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This thesis analyzed various approaches in order to improve plant survival and increase species diversity on an extensive green roof. Three different techniques were used: heterogeneous soil depth, interspecies facilitation and the use of moss to enhance vascular plant survival. This study found that multiple soil depths could create niches allowing species with different growth forms and water requirements to coexist. Three potential facilitators of a vascular plant were tested: moss, lichen and bunch grass. Of these, the moss had a net positive effect on growth of the target plant (suggesting facilitation), the lichen had no net effect and the bunch-grass had a net negative effect (suggesting interspecific competition). Interestingly, even though the moss assisted the growth of neighbouring species in one experiment this was not evident in the second experiment. This indicates that more research is necessary and that moss may only be able to facilitate some plant species.