PLANTS INFLUENCED BY GROWING MEDIA AND COMPOST ADDITION ON MOCK GREEN ROOFS WITHIN THE OZARK HIGHLANDS

Green roof technology and other low impact development practices help mitigate hydrologic impacts from urbanization.Green roofs are widely recognized for stormwater retention,and these systems provide many other ecological functions,such as habitat,air quality improvements,insulation,reduced noise pollution and aesthetic quality.Green roofs are composed of a plant palette(species selected for a specific condition),growing media and drainage system on top of a traditional roof membrane.This study investigated species survival under local environmental conditions,in the southwestern Ozark Highlands from September 2008 through 2009.There were four treatments consisting of two different growing media particle sizes and two different fertilization regimens(with and without compost).Sixteen plant species and/or varieties were monitored to determine the effect of treatments on survival and spread.Plant response varied by species,but the fine media with compost provided the greatest survival and spread.However,the fine media without compost treatment had similar survival rates and may provide similar cover over time.The coarse particle media treatments had greater mortality rates in most specimens and less coverage after one year.Local environmental conditions were detrimental to some species(Sedum moranense L.),whereas other species(Sedum reflexum L.;Phedimus sp.L.;and Sedum spurium L.‘Summer Glory’)thrived.Our results provide valuable knowledge on creating an appropriate plant palette for green roof designs.

MEDIA COMPOSITION INFLUENCES GREEN ROOF PLANT VIABILITY IN THE OZARK HIGHLANDS

Plant selection and establishment are critical components for green roof health and success. Plant palettes (sets of plant species selected for specific conditions) for green roofs vary in their ability to confer benefits depending on the species make-up and their adaptation to particular environments and climates. The response of various species to climatic factors on rooftops is unknown for the Ozark Highlands region. The objective of this study was to compare plant survival and spread in three growing medium treatments (course and fine texture with compost and fine texture with no compost) installed as part of a green roof system. The study was performed on a green roof system at the University of Arkansas in Fayetteville over 3 years. Data were collected on 13 species installed in September of 2006 and surveyed on three dates thereafter: April 30, 2007;May 19, 2009;September 10, 2009. The treatments with added compost had statistically greater vegetated cover (from 73 to 87%) compared to the fine medium without compost (36 to 43%). In most cases the spread of individual plants was not significantly different between treatments. Results indicated that rooting medium containing compost increased survival and overall vegetated roof coverage, and identified various potential green roof plant species for the Ozark Highland environment. Two species, Sedum middendorffianum var. diffusum and Sedum spurium ‘Roseum’, did particularly well in all treatments. One species, Sedum kamtschaticum, did well only in the treatments with compost.