Lateral Analysis of Vegetation Communities Along River Channel Cross Sections in Lower San Juan River

In the American southwest, water availability is becoming an increasingly scarce resource; consequently, the patterns of vegetation are anticipated to change as well. As a result, this report aims to examine the relationship of the vegetation communities to elevation and distance from the edge of a river. The study region of this report consists of 76 longitudinal river miles of the Lower San Juan river basin, which is a drier desert environment in comparison to the upper San Juan’s more precipitated dendritic headwaters. At 5 different study sites along the 76 miles, a cross section of the river channel was measured and at 4 of those sites a vegetation transect was taken parallel to the line of the cross section. We expected that there would be distinctive transitions between vegetation communities that correspond with changes in elevation and water availability. The first assumption was generally consistent with what we observed, being that vegetation communities do change over space laterally. However, the predictability of which plants would be present at a certain proximity was variable. This seems to reveal that although the existence of vegetation gradients are universal, the specific factors acting on
vegetation and creating the gradient are variable by location, and not primarily dependent on current surface water supply.