Riparian Environmental-Vegetation Interrelationships Along the Lower Escalante River, Glen Canyon National Recreation Area, Utah: Final Report

Irvine, James; West, Neil

Studies of environmental and riparian vegetation interrelationships along the lower Escalante River were conducted during 1974 and 1975. The study area included the Escalante River flood terraces between Harris Wash and Coyote Gulch. Methods were developed compatible for wilderness use. Sixty-nine 1 by 10 meter macro-plots were taken at 23 locations. Measurements were taken of those environmental parameters thought to influence riparian vegetation stratigraphy, soil texture and moisture, river bank angle and aspect, and height and width of flood terraces. Canyon profile was found to be strongly influenced by geologic strata. Resistance to erosion by these strata determines canyon width, number of meanders, and river bank profile. River bank profile is further modified by flooding which creates flood terraces. Vegetation was found to be roughly correlated with stratigraphy and flood terraces. Scirpus americanus and Equisetum laevigatum were found near the edge of the river on the lowest flood terrace. Salix exigua, Populus freemontii, and Tamarix pentandra occurred on the low, medium, and high flood terraces but showed increasing proportion of older individuals there. Population age structure differences were attributed to flooding which dynamically maintains each population. Regeneration by root suckers for Salix and Populus have a greater survival rate than Tamarix whose seedling source is washed away by periodic fluctuations in river level. Implications' of this research are that reduction in river flow or regulation of floods would remove population equilibrium controls. Tamarix, without the effect of its seed source being washed away, would have a successional advantage over the other two native tree species.