title: The Effects of Irrigation on Revegetation of Semi-Arid Coastal Sage Scrub in Southern California.
abstract: / To test the appropriateness and applicability of irrigation for restoration of coastal sage scrub, a semi-arid vegetation type native to southern California, a field study comparing four irrigation schedules-no irrigation, spring irrigation only, summer irrigation only, and irrigation year round as needed-was established. A seed mixture of six native shrub species was broadcast, and the effect of irrigation on emergence and establishment was evaluated. Restoration of arid and semi-arid vegetation is challenging because of the severe environmental conditions inherent to these ecosystems. In particular, the low and unpredictable nature of precipitation can limit the chances for successful establishment of perennial species. Under conditions where supplemental irrigation is available, irrigation may make the difference between successful or failed restoration. However, increasing the availability of water through irrigation may result in poor plant adaptation to surviving arid conditions or only temporary success followed by failure once supplemental water is withdrawn. In this study, irrigation stimulated germination in the irrigated plots about a month earlier than the plots dependent on natural rainfall, but this had little lasting effect. Spring and summer irrigation did not improve survival compared to the plots receiving no supplemental water. The largest effect of irrigation was a reduction in survival of several species grown under irrigated conditions as compared to nonirrigated conditions. In plots where water was applied all year long a single species, Artemisia californica, represented nearly 100% of the species present at the end of two growing seasons. Irrigation may speed revegetation under some conditions, but was not very effective in establishing natural vegetation structure.
authors.affiliation: Department of Botany and Plant Sciences, University of California, Riverside, California 92521-0124, USA
authors.initials: PE
authors.lastname: Padgett
authors.initials: SN
authors.lastname: Kee
authors.initials: EB
authors.lastname: Allen