Designed habitat heterogeneity on green roofs increases seedling survival but not plant species diversity

Urban areas benefit from the ecosystem services provided by low input green roofs. However, limited substrate depth on these green roofs creates challenging conditions for plant establishment and survival, leading to industry reliance on non-native succulents.
Through a green roof and glasshouse study, we assessed the impact of simple design modifications to the green roof surface, including redistribution of substrate and addition of logs and pebble piles, on both substrate temperature and moisture content. We added seeds of 26 native species and quantified seedling density, species richness and composition over a single growing season. Overall effects of microsite heterogeneity on species diversity were assessed using species accumulation curves.
The modifications altered substrate temperature and moisture. Deep substrate (10-12 cm) and the presence of surface features reduced temperature by 14.6°C and, while surface features had mixed effects on substrate moisture on the green roof...