SAND DEPOSITION AND VEGETATION PATTERNS ON A PARABOLIC DUNE ON THE SOUTHEASTERN SHORE OF LAKE MICHIGAN

Green Mountain Beach (GMB) dune is a large Lake Michigan coastal dune, transitional between a trough blowout and a fully-developed parabolic dune. Deposition pins were used to study the amount and pattern of aeolian sand deposition on the dune's lee slopes. In the late fall and winter, sand accumulated on the upper to midslopes, supported by ice between the grains. Mass wasting delivered sand to the lower slopes during the spring thaw. Very little sand was deposited on the lee slopes during the summer. Maximum sand deposition (>1 m per year) occurred near the dune axis; deposition decreased rapidly along the limbs (<5 – 10 cm per year). Five vegetation sampling transects were established on the lee slopes of the dune in areas of high, medium and low sand deposition; summer and winter quadrat sampling and percent cover data were collected to determine importance values, community composition and diversity along these transects. Community ordination and classification analyses were also performed on these data. Vegetation zonation reflects the sand deposition patterns; the plants' tolerance to fall/winter sand burial determines where they grow and thrive in summer. Pioneer species Ammophila breviligulata and Equisetum arvense dominated the area of highest sand deposition; vegetation on this slope was completely buried by sand during the winter and had to revegetate the slope each spring and summer. Ammophila, Lathyrus japonicus, Saponaria officinalis, and small Vitis riparia vines dominated areas of intermediate sand deposition. Various tree (Tilia americana, Quercus rubra), shrub (Cornus stolonifera), mature V. riparia and V. aestivalis vines, grasses (Calamovilfa longifolia and Andropogon scoparius), and herbaceous plants, such as Lathyrus, Saponaria, Solidago simplex, var. gillmanii, and Artemisia campestris, were observed in low sand deposition areas. The sand deposition pattern was inversely mirrored in the species diversity pattern on 4 of the 5 vegetation transects; transects with high sand deposition had low species diversity while transects with lower sand deposition rates had higher species diversity. Shady conditions on the remaining transect appeared to control species diversity more than the sand deposition rate.