Abstract Detail

Ecology

Nordstrom, Scott [1], Dykstra, Amy [2], Wagenius, Stuart [3].

Post-fire reproduction and recruitment promote persistence of a long-lived, herbaceous perennial.

Many plant species in fire-prone ecosystems have positive vital rate responses to fire. One common response to fire in herbaceous plants is increased flowering. We quantified the effects of fire-induced flowering on growth rates of the grassland perennial plant Echinacea angustifolia, comparing the magnitude of these effects with corresponding effects of post-fire changes in survival. Using matrix projection models, we estimated population growth rates over fifteen years for five small populations in a fragmented agricultural landscape in western Minnesota. We used Bayesian modeling to estimate survival, recruitment, and flowering, using sixteen years of observations of adult plants, seven years of observation of recruitment, and two separate datasets of juvenile survival. One experimental juvenile survival dataset included high estimates of juvenile survival (> 90% average annual survival), while a smaller observational dataset featured low survival (~ 65% average annual survival). All populations experienced at least one burn and we recorded post-fire transitions. We used vital rate estimates from these burns to estimate the stochastic growth rate of these populations under different burn frequencies. We then decomposed the growth rate responses to fire into individual contributions from each vital rate.
We found that all five populations we modeled are predicted to decline. Burning increased the probability of flowering and increased the number of seedlings sired per flowering plant. Survival at all ages was largely unaffected by fire. However, we found these fire-induced increases in reproductive activity increased population growth rates only when juvenile survival was high; otherwise, growth rates were unaffected. We estimate that if juvenile survival is high, four of five populations we modeled would experience growth with burning every three to five years. When juvenile survival is high, fire-induced increases in recruitment are the largest contributor to population growth. Our analysis suggests reproduction, not survival, benefits from fire, and that post-fire reproductive activity has the largest impact on population dynamics of our long-lived perennial forb. However, fire's positive impact on population growth can only be realized when a post-fire pulse of new recruits can survive to reproductive maturity. These results are especially relevant for conservation of populations experiencing threats in addition to fire-suppression, such as inbreeding depression, increased competition from invasive species, and environmental changes that reduce survival of juveniles.

1 - Univeristy of Colorado, Boulder, Department of Ecology and Evolutionary Biology, 1900 Pleasant St, Boulder, CO, 80309, USA
2 - Bethel University, Biological Sciences, 3900 Bethel Dr,, St. Paul, MN, 55112, US
3 - Chicago Botanic Garden, Conservation Science, 1000 Lake Cook Road, Glencoe, IL, 60022, United States

Keywords:
demography
matrix models
Fire
Fire-stimulated flowering
Fire-stimulated recruitment.

Presentation Type: Poster
Session: P, Ecology Posters
Location: Arizona Ballroom/Starr Pass
Date: Monday, July 29th, 2019
Time: 5:30 PM This poster will be presented at 5:30 pm. The Poster Session runs from 5:30 pm to 7:00 pm. Posters with odd poster numbers are presented at 5:30 pm, and posters with even poster numbers are presented at 6:15 pm.
Number: PEC025
Abstract ID:802
Candidate for Awards:None