OUR FORESTS ARE A VALUABLE RESOURCE THAT NEED TO BE PROTECTED AGAINST INVASIVE THREATS. WE AIM TO DESCRIBE MECHANISMS THAT GIVE RISE TO THE EMERGENCE OF PLANT PATHOGENS THAT CAN RAVAGE ECOSYSTEMS USING THE PATHOGEN PHYTOPHTHORA RAMORUM AS A MODEL IN PREDOMINATELY WEST COAST FORESTS. THIS PATHOGEN CAUSES SUDDEN OAK DEATH IN FORESTS, MOSTLY ON OAK AND TANOAK TREES. THIS DEVASTATING DISEASE WAS INTRODUCED TO THE US 25-30 YEARS AGO AND IS NOW AN EPIDEMIC IN OREGON AND CALIFORNIA FORESTS. THE PATHOGEN CAN BE THOUGHT OF AS AN INVASIVE SPECIES, AND SPREADS THROUGH FORESTS OF TREES SUCH AS TANOAK THAT ARE NOT ONLY NATIVE TO THE WEST COAST, BUT FOUND NOWHERE ELSE IN THE GLOBE. PROTECTING FORESTS FROM PATHOGEN THREATS IN THE LONG-TERM DEMANDS A GREATER UNDERSTANDING OF HOW PATHOGENS EMERGE FROM NATURAL POPULATIONS TO CAUSE DISEASE OUTBREAKS. EVOLUTIONARY STUDIES INVESTIGATING THE PATHOGEN AT ITS CENTER OF ORIGIN PROVIDEINSIGHT TO FACTORS LEADING TO PATHOGEN EMERGENCE. WE EXAMINE CHANGES IN POPULATIONS OVER TIME, AND FORCES SUCH AS ADAPTATION CAN ALLOW INVASIVE PATHOGENS TO SPREAD FARTHER AND FASTER. THESE FORCES CAN ONLY ACT ON GENETIC VARIATION AVAILABLE, AND THE LARGEST SUCH SOURCE ARE MUTATIONS. WE IDENTIFY SMALL, SIMPLE MUTATIONS IN GLOBAL POPULATIONS TO INFER WHERE THE PATHOGEN ORIGINATED, AND WORK TO DEVELOP A MODEL OF HOW NEW, LARGE-SCALE MUTATIONS MAY ARRIVE FASTER THAN EXPECTED BY CHANCE. THESE LARGE-SCALE MUTATIONS MAY HAVE A LARGE, IMMEDIATE EFFECT ON HOW WELL ADAPTED A NOVEL STRAIN IS TO A SUSCEPTIBLE HOST ENVIRONMENT. DETERMINING WHETHER NEW MUTATIONS ARE INFLUENCED BY STRESS THE PATHOGEN ENCOUNTERS, AND WHAT THOSE STRESSES ARE, FURTHERS OUR UNDERSTANDING OF WHAT GIVES RISE TO PATHOGEN EMERGENCE AND DOMINANCE.