Document type: DU ETD
Collection: Geology Theses  
Title The Role of Soil Characteristics and Seasonal Soil Moisture in the Distribution of Vegetation on the Palmer Divide, Colorado
Author(s) Skinner, Catherine P.
Institution University of Denver
Degree Type Master's
Degree Name M.A.
Type of Resource text
Degree Date 1995 August
Digital Origin reformatted digital
Rights Statement All Rights Reserved
Reason for Restrictions No restrictions
Type of Restriction No restrictions
Abstract The Palmer Divide separates the drainage basins of the South Platte and Arkansas Rivers in east-central Colorado. Situated between Denver and Colorado Springs, it joins the Front Range on the west, and gradually descends eastward for about 110 km, to near Limon, Colorado. The Palmer Divide major vegetation types—ponderosa pine (Pinus ponderosa) woodland, gamble oak (Quercus gambelii) scrub, and prairie grasslands form distinctive east-west distributional patterns. Several approaches were used in this study to investigate relations between plants and soil moisture. Methods selected provide quantitative data on soil characteristics including water retention and saturation capacity, pH, electrical conductivity, and variations in soil development. The study sites represent the four common plant associations on the Palmer Divide, and range from near the highest point on the Palmer Divide in the west, to the eastern-most stand of pines on the divide. Ponderosa pine stands predominate at the summits of hillslopes and in rocky outcrops; pines at the western end of the Palmer Divide grow on ridgetops and rocky outcrops where soil moisture fills rock fractures, where they do not have to compete with other vegetation for moisture. The porous soils on the west half of the divide appear to permit transport of moisture downward where it accumulates above the bedrock and in bedrock joints. Shallow depth to bedrock under pine may be an indication that pines in this location develop deep taproots that can take advantage of moisture in rock fractures below. Gambel oak at the higher elevations on the divide occupies transitional areas between grasses and pines, serves as understory with pines, or forms short, scrubby patches surrounded by mixed grasses and forbs on valley side slopes. Oaks may take advantage of subsurface flow of moisture which penetrates from higher rocky slopes above, avoiding competitive use of moisture by grasses. The eastern-most limit of the gamble oak range in Colorado is approximately 30 km east of the Front Range. Grasses appear to be good indicators of relative water availability; as soil moisture availability decreases from west to east, the proportion of short grass prairie species increases. Grasses utilize more of the available soil moisture than either oak or pine. The type and texture of soils has a direct influence on how much moisture soils can retain. Soil moisture availability to grasses decreases from west-to-east on the Palmer Divide. Rooting depth is greater in the west where soil moisture is greater and can penetrate to greater depths in rocky, porous soils; shallow rooting is more common in the east where moisture is less abundant and does not penetrate as deeply in finer-textured soils. Fine soils in the east, with a large amount of particle surface, can adsorb moisture in greater quantities; the energy required for plants to remove moisture from the soil, however, is greater in the east than in the west. Trends in soil moisture influence distribution of vegetation on the Palmer Divide. Soil moisture retention capacity tends to be less in the west than in the east. Available soil moisture, rooting depths and precipitation differences work together and are influenced by organic matter content and soil pH. Trends attributable to the influence of humus on retention capacity are most evident in soils under oak which show greater development than those under pine or grass.
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