Spatial Scale and Floristic Diversity on Shallow Limestone Rangeland

Studies of European limestone grasslands have suggested that when relatively small scale is considered, these grasslands are the most floristically rich sites on Earth. This study of shallow limestone communities in western Kansas was designed to examine their spatial aspects and floristic diversity, to assess the Willems\u27 (1993) hypothesis and to examine the habit at island hypothesis. Two study areas had 3 study sites and were located in the Central Great Plains physiographic region, near the city of Hays, Ellis County, Kansas. The 3 study sites each had 2 sample periods that produced 6 site/season combinations. The spring sample period began 7 June 1994 and was completed 5 July 1994, and the late summer sample period began 20 August 1994 and was completed 16 September 1994. The growing season had below average rainfall with short-term drought conditions existing during most of this study. At each site a 4 m2 square quadrat was used that had 14 nested sub-quadrants arranged following Wiegert’s (1962) method of determining optimum quadrat size for sampling the standing crop of grasses and forbs. Forty quadrats were examined for each site/season, yielding a total of 240, 4 m2 quadrats. Each quadrat was placed at 15 paces from the preceding quadrat, marked, and positioned parallel to the site slope. Data collected were presence/absence per quadrat, yielding species frequency, and species area data. Based on frequencies major and indicator species were designated. To measure similarity between sites and seasons, Jaccard (1912) coefficients were calculated. Sideoats grama, big bluestem, noseburn, and broom snakeweed were major species on shallow limestone sites. The relationship of number of species to quadrat size revealed a classic species/area curve. The species/area curve for grasses had a higher starting count class, increased sharply, and quickly became asymptotic. The species/area curve for forbs was more gradual than the curve for grasses, and had a lower starting count class. Each site had different indicator species, but 2 sites were more closely related 10 each other than 10 the third season had little effect on the similarity of each respective site/season. The general trend was for grasses to dominate in numbers of individuals and biomass, and forbs to dominate in number of species per quadrat and total number of species. The optimum size of square quadrat 10 be used on shallow limestone sites based on my study was 0.5 m2 to 1.0 m2. Climate and the low water holding capacity of shallow limestone communities probably limit species that are not drought tolerant and enhance species richness. The richness of these sites is determined by the combined effect of grazing management, patch and gap dynamics, disturbance, and environmental conditions