A suite of microclimate variables affected germination of five Great Plains native plants seeded on an extensive green roof. Germination was significantly (~' = 0.05) greater in a greenhouse control versus the green roof for shortbeak sedge and prairie spiderwort (Carex brevior (35% versus 23% Tradescantia occidentalis 19% versus 0%). No significant germination difference between the greenhouse and green roof existed for two, warm-season species, Liatris squarrosa and Eragrostis spectabilis. Significant differences in microclimatic conditions between green roof plot locations suggest a heterogeneous environment can decrease seed germination. This impact was attributed to differences in the receipt of solar radiant energy, surface temperature, and vapor pressure deficit. Light reflection and thermal emission from the adjacent buildings supplied additional energy in some locations (depending on time of year or time of day) that varied greatly over only a few meters. Designers must carefully analyze microclimate impacts and consider those implications for plant selection and seeding. Establishment of some native seeds in high temperature zones may take more irrigation or benefit from mulching than those in moderate temperature zones. Increased seeding rates and targeted seeding dates may also be useful strategies. Future green roof research should examine germination across steep microclimate gradients, seed a wider suite of native plants to broaden plant biodiversity, and follow seedling development and mortality.
Synthetic ecosystems such as rain gardens, green roofs, engineered wetlands and urban meadows are becoming increasingly popular for their intrinsic environmental and ecological benefits as well as for their aesthetic value. But, as in many emerging technologies, communication between the academic institutions generating basic and applied science and the design disciplines is not as efficient as it could be, and strengthening this link will improve the performance of these systems. The case study serves to illustrate the process of linking research, design and implementation. Scientific research, performed by the authors and found in the literature, is used to inform design, and design challenges are used to suggest avenues of research. The research itself is briefly outlined where appropriate, but the focus of this paper is the process of linking science and design in a feedback loop.
Although a paucity of bees on Chicago green roofs suggests some plants may experience reduced pollination and thus poor seed production, a previous investigation revealed high seed set in green roof plants. However, high quantity of seeds does not always imply high quality. In this study, we compared seed germination between green roof and ground-level locations. We hypothesized that forb seeds from green roofs would have lower germination due to differences in maternal provisioning and environmental stressors. We found that green roof seeds did not have lower germination; this supports the continued use of native forbs on green roofs.