Associate Professor of Landscape Architecture Kansas State University, Kansas, United States
It is possible to create low input living roofs that support native species in the Central Great Plains (USA) but essential drivers of plant health and survival must be understood and addressed through design and management. Well-drained full-sun green roofs in the Flint Hills Ecoregion (north-central Kansas) typically require supplemental irrigation for consistent native plant cover, however, they do not need daily irrigation (and may not need weekly irrigation) even during very hot, dry periods, depending on design and context. Mixed-species and mixed plant types seem to fare better. Nevertheless, even after more than eight years of closely observing several green roofs, many questions remain given the complexities of these evolving urban ecosystems. At Kansas State University we have observed that planted and seeded 10-22cm-deep green roofs in Manhattan, Kansas – directly seeded, or from plants producing and spreading seed on planted and/or seeded green roofs – tend to be resilient during dry periods. However, full sun green roofs without adequate rainfall or supplemental irrigation, coupled with too little afternoon and evening shade, are prone to brown-out and/or die-back, especially for tallgrass prairie species and less drought and heat tolerant Sedum species. Areas of unanticipated subsurface moisture help support greater amounts of living plants in areas exposed to long periods of solar radiation during the growing season. Reflection of sunlight from architectural elements likewise creates significant levels of stress and temporary vegetative brown-out or ultimate dieback. Understanding living roof ecosystem plant dynamics is enhanced by ongoing observation and monitoring, regular management of undesirable plant species, and detailed record-keeping of green roof conditions and dynamics. Frequent tours and other outreach activities provide opportunities to deepen what is learned from regularly taking notes and photographs of green roof conditions. This presentation encourages reflection and discussion about the role of observation and photography in helping reveal landscape and ecosystem change over time. Modes of learning and response include: integrated, collaborative green infrastructure planning, design, monitoring, and management; engaging in regular observation and systematic and spontaneous photography; and developing effective irrigation and maintenance protocols and programs. Documenting how living roofs perform using photographs and notes to assess plant health and dynamics, monitoring substrates using soil moisture and temperature sensors, analyzing substrate characteristics, properties, and microbiology in soil labs, and participating in ongoing management and outreach with maintenance staff, help designers and stakeholders create more resilient, reasonably well-vegetated, and acceptably messy socio-ecological systems.
