ARS | Publication request: Basal gaps in long-term (25 years) ungrazed and heavy grazed northern mixed-grass prairie

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 3, 2007
Publication Date: January 26, 2008
Citation: Whitman, A.J., Derner, J.D. 2008. Basal gaps in long-term (25 years) ungrazed and heavy grazed northern mixed-grass prairie. In: American Forage and Grassland Council and Society for Range Management annual mtng "Building bridges: Grasslands to Rangelands." Louisville, KY, January 2008. CDROM, Absract #2666).

Technical Abstract: Soil/site stability is one of three interrelated attributes of rangeland health. A quantitative assessment indicator of this attribute is the proportion of soil surface exposed by basal gaps between perennial plants. The amount and distribution of basal gaps is a direct indication of site susceptibility to wind and water erosion. We assessed basal gaps using a continuous line intercept method in two replicated pastures with long-term (25 years) heavy grazed and ungrazed treatments in a northern mixed-grass prairie. Four, 20 m long transects in each replicated pasture were randomly located in late July 2007 and the lengths of each basal gap were recorded. Mean basal gap size was 66% greater in ungrazed (14.8 ± 1.2 cm, n=8) than heavy grazed pastures (8.9 ± 0.4 cm). Although the number of basal gaps per transect was 26% greater with heavy grazing (154 ± 8) than no grazing (122 ± 9), the total amount of basal gap length was 27% higher in ungrazed (1734 ± 10 cm) than heavy grazed pastures (1365 ± 71 cm). This resulted in 87% of the transect length occupied by basal gaps without grazing, but only 68% with heavy grazing. Distribution of lengths of basal gaps differed with grazing as heavy grazed pastures, dominated by the bunchgrass blue grama (Bouteloua gracilis), had more gaps with shorter lengths; whereas, more gaps with longer lengths were observed in ungrazed areas dominated by the perennial mid-height grasses western wheatgrass (Pascopyrum smithii) and needleandthread (Hesperostipa comata). Although the amount and distribution of basal gaps was greater in ungrazed areas, the ecological consequences of these basal gaps regarding susceptibility to wind and water erosion of these sites may be lessened by the occurrence of more litter cover in these gaps (80%) compared to those in the heavy grazed pastures (56%).