Horticulture Meets Plant Ecology: Extensive Green Roofs Modeled from a Shortgrass Prairie Ecosystem
Document Type Article
This paper was presented in post format at the 2009 Green Roofs for Healthy Cities Conference in Atlanta, GA on June 5, 2009.
It has been suggested that the shortgrass prairie (aka, shortgrass steppe) of the western Great Plains be examined for native plant species suitable for cultivating on North American green roofs (Getter and Rowe 2006) and also as a model for an extensive green roof ecosystem (Dunnett 2004, Oberndorfer et al 2007, Sutton 2008). To help explain this unique ecosystem more fully, this poster reviews the autecology of dominant shortgrass prairie species, blue grama (Bouteloua gracilis) and the synecology of shortgrass communities. Next it discusses aspects congruent with extensive green roofs, and then proposes a different way of thinking about both above and below annual net productivity in the context of minimal maintenance inputs that is radically different from both strictly ecological and horticultural approaches.
Shortgrass prairie has six key climatic characteristics resulting in a precipitation and temperate regime with the negative yearly water balance also found on green roofs: 1) high winds, 2) high insolation 3) high summer temperatures, 4) low winter temperature, 5) diurnal and seasonal temperature fluctuations, and 6) seasonal and long-term drought cycles. Other pertinent characteristics must be added to the mix and deal with soil (functional depth, fertility, organic matter, micro-organisms, texture and structure) and ecosystem factors (grazing, fire, competition and facilitation). Most of the preceding characteristics also guide plant selection in all types of roofgreening. A shortgrass prairie model for extensive green roof plantings might be applied over a large geographical area from Calgary and Winnipeg to Chicago, to St Louis and Dallas, and Kansas City, to Omaha and Minneapolis.
After an establishment phase of 3-5 years, annual biomass production on extensive green roofs should not be an aim. Since the past approaches of both ecology and horticulture mostly focus on biomass production, they have been blind to the possibilities of a system of living plants managed to produce homeostasis with balanced inputs and output of water, nutrients and energy.