A comparison of native and novel ecosystems : green roof impacts on plant growth and pest abundance

Abstract

There is little research that supports the potential of green roofs to provide biodiversity similar to ground-level habitat. This study examined three hypotheses. (1) Due to the similarities in environmental stresses, plants native to the coastal barrens established on green roof ecosystems will display similar growth productivity as plants established in the native environment. (2) Plants established in novel green roof ecosystems are subjected to higher presence of plant enemies (aphid and rust) compared to plants in the native environment. (3) The presence of salt spray at the coastal barrens (the native environment) limits the presence of pests on plant individuals. Plant growth and pest presence were quantified at three different sites, two extensive green roofs with different levels of environmental stresses located in Halifax, NS and one coastal barren site located at Duncan’s Cove, NS. Data were collected biweekly on four native plant species over the 2015 growing season. Results indicated the harsher extensive green roof supported growth productivity similar to the plants established in the coastal barrens. Plants established at the coastal barrens had significantly lower abundance of pests than plants established on green roof ecosystems. These results varied depending on what pest or plant species was examined. Artificially created salt spray had some effect on reducing pest presence in the green roof environment however these results were not significant for all species and their associated pests. While the novel green roof environment supported more plant enemies than the native environment of these plant species, the prevalence of aphids and other pests on the roof may yet provide benefits to the ecosystem by increasing insect species diversity. The green roofs ability to support similar plant growth productivity as the native ecosystem, indicate green roofs developed to mimic coastal barrens ecosystems could help increase biodiversity and other beneficial functions.