School of Agriculture, Food and Ecosystem Sciences - Theses

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    Direct seeding onto green roof substrate supports species rich, high cover novel grassland
    Spencer, Pamela ( 2016)
    The vegetation of green roofs is central to their functioning and ability to provide ecosystem services. When vegetation performs well, green roofs contribute to storm water mitigation, thermally buffer buildings, improve biodiversity and provide aesthetic and recreational relief in the grey city landscape. However, poor vegetation performance is common, with a decline in both species richness and cover over time. This decline can in part be attributed to design, failing to consider community assemblage mechanisms that lead to quality vegetation performance. Direct seeding of grassland species could offer a randomness in distribution and abundance of seedlings that supports early community self-organization and co-existence. Comparatively, adult plant establishment does not provide this early opportunity. This thesis determines, the ability of a scoria based green roof substrate to support the germination and establishment of a species rich, high cover, novel grassland community, and the direct seeding sowing methods to achieve this. Additionally, species richness, and abundance were investigated as potential drivers of cover. A grassland forb only species seed mix was applied in two experiments. Experiment One (n=7), in glasshouse conditions, investigated application of seed with and without a sand bed, and depth of sowing; six treatments. Experiment Two (n=10) in green roof module conditions outside under irrigation, investigated depth of sowing and rate; four treatments. Main results showed a species rich and abundant germination on scoria based green roof substrate. Results indicated that both depth of sowing at greater than 10 mm and application in a sand bed, reduced species richness and abundance. In green roof module conditions, surface sowing indicated a slight species richness advantage and an abundance disadvantage, in comparison to sowing between 0 to 10 mm depth. Sowing rate approaching that of on ground grassland restoration rates, were shown to be as effective as a doubled sowing rate in producing a species rich, high cover. This study found; no support for species richness as a key driver of cover, however abundance is indicated as an early key driver of cover, and may not act in isolation during rapid cover development. These findings are relevant to management practices. Quality vegetation performance, achieved at sowing rates approximating on ground restoration, suggest that further investigation into lowering rate and species richness and cover response, is warranted. Long term studies investigating community dynamics, would give insight into this novel community’s ability to continue co-existence as a functional resilient system, as a predictor of ecosystem service potential.