For the last five years, scientists have been on the trail of a fungus, Seiridium, that has caused a deadly epidemic in the world’s forests. Cypress canker disease has felled up to 95 percent of the cypress trees — a family that includes junipers — growing in some timber plantations and forests across the globe. Last month, scientists from the University of California, Berkeley, and the National Research Council in Italy revealed that their genetic sleuthing had traced the pathogen’s roots back to Monterey cypresses in California.