The effects of fire on scarlet gilia: an alternative selection pressure to herbivory?

Abstract

The primary goals of this paper were to experimentally assess the relative importance of fire, a potentially important selective agent involved in shaping scarlet gilia's compensatory response and, in general, determine scarlet gilia's response to fire. Burn treatment results demonstrated that fire was not an important selective agent involved in shaping scarlet gilia's compensatory response. The most common response to fire was the production of one or more new clonally derived rosettes. This was an unexpected result; this typically monocarpic herb rarely produces clonal offspring. Although rosette production lessened the detrimental effects of fire by giving plants that cloned a second chance to flower, these newly formed rosettes delayed flowering for at least one year and had significantly higher overwinter mortality rates than rosettes from unburned control plots. In addition, significantly fewer individuals from the burn treatments flowered and there was significantly higher immediate mortality. There was, however, no detrimental effect on the reproductive success (seed production) of individuals that flowered following the burn. Overall, cumulative estimates of plant performance suggest that at the population level fire results in a 4.5-fold decrease in relative plant fitness. However, fire-induced seed germination could negate the detrimental effects of fire on the population dynamics of scarlet gilia. In the year of the burn there was a 116-fold increase in the number of germinating seeds and by the second year this translated into an approximate 6-fold difference in the number of surviving rosettes. Two alternative candidates, frost damage and ungulate trampling, can cause the removal of apical dominance and a response similar to that generated by ungulate and insect herbivores. However, they are probably minor factors favoring selection toward growth compensation; experimental and observational results deomonstrate that apical dominance was removed in only 3% of plants exposed to freezing temperatures and ungulate trampling caused breakage and release of apical dominance in only 0.2% of plants.

Keywords: Clonally derived offspring; Fire; Herbivory; Ipomopsis aggregata; Overcompensation.