Alternative Grazing Management Strategies Combat Invasive Grass Dominance

Abstract

Changes in historical disturbance regimes have increased the susceptibility of Great Plains ecosystems to various threats, including invasive species. Kentucky bluegrass (Poa pratensis; hereafter bluegrass) invasion in the northern Great Plains is displacing native species and has created novel ecosystems with no historical precedent to guide management. Traditional season-long (SL) grazing management increases bluegrass abundance, so we conducted a field experiment to determine if alternative early-intensive (EI) and patch-burn (PB) grazing management strategies can elicit more desirable outcomes in bluegrass-invaded pastures. Alternative EI grazing involved a triple of the stock density, compared to SL and PB stock density, for the first third of the grazing season while PB grazing incorporated SL grazing with prescribed burns. We randomly assigned treatments to 16-ha pastures with three replicates per treatment (n = 3). We conducted vegetation cover surveys and collected aboveground biomass samples to analyze plant community dynamics and production at study initiation and after 4 y of treatment. The SL grazing treatment increased bluegrass abundance by approximately 20% after 4 y of treatment while the alternative EI and PB grazing maintained its abundance at study initiation levels. Compositional differences also indicated increased native plant species cover with alternative management. Annual aboveground biomass production was not affected by management, but has the potential to become less variable with PB grazing in bluegrass-dominated pastures. Our results provide promising evidence that alternative grazing management may help combat bluegrass invasion by preventing additional increases in its abundance in the northern Great Plains.