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United States Department of Agriculture

Agricultural Research Service

Title: Grazing and Livestock Exclusion Effects on Northern Plains Diversity and Heterogeneity

Authors
item Vermeire, Lance
item Heitschmidt, Rodney
item Haferkamp, Marshall

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2005
Publication Date: February 1, 2006
Citation: Vermeire, L.T., Heitschmidt, R.K., Haferkamp, M.R. 2006. Grazing and livestock exclusion effects on northern plains diversity and heterogeneity. Society for Range Management Meeting Abstracts #365.

Interpretive Summary: Plant diversity and heterogeneity within landscapes are key issues, especially relative to maintaining rangeland productivity and stability and managing for at-risk wildlife species with diverse habitat requirements. We hypothesized that livestock grazing would produce greater diversity and heterogeneity of plant species biomass than 10 years of livestock exclusion because of the patchy nature of grazing distribution with moderate stocking. Four 12.1-ha livestock exclosures were established and paired with adjacent, moderately-grazed sites in 1993. Current-year live and dead biomass were sampled annually by species and species groups from 20, 0.25-m2 quadrats at each site to assess effects of livestock grazing and livestock removal on plant communities in a northern mixed prairie from 1994 through 2003. Heterogeneity was measured as proportional dissimilarity (PD) and diversity was assessed using Simpson's indices. Heterogeneity was similar among years (44.4 ± 4.4% PD) and between livestock-grazed (42.3% PD) and livestock-excluded sites (46.5% PD). Diversity and current-year biomass each changed among years, but were similar between livestock-grazed and livestock-excluded sites. The probability of two sampled plants being different species (1-D) was 0.55 to 0.72 ' 0.04. The number of equally abundant species required to achieve the same probabilities of two separate species in two samples (1/D) was 2.6 to 4.1 ' 0.3 throughout the period. Current-year biomass varied from 403 to 1886 kg•ha-1 over 10 years and averaged 1119 ' 158 kg•ha-1 across livestock-grazed and livestock-excluded sites. Results indicate diversity and current-year biomass are responsive to year (weather) effects, but the sites are resistant to moderate livestock grazing or the absence of livestock as measured by current-year biomass, diversity, and heterogeneity.

Technical Abstract: Plant diversity and heterogeneity within landscapes are key issues, especially relative to maintaining rangeland productivity and stability and managing for at-risk wildlife species with diverse habitat requirements. We hypothesized that livestock grazing would produce greater diversity and heterogeneity of plant species biomass than 10 years of livestock exclusion because of the patchy nature of grazing distribution with moderate stocking. Four 12.1-ha livestock exclosures were established and paired with adjacent, moderately-grazed sites in 1993. Current-year live and dead biomass were sampled annually by species and species groups from 20, 0.25-m2 quadrats at each site to assess effects of livestock grazing and livestock removal on plant communities in a northern mixed prairie from 1994 through 2003. Heterogeneity was measured as proportional dissimilarity (PD) and diversity was assessed using Simpson's indices. Heterogeneity was similar among years (44.4 ± 4.4% PD) and between livestock-grazed (42.3% PD) and livestock-excluded sites (46.5% PD). Diversity and current-year biomass each changed among years, but were similar between livestock-grazed and livestock-excluded sites. The probability of two sampled plants being different species (1-D) was 0.55 to 0.72 ' 0.04. The number of equally abundant species required to achieve the same probabilities of two separate species in two samples (1/D) was 2.6 to 4.1 ' 0.3 throughout the period. Current-year biomass varied from 403 to 1886 kg•ha-1 over 10 years and averaged 1119 ' 158 kg•ha-1 across livestock-grazed and livestock-excluded sites. Results indicate diversity and current-year biomass are responsive to year (weather) effects, but the sites are resistant to moderate livestock grazing or the absence of livestock as measured by current-year biomass, diversity, and heterogeneity.

Last Modified: 12/20/2014
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