Green roofs are harsh environments for plants, as they must cope with shallow soils, low nutrient availability, high solar radiation, low water availability and high pollution/disturbances. We are investigating if using nurse plants to provide shade affects the survivability of plants on a green roof. To this end 120 green roof mesocosms were set up to simulate green roof conditions across four sets of native species (four nurse plants and four target plants). These were arranged into four treatments; naturally shaded with a live nurse plant shading the target plant, artificially shaded with an artificial plant shading the target plant, unshaded natural which had a trimmed nurse plant providing no shade to the target plant and an unshaded treatment with the target plant growing alone. The experiment was run for 10 months with photographs taken monthly to record growth and visual health of the target plants. Soil moisture was collected fortnightly and biomass data was collected at the end of the experiment.
Results/Conclusions
Natural shade treated plants had the highest biomass at the end of the experiment, while unshaded plants had the lowest biomass. Unexpectedly, the shaded artificial and the unshaded natural had a similar moderate biomass. This suggests that while shading was a positive influence on plant growth, there was also a positive influence of growing with a nurse plant which is not accounted for by shading. We discuss the possibility of a below-soil facilitative relationship between nurse plants and target plants.