Effects of density and fire on the vital rates and population growth of a perennial goldenaster

Gornish
Image of Pityopsis aspera. Taken by E. S. Gornish.

In a novel analysis by Gornish published in AoB PLANTS, a regression-design life-table response experiment was used to determine how the interaction of fire and density affected vital rates of the perennial composite Pityopsis aspera, and ultimately how these changes in vital rates contributed to differences in estimated population growth rates. The shape of the relationship between population growth rate (λ) and density was modified by fire, primarily as a result of contributions from adult flowering stasis and survival, and first-year survival probabilities. Fire modified and even reversed the effect of extreme densities on adult flowering stasis and survival and of first-year survival, resulting in more positive contributions from these transitions to λ at the lowest and highest density values. These results demonstrate the first application of a regression-design life-table response experiment to elucidating the interactive effects of density and fire. They highlight the utility of this approach for both capturing the complex dynamics of populations and establishing a means of determining how vital rates might contribute to differences in demography across densities.