2017 ASHS Annual Conference

Abstract. Extensive green roof research has focused mainly on plants in monocultures, which are prone to environmental stress. In contrast, plant communities have been shown to be more robust than monocultures in green roof settings. In addition, native plants might be more ecologically sound plant choices than non-natives in green roof systems. The objectives of this research were to 1) compare the performance of plant communities with that of monocultures and 2) compare growth of natives to non-natives in a simulated green roof setting. We conducted an experiment at an outdoor site in a desert environment. Plants were randomly assigned to either a monoculture or community plot. Four morphological types (groundcover, small perennial, succulent, and grass) were chosen. Plants selected consisted of native (blackfoot daisy, candelilla, damianita, and mexican feather grass) and non-native taxa (lambs ear, orange stonecrop, iceplant, and blue fescue). Plots were 1 m x 1 m custom-built trays filled with 15 cm of a proprietary blend of 50% lightweight aggregate, 20% sand, and 30% compost (by volume), available commercially from American Hydrotech Inc. At Day 172, natives in communities had a higher (P=<.0001) coverage (1126 cm²) than non-natives in communities (316 cm²), though native groundcovers had lower (P=0.0045) coverage (248 cm²) than non-natives (400 cm²). All types in community had higher (P=<.0001 for all types) coverage than those in monocultures. Visual quality ratings within types were not significantly different at Day 172. Relative water content (RWC) at Day 172 was significantly different (P=<.0001) in communities. RWC showed no significant differences within types. Overall, native plants in community had higher coverage than non-natives and plants in community had higher RWC, regardless of native or non-native. These results indicate that plants, especially native plants, in community might be more successful than those in monocultures.