Climate, plant response and development of dunes on barrier beaches along the U.S. east coast

Lateral vegetation growth rates exert control on coastal foredune hummockiness and coalescing time

“…and alongshore continuity of plant establishment (Hesp, 1989(Hesp, , 2002Hesp and Walker, 2013), and variability in the location where plants initially grow can cause the formation of hummocky dunes. For example, Godfrey (1977) noted that in some settings vegetation initializes from drift lines (wrack), so discontinuous drift lines would cause an initially discontinuous or patchy development of dune plants (and therefore discontinuous dunes). Therefore, continuous or discontinuous plant initialization (in the alongshore direction) can control the initial alongshore continuity of the foredune (continuous or hummocky).…”

“…In this way, plant dynamics can also control the existence of hummocky dunes. Some plants grow laterally faster than others -Godfrey and coworkers (Godfrey, 1977;Godfrey and Godfrey, 1973;Godfrey et al, 1979) found that dunes of the northeastern US had more continuous ridges than the hummocky isolated dunes of the southeastern US, which they attributed to differences in plant lateral growth rates for the dominant species in each region.…”

“…Low areas without dunes can remain low because of shell or coarse-grained lags, a high water table that causes plant stress, and/or climatic conditions such as cold temperatures prohibiting plant growth (e.g., Russell, 2006, 2009;Wolner et al, 2013;Ruz and Hesp, 2014;Ruz et al, 2017a). Godfrey (1977) hypothesized that barrier island orientation relative to the prevailing winds exerts a control on foredune morphology, with taller dunes occurring when winds blow directly onshore, perpendicular to the shoreline. Sediment supply has also been implicated in causing alongshore dune height variability -specifically that a geomorphic and geologic framework influences the morphology of bars, beaches and sediment supply, therefore controlling the height of coastal dunes (Houser et al, 2008;Houser and Mathew, 2011).…”

“…Penland, 1988, 1990;Pye, 1983;Carter and Wilson, 1990;Davidson-Arnott and Fisher, 1992;Mathew et al, 2010;Montreuil et al, 2013). Such a conceptual model, consistent with widely observed field conditions, does not address why some initially hummocky foredunes coalesce to a linear foredune ridge, while others remain hummocky, having variable dune height in the alongshore direction, though Godfrey (1977) discussed the potential for recurring storm events to prevent the coalescing of hummocky dunes, even in locations where vegetation grows rapidly in the lateral direction.…”

“…Previous work by Moore et al (2016) has investigated the cross-shore dynamics. Our work here is a quantitative investigation of several of the hypotheses of Godfrey (1977), notably that vegetation exerts a fundamental control on alongshore dune morphology. Our findings suggest that, given no preexisting template and suf-ficient time prior to the occurrence of a storm event, alongshore hummocky dunes eventually coalesce to form a continuous coastal foredune ridge.…”