Effects of cross-shore location and deposition on dune grass growth

Coastal dunes arise from a feedback between dune vegetation and sediment transport. The size and shape of dunes are partially determined by the type and location of burial tolerant vegetation growing on the beach and dune. To explore how plant location and sand deposition affects plant growth, we transplanted 180 plants of three common dune -building species—Ammophila breviligulata, Spartina patens, and Uniola paniculata—in two cross shore swaths from the mean high water line to the crest of the foredune on Hog Island, VA. We measured leaf length and topographic change every month from May-October of 2014 and 2015. Results reveal that burial decreases aboveground leaf length at the monthly timescale, but that deposition significantly increases aboveground leaf length at the yearly timescale. Though the distance from shore that a plant is located does not appear to affect plant growth, the elevation at which a plant is found, which is tied to groundwater access, is negatively correlated with plant growth. Transplants at high elevations (>3 m) were, on average, over 1.5 meters above the water table and experienced high mortality rates. Transplants at elevations below 1.5 m (NAVD88) and close to shore also experienced high mortality rates and did not appear to have increased survivability relative to natural plants. Results provide insight into plant growth and survival in the foredune environment and can provide guidance for modeling coastal dune systems.