Appropriate Design Elements and Native Plant Selection

APPROPRIATE DESIGN ELEMENTS AND NATIVE PLANT SELECTION

FOR LIVING ROOFS IN NORTH CENTRAL TEXAS

JONATHAN WILLIAM KINDER

Bachelor of Science, 2006 Texas Christian University Fort Worth, Texas

Submitted to the Graduate Faculty of the College of Science and Engineering Texas Christian University in partial fulfillment of the requirements for the degree of

Masters of Science

May 2009

ACKNOWLEDGEMENTS

I want to sincerely thank everyone that helped us in this project, because it could not have been done without the support and collaborative efforts of many individuals and institutions. First, thanks to God; thanks to my beautiful wife for being my cheerleader, helper, and personal barista. Thanks to my parents, Gery and Shelley, and my family for their love. This thesis is a tribute to the support, values and everlasting encouragement you have given me. Thanks to Dr. Tony Burgess, a mentor and patient guide who helped me learn about plants and life; to Bob O’Kennon, our walking flora and guide; Dr. Michael Slattery for his expertise and departmental support, and for the opportunity to attend the GreenBuild conference which grew my knowledge of the industry beyond expectations. Thanks to Dave Williams, my resourceful partner in this project whose knowledge, cleverness and energy made our study a reality. Thanks to Rob Denkhaus and Susan Tuttle at the Fort Worth Nature Center and Refuge for plants, an area to work, research sites and friendship. I also want to thank Robert George, Pat Harrison, and all the staff at the Botanical Research Institute of Texas for being an indispensible resource and helping to give us a local voice; Lenee Weldon, my field buddy who has been there from the beginning; Molly Holden who gave us her help and knowledge, Bill Lundsford with Colbond Inc. and Steve Skinner and Nathan Griswold with American Hydrotech Inc. for their generous donations. Thanks also, to Dr. Magnus Rittby and TCU; the TCU Environmental Science Department; the TCU Living Roofs Applied Projects Team; Steve Windhager and the Ladybird Johnson Wildflower Center; Fort Worth Nature Center Master Naturalists; Cam Shoepp and Chris Powell from the TCU Art department; Balmori and Associates and Rana Creek; The Owner’s Group; Beck Construction; Marty Leonard; Dr. Art Busby and the TCU Geology department; Fellow TCU students and friends; and many others too numerous to name.

And last, but importantly, the prairie landscape itself.

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ...... ii LIST OF FIGURES ...... iv LIST OF TABLES ...... vi I. LIVING ROOF OVERVIEW ...... 1 II. OBJECTIVES ...... 9 III. LIVING ROOF PLANT PALETTE ...... 10 INTRODUCTION ...... 10 STATE OF THE ART ...... 11 IV. FORT WORTH PRAIRIE BARRENS AND GLADES ...... 14 INTRODUCTION ...... 14 DEFINING BARRENS AND GLADES ...... 16 WALNUT LIMESTONE COMMUNITIES ...... 19 V. PLANT PALETTE SELECTION AND INSTALLATION ...... 21 DEFINING A HABITAT TEMPLATE ...... 21 THE TEST MODULES ...... 23 TREATMENTS ...... 24 PLANT PALETTE ...... 27 TRANSPLANTING INTO ROOF MODULES...... 32 VI. PLANT PERFORMANCE...... 36 MONITORING: PHENOLOGY AND GROWTH ...... 36 PHOTOGRAPHIC DOCUMENTATION ...... 43 RESULTS: GROWTH FORMS ...... 44 RESULTS: SURVIVORSHIP ...... 45 RESULTS: PHENOLOGY AND GROWTH ...... 49 FALL RESURRECTION DATA ...... 53 RESULTS: PHOTOGRAPHIC PROGRESSION ...... 53 VII. SPECIES ACCOUNTS ...... 55 VIII. DISCUSSION AND CONCLUSIONS ...... 65 REFERENCES ...... 70 VITA ABSTRACT

iii

LIST OF FIGURES

Figure 1: Example living roof layout, courtesy American Wick Drain Corp...... 1

Figure 2: Alternate drainage layer, courtesy Green Roof Service, LLC ...... 2

Figure 3: St. Xavier University, Chicago IL...... 8

Figure 4: Ecoregions of North Central Texas. Adapted from EPA ...... 14

Figure 5: Walnut limestone glade, Inset: close‐up of Walnut surface ...... 19

Figure 6: Thin soil on Walnut barren...... 20

Figure 7: Dalea reverchonii, a rare and endangered species...... 20

Figure 8: Peggy Notebaert Nature Museum, Chicago IL...... 22

Figure 9: Test modules. Inset: Digital design of test module, courtesy David Williams...... 23

