Effects of fire, rainfall, and herbivory on flowering in Calochortus plummerae

Background/Question/Methods

Plummer’s mariposa lily (Calochortus plummerae E. Greene) is a California endemic that is restricted to five counties in southern California. It is a geophyte with an underground corm. Although rarely observed during most years, it flowers abundantly after fires. In the spring of 2004, after the massive 2003 wildfires in southern California, a population of C. plummerae was discovered on the campus of California State University, San Bernardino. Long-term study plots were established to monitor year-to-year variation in emergence, growth, and flowering of C. plummerae, and to explore potential causes of decreased flowering in years without fire. Plants in the plots were monitored for ten years. The role that increasing competition for water by recovering vegetation plays in suppressing flowering was indirectly assessed by analyzing the relationship of interannual variation in precipitation to interannual variation in flowering of C. plummerae. The role that herbivory plays in suppressing flowering was assessed by analyzing the relationship between interannual variation in leaf herbivory and flowering, and by simulating herbivory in the field to determine its impact on flowering.

Results/Conclusions  

In general, the number of C. plummerae plants that flowered in plots each year was well predicted by a combination of annual precipitation and time since fire. In the first year after fire, more plants flowered than were predicted from the relationship that held during the following nine years. Early-spring leaf-area removal eliminated flowering of C. plummerae plants for that year, and natural herbivory was particularly heavy during the last years of the study. Overall, multiple effects of large fires (reducing competition for water and reducing herbivore populations) appear to contribute to the abundant flowering of C. plummerae after fire, and subsequent recovery of plant and herbivore communities  contributes to flowering suppression between fires.