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Wooden access mats (e.g.. temporary roads) are a mitigation technique thought to limit traffic impacts on soils and vegetation during industrial activities in grasslands. Mats redistribute weight from vehicle traffic but also prevent photosynthesis by blocking sunlight and reducing gas exchange. Here we assess the effect of timing and duration of mat placement and compare these to un-matted plots, both with traffic treatment, and non-treated controls. Mats were placed onto grassland study sites on April 30 for 6, 12, or 24 weeks, and on July 22, 2015 for 6 or 12 weeks. Traffic was simulated by driving a 28 ton loader over matted and un-matted plot pairs to simulate construction activity. Plant cover and biomass were measured in August 2016. Preliminary findings indicate that longer durations of mat placement caused larger shifts in community composition towards weedy species and a reduction in perennial native grass cover. Total biomass increased with longer durations of mat placement due to an increase in weedy species, which over compensated for a decrease in perennial grasses. Mat placement on actively growing vegetation (July) resulted in greater litter accumulation and general increases in biomass. Short duration placement prior to active plant green up resulted in the least negative effects on perennial grass cover. While further recovery of plant communities will be monitored to fully assess their resistance to disturbance regimes, our preliminary results suggest short-term mat placement (? 12 weeks) may be compatible with maintaining mixedgrass prairie.