Figure 10: View of aluminum water‐proofing in hydrologically monitored test modules...... 24

Figure 11: Growth Form Spectrum, as proportion of species from 2007 study...... 31

Figure 12: Planting diagrams. Top left clockwise: treatments 1,2 and 4; treatment 3; treatment 5 .. 33

Figure 13: Overview map showing field sites and Walnut Limestone geology. Adapted from Texas

Natural Resources Information System, 2008...... 37

Figure 14: Rhome field site, aerial view. (Texas Natural Resources Information Systems, 2008) ...... 39

Figure 15: Fort Worth Nature Center and Refuge field site, aerial view. (Texas Natural Resources

Information Systems, 2008) ...... 40

Figure 16: Average phenologic representation for Bouteloua rigidiseta found in test modules...... 42

Figure 17: Simple growth axis diagram. Left, cross section; Right, top view...... 43

Figure 18: Test module 11, left to right, April 24, transplants established; August 26, post drought;

October 2, after resurrection and germination...... 44

Figure 19: Growth form spectra as proportion of species found, top, 2008 test modules; bottom,

2007 Walnut barrens study...... 46

Figure 20: Survival rates among living roof treatments over time showing standard deviation...... 47

Figure 21: Total Vegetated Canopy Extent among Living Roof Treatments over Time...... 48

Figure 22: Test Modules’ and Field Sites’ Phenology Represented by Length of Horizontal Bar...... 50

Figure 23: View of sexual development of field phenologies of Muhlenbergia reverchonii ...... 51

Figure 24: Average heights across treatments over time (with standard deviation) ...... 52

Figure 25: Muhlenbergia reverchonii in September bloom, Fort Worth Nature Center and Refuge .. 60

LIST OF TABLES

Table 1: Comparison of living roofs and conventional roofs (adapted from Cantor, 2008) ...... 4

Table 2: Test module treatments ...... 25

Table 3: 2007 Walnut barrens plant survey, nomenclature follows Diggs et al., 1999 ...... 28

Table 4: Test module list of perennial species transplanted 2008, grouped by growth form...... 31

Table 5: Test module list of germinated annual and perennial species 2008 ...... 44

I. LIVING ROOF OVERVIEW

“Modern Man does not experience himself as a part of nature but as an outside force destined to dominate and conquer it. He even talks of battle with nature, forgetting that, if he won the battle, he would find himself on the losing side.”

-- E. F. Schumacher, Small is Beautiful.

Space is wasted in the urban setting, namely rooftops. Black‐tar deserts silhouette huge

HVAC machines against bare geometric surfaces, spilling precipitation into overloaded sewers below. Cities suffer from local environmental degradation. There is usually too little green space to ameliorate acres of impenetrable hardscape. Automobile pollution and off‐gassing from manufactured products degrade local air quality. Many do not experience the natural environment and are neither emotionally invested in it nor realize the harm being done to it. Living roofs mitigate and solve environmental harms and reconnect the urban world to the natural world.

Living roofs invite nature (in our case, the shortgrass prairie) back into the city. A typical installation (Figure 1) includes a waterproofing membrane above the roof deck, then a root‐blocking layer. Above this is typically an insulation layer, although sometimes the insulation is placed below the waterproofing layer or left out of the design altogether. Next, an optional water storage layer and drainage layer is installed (Werthmann &

Associates, 2007). The drainage layers Figure 1: Example living roof layout, courtesy American Wick Drain Corp. differ; some roofs use a lightweight

1 aggregate similar to soil (Layer 3 in Figure 2), whereas others use a mat that allows subsurface water flow while holding the soil in place (Figure 1).

