Successional dynamics of a Nebraska Sandhills blowout*

Plant communities are highly diverse and dynamic systems, both spatially and temporally, that often depend on differing forms of disturbance to maintain diversity. Understanding the successional dynamics of a system is fundamental to our understanding of ecosystems and their management. The objective of this descriptive 15-year study, conducted at the Nature Conservancy Niobrara Valley Preserve near Johnstown, Nebraska, was to quantify and interpret patterns of seral change occurring in a Sandhills blowout [Valentine Association (mixed mesic Typic Ustipamments)] by defining consistent patterns of plant community change. Grazing was excluded from two active blowouts (12 ha and 5 ha) in 1981 and 1990, respectively. Each study area was overlain with a permanent grid system to facilitate mapping of the vegetation and sand erosion/deposition annually through 1995. Sand erosion/deposition patterns and plant community data were digitized into a Geographic Information System (GIS) to produce community maps. Spatial data for patches, class and landscape-level plant communities were rasterized, and analyzed for multiple spatial statistics by FRAGSTATS. The shape index was superior to a two-dimensional fractal analysis in characterizing patch and class dynamics. Four successional trajectories within a Nebraska Sandhills blowout were evident: (1) seral advancement of minimally disturbed perennial grass patches, (2) edge closure, (3) bare sand to blowoutgrass to blowoutgrass/sand muhly to perennial grass/sand muhly to perennial grass, and (4) bare sand to annuals to annual/perennial mixture to perennial grass. Areas of minimal disturbance had attained a high seral stage in at least 10 years. Within 8 years, there were minimal levels of vegetation established on the most disturbed sites. However, these areas may require in excess of 15 years of grazing exclusion to attain a high seral stage. Research on the causal mechanisms of these different successional trajectories is needed to enhance our management of blowouts. *Follows the style and format of Ecological Monographs