Evaluating the Ecological Impact of Urban Green Roof Plant Selections

Thesis Abstract

Urban green roofs are increasingly recognized as vital components of sustainable urban infrastructure, offering ecological, social, and economic benefits; however, the specific ecological impacts of diverse plant selections on urban biodiversity, microclimate modulation, and ecosystem services remain inadequately understood. This study aims to evaluate the ecological effects of different plant species and assemblages used in green roof systems within metropolitan settings to inform optimal plant selection strategies for maximum ecological benefits. The specific objectives include identifying primary plant species used in green roofs, assessing their contribution to biodiversity conservation, evaluating their influence on microclimatic conditions, and analyzing the extent to which plant choices enhance ecosystem services such as stormwater management and urban heat island mitigation. The research adopts a mixed-methods approach comprising quantitative and qualitative analyses. The study design is primarily cross-sectional, involving the systematic sampling of 60 green roof sites across three major urban districts, selected via stratified random sampling to ensure representative diversity in plant selection and roof age. Quantitative data collection involves standardized ecological surveys, including vegetation inventory, biodiversity indices (Shannon-Wiener and Simpson's Diversity), microclimate measurements (temperature, humidity, and insolation), and ecosystem service metrics (stormwater retention capacity measured through runoff analysis). Qualitative data are obtained through semi-structured interviews with roof gardeners, landscape architects, and urban planners, and analyzed through thematic analysis to explore perceptions regarding plant performance and ecological impact. Data analysis employs descriptive statistics to characterize plant compositions, and inferential statistics—including one-way ANOVA and multiple regression analysis—to examine relationships between plant types, biodiversity indices, and microclimate variables. Structural equation modeling (SEM) will be used to test the hypothesized causal pathways linking plant selection, biodiversity, microclimatic modifications, and ecosystem services. The theoretical framework is grounded in the Biodiversity-Ecosystem Function theory and the Ecological Niche concept, providing insights into how plant diversity influences ecological functions on green roofs. It is anticipated that findings will reveal significant variations in biodiversity and microclimate regulation attributable to plant species composition, with native and drought-tolerant species demonstrating higher contributions to biodiversity conservation and thermal regulation. The research expects to establish that diverse plant assemblages promote synergies that enhance stormwater retention and reduce urban heat island effects, thereby substantiating the ecological advantages of strategic plant selection. These results aim to fill existing gaps in the empirical literature concerning species-specific contributions to urban ecological functions and offer a scientific basis for guiding green roof plant selection policies. The study's contribution to knowledge lies in its comprehensive assessment linking plant choices with measurable ecological outcomes, providing a framework for optimizing green roof design for ecological resilience. The main conclusion emphasizes the importance of tailored plant selection strategies that prioritize native, diverse, and drought-resistant species to maximize ecological benefits. Recommendations include revising green roof planting guidelines to emphasize biodiversity promotion, adopting adaptive plant management practices, and integrating ecological considerations into urban planning policies. The findings also suggest avenues for future research, such as longitudinal studies on plant succession and ecosystem services over time and comparative analyses across different climatic regions to generalize the results. This research ultimately aims to support urban sustainability efforts by advancing scientific understanding of the ecological impacts of green roof plant selections and informing best practices for sustainable urban greening initiatives.