Stability of coastal systems are
threatened by oceanic and atmospheric drivers of climate change. Sea-level rise compounded with increased
frequency and intensity of storms emphasizes need for protection of inner island
systems by dune formations. Dune
building processes are affected by interactions between growth of ecosystem
engineering dune grasses and environmental factors associated with disturbance
such as sand burial and salt spray.
Climate change may also cause latitudinal expansion of some species,
resulting in emergence of competitive interactions that were previously
absent. Topographic structure of
coastlines, traditionally influenced by sand burial, could change as a result
of competition emergence. The master's work of Joseph Brown was to
determine if species functional trait responses to common abiotic factors are
altered by novel and current biotic interactions. He performed a multi-factorial greenhouse
experiment by planting three common dune grasses (Ammophila breviligulata, Uniola paniculata, and Spartina patens) in
different biotic combinations, using sand burial and salt spray as abiotic
stressors. He hypothesized that biotic
interactions would cause these dune grasses to shift functional trait responses to abiotic
factors that are associated with dune building.
The results of this study found that plants consistently decreased in biomass when buried. When grown together, competition between A. breviligulata and U. paniculata negatively affected dune
building function traits of A.
breviligulata. This indicates that
competition, if future northward expansion of U. paniculata continues, could lead to dune engineering
alterations, especially in the Virginia barrier islands. In comparison A. breviligulata had a positive
interaction with S. patens which
increased functional trait responses to abiotic stress. Coexistence between these three species is possible via competitive
intransitivity. In intransitive competition, varying species-to-species interactions create a rock-paper-scissors scenario in which competitive hierarchy no longer exists. Current models suggest that within plant communities, intransitive interactions are most commonly found between dominant species, and dependent on short disturbance intervals and abiotic stress. Overall, these results can be used to make implications
on cross-scale consequences of novel competitive events. This experiment also provides evidence that
consideration of biotic interactions is important in substantiating connections
between plant level dynamics and large-scale landscape patterns in high stress
environments.
Joe will defend his thesis on March 29, 2016!
Conceptual model by Joe Brown on how plant functional responses ultimately affect island level processes
High habitat complexity co-occurs with high dune ridge formation
Low habitat complexity co-occurs with overwash and small hummock dunes
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