions of 6 to 10 mm (10 percent) and 10 to 25 mm (15 percent) were frequent. Phytophthora was isolated from 81 percent of the wood panels. In 66 cases, both a wood panel and an overlying...

This is the fifth in a series of studies to evaluate perceptions of the roles, responsibilities, and issues entailed in the jobs of U.S. Department of Agriculture Forest Service law enforcement and investigations (LEI) personnel. An e-mail survey was administered to the 537 Forest Service forest supervisors and district rangers (National Forest System [NFS] line officers) across the United States. Two-hundred and seventy-six completed and returned the questionnaire. Interaction, collaboration, and teamwork were important to the NFS line officer respondents—they reported the need for...

Aerial surveys have been conducted since 2001 to map recent hardwood mortality and consequently target ground visits for detection of Phytophthora ramorum, the pathogen that causes sudden oak death (SOD). Each year the aerial and ground surveys monitored much of California?s forests at risk for SOD resulting in new maps of hardwood mortality, detection of new P. ramorum infestations, and identification of areas unlikely to be infested by P. ramorum. Nearly 50,000 miles of California forest and woodland were flown by helicopter and fixed-wing aircraft over six years of aerial surveys. Of...

Sudden oak death (caused by Phytophthora ramorum) is currently having a dramatic impact on the flow of ecosystem services provided by trees and forests in California. Timber species in California are not thought to be at risk of mortality from this pathogen and, consequently, economic impacts accrue to non-market values of trees such as aesthetics, shading, and the knowledge that healthy forest ecosystems exist. Because non-market valuation studies are expensive to design and implement, we propose that spatial benefit transfer methods can be used as a pragmatic means for obtaining second-be...

As part of the EU project ?Risk analysis for Phytophthora ramorum, a recently recognised pathogen threat to Europe and the cause of Sudden Oak Death in the USA? (acronym RAPRA) outbreak scenarios are defined and existing strategies for eradication and containment of Phytophthora ramorum evaluated. Based on the current knowledge about disease epidemiology three types of outbreaks have been identified: the rhododendron system in northern Europe, a hypothetical system in southern Europe, and the nursery system. The logistic curve is suggested as a model to describe the geographical spread of...

Culture, detection with diagnostic PCR, and microscopy demonstrated the presence of Phytophthora ramorum in the sapwood of mature, naturally infected tanoak (Lithocarpus densiflorus) trees in Curry County, Oregon. The pathogen was strongly associated with discolored sapwood (P

On March 3, 2007 the North American Plant Protection Organization (NAPPO) sponsored a ?Risks to Conifers? discussion panel to review the state of scientific knowledge regarding Phytophthora ramorum Werres, De Cock & Man in 't Veld and conifers and the potential for the pathogen to be transported with conifer forest products moving in international trade. This panel took place during the third Sudden Oak Death Science Symposium organized by the USDA Forest Service Pacific Southwest Research Station, and the California Oak Mortality Task Force (COMTF) in Santa Rosa, California. It was...

Scientists have long inferred the locations of past treelines from the distribution of deadwood above modern tree boundaries. Although it is recognized that deadwood above treeline may have decayed, the absence of such wood is routinely taken to imply the absence of trees for periods ranging from the past few millennia to the entire Holocene. Reconstructed treeline histories are then explained in terms of such variables as slope, drainage, temperature, solar insolation, and precipitation. While these variables certainly help determine where deadwood is to be found above treeline today, we...