I stumbled on this list of wood densities
http://www.engineeringtoolbox.com/wood-density-d_40.htmlIt may help to identify which local trees to use while creating a mesh. Lower density would be better for flotation (Pine, basswood, spruce, willow, balsa). Thin branches could be mixed in with the grass/compost and left to dry out. Like Leo and phytomike said, plants would then need to grow their rhizome networks throughout the mesh.
