Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Role of high fire frequency in destruction of mixed chaparral.

Abstract

Regeneration of Adenostoma fasciculatum and Salvia mellifera dominated chaparral was studied in adjacent sites on the N. side of the Verdugo Mountains, S. California, burned once, twice or 3 times in 6 years, at intervals of 1, 4 and 6 years before the study in 1992. Marked changes in plant community composition occurred as fire frequency increased. On a site burned only once in the past 20 years, the dominant shrubs, A. fasciculatum and S. mellifera established abundant seedlings in the first growing season after burning. Seedling establishment was 62 and 83% less, for A. fasciculatum and S. mellifera, respectively, on the site that had also been burned 6 years previously and zero on the site burned 1, 4 and 6 years ago. Lotus scoparius also showed its lowest establishment on the site burned most frequently; it did best on the site burned 1 and 6 years ago. Although A. fasciculatum regenerated after fire, the was some mortality after each fire and the number of resprouting individuals diminished as fire frequency increased. Postfire annual species were abundant on all sites burned the previous year, regardless of the previous fire frequency. Non-native species such as Brassica nigra, Bromus spp. and Schismus barbatus were absent or poorly represented on the 1-year-old burn that had last been burnt >20 years ago, however, postfire recruitment of these aliens was increased on sites which were repeatedly burned. Species richness was greatest on the site burned 1 and 6 years ago (16 spp.) and lowest on the site burned 1, 4 and 6 years ago (10 spp.). It is suggested that high fire frequency has played an important role in the establishment of the alien species and the conversion from shrub-dominated to herbaceous-dominated ecosystems in California.