Increasing energy development and recreation use has led to an increase in gravel road mileage across arid and semi-arid ecosystems. Traffic on these roads creates "fugitive" dust that may affect immediately adjacent plants and soils. Dust deposition can potentially reduce fitness of mature plants while reducing recruitment, germination and seedling survival. Differences in species' resistance to dust effects among species could change plant community composition or make them more invasible by non-native species. Because dust reduces localized air quality, land managers may use dust-abatement chemicals such as magnesium chloride to reduce fugitive dust levels, and addition of these chemicals also may affect roadside plant communities through direct physiological effects or changes in soil chemistry. Accordingly we assessed effects of dust loading and of magnesium chloride application on plants and soils of Colorado Plateau deserts. In Arches National Park, Utah, we measured dust production by traffic on a gravel road, as well as changes in soil chemistry after magnesium chloride was applied. In greenhouse experiments we measured seedling survival for three grass species common to Arches under different rates of magnesium chloride application, and measured leaf dust-trapping capacity and physiological parameters (transpiration, stomatal conductance, leaf temperature, chlorophyll content) while applying dust at different wind speeds to four species of common Colorado Plateau forbs over an 8-week experiment.
Results/Conclusions
Magnesium levels in roadside soils dissipated relatively quickly, returning to ambient levels within four months after chemical application to the road. In the greenhouse, seedlings tolerated low levels of magnesium chloride concentration but survival was greatly reduced at higher concentrations. The warm-season grass (Pleuraphis jamesii) was more sensitive to chemical application than a cool-season grass (Hesperostipa comata) and non-native annual (Bromus tectorum). Combined, these results suggest that dust-abatement activities can negatively affect roadside plant communities but the effects appear to be relatively short-lived and may differ depending on the timing of chemical application. Physiological measurements in the greenhouse were inconclusive. Stomatal conductance was reduced with dust application when compared to a control, but measurements of other parameters were too variable to detect a difference associated with dust loading. Measurement of dust-trapping capacity across forb species showed that some species, especially those with trichomotous leaves, trap more dust than others exposed to the same loading rates. Thus some species in roadside plant communities may be negatively affected by fugitive dust more than others, although the impacts on plant community composition are still not known.