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The Impact of Sudden Oak Death on California Spotted Owl in Big Sur
Principal Investigator: Karen Ritchie Shihadeh
Project Biologists: Nellie Thorngate, Mike Tyner, James Hart
Project Funded By: US Forest Service
 Studying the effects of Sudden Oak Death |
 Sudden Oak Death effects |
 Field Surveys of California Spotted Owl locations |
 Spotted Owl Habitat |
In June 2005, the US Forest Service awarded Ventana Wildlife Society (VWS) $50,000 to assess the impact of Sudden Oak Death on foraging and nesting habitat of the California Spotted Owl (Strix occidentalis occidentalis) in Big Sur. Unlike its close relatives, the Northern and Mexican Spotted Owl, the California Spotted Owl is not considered endangered or threatened but is a species of concern in California. This is primarily due to healthy population centers in the Sierras. In the Coast Ranges, the California Spotted Owl prefers cool, moist valleys dominated by tanoak and redwood where it feeds voraciously on dusky-footed woodrat. Abrupt and large-scale vegetation changes in the wilderness valleys of Big Sur are serious cause for concern for local Spotted Owl populations. In 2004, California drafted a Conservation Strategy for the California Spotted Owl in the National Forests of Southern California. This action plan called for protection of all existing and potential spotted owl habitats. The objectives of this study were to identify and map current occupancy of spotted owls on the western slope of northern Los Padres National Forest and to compare those occupancy areas with historic use and habitat features including vegetation, distance to stream, slope, aspect, and tree mortality.
Studying the effects of Sudden Oak Death
Sudden Oak Death (SOD) is caused by the fungal blight Phytophthora ramorum. Phytophthora attacks plant xylem and phloem, the major vessels that carry water and nutrients from the soil to plant leaves and tissue. It causes external cankers, lesions, leaf wilt, and spots in a wide variety of trees, shrubs and herbs. In some hosts, like tanoak, death follows rapidly after infection. In other plant hosts, such as rhododendron, bay laurel and coast redwood, Phytophthora resides in the leaves and twigs where it can persist for many years, continually infecting plants in the surrounding community.
Coastal Big Sur is considered one of the areas hardest hit by SOD. Like a slowly advancing army, it marches continually inland fanning out in wet years and retreating or lying dormant during dry summers and fire. Phytophthora is also spread by humans hiking through infected areas or collecting bay leaves, and carrying the microscopic fungi back home or into a new area of wilderness. Truly, we are just beginning to understand the wider ecological and economical implications of SOD for the region. Ventana Wildlife Society’s research on Spotted Owls is just one part in a larger investigative effort by state, federal, and university scientists to uncover all of those impacts.
Sudden Oak Death effects
Methodology employed followed that described in USFS (1998) modified to inventory large areas. Six survey areas were designated and named Palo Colorado/ Pico Blanco, Big Sur, North Ridge Road, Big Creek, Nacimiento Road, and Gorda. For each area, between 10-75 permanent, fixed calling stations were delineated along survey routes. Variable plot vegetation surveys were conducted at 34 owl pair detection sites. Owl occupancy data were transformed into map features and spatially analyzed using ArcGIS 9.1. A total of 112 owls at 62 detection locations were identified between March and August 2006. Owl detection sites were often associated with redwood-tanoak forests and found near historic sites suggesting habitat specialization and high site fidelity. Eighty-five percent of owl detection sites were located within 200 meters of a stream; 40% were located within or within 500 meters of SOD mortality polygons; 66% were located within or within 500 meters of some tree mortality polygon. Continued intensive short-term monitoring in addition to prey-base sampling, radio-tracking, GIS modeling, and periodic population inventory will further elucidate habitat requirements, subpopulation targets and parameters, and the impacts of sudden oak death on this sensitive key management species.
Field surveys conducted by VWS were the first to comprehensively document Spotted Owl locations since 1984. For more information on SOD research in Big Sur, go to the California Oak Mortality Task Force Website.
Click here to view the VWS final report issued in December 2006 (pdf, 4.64 MB)