Characterising the response of green roof plant species to their environment - Zoë Dunsiger

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

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.

Figure 1 – Seed sowing in situ at high density

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

plasticity to be quantified under conditions of

plant competition for resources, across a

variable roof surface environment. Monitoring

of various growth forms allowed the

comparison of plant coverage and expansion

to be compared during establishment, with a

view to predicting likely response of novel

roof species. The method has been seen to

be applicable as growth forms have changed

over two growing seasons. A range in plant

responses has allowed selected plant typing

in terms of their optimal performance within

the environmental matrix.

Greater attention has been applied to relating plant performance to available substrate

water, an extension of previous roof studies.

a 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.

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Figure 2 - Comparison of early and late season growth measures by species type