The drainage layer is meant to hold various plants rooted into growing medium; however, there are modifications of this basic design. For example, the drainage system on Figure 1 uses small cups as a water storage layer while Figure two uses an aggregate medium.

There are two basic types of

living roofs: extensive and

intensive. Extensive green roofs

usually have less than six inches of

a commercial growth medium,

limiting plant selection to grasses

and herbs, commonly Sedums.

Intensive living roofs typically have

deeper soils (over six inches or 15

cm) allowing a greater variety in Figure 2: Alternate drainage layer, courtesy Green Roof Service, LLC plant choice, including trees.

Getter and Rowe (2006) describe intensive green roofs as having “intense” maintenance needs. On the other hand, Cantor (2008) notes that the name of intensive roofs originated with the German term, “intensiv,” loosely translated as “intensive” in English. Intensive roofs cost and weigh more and require more maintenance. A third distinction, becoming increasingly common, is a semi‐ intensive hybrid, which uses more than six inches of soil, but still not so much more that it requires the load‐bearing cost or maintenance of intensive garden design (Cantor, 2008; Dunnett & Nolan,

2002; Emilsson, 2006; Emilsson & Rolf, 2005; Getter & Rowe, 2006; Rezaei et al., 2005).

Living roofs encompass multiple design modes and thus have many names, though commonly all are referred to as green roofs. This study uses the term “living roofs” as coined by Dusty Gedge

(Cantor, 2008) implying habitat and stressing the biodiversity function of promoting invertebrates, birds and other life on a roof ecosystem. Although “green” roofs are not typically green year round, this term is used most widely in professional landscape literature. Other terms such as “bioroof” or

“ecoroof”, preferred in Portland (Cantor, 2008), suggest the economics and ecologic functions of the roof, while “brown roofs” or biodiverse roofs (Kadas, 2006) are living roofs meant to closely resemble brownfield environments aiming to conserve urban biodiversity. Brownfields exhibit high biodiversity and provide habitat for species not otherwise seen in urban environments (Kadas,

2006).

Whatever the style of living roof constructed, all realize similar benefits. Cantor (2008) compares the benefits of living roofs to conventional roofs for Portland, Oregon (Table 1). Cantor does not cover certain negative aspects of living roofs; therefore infrastructure, roof weight limit, and general problems were added to this table to address some of the more apparent issues.

Living roofs mitigate stormwater runoff in two ways. First, the commercial growth medium retains 10% to 35% of the rainfall during the wet season and 65% to 100% of the water during the dry season for Portland, Oregon (Cantor, 2008). Retained water either evaporates or is transpired by plants (VanWoert et al., 2005). Second, the peak flow of the storm event is both reduced and delayed. When a storm hits an urban area, conventional roofs drain nearly all of the water rapidly into gutters and storm drains. A living roof drains only a fraction of fallen precipitation, and the remainder releases slowly over a few hours or days following the rain event (VanWoert et al., 2005), thus lessening and delaying the storm surge. These benefits could be attractive to commercial developments that are not allowed off‐site stormwater runoff or to municipalities with stormwater

3 infrastructure issues. Municipalities would retain more stormwater from large‐scale implementation living roofs (Cantor, 2008; Getter & Rowe, 2006; Yocca et al., 2007).

Table 1: Comparison of living roofs and conventional roofs (adapted from Cantor, 2008)

Function Living Roof Conventional roof Stormwater: 10‐35% during wet season, 65‐100% during dry None Volume retention season Stormwater: Peak All storms reduced runoff peaks and lagged None flow mitigation response Temperature Provides cooling and insulation in addition to None mitigation building envelope Improved runoff Retains atmospheric deposition and retards roof No water quality material degradation, reducing pollutant loadings Urban heat island Prevents temperature increase None Air quality Filters air, stores carbon, increases None evapotranspiration Energy Insulates buildings None conservation Vegetation Allows seasonal evapotranspiration; provides None photosynthesis, oxygen, carbon, water balance Green space Replaces green space lost to building footprint None Habitat For insects and birds None Livability Buffers noise, eliminates glare, serves as None alternative aesthetic, offers passive recreation Costs Highly variable: $5‐$12 per square foot ($53 – Highly variable:$2‐$10 per $129 per square meter) for new construction; square foot ($21 – 107 per and $7‐$20 per square foot ($75‐$215 per square square meter) for new meter) for retrofits construction, and $4‐$15 per square foot ($43‐$161 per square meter) for retrofits Cost offsets Reduced stormwater facilities, energy savings, None higher rental value, increased property value, reduced need for insulation materials, reduced waste to landfills, added jobs and industry

