Spatio-temporal patterns of rangeland forage nutritive value and grazer selection with patch-burning in the US northern Great Plains

Authors: SPIESS, JONATHAN - Chadron State College; McGranahan, Devan; BERTI, MARISOL - North Dakota State University; GASCH, CALEY - North Dakota State University; HOVICK, TORRE - North Dakota State University; GEAUMONT, BENJAMIN - North Dakota State University

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2024
Publication Date: 3/28/2024
Citation: Spiess, J.W., McGranahan, D.A., Berti, M., Gasch, C., Hovick, T.J., Geaumont, B. 2024. Spatio-temporal patterns of rangeland forage nutritive value and grazer selection with patch-burning in the US northern Great Plains. Journal of Environmental Management. 357. Article 120731. https://doi.org/10.1016/j.jenvman.2024.120731.
DOI: https://doi.org/10.1016/j.jenvman.2024.120731

Interpretive Summary: Livestock choose where to graze based on forage quality and quantity, but few studies repeatedly measure forage nutritive value, available biomass, and grazer selection within rangelands throughout the grazing season. This paper describes how patterns in rangeland forage drive grazer selection in semi-arid rangeland over four grazing seasons at monthly intervals on patch-burn grazing pastures stocked with either cattle or sheep. We used near-infrared spectroscopy to determine multiple measures of forage nutritive value from monthly forage clippings and evaluated livestock performance as the average daily weight gains of each animal. Cattle and sheep consistently preferred recently burned patches throughout grazing seasons. Although lower in available forage, burned patches had lower acid detergent fiber, acid detergent lignin, and neutral detergent fiber, and higher crude protein and moisture content than elsewhere in the landscape. This study indicates that patch-burn grazing can create and maintain heterogeneous grazer selection and forage biomass patterns desirable for increasing structural heterogeneity in rangelands regardless of grazer type. These findings provide a baseline of expectations for practitioners and land managers implementing patch-burn grazing and illustrate how grazing livestock can benefit from the patch contrast in forage nutritive value and biomass.

Technical Abstract: 1. Variability in forage nutritive value and quantity influences herbivore site selection. However, few studies repeatedly measure forage nutritive value, available biomass, and grazer selection within rangelands throughout the grazing season. 2. We describe how patterns in rangeland forage drive grazer selection in semi-arid rangeland over four grazing seasons at monthly intervals on patch-burn grazing pastures stocked with either cow-calf pairs or gestating ewes. We used near-infrared spectroscopy to determine multiple measures of forage nutritive value from monthly forage clippings. We evaluated livestock performance as the average daily weight gains of each animal. We used mixed-effect models and ordination to compare patches across the time-since-fire gradient and across pastures in different grazer treatments. 3. Cattle and sheep consistently preferred recently burned patches throughout grazing seasons. Although lower in available forage, burned patches had lower acid detergent fiber, acid detergent lignin, and neutral detergent fiber, and higher crude protein and moisture content than elsewhere in the landscape. 4. Synthesis and applications: Our study indicates that patch-burn grazing is capable of creating and maintaining heterogeneous grazer selection and forage biomass patterns desirable for increasing structural heterogeneity in rangelands regardless of grazer type. These findings are especially relevant to the northern Great Plains where introduced grasses are homogenizing the structural environment of remaining rangelands. With prescribed fire currently an uncommon practice throughout the region, these findings provide a baseline of expectations for practitioners and land managers implementing patch-burn grazing and illustrate how grazing livestock can benefit from the patch contrast in forage nutritive value and biomass.