Geomorphology of the hanging gardens of the Colorado Plateau
Proceedings of the Second Biennial Conference on Research in Colorado Plateau National Parks, 25-28 October 1993. National Park Service Transactions and Proceedings Series NPS/NRNAU/NRTP- 95/11
A roughly J-shaped archipelago of island habitats is distributed within the drainage system of the Colorado Plateau from the Zion area at the southwest to the canyons of the Green and Yampa rivers in the northeast. This is the hanging garden habitat. Hanging gardens are isolated mesophytic communities physically and biologically distinct from surrounding xerophytic or riparian communities. Geologic and hydrologic parameters control the existence, distribution, and physical attributes of the banging-garden habitat. Attributes vary with the sedimentologic type of the different aquifer-bearing geologic formations in which gardens develop. Within a given formation, garden habitat attributes are relatively consistent. This observation allows a simple, informative. and predictive model of garden geomorphology to be applied across the geographic range of the system. The sandstone aquifers of the Colorado Plateau provide the necessary condition for hanging garden development-a perennial, seep-delivered water supply and an absence of significant fluvial processes. An erosional process called groundwater sapping yields protective geomorphology that shields the habitat from the aridity of the region as well as extrinsic erosional processes. Discharge rate and the lithology of the seep·supplying geologic fonnation determine the size, shape, distribution, and abundance of microhabitats within a hanging garden. Colonization of microhabitats is determined by the ecological requirements and by the biogeographic and evolutionary history of individual species making up the hanging-garden community. Diversion of the seep supply and erosion of colluvial soil by human foot traffic and livestock use affect garden ecology negatively. Hanging gardens should be protected from both activities. Local and regional alteration of patterns of aquifer flow may affect the hanging-garden ecosystem.
May, C. L., J. F. Fowler, and N. L. Stanton. 1995. Geomorphology of the hanging gardens of the Colorado Plateau. Pages 3-24 in C. van Riper, III, editor. Proceedings of the Second Biennial Conference on Research in Colorado Plateau National Parks, 25-28 October 1993. National Park Service Transactions and Proceedings Series NPS/NRNAU/NRTP- 95/11.