| Description |
An analysis was made of the basic ecological relationships of grasslands that occur along the foothills of the Wasatch Mountains in Northern Utah. Based on species occurrences at 93 study sites, the species associational relations were examined by chi-square and by covariation methods,. Both methods resulted in three quite distinct species associations, hereafter called communities. Each community was named after the perennial grass which gives the visual impression of being dominant in that community. They are the bluebunch wheatgrass (Agropyron spicatum) community, the needle-and-thread grass (Stipa comata) community and the sand dropseed (Sporobolus cryptandrus) community. In order to study environmental relations, stand groupings were delimited to represent the species communities by a numerical taxonomic technique. The process grouped 31 stands into a bluebunch wheatgrass community; 31 stands into a needle-and-thread grass community; and 27 stands into a sand dropseed community. Testing environmental differences between these stand communities revealed that physiographically the bluebunch wheatgrass community is characterized by occurring at relatively higher elevations and on steeper, more northerly facing slopes. The needle-and-thread grass and sand dropseed community stands are generally at lox^er elevations and on more gentle, southerly facing slopes. The sand dropseed community stands are on the most gentle topography. Due to these physiographic differences the mid-June soil temperature at dm was cooler in the bluebunch wheatgrass community than in the other two communities. The bluebunch wheatgrass community usually occurs on clay loam to silt loam textured soils* which are calcareous and moderately alkaline. On the average, these soils had the greatest storage of nitrogen, magnesium, calcium and water. The needle-and-thread grass community generally occurs on fine sandy loam soils, which are also strongly calcareous and moderately alkaline. They also have a good storage of nitrogen, calcium and water. These soils are low in magnesium. The sand dropseed community stands are on coarse sandy loams and are excessively drained. They generally have a low storage of water, nitrogen, calcium, magnesium, potassium and phosphorus, but are relatively high in sodium. By analysis of variance a number of the differences noted above were found to be significant. However, when these same data are subjected to the rigors of a multivariate test (discriminant analysis), the number of significant environmental differences between the communities reduces to soil ix temperature, water, magnesium and sodium between bluebunch wheatgrass and needle-and-thread grass; to soil temperature and calcium between bluebunch wheatgrass and sand dropseed; and to nitrogen, water and calcium between needle-and-thread grass and sand dropseed communities. Of these variables, only soil temperature and calcium are consistently powerful discriminators between the communities. One may generalize that the bluebunch wheatgrass community occurs on cooler sites with calcareous soils. The needle-and-thread grass community occurs on warmer sites with calcareous soils. The sand dropseed community occurs on warmer sites with noncalcareous soils. The individual species of each community shoi^ a general common response to the functional variables of the community to which they belong. For example, most of the species of the bluebunch wheatgrass community have a n e g a tive regression on soil temperature. However, in addition each species exhibits Its own particular set of responses. One may generalize that species respond in common to certain variables which control their occurrence in a particular community, but that species variability within a community is controlled by other environmental variables. For example, the variability that a species of the bluebunch wheatgrass community shows may be due to its response to water. |
