NITROGEN AND PHOSPHORUS EFFECTS ON SECONDARY SUCCESSION DYNAMICS ON A SEMIARID SAGEBRUSH SITE

A sagebrush steppe community in northwestern Colorado was disturbed in 1984 and subjected to annual applications of nitrogen and phosphorus, and successional responses were studied over a 5-yr period. Phosphorus was not found to be significant but nitrogen did significantly affect succession for all years except the first. Three seral groups developed on the non-fertilized plots, the first two dominated by annuals and lasting 3 yr, the third transitional and dominated by perennials. The addition of N altered this successional pattern by allowing annuals to remain as site dominants through the 5th yr. Results of this study suggest that dominance of a site by annuals in early stages of secondary succession is related to high nutrient availability.