In 1984, in the vicinity of Malibu, a yellow, chlorotic patch of ceanothus appeared, covering an area of 8 by 10 meters. By the spring of 1985, large areas throughout the Santa Monica Mountains were displaying the same characteristics, with Toyon, Manzanita and Sumac also affected.
In the late spring, the same condition was observed in the San Gabriel and Santa Susana Ranges. By 1986, the dieback was observed from Gaviota Pass in Santa Barbara County, to Camp Pendleton and interior San Diego County.
Theories abound regarding the cause of the decline in chaparral.
The period from 1978 through 1983, cumulatively, was the wettest period of record. From 1983 to the present ranks high as one of the driest periods of record. One theory is that the dieback is drought related. (It should be noted that during past droughts there were indications of some stands dying off, particularly in chamise, but none documentation of the magnitude that we're seeing today).
Another theory suggests that the "El Nino" that occurred in 1983, with significant summer and fall rainfalls is causing the problem. The third theory is that a very wet period, followed by an extremely dry period caused an over-extension of canopy and subsequent stress as available soil moisture declined. A fourth speculation is that air pollution is the culprit. (Studies have shown, in the Glendora area, that air pollution has deposited several pounds per acre of nitrates, causing significant growth while moisture is present, but in turn causing severe stress when moisture is absent). The fifth concept is that the decline is the harbinger of the " Greenhouse Effect".
Since 1984, Dr. Phil Riggan, USDA-Forest Service, Pacific Southwest Forest and Range Experiment Station (PSW) has been tracking the problem. A pathogen, or cancer fungus, Botryospaeria dothidea or B. ribis, was found on samples collected in the Santa Ynez, Santa Monica and San Gabriel Ranges.
It is significant, that in addition to Ceanothus, Rhus, Toyon and Manzanita, the fungus was also present in Quercus agrifolia, the California live oak, and may be an explanation for a high current rate of oak mortality.
During the 1990 state legislative session, SB 360 was passed, directing the California Department of Forestry and Fire Protection to investigate the "Biology, fire effects and remediation of widespread die-back of chaparral in southern California". A cooperative agreement was initiated between the California Department of Forestry and PSW-Fire Lab, Riverside, with Phil Riggan as principle scientist. Assisting Dr. Riggan will be Dr. Fred Brooks, Dept. of Plan Pathology at U.C. Riverside and James Brass, Ecosystems Science and Technology Branch, NASA Ames research center.
For more information may call Scott Franklin at (805) 254-2376 or Phil Riggan at (714) 276-6516.
