Susceptibility to Phytophthora ramorum in California bay laurel, a key foliar host of sudden oak death

Sudden oak death, caused by the water mold Phytophthora ramorum, is a plant disease responsible for the death of hundreds of thousands of oak and tanoak trees. Some foliar hosts play a major role in the epidemiology of this disease. Upon infection by P. ramorum, these foliar hosts express non-fatal leaf lesions from which large amounts of inoculum can be produced and spread to neighboring host individuals, including oak species. Umbellularia californica (California bay laurel) may be one of the most important foliar hosts of sudden oak death due its observed ability to produce inoculum and its high abundance in the woodlands of coastal California. While previous research on susceptibility to P. ramorum in U. californica has shown significant variability among trees, with more resistant individuals in northern areas of its range, little is known about the causes or extent of this variability. Here, we ask three research questions: (1) How does susceptibility vary among U. californica individuals and P. ramorum isolates? (2) Are U. californica phenotype and genotype related to susceptibility? (3) What factors influence disease expression in nature

Epidemiological modeling of invasion in heterogeneous landscapes: Spread of sudden oak death in California (1990-2030)

10.1890/ES10-00192.1Ecosphere22

Effects of Fire on Landscape Heterogeneity in Yellowstone National Park, Wyoming

A map of burn severity resulting from the 1988 fires that occurred in Yellowstone National Park (YNP) was derived from Landsat Thematic Mapper (TM) imagery and used to assess the isolation of burned areas, the heterogeneity that resulted from fires burning under moderate and severe burning conditions, and the relationship between heterogeneity and fire size. About 80% of the park is covered with coniferous forests dominated by lodgepole pine (Pinus contorta var. latifolia). The majority of severely burned areas were within close proximity (50 to 200 m) to unburned or lightly burned areas, suggesting that few burned sites are very far from potential sources of propagules for plant re-establishment. Fires that occurred under moderate burning conditions early during the 1988 fire season resulted in a lower proportion of crown fire than fires that occurred under severe burning conditions later in the season. Increased dominance and contagion of burn severity classes and decrease in the edge:area ratio for later fires indicated a slightly more aggregated burn pattern compared to early fires. The proportion of burned area in different burn severity classes varied as a function of daily fire size. When daily area burned was relatively low, the proportion of burned area in each burn severity class varied widely. When daily burned area exceeded 1250 ha, the burned area contained about 50% crown fire, 30% severe surface burn, and 20% light surface burn. Understanding the effect of fire on landscape heterogeneity is important because the kinds, amounts, and spatial distribution of burned and unburned areas may influence the reestablishment of plant species on burned sites