This study provides an ecological impact assessment of factors affecting the health of roadside vegetation in the state of Colorado including potential biotic and abiotic plant stressors and deicer applications. Across eight field sites, an evaluation was completed for foliar injury, physiology by leaf-level gas exchange, salt exposure, long-term drought stress, nutrient availability, pollutant exposure, disease, and insect damage in roadside lodgepole (Pinus contorta) and ponderosa (Pinus ponderosa) pines. These measures were compared with conifers away from the roadside environment in the same location in the winter/spring and summer/ fall of 2004. Additionally, a controlled assessment of the impacts of sand/salt and magnesium chloride deicers on foliar injury and leaf-level gas exchange in saplings of P. ponderosa and P. contorta was performed. Seed germination and viability in response to various commercial deicers was also evaluated in native Colorado plant species. Generally, roadside conifers exhibited significant foliar injury and needle loss compared to their off road counterparts, while roadside plant tissues and soils exhibited elevated levels of sodium, magnesium, and chloride. Injury to the tree crown correlated most strongly with levels of chlorides in older needle foliage (R2 = 0.696, p < 0.0001). A significant depression of leaf-level photosynthesis rates was observed in roadside trees during the winter deicing season but not during the subsequent growing season. Roadside and off-road trees did not evince any difference in long-term drought stress as demonstrated by pre-dawn leaf tissue water potentials. Colorado roadside soils were relatively nutrient poor, although a concomitant deficiency of nutrients in plant tissues was not observed. Measures of pollutant exposure including nitrous oxides, sulfur dioxides and heavy metals were significantly elevated in roadside tree tissues and soils compared to their off-road counterparts. Overall, nutrient availability and pollutant exposure levels correlated much less strongly with conifer foliar injury than salt exposure. Although evidence of disease and insect, animal, and abiotic damage occurred in Colorado conifers, these phenomena were not serious enough to affect either tree health or physiology. Magnesium chloride deicer, especially when applied to sapling foliage, was far more damaging to conifer saplings than exposure to sand/salt, and led to foliar injury, overall depression in leaf-level photosynthesis rates, and sapling mortality. Exposure to commercial deicers reduced or inhibited native seed germination percentages but not seed viability. Recommendations for future research include: reductions in the use and amount of deicing salt on Colorado highways; the impacts of non-chloride based deicers on roadside vegetation; application feasibility and ameliorative effects of soil additives; removal of needle surface depositions in roadside trees; reducing vegetation deicer exposure by minimizing the deicer splash zone and aerial drift of deicing particulates; and salinity tolerances of other species potentially impacted by deicer applications.