Semiarid rangeland is resilient to summer fire and post-fire grazing utilization

Authors: Vermeire, Lance; CROWDER, JESSICA - Wyoming Department Of Agriculture, Natural Resources & Policy; WESTER, DAVID - Texas A&M University

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2013
Publication Date: 1/1/2014
Citation: Vermeire, L.T., Crowder, J.L., Wester, D.B. 2014. Semiarid rangeland is resilient to summer fire and postfire grazing utilization. Rangeland Ecology and Management. 67:52-60.

Interpretive Summary: Most wildfires occur during summer in the northern hemisphere, the area burned annually is increasing, and fire effects during this season are least understood. Livestock grazing is a primary use of rangelands affected by wildfire, but post-fire grazing management is not well-supported with data. Understanding plant community response to grazing following summer fire is required to reduce ecological and financial risks associated with wildfire. Forty 0.75-ha plots were assigned to summer fire then 0, 17, 34 or 50% biomass removal by grazing the following growing season, or no fire and no grazing. Root, litter, and aboveground biomass were measured before fire, immediately after grazing, and 1 yr after grazing with the experiment repeated during two years to evaluate weather effects. Fire years were followed by the 2nd driest and 5th wettest springs in 70 yr. Biomass was considerably more responsive to weather than fire and grazing, with a 452% increase from a dry to wet year and 31% reduction from a wet to average spring. Fire reduced litter 53% and had no first year effect on productivity for any biomass component. Grazing after fire reduced post-grazing grass biomass along the prescribed utilization gradient. Fire and grazing had no effect on total aboveground productivity the year after grazing compared to non-burned, non-grazed sites (1327 versus 1249 ± 65 kg ha-1). Fire and grazing increased grass productivity 16%, particularly for the forage species western wheatgrass. The combined disturbances reduced forbs (51%), annual grasses (49%), and litter (46%). Results indicate grazing with up to 50% biomass removal the first growing season after summer fire was not detrimental to semiarid rangeland plant communities. Livestock exclusion the year after summer fire did not increase productivity or shift species composition compared to grazed sites. Weather-induced interannual differences in forage availability were greater than those caused by fire or grazing and reduction of previous years’ standing dead material was the only indication that fire may temporarily reduce forage availability. The consistent responses among dry, wet, and near-average years suggest plant response is species-specific rather than climatically controlled.

Technical Abstract: 1. Most wildfires occur during summer in the northern hemisphere, the area burned annually is increasing, and fire effects during this season are least understood. Livestock grazing is a primary use of rangelands affected by wildfire, but post-fire grazing management is not well-supported with data. Understanding plant response to grazing following summer fire is required to reduce ecological and financial risks associated with wildfire. 2. Forty 0.75-ha plots were assigned to summer fire then 0, 17, 34 or 50% biomass removal by grazing the following growing season, or no fire and no grazing. Root, litter, and aboveground biomass were measured before fire, immediately after grazing, and 1 yr after grazing with the experiment repeated during two years to evaluate weather effects. 3. Fire years were followed by the 2nd driest and 5th wettest springs in 70 yr. Biomass was considerably more responsive to weather than fire and grazing, with a 452% increase from a dry to wet year and 31% reduction from a wet to average spring. 4. Fire reduced litter 53% and had no first year effect on productivity for any biomass component. Grazing after fire reduced post-grazing grass biomass along the prescribed utilization gradient. 5. Fire and grazing had no effect on total aboveground productivity the year after grazing compared to non-burned, non-grazed sites (1327 versus 1249 ± 65 kg ha-1). Fire and grazing increased grass productivity 16%, particularly for the forage species Pascopyrum smithii. The combined disturbances reduced forbs (51%), annual grasses (49%), and litter (46%). 6. Synthesis and applications. Results indicate grazing with up to 50% biomass removal the first growing season after summer fire was not detrimental to semiarid rangeland plant communities. Livestock exclusion the year after summer fire did not increase productivity or shift species composition compared to grazed sites. Weather-induced interannual differences in forage availability were greater than those caused by fire or grazing and reduction of previous years’ standing dead material was the only indication that fire may temporarily reduce forage availability. The consistent responses among dry, wet, and near-average years suggest plant response is species-specific rather than climatically controlled.