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FACTORS AFFECTING NATIVE GRASS SEEDLING ESTABLISHMENT ALONG TOPOGRAPHIC GRADIENTS IN THE NEBRASKA SANDHILLS: AN EXPERIMENTAL APPROACH
Abstract
In the Nebraska Sandhills, the distribution of co-dominant perennial grasses varies along steep topographic gradients. To determine whether these distributions result from the differential colonizing abilities of seedlings, reciprocal seed planting experiments were conducted on several topographic sites in the presence and absence of competitors. In years of average rainfall, upland species had the highest seedling survivorship on lowland sites when the vegetation was removed by clipping or rototilling. When seeds were planted in the native vegetation, they had higher survivorship on upland sites. In contrast, in a year of above-average precipitation, while both uppland and lowland species had the highest survivorship on lowland sites with vegetation removal, on the vegetated plots, higher seedling survivorship occurred on lowland sites. These seedling survivorship patterns were correlated with the availability of soil moisture. In years of average precipitation, soil moisture is depleted on vegetated lowland sites, likely resulting from the higher transpiration rates and vegetative cover on these sites. As a result, these sites had lower seedling survivorship. With soil disturbance or above-average growing season precipitation, seedling survivorship was higher on the lowland sites where the soils have a higher moisture holding capacity. The plant distributions along these topographic gradients are not determined by species-specific seedling characteristics which allow higher seedling survivorship on topographic sites where the adults are the most common. Rather, it appears that competitive sorting occurs along the gradient subsequent to the seedling stage causing displacement of the upland species to upland sites where there is typically lower but more reliable soil moisture during the growing season. I believe that the lowland species are continually eliminated from the upland sites by high levels of abiotic stress, such as erosion, which they cannot tolerate as well as the ridge species. Natural regeneration from seed in this grassland type is rare and thought to be a result of low levels of seed production by the co-dominant perennial grasses (ca. 3 seeds m('-2)) and high levels of seed predation.
Subject Area
Ecology
Recommended Citation
POTVIN, MARTHA ANN, "FACTORS AFFECTING NATIVE GRASS SEEDLING ESTABLISHMENT ALONG TOPOGRAPHIC GRADIENTS IN THE NEBRASKA SANDHILLS: AN EXPERIMENTAL APPROACH" (1984). ETD collection for University of Nebraska-Lincoln. AAI8427911.
https://digitalcommons.unl.edu/dissertations/AAI8427911