Durability Waterproof membrane protected from solar and Little protection, exposure temperature exposure lasts more than 36 years; to elements, lasts less membrane protected from operations and than 20 years. maintenance staff damage Commercial Infrastructure for design and construction Wide‐scale infrastructure Infrastructure present only in select areas. Little to none in in place most areas.

Function Living Roof Conventional roof Roof weight limit Can impede and restrict design Typically not a concern

General problems Suffers from leaks and improper installation Suffers from leaks and improper installation

A living roof is often guaranteed by the manufacturer for 25 years and frequently lasts much longer. In Germany, many living roofs are still functioning beyond 50 years (Porsche & Kohler, 2003) because the roof system protects the roofing deck from harmful ultra‐violet radiation, as well as from hail, wind and other atmospheric antagonists.

Often, a living roof is installed during initial construction of a building; however, an increasing number are retrofitted to an existing structure. Living roofs can be applied on most flat roofs as well as angled roofs; 30‐45% is typically the limit of the slope; however, some manufacturers also produce vertical living walls (Beryhage et al., 2007). Roofs at steeper angles can have problems with hydrology such as soil moisture differential, erosion and slope stabilization (VanWoert et al., 2005) but solutions exist (GreenBuild, 2007).

Some local governments encourage living roofs. Chicago mandates any newly constructed building receiving municipal funding must include at least 70% green roof cover. Furthermore, any new buildings including a living roof can benefit from an accelerated permit process which can cut the application time by half (Beryhage et al., 2007).

Living roofs are not a new technology. One could argue the technology is as old as the plant origins themselves, but at the very least there is historical documentation spanning human existence. The first recorded green roof was the Hanging Gardens of Babylon built by King

Nebuchadnezzar for his wife Amyitis who missed her lush homeland (Cotterell, 1988; Osmundson,

1999). The Nordic Vikings covered their dwellings and great halls with sod for insulation from the

9th through 11th centuries. Sod structures have been used for cabins in Alaska, probably as an adaptation from Scandinavia (Partnow, 2004). Roof gardens were popular with the upper class

5 throughout the Renaissance. More recently, sod roofs were used throughout North America in the

1800s because it was more available than timber (Conrad, 1991). In the 1930s, the British used living roofs for camouflage on military installations and the Germans installed roof gardens on residences (Beard & Green, 1994; Frith, 2005; Getter & Rowe, 2006). Living roofs are not a sudden innovation, but a straightforward, simple technology with a history and a wide implementation of uses (Oberndorfer et al., 2007).

Living roofs will be important in the future as well, as it becomes increasingly necessary to design in ways that meet society’s needs without externalizing environmental costs and consequences to future generations. This idea, known as sustainable design, eco‐design or green design, attempts to maintain social, economic and environmental welfare. Sustainable design encompasses fields including architecture, landscape design, manufacturing, construction and various forms of fabrication and creation (McLennan, 2006).

The northern and eastern United States currently seem to have the greatest success in green roofs, apparently because they use a similar plant palette as Europe combined with species native to

North America. This raises several issues for other regions of the country. Plants adapted to colder climates are stressed by the intense heat of the South. Furthermore, many living roof manufacturers restrict their plant selection to a few species that are in large‐scale commercial production, which limits biodiversity and restricts the beneficial potential of their green roofs.

There are good economic reasons since the widely used Sedums are easier to purchase and guarantee (Snodgrass & Snodgrass, 2006). Furthermore, Sedums outperformed native grasses and forbs in some areas according to a study at Michigan State (Snodgrass & Snodgrass, 2006; Van

Woert et al., 2005).

