Barrier island response to changing climate: the role of woody vegetation
Speaker: Julie Zinnert (Virginia Commonwealth University)
Within the most extensive stretch of coastal barriers, Virginia barrier islands represent a unique opportunity to study vegetation responses to climate drivers with little direct anthropogenic disturbance. In this portion of the mid-Atlantic coast, shoreline erosion rates are highly variable and sea-level rise is 3-4 times higher than the global average. Over the past 32 years, Virginia barrier islands have lost over 25% of terrestrial upland area and island width has been reduced, yet salt-sensitive woody vegetation has expanded across the landscape into grassland. The evergreen shrub, Morella cerifera, is the primary expanding species, with unique engineering features that confer an advantage in nutrient poor coastal soils. In this seminar, plant ecologist Julie Zinnert will address the patterns and mechanisms of shrub expansion at the Virginia Coast Reserve, biotic consequences of these transitions and potential landscape level consequences of woody dominated communities. The transition from grassland to shrub thicket is facilitated and maintained by positive feedbacks where shrubs alter the microclimate, causing warmer winter and cooler summer temperatures, and fewer extreme temperature events. This state change increases annual net primary productivity 3.5-fold, and soil organic matter, nitrogen and carbon. After shrubs establish, there is no evidence of succession to maritime forest; instead there is a strong relationship between shrubs and woody liana vines, which may stabilize the shrub thicket and delay or prevent forest transition. Vegetation type is an important functional component of coastal systems affecting sediment dynamics. As barrier islands respond to sea-level rise by landward migration, vegetative composition of the upland may influence the long-term response of barrier islands to changing climate.
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