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Plant Community Patterns on Upland Prairie
in the Eastern Nebraska Sandhills

Introduction


The vegetation of the Nebraska Sandhills has been described as a unique mixture of plant species from other prairie types, including the tallgrass and shortgrass prairies (Kaul 1998). The Nebraska Sandhills covers about 50,000 km² and provides a wide variety of habitats from xeric dune tops to wetlands. The dune formations, or upland prairie, dominate the landscape and compose about 90% of the land area. Hydrologic properties of the sandy soils on uplands allow for rapid infiltration of precipitation, with little or no runoff, and provide adequate growing conditions for the dominant tall grasses (Burzlaff 1962). Mid and short grasses are in the understory of tall grasses or form the grass canopy in areas where conditions are not favorable for tall grasses. A wide variety of forbs are common but are secondary to the grasses in terms of cover and biomass production. Shrubs are present but account for relatively little cover or biomass production except in localized areas (Tolstead 1942, Kaul 1998). The Nebraska Sandhills region is dominated by C4 grass species, but there is a rich mixture of C3, C4, and CAM species across the landscape.

Plant species composition of the upland vegetation is dynamic, temporally and spatially. Pool (1914), in the first detailed survey of Nebraska Sandhills vegetation, reported that a bunchgrass association was the most characteristic type of vegetation on the uplands. Although he mentioned sand bluestem (Andropogon hallii Hack) as a dominant, he rated little bluestem [Schizachyrium scoparium (Michx.)] as the most frequent and dominant plant of the bunchgrass association and of the Nebraska Sandhills as a whole. By the mid- to late-1930's, however, Frolick and Shepherd (1940) reported that prairie sandreed [Calamovilfa longifolia (Hook) Scribn.], hairy grama (Bouteloua hirsuta Lag.), and sand dropseed [Sporobolus cryptandrus (Torr.) A. Gray] were the dominants and that little bluestem was relatively uncommon on upland range in Cherry County of the northcentral part of the Nebraska Sandhills. Tolstead (1942) also reported that prairie sandreed was the most characteristic grass of the Sandhills in Cherry County; however, depending on the site and successional stage, it was commonly a codominant with sand bluestem, hairy grama, blue grama [Bouteloua gracilis (H.B.K.) Lag. ex Griffiths], or needle-and-thread (Stipa comata Trin. & Rupr.). This apparent decline in prevalence of little bluestem on the uplands between the early 1900's and the late 1930's was considered to be an effect of the 1930's drought (Weaver and Albertson 1939, Frolik and Shepherd 1940). Recent reports (Burzlaff 1962, Barnes et al. 1984, Bragg 1998) indicate that little bluestem is again a codominant on Nebraska Sandhills upland sites.

Topographic position on upland prairie plays a critical role in species composition as certain species are characteristic of dune tops whereas others are found principally in the dry interdunal valleys. Barnes and Harrison (1982) reported that the distribution of plants on uplands in the western Sandhills of Arthur County, Nebraska was related to soil texture and subsurface moisture availability. Dry, interdunal valleys had finer-textured soils with relatively high moisture content in the upper part of the soil profile until mid-summer when usable water was largely depleted by a dense stand of early-growing, shallow-rooted grasses (e.g., blue grama), sedges (Carex L. spp.), and forbs (Barnes and Harrison 1982, Barnes et al. 1984). Dune tops and slopes had coarse-textured soils and tended to be dominated by tall grasses, e.g., prairie sandreed, sand bluestem, and little bluestem, with extensive root systems that exploited deeper sources of soil water. Effect of aspect, e.g., north-facing vs. south-facing slopes, on plant community distribution was not determined. On another site in the western Sandhills, Bragg (1978) reported that vegetation on south-facing slopes of a choppy sands range site was predominantly prairie sandreed, a warm-season grass, whereas north-facing slopes were dominated by needle-and-thread, a cool-season grass. Differences in temperature, humidity, and evaporation rate between north and south aspects probably affected plant distribution across topographic position (Bragg 1978).

These earlier studies were key in characterizing the relationship between topographic position and vegetation cover; however, they were conducted on areas not grazed by livestock (Barnes and Harrison 1982, Barnes et al. 1984), did not include the full range of topographic positions (Barnes and Harrison 1982, Barnes et al. 1984), were designed as descriptive studies (Tolstead 1942, Barnes et al. 1984), and/or were conducted in the western Nebraska Sandhills (Barnes et al. 1984, Bragg 1978). The objective of our study was to determine the effect of topographic position on plant species composition of upland sites grazed by cattle in the eastern Sandhills of Nebraska.


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