Abstract Disturbance effects are rarely distributed uniformly over space or time. Thus, scaling up the effects of disturbances requires detailed measurements across multiple spatial scales. To characterize disturbance from wrack we used monthly images from an unmanned aerial vehicle (UAV) in a 144,500 m 2 Spartina alterniflora saltmarsh on Sapelo Island, Georgia (USA), from March 2020 to December 2022. Prior work as well as the results of our study demonstrated that wrack persisting for ≥ 2 months (“persistent wrack”) affects underlying vegetation. During our study, persistent wrack comprised ~ 30% of the average monthly wrack area (161 m 2 or ~ 0.10% of the total S. alterniflora marsh) and showed an annual peak between July and September. We quantified the effects of persistent wrack on live S. alterniflora , two invertebrate taxa (snails and burrowing marsh crabs), and porewater via field surveys of paired wrack-affected and wrack-free controls. At each monthly sampling point relative to controls, S. alterniflora stem density in wrack-affected plots was 41% lower on average and snail density lower by 25%, while crab burrow abundance and porewater parameters remained similar between controls and disturbed plots. Using wrack area from monthly UAV imaging, we scaled-up plot-level effects to marsh-level and found a < 1% change per species in abundance. Thus, our data suggest that even if wrack has strong local effects, the effects can be minor in S. alterniflora marshes at a landscape scale. This study demonstrates that field monitoring to quantify the effects of disturbances, coupled with repeat UAV imagery, allows for scaling that better contextualizes the overall impact than either method alone.
Pierce et al. (Mon,) studied this question.