OOS 22-3 - What does it take to restore mesic grasslands from woody encroachment?

Background/Question/Methods
Woody plants are increasing in cover and abundance in many grasslands globally. In North American mesic grasslands, fire is a major local driver, however past research has shown that it is no longer a viable tool for restoration in of itself where resprouting woody plants are present. To determine what other restoration treatments are possible in conjunction with fire we asked whether cutting and mowing of trees and shrubs in a mesic grassland followed by a restart of annual spring burns could reduce the overall impact of woody plant expansion. To answer our question, we setup a case study within an 83-Ha watershed at the Konza Prairie Biological Station that recently had trees cut (herbicide added to stumps), and shrubs mowed (no herbicide) where we monitored the plant community over several years following woody plant removal. Additionally, one year after the cutting and mowing treatments were applied fire was re-established as an annual burn. We used a series of 100-m transect lines at different topographic positions (upland, slope, lowland) to determine plant community change from these restoration treatments.

Results/Conclusions
We found that after cutting, mowing, and burning treatments were implemented together, there was a 62% reduction in tree species abundance but a 12% increase in shrub abundance overall after three years. When we look at how trees and shrubs responded based on topography, we found that tree species abundances were reduced on all topographic positions while shrub species became the dominant functional group on the landscape, regardless of topographic position. Resprouting shrub species became most dominant in the uplands, including Zanthoxylum americanum, Ceanothus americanus, and Rhus glabra. On slopes, we saw large increases in abundances for nearly all (10 of the 11) documented shrub species from our sampling. However, lowlands had the largest increase of shrub abundances overall, with Rhus aromatica, Symphoricarpos orbiculatus, Prunus americana, and Amorpha canescens being the dominant species. Cutting, mowing, and restarting of the fire cycle may work well as a restoration method to remove trees and non-resprouting species, but resprouters likely require additional, more frequent management treatments. There needs to be consistent inter- and intra-seasonal management of woody plant species to adequately reduce their presence.