Reconsidering rest following fire: Northern mixed-grass prairie is resilient to grazing following spring wildfire

Current federal post-fire land management recommendations in the United States suggest that rangelands be rested from grazing for two growing seasons following fire to allow for proper recovery, despite the lack of empirical literature supporting this recommendation. This project was designed to determine if grazing the first growing season following a spring wildfire alters subsequent productivity and species composition of northern mixed-grass prairie. Following the April 2013 Pautre wildfire in northwestern South Dakota, 100 m2 exclosures were erected in three burned pastures to simulate two growing seasons of rest. Grazing exclosures were paired with sites grazed both the first and second growing seasons following the fire and replicated across loamy and sandy ecological sites. Prior to grazing the second growing season, five 2 m2 cages were placed at each grazed site to assess first-year grazing effects. Following the second growing season, productivity and species composition were determined for exclosures and cages. Productivity was greater for loamy than sandy ecological sites (loamy = 2764 kg ha−1, sandy = 2356 kg ha−1; P = 0.0271), but was similar between grazing treatments (rested = 2556 kg ha−1, grazed = 2564 kg ha−1; P = 0.9550). Ecological site strongly determined species composition. Loamy sites consistently contained more Pascopyrum smithii, Bouteloua gracilis and Carex duriuscula than sandy sites (30 v 0%, 18 v 8%, 4 v 1%; P = 0.0004, 0.0457 and 0.0382 respectively). The effects of grazing exclusion were limited to Hesperostipa comata and the non-native Agropyron cristatum composition. H. comata was more prevalent on rested sites (22 v 15%, P = 0.0096). A. cristatum experienced a grazing treatment by ecological site interaction as it was reduced by grazing on sandy sites, but was not affected on loamy sites (P = 0.0226). Results do not support the notion that a two growing season rest period following fire is required in the northern mixed-grass prairie.