Treesearch

Fire is returning to many conifer-dominated forests where species composition and structure have been altered by fire exclusion. Ecological effects of these fires are influenced strongly by the degree of forest change during the fire-free period. Response of fire-adapted species assemblages to extended fire-free intervals is highly variable, even in communities with similar historical fire regimes. This variability in plant community response to fire exclusion is not well understood; however, ecological mechanisms such as individual species’ adaptations to disturbance or competition and...

Determining how changes in abiotic conditions influence community interactions is a fundamental challenge in ecology. Meeting this challenge is increasingly imperative in the Anthropocene where climate change and exotic species introductions alter abiotic context and biotic composition to reshuffle natural systems.

A survey of areas previously anthropogenically disturbed and revegetated with woody nursery-reared native Californian vegetation was conducted in Santa Clara County between August and December of Previous sampling of revegetation sites had found nursery-origin transplants to be infested withPhytophthora species. Samples of roots and soil were collected from underneath dead, symptomatic, and non-symptomatic transplants at 24 sites and baited with a combination of pear fruit and Rhododendron leaves. Strains were isolated in 18 (75%) of the sites surveyed and 55 of the 145 samples baited,...

Over the past 14 years, a variety of native plant communities in northern California have been identified where introduced root-rotting Phytophthora species, most notably Phytophthora cinnamomi, P. cambivora, and P. cactorum, are causing decline and mortality of native species. In many older infested sites, the source(s) of the original Phytophthora introductions are not clear. Movement of contaminated soil is the most likely source in some sites that are located along roads and trails. In other cases, introductions are associated with plantings of nursery stock. In one site, a multi-specie...

To compensate for unavoidable impacts associated with critical water infrastructure capital improvement projects, the San Francisco Public Utilities Commission (SFPUC) restored over 2,050 acres of riparian, wetland, and upland habitat on watershed lands in Alameda, Santa Clara, and San Mateo Counties. Despite strict bio-sanitation protocols, plant pathogens (Phytophthora spp.) were detected at multiple restoration sites on SFPUC lands. SFPUC staff will provide an overview of various treatments employed to contain and treat the pathogens using multiple in-situ treatment techniques including...

Phosphite compounds have been used in the control of sudden oak death; however, their precise mode of action is not fully understood. To study the action of phosphite compounds in the context of naturally occurring host resistance, we first identified open-pollinated family groups that carried resistance, that is in which approximately 20% of offspring demonstrated a quantitatively resistant phenotype, with zero or little dieback post-inoculation. Then, multiple inoculations were performed on previously unchallenged members of these families, half of which had been treated with phosphite....

Rapid phenotypic diversification in clonal invasive populations is often observed, although the underlying genetic mechanisms remain elusive. Lineages of the sudden oak death pathogen Phytophthora ramorum are exclusively clonal, yet isolates of the NA1 lineage from oak (Quercus spp.) frequently exhibit hostdependent, unstable colony phenotypes called non-wild type (nwt, fig. 1) (Brasier and others 2006). This phenotypic variation is seen despite the fact that population genetic and host-specificity studies negate any host-driven population subdivision. We also found comparable nwt phenotype...

Sudden oak death, caused by the oomycete Phytophthora ramorum, was first discovered in California toward the end of the 20th century and subsequently emerged on tanoak forests in Oregon before its first detection in 2001 by aerial surveys. The Oregon Department of Forestry has since monitored the epidemic and sampled symptomatic tanoak trees from 2001 to the present. Populations sampled over this period were genotyped using microsatellites and studied to infer the population genetic history (Kamvar and others 2015). To date, only the NA1 clonal lineage is established in this region,...

It is now generally accepted that the four evolutionary lineages of Phytophthora ramorum (informally designated NA1, NA2, EU1, and EU2) are relatively anciently divergent populations, recently introduced into Europe and North America from different, unknown geographic locations; that recombinants between them are genetically unstable and probably unfit to survive, indicating reproductive isolation; and that they differ in growth rates and aggressiveness. EU1 lineage, for example, is on average faster growing in culture and more pathogenic on Quercus rubra bark than the NA1 lineage. Our...

Bloedel Reserve is a 150-acre botanical garden and nature preserve on the north end of Bainbridge Island in Washington on the Puget Sound. The grounds encompass undeveloped forest, pastures, a bird marsh, woodland plantings, and intensely maintained gardens within the limits of the City of Bainbridge Island. The garden is part of the Sentinel Plant Network, a partnership between the American Public Gardens Association and the National Plant Diagnostic Network that engages public garden professionals, volunteers, and visitors in the early detection of serious plant pests and diseases. With...