Some plant pathogens cause destructive epidemics in natural plant communities, but many others have limited impacts, or can even act as important agents in maintaining structure and diversity in species-rich plant communities. Predicting the spread and impacts of a particular plant pathogen depends on understanding the range of plant species it can infect as well as the spatial arrangement and abundance of host species in the landscape. Here we will work in both the moist tropical forest of lowland Panama and the mixed temperate forest on the central coast of California to examine how the composition and spatial patterns of plant species in the forest affects the potential for disease spread in high- and low-diversity plant communities. Through a series of cross inoculations we will measure directly the potential for pathogens to be shared among hosts that are evolutionarily closely or more distantly related. Using a spatially-explicit epidemiological simulation model, we will couple these empirical estimates of host range with the known spatial pattern of tree species in mapped plots in the forests, to examine the likelihood of spread through forest communities of pathogens with different life histories and different host breadths. The results of this research will inform issues of forest management, plant pest quarantine, and a basic understanding of the importance of host range in plant-pathogen interactions in natural communities.
