DMF salt marsh shading study. Mass Bays Research & Planning Grants 2013.

Proliferation of small docks and piers in salt marsh habitats poses potential cumulative impacts through shading and displacement of marsh vegetation. Environmental permitting guidelines provide construction recommendations regarding various dock characteristics (e.g., height, orientation, deck spacing, deck materials), but few quantitative data exist to substantiate these guidelines. 

In a project funded by the 2013 MassBays Research and Planning Grant, the Massachusetts Division of Marine Fisheries (MarineFisheries) constructed an experimental dock matrix in Marshfield, MA  to specifically address the effect of dock height on underlying marsh communities. These results provided useful information on the ideal dock height and data on short-term shading effects. Findings after one year indicated the need to maintain at a minimum the1:1 height to width ratio and that taking into consideration that other dock features were designed to maximize light penetration, results suggest that standard four foot wide docks with traditional decking set over low marsh vegetation at less than a 1:1 ratio would significantly reduce impact marsh vegetation under all dock orientations. Results were observed over a brief, single season time scale and preliminary experimental results provide cautious support for the 1:1 height to width ration. Further monitoring was recommended to apply existing guidelines to a more rigorous test. 

Details of the methodology applied, results obtained, and recommendations are described in the final report: Shading Impacts of Small Docks and Piers on Salt Marsh Vegetation in Massachusetts. MA Division of Marine Fisheries. 2013 pdf format of Shading Impacts 2013
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