A demographic analysis of fire-stimulated seedling establishment of Sarracenia alata (Sarraceniaceae).
Recurring fires are thought to be critical to maintaining populations of carnivorous plants in wet pine savannas. Nevertheless, the impact of fire on population dynamics of these unique and sometimes rare plants is poorly understood. In this study, I analyzed stage-structured matrices for Sarracenia alata. To examine the effects of fire-stimulated increases in seedling establishment, five matrices were constructed, which differed in fecundity rates associated with different fire frequencies (annual fires, 1/3, 1/7, 1/20, and 0/20 yr). In addition, I analyzed the sensitivity of population growth and dynamics to changes in other vital rates. Fire-stimulated increases in fecundity were not necessary to maintain viable populations of Sarracenia alata. Although increases in fecundity increased population growth rate, all five fire frequencies (including the "no-fire" scenario) produced either stationary or increasing populations. Adding year-to-year stochasticity in vital rates did not alter these general trends. Population growth and decline were much more sensitive to reductions in the survival of large adult ramets (which were projected to have a life expectancy of 59 yr). Population growth was also more sensitive to changes in juvenile persistence than to juvenile growth, suggesting that conservative use of captured resources by juveniles has a greater impact on fitness than rapid growth and maturation. Given that a previous study showed that modest variation in fire frequency had no impact on either adult or juvenile survival, I conclude that Sarracenia alata relies on fire-regulated plasticity in allocation to pitchers to increase the survival and lifetime fecundity of iteroparous ramets.
Brewer
J S
JS
Department of Biology, University of Mississippi, University, Mississippi 38677 USA.