CAUSES AND CORRELATES OF INTERANNUAL VARIATION IN FLOWERING OF CALOCHORTUS PLUMMERAE (LILIACEAE)

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Calochortus plummerae Greene (Liliaceae) is a mariposa lily that is restricted to five counties in southern California. Although rarely observed in late seral chaparral during most years, it flowers abundantly after fires. In the spring of 2004, a population of C. plummerae was discovered in recently burned chaparral on the campus of California State University, San Bernardino. Long-term study plots were established to monitor year-to-year variation in flowering of C. plummerae, and to explore potential causes of this variation. We explored the relationship between annual precipitation and flowering of C. plummerae. We also examined the relationship between precipitation and growth of the strap leaf. Finally, we tested effects of experimental herbivory (leaf cutting) on current-year flowering. Flowering was monitored for 10 years, and leaf characteristics (leaf size and leaf loss to herbivory) were monitored for six years. During the driest year of our study, no plants flowered, but a substantial number flowered during wet years. Plants also produced narrower leaves during the driest years of the study. Leaf loss (experimental removal of most of a strap leaf) resulted in failure to flower. Overall, flowering between fires appears to be suppressed by factors that reduce current-year carbon gain: drought and leaf loss to herbivory. Although our data on herbivory were too incomplete to assess its importance in driving the dynamics of flowering in years after fire, the remaining two factors we studied (time since fire and annual rainfall) were sufficient to predict the number of C. plummerae plants that flowered each year.