Species interactions affect dune grasses

 

Barrier islands are on the forefront of sea level rise and climate change. High disturbance regimes and sediment mobility make these systems sensitive, dynamic, and sentinels of climate change. Island foredunes act as protective structures against storm included overwash. Dune grasses are integral to the biogeomorphic feedback that create and alter foredunes. Shifts in dune grass dominance on foredunes could have implications on dune morphology and susceptibility to overwash, altering island stability. In a recent study by MS student April Harris, two dune grasses Ammophila breviligulata and U. paniculata were planted together and subjected to a 20 cm burial to quantify morphological and physiological response. These species form different types of dunes based on vegetative propogation strategy. Ammophila breviligulata uses a network of horizontal rhizomes to stabilize substrates and U. paniculata exhibits a dense compact growth form that binds substrates. The effect of these different strategies is seen in the types of dunes formed (ridge vs. hummock). In the glasshouse experiment the most significant finding was a decline in physiological and morphological performace in A. breviligulata when planted with U. paniculata while U. paniculata was not affected when planted with A. breviligulata. As U. paniculata migrates into A. breviligulata dominated habitat, changes in dune formation could result in altered island stability via increased overwash due to reduced growth in A. breviligulata. Burial had a positive effect on both species as indicated by increased electron transport rate and total biomass. This is typical of dune grasses as the need to rebound after burial is necessary to survive in foredune environments which frequently experience sediment deposition. The decline in growth of A. breviligulata when interacting with U. paniculata can alter foredune community structure by shifting dominant species. Overall, due to the biogeomorphic feedbacks that couple dune morphology to vegetation type on barrier islands, any shifts in dominance could alter island stability and structure over time leading islands to experience new, previously unachieved states.

April Harris will defend her Master's thesis next Thursday!

 

 

 

 

Ammophila breviligulata

Uniola paniculata