Sudden oak death: endangering California and Oregon forest ecosystems

had major impacts on forest ecosystems around the world. Classic examples include chestnut blight in North America, caused by Cryphonectria parasitica, and jarrah dieback in western Australia, caused by Phytophthora cinnamomi (Anagnostakis 1987; Weste and Marks 1987). Some exotic diseases, such as chestnut blight and white pine blister rust, have severely impacted populations of a single plant species, leading to a cascade of changes in forest ecosystems. In fewer cases, a pathogen with a broad host range has affected forest ecosystems directly. Since it was introduced in the 1920s, P cinnamomi has virtually eliminated most tree species over hundreds of thousands of hectares of the jarrah (Eucalyptus marginata) forests of western Australia, converting them to grassland or shrubland (Weste and Marks 1987; Erwin and Robiero 1996). The emergence and introduction of new plant diseases continues to this day (Baskin 2002; Campbell and Schlarbaum 2002). One of the most recent examples of an emerging forest disease is “sudden oak death”. The symptoms that define it were first recognized during 1994–95, and over the next few years it reached epidemic proportions in oak forests along approximately 300 km of the central California coast (Garbelotto et al. 2001). The most visibly affected hosts included tanoak (Lithocarpus densiflora), coast live oak (Quercus agrifolia), California black oak (Quercus kellogii), and Shreve’s oak (Quercus parvula var shrevei) (Rizzo et al. 2002a). Eventually it was shown that the pathogen Phytophthora ramorum, recently described from rhododendron (Rhododendron spp) and viburnum (Viburnum spp) in Europe (Werres et al 2001; Rizzo et al. 2002a), was causing the disease. Research soon revealed that P ramorum could infect other plant species as well. Over the past year and a half, over 20 additional species from 12 plant families have been identified as potential hosts (Rizzo et al. 2002b; Garbelotto et al. 2003; Table 1). Additional hosts are likely to be found, as many other plant species are susceptible to infection under laboratory conditions (Hansen and Sutton 2002; Linderman et al. 2002; Parke et al. 2002; Tooley and Englander 2002). What is sudden oak death, and what are the ecological implications of this new disease? Here we review what is known about the biology, ecological implications, and management of P ramorum in the coastal forests of California and Oregon.