The response of an obligate plant-pollinator mutualism to fire: Years 2 and 3

In this presentation we provide an update on a study of the effects of fire on the obligate mutualism between the monocarpic yucca, Hesperoyucca whipplei, and its pollinator, the yucca moth, Tegeticula maculata. Since 2001 we have monitored the flowering ecology of Hesperoyucca at two sites. One site, the Elliot Chaparral Reserve (ECR) near San Diego, was burned in the Cedar Fire in October 2003. The unburned site, approximately 50km N on the Santa Margarita Ecological Reserve (SMER), is physiographically similar. We use pre- and post-fire census data at these sites to examine the influence of fire on survival, flowering, pollination, and reproductive success of yucca, and on the dynamics of the pollinator population. We reported earlier that survivorship of established yuccas was high and the effects on the number of plants flowering and on flowering phenology in Spring 2004 were minor. In contrast, pollinator abundance at ECR in 2004 was severely reduced, resulting in very low fruit set. Over the two years since that report, pollinator abundance has begun to recover, leading to progressive increases in fruit production at ECR in 2005 and 2006. Pollinator abundance and plant reproductive success, however, remained significantly lower than pre-fire levels at ECR and post-fire levels at the unburned site. Although the mutualism seems to be recovering, the fire’s long-term influence remains unclear. Slow recovery of pollinators could lead to a delayed decline in the yucca population.