An Alpine Vegetation Map of Niwot Ridge, Colorado^∗

Abstract

Niwot Ridge represents an altitudinal, east-west oriented gradient on the east slope of the Front Range. A large scale (1:10,000) map of its alpine vegetation provides information on the extent and the spatial and environmental relationships of the mapped units of a Braun-Blanquet vegetation classification hierarchy. Patterns of moisture and snow, influenced to a high degree by wind and topography, appear to be the factors controlling vegetation distribution. Distance from the Continental Divide combined with altitude, rather than altitude alone, appears to be of importance for the distribution of most vegetation units. The average elevation of treeline on the ridge is 3406 m s.m. Treeline is lowered on the south slope by strong westerly winds; it is higher in valleys than on ridges, lowest positions occurring below snowpatches. The net aboveground vascular productivity of the mapped alpine area is estimated at 1.725 ton ha⁻¹ yr⁻¹. The Braun-Blanquet system was found to be very suitable for mapping and analyzing vegetation at this large scale. Areas with vegetation composition of higher units of the Braun-Blanquet hierarchy (alliances in particular) that appear to represent average environmental conditions on the ridge are considerably larger than the areas of individual associations.