Vegetation diversity in an interconnected ephemeral riparian system of north-central Arizona, USA.

摘要

A vegetation survey was conducted during the summer of 1996 in the Pumphouse Wash canyon system in the Coconino National Forest, south of Flagstaff, Arizona. Plant species distribution, abundance and diversity were quantified within and among canyons in this sensitive ephemeral riparian area. Abiotic variables were also studied in relation to the prediction of vegetation diversity. Stand ordination and cluster analysis indicated that variation in vegetation distribution and composition was explained by a complex gradient of temperature, moisture and substrate. Understorey diversity in general was related to changes in slope and sand/gravel substrate. Each tributary canyon supported unique plant species and the riparian vegetation in one tributarycanyon was significantly less diverse than in each of the other canyons. The 2 canyons with the lowest understorey diversity contained rare plant species not found in the other, more diverse canyons. Overall diversity was demonstrated to be a poor predictor of the presence of rare species. Similarly, abiotic variation was useful at predicting diversity levels but was not useful at predicting species occurrence or ecological quality. It is concluded that attributes frequently considered of use for predicting conservation value of one type (e.g. diversity) were not good at predicting other conservation values (e.g. rarity).