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Spatial Patterns of Exotic Plant Invasions - Controls by Parent-material Geochemistry

We are investigating relations between patterns of cheatgrass (Bromus tectorum) invasion and parent-material geochemistry on lands in and around Canyonlands National Park. Soils derived from different geologic parent materials such as Navajo Sandstone, Cedar Mesa Sandstone, and Organ Rock Shale vary widely in the composition, abundance, and relative chemical activity of carbonate and iron-oxide compounds that strongly control the dynamics and bioavailability of phosphorus (P) - an important macronutrient that strongly affects the structure and productivity of arid-land ecosystems. These soils, and the ecosystems they support, also vary widely in their degree of invasion and dominance by cheatgrass. Our work suggests that soils derived from Navajo Sandstone and Organ Rock Shale are relatively resistant to cheatgrass invasion because of low P-sorption capacity (low levels of carbonates and iron oxides) and high P-sorption capacity (very high levels of carbonates and iron oxides), respectively. In contrast, we hypothesize that soils derived from Cedar Mesa Sandstone are particularly susceptible to cheatgrass invasion, because moderate levels of finely dissimenated carbonate minerals (1) retain more P than Navajo-derived soils and (2) release more P to cheatgrass than soils derived from Organ Rock Shale (Fig. 1). A greater understanding of the effects of geologic parent materials on soil characteristics governing soil resource availability may facilitate predictive modeling of invasions by exotic plants.

Our work on spatially heterogeneous patterns of plant invasions and ecosystem resilience to land-use activities and natural disturbances are particularly important to managers of public lands. Land managers require solid scientific information about factors responsible for such heterogeneity in order to make well-informed management decisions.

Figure 1. Hypothesized effects of parent material geochemistry on phosphorus bioavailability and physiological performance of the invasive exotic cheatgrass (Bromus tectorum) on the Colorado Plateau.

For additional information, please visit:

• Monitoring Changes in Vegetation and Land Surfaces by Remote Sensing on the Colorado Plateau
• Forecasting Ecological and Landscape Change
• Dust and Substrate Geochemistry - Links to Ecosystem Development