Roof gardens are becoming an increasingly common feature of urban and suburban skylines. Not only do they make for a great garden party, but they also help in making a city more environmentally friendly. Garden roofs have been shown to offset heat and decrease water runoff during rainstorms. These ecosystem services can directly contribute to lower building energy use and potential economic savings.

Green roof in Manhattan. Photo: Alyson Hurt/Creative commons

In the latest issue of the open access journal PloS One, a group of Canadian researchers investigated how the delivery of services from roof gardens relates to the type of plants grown in them. In essence, they looked if a diverse set of plant functional groups (e.g. grasses, shrubs, succulents and forbs) would enhance roof cooling and water capture. They found that mixtures containing three or five different fucntional groups, simultaneously optimized several green roof ecosystem functions, and outperformed monocultures. This are fascinating results, that mirror the substantial body of evidence showing positive relationships between functional diversity and the provision of ecosystem services in natural and agricultural systems.

So it seems that ecosystem services from green roofs can be improved by planting certain functional groups in combination. These improvements, and the continued popularity of green roofing can directly contributing to climate change mitigation and adaptation strategies.