We examined the relative strengths of top-down and bottom-up effects acting on insect herbivores feeding on five species of plants growing in coastal or upland regions of a Florida salt marsh. Three of the plant species, Borrichia frutescens, Coccoloba uvifera, and Baccharis halimifolia, grew close to the shore, while the two remaining species, Myrica cerifera and Persea borbonia, grew in upland areas with lower salinity and no tidal input. For each species, we added nitrogen fertilizer and reduced parasitism with sticky traps in a fully factorial design, and assessed the relative impacts of these bottom-up and top-down manipulations on the most common herbivores of each plant. We then used a within-study meta-analysis to integrate the results and quantitatively compare the strengths of top-down and bottom-up effects on the herbivores of these coastal and upland plants. Both fertilization and reduction of parasitism resulted in significant increases in herbivore densities, and the effects of these treatme...