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

Abstract

Abstract. Coastal foredunes form along sandy, low-sloped coastlines and range in shape from continuous dune ridges to hummocky features, which are characterized by alongshore-variable dune crest elevations. Initially scattered dune-building plants and species that grow slowly in the lateral direction have been implicated as a cause of foredune "hummockiness". Our goal in this work is to explore how the initial configuration of vegetation and vegetation growth characteristics control the development of hummocky coastal dunes including the maximum hummockiness of a given dune field. We find that given sufficient time and absent external forcing, hummocky foredunes coalesce to form continuous dune ridges. Model results yield a predictive rule for the timescale of coalescing and the height of the coalesced dune that depends on initial plant dispersal and two parameters that control the lateral and vertical growth of vegetation, respectively. Our findings agree with previous observational and conceptual work -whether or not hummockiness will be maintained depends on the timescale of coalescing relative to the recurrence interval of high-water events that reset dune building in low areas between hummocks. Additionally, our model reproduces the observed tendency for foredunes to be hummocky along the southeast coast of the US where lateral vegetation growth rates are slower and thus coalescing times are likely longer.

Investigating dune‐building feedback at the plant level: Insights from a multispecies field experiment

“…Similarly, on the U.S. east coast, Ammophila breviligulata tends to be associated with tall, continuous dunes whereas Uniola paniculata, which grows more slowly in the lateral direction, tends to be associated with dunes that are discontinuous or hummocky (e.g., Godfrey, 1977;Godfrey et al, 1979;Stallins and Parker, 2003;Stallins, 2005). Recent numerical work by Goldstein et al (2017) builds on previous conceptual work from Godfrey (1977), suggesting that differences in the lateral growth rates between these two species, combined with physical processes that tend to reset dune-building in low areas, explain the observed relationships between alongshore dune morphology and grass species dominance on the U.S. East Coast.…”

Interaction of seed dispersal and environmental filtering affects woody encroachment patterns in coastal grassland

“…Biogeomorphic interactions between topography and vegetation are important drivers in barrier islands (Duran Vinent and Moore , Goldstein et al. , Zinnert et al. , Stallins and Corenblit ) and may affect suitability of germination and seedling growth based on access and amount of freshwater (Young et al.…”

“…Morella cerifera occupies low-elevation swales at a minimum distance from the shoreline . Biogeomorphic interactions between topography and vegetation are important drivers in barrier islands (Duran Vinent and Moore 2015, Goldstein et al 2017, Stallins and Corenblit 2018 and may affect suitability of germination and seedling growth based on access and amount of freshwater .…”

Defining Coastal Resilience

“…Barrier dunes express two end-member states-low and high-that are sensitive to vegetation as a control on sediment-transport pathways and storage [64][65][66][67]. As storm impacts erode dunes and aeolian processes construct them, both alternative states of high and low dunes can exist in space immediately adjacent to each other, with dune vegetation serving to both resist storm-driven flattening and augment dune growth by trapping windblown sediment [68,69]. A low, overwash-reinforcing state [64] exhibits a weakly positive sediment budget, burial-tolerant grasses, flat topography, and frequent overwash.…”