Temporal variation in microclimatic edge effects near powerlines, highways and streams in Australian tropical rainforest

We investigated diurnal variation in edge gradients of air temperature, vapour pressure deficit (VPD) and wind speed in tropical rainforest in northeastern Australia, adjacent to three types of linear canopy openings: a powerline, a highway and a perennial stream. Edge gradients were compared between the wet and dry seasons. Diurnal ranges of air temperature and VPD were elevated near powerline, highway and stream edges and were greater in the dry season than the wet season although this seasonal difference in temperature ranges was less pronounced near powerline than highway or stream edges. Maximum wind speeds were elevated near all three forest edge types, this increase being most pronounced at stream edges. In contrast, although daytime temperature and VPD were also elevated near all three forest edges, stronger effects were experienced at powerlines and highways compared with streams. Wind speed was greater near forest edges than in the forest interior during the daytime, but this effect varied between seasons and among edge types. Edge gradients in wind speed were present near powerline edges in both wet and dry seasons, but only occurred near highway edges during the dry season and near stream edges during the wet season. Nocturnal microclimatic edge gradients were seldom detected. They were observed only for air temperature near powerlines during the dry season, air temperature being reduced at the forest edge compared with the forest interior. These data indicate that linear clearings for roads and powerlines are associated with microclimatic edge gradients qualitatively similar to those observed in other studies at forest edges adjacent to larger clearings. Such gradients have the potential to substantially increase the edge exposure of forest areas internally fragmented by clearings for human infrastructure.