| Utilizing a combination of field studies, laboratory work and greenhouse experiments, I consider in this dissertation the relationship between soils and vegetation in the Upper Clark Fork River (UCFR) National Priority List Site, Montana, USA. Specifically, I found that UCFR soil textures and colors are highly heterogeneous, indicative of the disturbance-driven nature of the UCFR floodplain. Soil solution pH values, however, are generally homogeneous within soil layers at 5 meters horizontal distance. This indicates that one can relate soil pH data to the plant life found at closely co-located points.;I found that soil pH has a significant, but secondary influence on vegetative characteristics in the UCFR. This influence is more likely due to the control of pH over trace element availability than to direct proton effects. The pH threshold for a significant loss of forb cover in the UCFR is 6.5; the overall pH threshold for a significant loss of total plant cover is 5.8. This suggests that non-forb species may be more tolerant of soil acidity effects than the general class of forbs. This also suggests that a pH of 5.8 is the level at which tailings-related soil acidity begins to have a significant influence on plant life in the UCFR.;I also found that selected plant species are tolerant of very acidic soils in the UCFR, especially: Deschampsia cespitosa (tufted hairgrass), Euphorbia esula (leafy spurge) and Agrostis stolonifera (redtop). Comparatively, Salix exigua (sandbar willow) is a pH generalist capable of thriving under a wide range of soil pH. Further, while Salix exigua (sandbar willow) tissues accumulate more copper when exposed to lower pH levels and therefore greater soluble concentrations of the trace element, a tolerance mechanism exists that reduces the rate of copper accumulation in aboveground tissues. This preferential, belowground pooling and generalist niche strongly supports the use of this species for the restoration of the UCFR floodplain. |
