Climate Host Mapping of Phytophthora ramorum, Causal Agent of Sudden Oak Death
Glenn Fowler1, Roger Magarey1, Manuel Colunga2, Bill Smith3 and Ross Meentemeyer4
We generated a risk map for the conterminous United States that visualized areas at-risk for P.
ramorum infection based on climate suitability and host presence. We used the North Carolina
State University-Animal and Plant Health Inspection Service Plant Pest Forecasting System
(NAPPFAST) to perform the climate modeling (Borchert and Magarey, 2004). Our climate
match model was based on 10 year historical daily data. The model parameters were: 1)
minimum daily temperature ≥ 3˚C, 2) optimum daily temperature of 20˚C, 3) maximum daily
temperature ≤ 28˚C, 4) ≥ 12 hours of accumulated leaf wetness and 5) ≥ 60 accumulated days
meeting these conditions annually (Huberli et al., 2003; Orlikowski and Szkuta, 2002; Tooley
and Kyde, 2005; Werres et al., 2001). We converted the 10 year climate match frequency output
to percentages.
We used both hardwood and understory hosts in the risk map. We obtained the hardwood host
layer from the National Land Cover Dataset for the conterminous United States (Vogelmann et
al., 2001). This data layer expresses forest composition in percentages. We queried this data set
for all hardwoods plus fifty percent of mixed forests. We obtained the understory host layer from
NatureServe (2002). We estimated the distribution of seven Ericaceae hosts of P. ramorum as a
shapefile and converted this to a raster. This raster was converted to percentages by dividing it
by seven and multiplying by 100. These layers were visualized at a one km2 resolution.
We generated the risk map by summing the climate, hardwood hosts and understory hosts
percentages and dividing the total by three. The raster spatial resolution was one km2. We then
masked out areas where: 1) no climate match occurred, 2) no hardwood hosts occurred, 3) no
understory hosts occurred and 4) the lethal cold temperature for P. ramorum, i.e. -25°C, occurr