Many species have lost their natural habitat due to anthropogenic land use change. Ecologists are increasingly looking at habitat in cities to bolster efforts to conserve biodiversity. Green roofs are examples of urban habitats that are becoming more common globally. Green roofs can provide resources to support life in an otherwise inhospitable space. However, the harsh abiotic conditions found on green roofs preclude many species from establishing and persisting. Typically, non-native succulent species are planted on green roofs because of their ability to survive and provide beneficial ecosystem services to humans. However, greater support for biodiversity could be achieved with an increased diversity of plants. To support the fullest range of biodiversity possible, green roofs would support species diversity, community diversity, and genetic diversity. In my dissertation, I aim to determine if green roofs can contribute to all three aspects of biodiversity and thereby aid in the conservation of native plant species in cities. The first two chapters of my dissertation examine how species diversity on green roofs changes over time and which traits plant species possess to help them to survive for many generations. I hypothesized that the diversity of unmanaged plants and arthropods on green roofs would change in a deterministic pattern and be affected by abiotic factors. I also hypothesized that persistent plant populations would possess similar traits that contributed to stress tolerance. I used long-term vegetation surveys and collected plant and arthropod data from a 1-93 year chronosequence of green roofs in northeast Germany to addresses these hypotheses. I found that the plant and animal diversities did not change on green roofs in predictable ways but that site conditions such as substrate depth and water infiltration may affect how many species are present. Functional diversity explained more of the patterns in the vegetation than species diversity alone, as over time green roofs became dominated with plants that shared similar traits. Persistent species tended to have traits to tolerate stress and repeated disturbance. Together, these results highlight the need to carefully consider the characteristics of species that are originally planted, and continue to manage green roofs to support a rich diversity of both plants and arthropods. The third and fourth chapters of my dissertation address the potential for green roofs to support greater community diversity by experimentally testing a proposed habitat analog approach. This approach looks to mimic natural plant communities with abiotic properties similar to those of green roofs. I surveyed dry prairies in northeast Illinois and attempted to mimic the cover of the most common species on green roofs with both continuous substrate and modular trays. The plant communities from the most analogous habitat were the most successful at establishing in the continuous substrate, supporting my hypothesis that a habitat analog approach can promote community diversity. However, green roofs are typically built to provide ecosystem services to humans and do not typically consider biodiversity support the main priority. Therefore, I also evaluated the ability of the native plant communities to provide the ecosystem services of stormwater retention and thermal insulation and compared their performance to commonly planted non-native succulent Sedum species. I found that the industry standard Sedum communities provided more thermal insulation but that native prairie communities absorbed more stormwater and could release it quickly to be ready for more rain. I, therefore, suggest that a combination of native plants and non-native succulents might be best to maximize green roof function that includes both ecosystem services and biodiversity support. The fifth chapter of my dissertation uses a two-part study to address how genetic diversity can be supported on green roofs. I used neutral alleles at ten microsatellite loci to compare the genetic diversity of a self-compatible forb, Penstemon hirsutus, between natural prairie populations and established green roof populations. I hypothesized that the green roof populations started from nursery stock would fail to capture the full amount of genetic diversity that was found in natural populations because commercially produced plants tend to underrepresent the genetic diversity found in the wild. My hypothesis was supported, although the sampled natural populations had higher inbreeding than the populations on the green roofs. In the case of self-compatible species like P. hirsutus, pollinators are necessary to maximize gene flow by carrying pollen between populations. But previous work has found that some pollinators are lacking on green roofs, especially the small bees that pollinate P. hirsutus. Therefore, for the second part of this study, I measured the degree of inbreeding between ten parental green roof populations and their offspring and conducted a paternity analysis to measure the frequency with which bees move pollen between populations. Despite the very low genetic diversity in both the parental and offspring populations and a large amount of self-pollination, I detected gene flow occurring between populations. This suggests that plant populations on green roofs are not necessarily isolated from one another and might be connected in a larger urban metapopulation. Therefore, my results show that some native plant populations on green roofs may be able to maintain genetic diversity, thereby contributing to population sustainability. In summary, many biotic and abiotic factors make extensive green roofs difficult or impossible places for life to thrive, but a number of native plant species with specific traits can establish, survive, reproduce, and maintain diversity in future generations. Overall, my research suggests that green roofs can be used for conservation of native species. While I looked mainly at dry grassland species in the temperate climates of northeast Germany and the Midwest USA, these findings have applications for other analogous habitats in various parts of the world. This dissertation contributes to the burgeoning field of urban ecology at a time when cities are rapidly expanding and putting increased pressure on biodiversity. The lessons learned here can lead to new advances in green infrastructure and allow humans to more successfully share our living space with other organisms.

Last modified

• 01/23/2019

Creator

• Kelly Ksiazek Mikenas

DOI

• https://doi.org/10.21985/N2FB4H

Subject

• Plant Biology and Conversation

Keyword

• Plant Biology and Conversation

Date created

• 2017-01-01

Resource type

• Dissertation

Rights statement

• In Copyright