Vegetation of exclosures in southwestern North Dakota

  • Published source details Brand M.D. & Goetz H. (1987) Vegetation of exclosures in southwestern North Dakota. Journal of Range Management, 39, 434-437.


A 3-year study of the vegetation in four long-term livestock exclosures (3 established in 1937 and the fourth in 1938) was begun in 1976 in mixed grass prairie in the Little Missouri Badlands of North Dakota (northern USA) to help inform prairie management.

The exclosures were on each of four prairie sites within 14 km distance of one another. Dominant species were blue grama Bouteloua gracilis, thread-leaf sedge Carex filifolia, western wheatgrass Agropyronsmithii and needle-and-thread Stipa comata.
A grazed plot was established in 1976 adjacent to each exclosure. Plots and exclosures ranged 0.2 to 1 ha in area. On grazed plots (part of larger cattle grazing units) grazing was permitted from 1 May to 31 December.
Vegetation was sampled during the summers of 1976, 1977 and 1978. Percent cover of lichens and mosses was measured using a 10-pin point- frame systematically placed 300 times in each plot/exclosure each year.
Forb and graminoid production was sampled (10, 0.5-m² quadrats clipped at ground level in each plot/exclosure each August i.e. end of main growth period). Grazed plot quadrats were protected from grazing with cages in the first year. Mulch (i.e. standing dead matter from the previous year and litter) was hand collected. Mulch and herbage samples were dried and weighed. Heights of the longest leaves of randomly selected plants were measured before clipping.
Belowground plant biomass was sampled in early August 1978 via 20 cores (2.1 cm diameter) within each plot. Biomass was dried and weighed.

The exclosures had greater graminoid leaf heights (but not always significantly so) and greater mulch accumulations than grazed plots. However, total yield and belowground biomass were similar between plots and their paired exclosures in three of the sites. Production of blue grama was lower, and production of thread-leaf sedge and sun sedge Carex heliophila was greater in the exclosures than on grazed plots. Midgrass and tallgrass species groups overall, were perhaps surprisingly, only more dominant in one exclosure.
Whilst the main difference between exclosures and grazed plots was plant species composition, individual site characteristics appeared very important in influencing vegetation development in the exclosures.
The authors therefore suggest that managers need to make evaluations on a site specific basis rather than assuming that a reduction in grazing pressure will quickly influence vegetation characteristics, such as increases in midgrass and tallgrass dominance or total yield.
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