Treesearch

Novel interactions between compounded disturbances can leave lasting ecological legacies on communities and alter regeneration trajectories. Sudden oak death (SOD), caused by Phytophthora ramorum, is a biotic disturbance, an emerging disease causing widespread oak and tanoak mortality in California’s coastal forests. In these redwood-tanoak forests, wildfire is a keystone process, shaping stand structure and composition. Dominant tree species can resprout rapidly after being “top-killed” by fire, in addition to regenerating via seed. Yet, in SOD-impacted areas, fuels generated by disease-re...

Sudden oak death, caused by Phytophthora ramorum, is lethal to tanoak (Notholithocarpus densiflorus) and threatens this species throughout its range in Oregon. The disease was first discovered in coastal southwest Oregon forests in July 2001. An interagency team attempted to eradicate the pathogen through a program of early detection and mandatory destruction of infected and nearby host plants. Eradication treatments eliminated disease from most infested sites, but the disease continued to spread slowly, mostly in a northward direction. Following a sharp increase in disease in 2010 and...

Monitoring host composition and disease impacts began 15 years ago in what would become a network of permanent forest monitoring plots throughout the known and predicted range of Phytophthora ramorum in California coastal forests. Stretching ~500 miles from Big Sur to the Oregon border, the network captures variation in interactions among the pathogen, its potential hosts, and the environment across wide gradients in climate, topography, land use, and host species abundance. Within each plot, standardized methodology has been used to track forest dynamics and disease impacts of individual...

Many new Phytophthora pathogens have arrived in the UK via the plant trade in recent decades, but arguably Phytophthora ramorum has been one of the most significant introductions to affect trees. From 2002 onwards during the early stages of the epidemic, the first impacts of P. ramorum were seen in ornamental plant nurseries, then affecting valuable heritage plants in gardens important to the tourist trade, and eventually in broadleaf dominated woodlands (Brasier and others 2004). In the latter, a few tree species, such as European beech (Fagus sylvatica) and sweet chestnut (Castanea...

The potential for biodiversity to mitigate risk of infectious diseases in ecological communities – known as the diversity-disease risk hypothesis – is fundamental to understanding links between landscape change and environmental health of forests affected by sudden oak death (SOD). Previous research of the Phytophthora ramorum pathosystem found evidence for a dilution effect, where areas of high woody plant diversity were found to have significantly lower disease prevalence. However, little is known regarding the resilience of biodiversity effects subject to ecological disturbances. We...

Our knowledge of sudden oak death (SOD) disease dynamics indicate that without bay laurel (Umbellularia californica) there is seldom oak (Quercus) infection. This requirement of an alternate host species for disease transmission to oak species is an example of pathogen spillover. We developed a path analysis to test specific hypothesized relationships between physical and ecological factors affecting pathogen spillover. Path analysis enables simultaneous examination of direct and indirect effects from multiple factors, which can enhance our understanding of the multiple influences on...

Failure to build consensus amongst stakeholders has been a primary obstacle barring progress in developing and implementing strategies to manage sudden oak death (SOD). Consensus as to the goals of in situ management of SOD has rarely been reached, because stakeholders’ visions of success vary widely and often compete with each other across the complex landscape of forest resources, ownership types, and overlapping jurisdiction in which this epidemic unfolds. Investments in research on the pathology of P. ramorum have yielded dynamic spread models identifying and ranking communities at...

Since Phytophthora ramorum established in the wildlands of California during the 1990s, the disease has spread rapidly throughout the state’s coastal and adjacent counties, likely by a combination of human-aided events (e.g., nursery plant introductions) and natural dispersal. While human-aided events are almost impossible to predict, dedicated efforts have been made to model the natural spread of the disease throughout California. These models have been built upon aerial survey mortality data and/or extensive plot-level data gathered for infested and non-infested locations throughout the...

The Sudden Oak Death Sixth Science Symposium provided a forum for current research on sudden oak death, caused by the exotic quarantine pathogen Phytophthora ramorum. More than 50 submissions describing papers or posters on the following sudden oak death/P. ramorum topics are included: biology, genetics, nursery and wildland management, monitoring, and ecology. Abstracts are also provided from a special session on Phytophthoras in California native plant nurseries and restoration sites.