Long‐Term Responses of Cistus and Certain Other Introduced Shrubs on Disturbed Wildland Sites in Southern California

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Abstract
The performance of seven introduced shrubs in four genera planted for erosion control on 12 disturbed sites, was observed over a 10— to 20—yr period. The sites differed widely in elevation, steepness, soils, and climatic factors. Three species of Cistus proved satisfactory on most sites for 3 to 5 yr. On several sites they persisted as useful stands for 10 yr or longer, with promise of permanent self—maintenance in at least five cases. Plantings of Atriplex, Rosmarinus, and Baccharis species generally decline and did not reproduce. The length of the effective life of the Cistus stands depended on (1) water availability, in which the chief factor was sufficiency and timing of the winter rains, and (2) the development of tall native shrubs on the sites. Cistus plantings declined and did not reproduce when overtopped by tall chaparral. This failure is ascribed to lack of light. The need of Cistus seedlings for high light intensities was established experimentally. When low—growing native species invaded a site, Cistus grew compatibly with them. Cistus seedlings competed successfully with forbs and weeds but did not survive in thick grass. They spread aggressively over level areas of thin cover. On the hottest, driest inland sites, the original Cistus bushes became woody and senescent in about 12 yr. Management is recommended to reduce the fuel load in case of fire, and to stimulate growth of new bushes. Limits of cold tolerance were established for C. villosus at 1,790 m and for heat/drought tolerance of C. laurifolius at 930 m. The latter thrived at temperatures far lower than those of a mediterranean climate.

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