Marie-Curie IAPP ‘Green Roof Systems’ Project
The Green Roof Research Conference 18-19 March 2013, Sheffield
Characterising the response of green roof plant species to their environment – developing a model Zoë Dunsiger University of Sheffield z.dunsiger@sheffield.ac.uk Introduction A system was designed to allow testing of a range of green roof species in a controlled monitored environment which could be expanded to other test sites. It allows the study of the difference in response due to microclimatic or regional climatic conditions. An environmental matrix tested the influence of total water availability through the interaction of substrate depth i.e. rooting volume, and supplementary irrigation. The imposition of the irrigation regime is based on the measured water holding capacity of the growing medium with a laboratory pressure plate method in Sheffield. Known methods of growth monitoring are developed to detect an appropriate sensitive method for roof species at early growth stages before and during establishment. Comparison can be made with a parallel study in a controlled climate chamber on a short time scale in Germany.
Overview of Methodology
Figure 1 – Seed sowing in situ at high density
The study successfully established plants in situ from seed, avoiding transplant shock seen in green roof installation with plug plants. It imposed competition between individual plants of the same or other species in mixed groups to include this factor in plant performance examination. Controlled irrigation was applied to the experimental site to ensure successful establishment from seed and then to impose a regime of minimal supplementary water during the growing season, testing the quantity and frequency of water needed to maintain expansive growth. In contrast to previous studies, which tended to focus on the imposition of drought conditions in the early or late period of establishment, this study sought to reflect a range related to typical rainfall data in the region, over a growing season.
Marie-Curie IAPP ‘Green Roof Systems’ Project
The Green Roof Research Conference 18-19 March 2013, Sheffield
Key Findings This use of the wide range of species examined permitted performance and 120 plasticity to be quantified under conditions of 100 plant competition for resources, across a 80 variable roof surface environment. Monitoring of various growth forms allowed the 60 comparison of plant coverage and expansion 40 to be compared during establishment, with a 20 view to predicting likely response of novel 0 roof species. The method has been seen to 0 20 40 60 be applicable as growth forms have changed Dry weight (g) over two growing seasons. A range in plant responses has allowed selected plant typing Figure 2 - Comparison of early and late in terms of their optimal performance within season growth measures by species type the environmental matrix. Greater attention has been applied to relating plant performance to available substrate water, an extension of previous roof studies. Extension growth (mm)
140
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b
Figure 3 – Mixed species growth in controlled competitive groups; (a) maximum irrigation, (b) minimum irrigation
Further Reading Dunnett, N. and Nolan, A., (2004), The Effect of substrate depth and supplementary watering on the growth of nine herbaceous perennials in a semi-extensive green roof, Proc. IC on Urban Horticulture Eds: R. Junge-Berberovic et al., Acta. Hort. 643, ISHS Korner, C.H. (1991), Some often overlooked plant characteristics as determinants of plant growth: a reconsideration, Functional Ecology, 5, 162-173.