9507532 Chaparral vegetation in southern California neighbors one of the largest metropolitan areas in the United States and occupies invaluable watershed land. Chaparral deters soil erosion, maintains slope stability, furnishes browse and cover for wildlife, and provides aesthetic and recreational value. While research has previously focused on the response of chaparral to fire and water stress, there is growing evidence that low temperature tolerance is an important factor underlying chaparral distribution and abundance. Based on frequency, subzero temperature episodes may be as important to chaparral communities as fires and drought. Loss in productivity, injury, and in some cases death of native plants has been observed after freezing events. Seedlings may be particularly vulnerable as the reduction of plant cover after fire can expose them to potentially lethal radiation freezes at night. This research will examine the hypotheqes that seedlings are more vulnerable to low temperature damage than adults, freezing- induced embolism (air blockage) of the stem xylem (wood) can cause shoot death, and the amount of freezing-induced embolism is related to both wood structure and rate of thaw. The combination of a steep gradient in minimum temperatures from the coast inland and recently burned sites in southern California provide an excellent model system. The results will have implications for land use management, such as mitigation of fire-burned areas in southern California; for revegetation projects; and for the use of temperature sensitive species of chaparral as climate indicators.
