Factors related to the occurrence of certain prairie graminoid species in Black Hawk County, Iowa, roadsides

The native vegetation of Iowa was primarily tallgrass prairie and currently exists only in small isolated parcels, including some remnants occurring in roadsides. Roadside prairie remnants are important for historical, environmental, aesthetic, scientific, and economic reasons. Information about factors influencing the occurrance of roadside prairie vegetation could be useful to roadside vegetation managers in development of initial vegetation surveys and subsequent to restoration of roadside prairie vegetation. This study was conducted to determine what factors most affected the percent coverage of prairie graminoids in roadsides; particularly soil moisture availability, drainage, soil disturbance, and availability of a prairie seed sources. Prairie vegetation of the study was confi ned to graminoid species selected from roadside segments of the Black Hawk County Roadside Vegetation Survey. Cover categories of prairie vegetation were 1) 0%, 2) 5 -15%, 3) 16-49%, and 4) 50-100%. Of the total 494 roadside segments taken, an approximate 4:2:2:1 ratio was noted among cover categories in decreasing order from cover category 1 through 4. In Chi-square tests, prairie vegetation cover was significantly related to road age, soil association, and road type, but was not significantly related to permeability, erodibility, original vegetation, and adjacent land use. Statistical analyses of roadside slope were inconclusive. The relative amount of prairie vegetation that occurred in roadsides increased with road age. Samples in roadsides along roads -- more than 51 years old had the highest percentage of prairie vegetation (37%) in cover category 4, and most samples (67%) in roadsides less than 21 years old contained no prairie vegetation. Soils well suited for agricultural use generally had a higher proportion of prairie vegetation than soils poorly suited to agricultural use. Among soil associations poorly adapted to agriculture, Sparta-Olin -Dickinson, had a relatively higher number of samples in cover category 4, and also was adjacent to relatively large remnants of non-roadside prairie. Prairie vegetation occurs in greater frequency and in higher cover values adjacent to gravel roads than adjacent to paved roads