Fire and Grazing Reduce Invasive Grass Thatch in Rangelands

Abstract

Rangelands globally are invaded by exotic species. In the northern Great Plains, Kentucky bluegrass (hereafter, “bluegrass”) invades rangelands by forming a thick thatch layer that alters water and nutrient cycling and prevents seed germination by native plants. Consequently, management actions that focus on reducing the bluegrass thatch layer have a greater chance of successfully promoting native plant diversity. To determine how different rangeland management practices impact bluegrass thatch, we measured thatch depth at multiple points across pastures invaded by bluegrass in south-central North Dakota. Each pasture was managed with either patch-burn grazing, modified twice-over rest-rotational grazing (MTORG), or season-long grazing. We also measured thatch in a control pasture that was neither burned nor grazed the previous 5 years. Both the patch-burn grazing and MTORG pastures were designed to increase landscape-level heterogeneity and promote biodiversity. We found that all forms of rangeland management resulted in a thinner thatch layer than our control pasture (3.92 ± 0.27 cm). However, pastures managed with patch-burn grazing had less thatch (1.79 ± 0.03 cm) than those managed with either MTORG (2.60 ± 0.03 cm) or season-long grazing (2.59 ± 0.05 cm). These results suggest that any form of cattle grazing can reduce bluegrass thatch, however fire followed by grazing can further reduce bluegrass thatch. A reduction in thatch resulting from interacting fire and grazing may lessen the impact of bluegrass on rangelands.