Surface energy exchanges over contrasting vegetation types on a sub-tropical sand island

The surface energy balance of sub-tropical coastal vegetation has received little attention. Here we present a multi-year observational data set using the eddy covariance method to quantify, for the first time, the surface energy balance over three contrasting representative vegetation types on a sub-tropical sand island in eastern Australia: a periodically inundated sedge swamp, an exotic pine plantation and a palustrine wetland. On seasonal time scales, the palustrine wetland exhibited a Bowen ratio (beta) approximate to 1, the pine plantation beta > 1, and the swamp beta varied from beta <= 1 during wet seasons and inundation to beta > 1 during dry seasons. The partitioning of energy is similar to a variety of Australian ecosystems and coastal vegetation types in other latitudes. Energy fluxes responded to seasonal changes in background meteorology with the most important influences being net radiation and the surface layer temperature gradient, with the soil temperature-ambient temperature gradient, ground temperature, and vapour pressure deficit also important. Sites differed according to soil water content, with the remnant palustrine wetland and swamp having ready access to water but the exotic pine plantation having much drier soils. We conclude that should the current balance between vegetation types change, there would be a corresponding shift in the overall surface energy balance of the island, affecting its micrometeorology, and water table depth.