SUCCESSION OF DESERT PLANTS ON DEBRIS FLOW TERRACES, GRAND-CANYON, ARIZONA, USA

Vegetation sampling on 11 debris flow terraces in Grand Canyon Nationa l Park, Arizona, U.S.A., showed that plant assemblages changed as age of surface increased. The terraces ranged in age from about 5 to about 3100 years. There were distinct differences among sites in the life h istory characteristics of the dominant plants. Young terraces (5-55 ye ars) were dominated by short-lived plants that had high reproductive p otential. Older surfaces were dominated by species with longer life-sp ans and lower reproductive potential. Density and cover of long-lived species increased with age of surface; for short-lived plants, density was inversely related to surface age. Species composition was also co rrelated with site age; however, location, exposure, and other factors ensured that no two debris hows supported identical mixtures of speci es. Succession on recent Grand Canyon debris flows is driven in part b y life-history strategies, particularly life-span and seed dispersal t raits, and also by climatic factors, especially those that control ger mination and establishment of the long-lived dominants. (C) 1997 Acade mic Press Limited.