The Pennsylvania State University The Graduate School Department of Horticulture NORTHEASTERN U.S. NATIVE AND NATURALIZED PLANT PERFORMANCE IN SHADED MICROCLIMATES ON GREEN ROOFS A Thesis in Horticulture by Peter Vanco 2015 Peter Vanco Submitted in Partial Fulfillment of the Requirements for the Degree of Master’s of Science August 2015 The thesis of Peter Vanco was reviewed and approved* by the following: Robert D. Berghage Associate Professor of Horticulture Thesis Advisor Eric P. Burkhart Faculty Instructor, Ecosystem Science and Management Department and Plant Science Program Director, Shaver's Creek Environmental Center Elsa S. Sánchez Associate Professor of Horticultural Systems Management Rich P. Marini Professor of Horticulture Head of the Department of Horticulture *Signatures are on file in the Graduate School ii ABSTRACT Being comprised of thin, porous, heat-retentive media, and being exposed to wind and sun, green roofs are typically hot and droughty. As such, green roofs are taxing environments for the plants which inhabit them. There exist, however, various microclimates on many roofs which may provide growing conditions different from those on a typical section of green roof. One category of such microclimates is shaded areas. The goal of this thesis was to explore the possibilities available in these areas to non- traditional green roof plant species. Fifteen species of plants, twelve of which are native to the Northeastern United States, were chosen to be grown in both shaded an non-shaded conditions on a green roof with two sections, one being nominally four inches, and one being nominally six inches thick. Four replicates were included in the resultant four treatment groups, with each plant being allotted a 75cm x 75cm area in which to grow for one year. Plants which were grown in the deeper media showed significantly better health and growth after one year than their counterparts in the shallow media, likely due in part to a deeper media’s inherent larger water-storage capacity. This trend has been seen in many previous experiments. Testing of the roof’s media and conditions, however, showed that the shaded areas in both media depth sections of the roof had significantly lower surface, plant, and subsurface temperatures, significantly higher water retention capabilities, and significantly higher humidity levels near the roof’s surface. It was most likely due in part to these factors as well that the plants in the shaded sections of the green roof in both the deeper and shallower sections showed increased growth and more robust health than their non-shaded counterparts. Differences in performance between species were seen during the experiment. Among the species tested, those which showed higher levels of aptitude for growth and survival in shaded areas on green roofs included Achillea millefolium, Dicentra eximia, Eurybia divaricata, Fragaria virginiana, iii Potentilla simplex, Scutellaria ovata, Sedum spurium, Viola sororia, and Waldsteinia fragarioides. To a lesser degree, Geranium maculatum, Glechoma hederacea, and Iris cristata showed promise as potential candidates for inclusion in a shaded green roof plant community. Three species used in this project which would not be recommended for green roofs are Ajuga reptans, which could not withstand the cold temperatures of a central Pennsylvania winter, Meehania cordata, and Pachysandra procumbens. During the course of this roof-top study, morphological changes such as etiolation were observed in many species in the shaded treatment groups. Previous studies of non-Sedum plants on green roofs have found that due to differences in anatomy, they can increase the amount of water a green roof can retain, and the rate at which the roof loses water due to evapotranspiration, when compared to a roof planted with Sedums. Two of the species from this study, Eurybia divaricata ‘Eastern Star’, and Sedum spurium ‘Dragon’s Blood’, were grown in both shaded and non-shaded conditions in green roof media in greenhouse conditions to determine if morphological and physiological changes due to growing in a shaded environment affected the plants’ abilities to retain and mobilize water. Water loss over a two- week period without watering, as well as water retention levels before and after the drying-out period was measured. In addition, plant root and shoot lengths were measured at the beginning and end of the experiment, as well as plant live mass and dry mass. The E. divaricata plants used displayed no significant differences in root and shoot tissue amounts at the end of the experiment due to the shade treatment, and yielded statistically similar water retention and evapotranspiration rates in both treatments. The S. spurium plants however, showed significant reduction in root and shoot production, water retention, and evapotranspiration capabilities when grown in the shaded treatments. The results found in these studies suggest that by utilizing the benefits of shaded microclimates on a green roof, a wider, more diverse plant palette can be implemented on thinner green roofs. Additionally, the potential benefits of including non-sedum species on a green roof were not seen to diminish in shaded areas. iv TABLE OF CONTENTS List of Figures ......................................................................................................................... vii List of Tables ........................................................................................................................... xiv Acknowledgements .................................................................................................................. xv Chapter 1 Literature Review .................................................................................................... 1 1.1 Green Roofs ....................................................................................................................... 1 1.2 Green Roofs as a Plant Habitat .......................................................................................... 3 1.3 Non-Sedum Plants on Green Roofs ................................................................................... 5 1.4 Native Plants ...................................................................................................................... 6 1.5 Shaded Microclimates on Green Roofs ............................................................................. 7 1.6 Green Roof Plant Selection Criteria................................................................................... 8 1.7 Works Cited ....................................................................................................................... 8 Chapter 2 Evaluation of Native and Naturalized Species in Shaded and Full Sun Green Roof Conditions ................................................................................................................................ 12 2.1 Introduction ........................................................................................................................ 12 2.2 Materials and Methods ....................................................................................................... 13 2.2.1 Site Evaluation and Preparation ...................................................................................... 13 2.2.2 Selection and Organization of Treatments ...................................................................... 16 2.2.3 Evaluation of Effects Provided by Treatments ............................................................... 17 2.2.4 Selection of Plant Species ............................................................................................... 19 2.2.5 Evaluation of Plant Seeding ............................................................................................ 25 2.2.6 Evaluation of Plant Performance .................................................................................... 26 2.3 Results and Discussion ...................................................................................................... 28 2.3.1 Treatment Effects on Test Site’s Physical Properties ..................................................... 28 2.3.2 Treatment Effects on Individual Plant Species Performance .......................................... 35 2.3.3 Treatment Effects on Pooled Plant Performance ............................................................ 78 2.3.4 Seed Germination ............................................................................................................ 87 2.5 Works Cited ....................................................................................................................... 101 Chapter 3 The Effect of Shade on Green Roof Plant Water Retention and Evapotranspiration Capabilities .............................................................................................................................. 104 3.1 Introduction ........................................................................................................................ 104 3.2 Materials and Methods ....................................................................................................... 107 3.3 Results and Discussion ...................................................................................................... 113 3.3.1 Treatment Effects on Plant Tissue .................................................................................. 113 3.3.2 Treatment Effects on Water Retention ...........................................................................