PRESCRIBED FIRE EFFECTS ON THE INVASIVE SPECIES ACHYRANTHES JAPONICA IN SOUTHERN ILLINOIS

Author

Kory M. Garrie, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2018

Degree Name

Master of Science

Department

Forestry

First Advisor

Ruffner, Charles

Second Advisor

Gage, Karla

Abstract

Prescribed fire has become a known silvicultural disturbance on public and private lands in the United States. Implementation of fire as a treatment allows land managers to reach specific goals through lower operational costs compared to mechanical or chemical means. Differences in management strategies for forested ecosystems often lead to individual plant species being overlooked. With an increasing number of invasive plants spreading into North American ecosystems, response of invasive plants to fire could potentially affect management decisions. It is important to understand the fire-response of invasive plants as stimulatory, neutral or suppressive to aid in future management of ecosystems. This study quantified the impact of small-scale prescribed fire on the invasive plant Japanese chaff flower (Achyranthes japonica; hereafter Chaff), at three different sites in Southern Illinois. The hypothesis was that fire would decrease the density and survival of chaff. Fixed sample plots were created (24 plots per site). At each site a set of unburned plots (control 8-16 plots) and treatment plots (burned 8-16 plots) were established, resulting in 32 burned plots and 32 unburned plots between 2015 and 2016. To best understand the effects fire had on Chaff, plant phenology was classified into four different life stages (cotyledons, seedlings, juveniles, adults) during each survey of the study plots. Using multi-model inference, one candidate model set was created to evaluate the survival of adult chaff flower, and 4 model sets to investigate the change in density of adults, juveniles, seedlings, and cotyledons respectively. The models had sites, treatment (burned versus unburned), and year (2015 and 2016) as explanatory variables. We compared the models using Akaike’s Information Criterion corrected for sample bias (AICc) to compare and rank models. The top model described survival of adult chaff flower, retained only treatment (burn vs. unburned) as a variable, and showed that Chaff survival was lower in burned plots than in unburned plots (β = -0.30, SE = 0.02), with the effect being greater at site 3 where about 46% of adult plants died after being treated with fire. The top model describing the change in adult plant density retained an interaction between year and site, and showed that adult chaff density increased from 2015 to 2016 on sites 1 and 2 by 32% and 14%, respectively. However, on site 3 there was nearly a 50% decrease in adult chaff flower plants in 2016. The juvenile and cotyledon stages showed similar results, by retaining an interaction between site and treatment, with an addition to year; the data showed a higher number of juveniles and cotyledons in the unburned plots than the burned plots going from 2015 to 2016. Seedling density decreased from 2015 to 2016 on sites 2 and 3, but on site 1 there was a slight increase. This increase could be largely due to the ability of the plants independent ability to replenish gaps in the population. Chaff can grow from the cotyledon class to an adult plant in a single growing season with sufficient sunlight, nutrient, and space. This study showed that a single entry of low intensity prescribed fire can kill established adult chaff plants. A single entry of prescribed fire had a direct negative impact on emerging young chaff plants, but the traits and characteristics of this invasive species which enable it to persist after a disturbance, as well as the documented variability on control associated with seasonal and local site differences, suggest that fire treatment alone may not be enough to halt its spread. Future work could focus on more burns, with repeated entry of fire in chaff flower populations and burns conducted at higher intensities and at different times of the year to further explore the impacts of fire on this invasive species.