Phenological Pattern in the Shortgrass Prairie

Data were collected for 1 year on 34 range plant species and for 2 years on six species to describe phenological timing in the shortgrass prairie of northeastern Colorado and also to determine whether there were any distinct groups of plants for which a single species could be used as a phenological indicator. Observations were made in four grazing treatments and two water amendment areas (one with 100 kg/ha mineral N ad'ded). Water amendments altered the phenology of some species, while grazing and nitrogen treatments had no measurable effects on phenology. Standard cooland warm-season classification of plants does not adequately describe the phenological dynamics of the shortgrass prairie. For example, Buchloe dactyloides, a warm-season grass, flowers with Agropyron smithii, a cool-season grass, rather than with Bouteloua gracilis, another warm-season grass. Four general categories of plants having different flowering capacities are recognized: blooming only once very early in the growing season; blooming twice with a summer dormancy period; blooming once during midsummer with blooming delayed during drought; and blooming only once late in the growing season. INTRODUCTION An understanding of phenological progression of plants is basic to understanding the functioning of a grassland ecosystem and is important in sound resource management (Costello, 1939; Lieth and Radford, 1971). Phenology is associated with plant growth rates (Taylor, 1972), nutrient transfer (Sosebee and Wiebe, 1973), thermal requirements (Nuttonson, 1955), plant-water relationships (Blaisdell, 1958) and perhaps even evolutionary change (Leopold, 1961). The objectives of this study were: (1) to describe the phenological progression of a broad spectrum of shortgrass prairie species; (2) to develop an approach for monitoring the phenological progress of the shortgrass prairie plant community by observing a few indicator species, and (3) to compare water treatment and annual weather variation effects as well as any observable differences in phenological state between grazing treatments or fertilization. These measurements, when combined with abiotic and other biotic measurements, will lead to a clearer understanding of the structure and function of the shortgrass prairie ecosystem. SiTE DESCRIPTION The Pawnee Site (intensive research site of the US/IBP Grassland Biome) ig located on the western edge of the USDA Central Plains Experimental Range, approximately 12 km N of Nunn, Colorado, at an elevation of 1652 m. Topography is gentle rolling plains. The major soil types are Ascalon, Vona, Renohill and Shingle, with Ascalon predominating on the sampling areas (Reuss, 1971). Annual precipitation varies from 254 to 381 mm, about 80% occurring from May to