INVESTIGATION OF METHODS AND BENEFITS OF EXPANDING EXTENSIVE GREEN ROOF PLANT DIVERSITY
Open Access
- Author:
- Razryadov, Julie Ann
- Graduate Program:
- Horticulture
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 08, 2018
- Committee Members:
- Robert Berghage Jr., Dissertation Advisor/Co-Advisor
Robert Berghage Jr., Committee Chair/Co-Chair
Richard P Marini, Committee Member
Armen R. Kemanian, Committee Member
Eric Paul Burkhart, Outside Member - Keywords:
- Green Roof
Extensive
Lysimeter
Water Use
Complex plant communities
Mixed plants on green roofs
Green roof plants
Green roof unconventional plants
plant trials
green roof stormwater - Abstract:
- Green roofs are becoming a staple of urban infrastructure. Despite widening adoption, it is as yet uncommon to venture outside of conventionally used plant material. However, limiting the scope of green roofs in this way obscures the potential for these spaces to be active ecosystems. In pursuit of the expansion of the commonly conceived conception of green infrastructure, this work identifies three pitfalls of viewing green roofs as landscapes. The first chapter challenges the view of a rooftop as a monolith. Even a small system like a rooftop has microniches which vary the abiotic environment enough to change the system’s potential for life. This experiment analyzed the incoming radiation, wind speed, and moisture across five green roofs atop a single building, the Millennium Science Complex at the University Park campus of Pennsylvania State University. It was found that the shaded portion of the green roofs act as seed banks which allow the spread of broad leaved introduced plants to spread during years of favorable conditions. Furthermore, this study reveals that variations of conditions across a green roof are over all beneficial, bringing different benefits depending upon seasonal weather. Using protected areas to introduce unconventional plants with higher levels of evapotranspiration than the traditional Sedum spp increases carbon sequestration, increases utility of the green roof for pollinators, birds, and other fauna, and increases the aesthetic interest of the space. The second chapter focuses on the benefits within water use of unconventional plants in complex communities. Using weighing lysimeters, five species habituated to dry environments yet uncommon on green roofs were tested for water retention and evapotranspiration in an extensive green roof simulation as a community and compared to how these species act in monoculture. It was found that biomass accumulation was higher among mixed communities than the average of the monocultures and yet water retention was lower and rate of evapotranspiration was about equal. Despite the relatively rapid rate of growth with relatively low water availability, the mixed communities reached permanent wilt at approximately the same rate as the monocultures. Furthermore, the most active growing and fastest colonizing plants, while exhausting their resources quickly in monoculture, were more measured and took a longer time to expire in the community tests. With only a single addition of water, all plants showed a remarkable ability to withstand at least a two week drought prior to reaching perceived permanent wilt. This experiment showed that unconventional plants have the capacity to survive dry conditions and putting them in mixed communities ensures that empty space will be colonized and the composition can shift in response to stress. The third chapter brings these two ideas together: using unconventional plants in a shaded environment. Weighing lysimeters were again employed to measure water use by Fragaria virginiana plants under metal halide lamps emitting heat and radiation when they were fully exposed or under shade clothe. Results indicated that shading does increase water retention while maintaining growth over time as measured by leaf production while underperforming in biomass accumulation. While the plants exposed to full light produced the best growth, shade used was likely too dense for the purpose. Despite this, shading looks like a good candidate for an establishment maintenance protocol that can encourage growth while decreasing evaporation and exposure to the elements in the first year of growth when plants are most vulnerable. Further work is necessary to develop maintenance protocols that would allow a more diverse green roof plant community to flourish. Work of this nature displays the new frontiers of green roof establishment and should be pursued in concert with infrastructure engineering.