Assessing Urban Green Roof Plant Resilience in Singapore’s Construction Sector

Thesis Abstract

Urban green roofs (UGRs) offer potential benefits for Singapore’s densely built environment, yet plant resilience under local climatic stresses and construction practices remains insufficiently understood, limiting design optimization and long-term performance. This study investigates resilience of plant assemblages on UGRs by examining physiological tolerance, establishment success, and survival under Singapore’s tropical climate, rapid urbanization, and intensive roofing activities. The aim is to identify key drivers of resilience and provide actionable guidance for policymakers, developers, and landscape practitioners. Specific objectives are (1) to evaluate species-level drought, heat, and salinity tolerance using physiological indicators (chlorophyll fluorescence, turgor loss point, osmotic potential) for a curated suite of 24 species commonly used in Singapore’s UGRs; (2) to quantify survival rates and growth performance of plant assemblages across 18 green-roof installations representing varied substrate depths, irrigation regimes, and drainage configurations; (3) to assess the influence of microclimate, substrate properties, and maintenance practices on resilience using multivariate modeling; (4) to test the applicability of the stress–coping framework and the theory of plant functional traits in predicting performance on UGRs within tropical urban settings; and (5) to develop evidence-based guidelines for species selection, substrate design, and maintenance to enhance long-term resilience. Methodologically, a mixed-methods approach is employed. The population comprises 18 commercial and municipal green roofs across Singapore, with a purposive stratified sample of 24 plant species representing herbs, grasses, and small shrubs. Quantitative data will be collected via in situ measurements of physiological stress indicators (photosynthetic rate, stomatal conductance, chlorophyll fluorescence), biometric growth metrics (height, biomass, canopy cover), substrate parameters (moisture content, pH, nutrient status), and microclimatic variables (air temperature, relative humidity, solar radiation) over 12 months at monthly intervals. Data collection instruments include portable chlorophyll fluorometers, LI-COR gas exchange systems, soil moisture sensors, and data loggers. Qualitative insights will be gained from semi-structured interviews with 10 landscape professionals and maintenance personnel to elucidate practices influencing resilience. Statistical analyses will encompass regression analysis to identify predictors of survival and growth, survival analysis for time-to-event data, and multivariate techniques (principal component analysis, redundancy analysis) to relate plant performance to substrate and microclimate factors. Theoretical framing will integrate the stress–coping theory, plant functional trait theory, and the envelope of green roof design principles. A conceptual model will be tested to reveal interactions among environmental stressors, plant traits, and management interventions. Expected findings include (i) identification of species with superior tropical drought and heat tolerance and adaptable root architecture, (ii) quantification of the relative importance of substrate layer depth, irrigation frequency, and drainage efficiency on survival and growth, (iii) validation of trait-based predictors (specific leaf area, SLA; woodiness index; rooting depth) as robust indicators of resiliency on UGRs, and (iv) practical guidelines for species selection, substrate composition, irrigation regimes, and maintenance schedules tailored to Singapore’s climate and building codes. The study anticipates that resilience will be maximized where substrate depth supports adequate water storage, irrigation is calibrated to ambient heat stress, and species with conservative water-use traits are combined with routine maintenance that mitigates thermal extremes. Contributions to knowledge include providing empirical, context-specific evidence on plant resilience for tropical UGRs, refining trait-based selection frameworks for urban horticulture, and offering a replicable methodological protocol combining physiological, ecological, and management perspectives for resilient green roof systems in high-density tropical cities. The main conclusion is that resilience in Singapore’s UGRs emerges from a synergistic interaction among plant traits, optimized substrate design, and informed maintenance; neglecting any element reduces performance and longevity. Recommendations emphasize selecting drought-tolerant, heat-tolerant species with compatible rooting depths, adopting substrate mixes with enhanced water-holding capacity, implementing adaptive irrigation schedules aligned with seasonal heat stress, and standardizing maintenance routines to manage substrate salinity and nutrient build-up. Further research should explore long-term carbon sequestration and biodiversity outcomes of resilient UGR configurations under evolving climatic conditions.