Evaluation of shrub removal effects on understory richness and diversity in a native grassland

Tallgrass prairie is a highly endangered ecosystem in North America, and woody plant encroachment is one of the leading stressors facing prairie remnants. Insights into factors that predict vulnerability and resistance to invasion and information concerning the most effective treatment combinations are needed to preserve and restore remaining remnants. The study site, located in Lake County, Illinois, is an approximately 65 ha matrix of native tallgrass prairie and old field habitats that underwent treatment for wide-spread and intensive shrub encroachment in 2010. The study questions were: (1) How does shrub removal affect plant communities, both in terms of the vegetation parameters and the community trajectories, (2) Is there a legacy effect of buckthorn (Rhamnus cathartica) on plant community recovery, and (3) Does the intensity or composition of shrub re-invasion vary across soil moisture gradients? Data were collected on both ground layer and overstory composition and structure across 44 sampling plots in three community types (high-quality reference prairie, disturbed prairie referred to as transect prairie and old field) and span a total of 6 years, with a baseline sample before treatment and 4-5 years of post-treatment data, depending on the plot. In 2013, 5 plots were also added in a patch of shrub-encroached prairie adjacent to the site to serve as an approximation of untreated control for future monitoring. Restoration progress was evaluated using metrics of diversity and habitat quality, and restoration goals included convergence between the lower-quality habitat types (old field and transect prairie) and the reference prairie over time. Overall, the response following treatment was somewhat ambiguous. Profile analysis revealed significantly non-parallel trajectories by community type, and significant overall change regardless of community type, but definitive evidence of restoration progress, particularly among the transect prairie and old field community types, has not yet appeared. Reference prairie has remained fairly stable and high-quality, possibly due to the fact that it received the least intensive treatment. Transect prairie and old field community types, on the other hand, showed undesirable responses in several variables immediately following treatment (e.g., increases in non-native species richness and density and decreases in mean C and FQI) followed by moderating trends over the course of the study that, by 2014, returned to levels similar to baseline measurements. These trajectories combined with amalgamative grouping of the 2014 data indicate that old field and transect prairie may be converging with one another rather than reference prairie. The early fluctuations in trajectories and the apparent convergence of old field and transect prairie likely result from disturbance due to management activities as well as seeding activities. Generally desirable trends following initial decreases (notably FQI, percent bare ground, percent cover native species richness and native species density) imply that plots have recovered from initial stressors due to management action, but it will likely take several more years of subsequent monitoring to determine whether the old field and transect prairie communities continue to recover.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Natural Resources & Environmental Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Grant, Hannah Lisa

Contributors dc:contributor

• Taft, John B.

• soil magnetic susceptibility
• alternate stable state
• Shrub encroachment
• prairie
• restoration
• buckthorn
• Rhamnus cathartica

Statement dc:rights

• Copyright 2015 Hannah Grant

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/87990

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/87990