It seems wiser to research native species rather than bring plants in since Sedums might be out‐performed in other areas, and it seems the morally correct thing to do. Using native locally‐

6 grown species could reduce transport costs, but more importantly, using native species can re‐ establish ecosystems to their original geographic areas. Logically, an ecosystem evolved to a locality will do better than a manufactured one. This would not be the case if these native species were grown in a different growth medium. The question is can a growth medium be tailored to be lightweight as well as simulate the soil in which native species thrive?

It is uncertain whether living roofs should resemble existing natural communities, be created without any natural community as a blueprint, or integrate both options. The design goals of the roof greatly influence this argument. The Sedum roof developed from the plants Europeans noticed growing on roofs. Some living roof researchers have studied alpine cliff environments, Sedums included (Cantor, 2008). If the design goal of the roof is conservation or to resemble a local ecosystem, it would make sense to tailor the roof layers and substrate to what naturally occurs; however, many current living roof designs are horticultural abstractions, effective at retaining stormwater, creating natural aesthetic and insulating (Werthmann & Associates, 2007).

This thesis proposes that by using local natural systems as models one can learn how to produce a more effective living roof. The architectural and landscaping industries seem to want a simple and well‐documented plant palette that delivers a controlled appearance and minimizes the plant mortality risk rather than a designed local ecosystem. This thinking, however, contradicts the author’s belief that the natural system should be imitated to attain the highest biodiversity, and therefore resilience (Tilman, 1996), and attain the best‐adapted ecological community according to the region.

The simplistic nature of some living roof installations, such as the St. Xavier University living roof in Chicago (Figure 3) have little apparent scientific basis in local natural conditions (plant species, soils, climate). It is not to say these roofs will not provide any benefits to the structures they crown; however, additional benefits can be attained by installing a more naturalistic approach.

In all, living roofs have come a long way, but there is still much that is unknown about these systems, especially in Texas.

Figure 3: St. Xavier University, Chicago IL.

II. OBJECTIVES

This study attempts to contribute to the current body of knowledge of living roofs.

Specifically, it proposes that living roofs will be more effective when tailored to bioldiversity conservation rather than aesthetic conventions. It also proposes that the Walnut Prairie barrens and glades habitats present a suitable template for designing living roofs in north central Texas. The project monitored two field sites while simultaneously utilizing test modules for direct comparison to the native barrens and glades systems, specifically comparing mortality rates, growth, and phenologic progression.

Mortality rates for multiple treatments in living roof design are presented. Moreover, this study will present a series of tables representing the six months (April to September of 2008) of phenology of each species studied, both for specimens in the field site and those in the test modules. Practices that may improve plant performance for living roofs in this area are identified.

III. LIVING ROOF PLANT PALETTE

INTRODUCTION

Although plants did not evolve on rooftops, some species are naturally adapted to similar habitats. Logical rooftop vegetation design either changes the rooftop to resemble the plant’s natural habitat, or selects species already adapted to roof‐like environments. This study searched for common ground between these options, selecting plants adapted to dry, shallow soils and modifying the growth medium to adequately support the species chosen. Modifications must be appropriate within the context of climate, roof‐weight load, budget and the stated goals for the roof. Roof modifications include drainage mats, water storage layers, waterproofing, root‐ impermeable membranes and lightweight commercial growth medium. Commercial growth medium simulates soil, yet typically is coarser in texture, containing lightweight aggregates such as expanded shale and only limited organic matter (Beryhage et al., 2007; Dunnett & Nolan, 2002).

Selected plants should be able to survive in this growth medium as well as withstand the stresses of a roof microclimate.

In temperate climates, living roof candidate species must be drought tolerant and cold hardy.

Growth form is important because it indicates a plant’s ability to survive stress. A desert plant with an extensive root system growing through fractured rock to access deep soil moisture, such as honey mesquite (Prosopis glandulosa), would be a poor choice for most applications. However, a desert plant growing shallow roots to absorb sparse rainfall at the soil surface, such as prickly pear

(Opuntia phaeacantha), could be a prime candidate (T. L. Burgess, 1995; Snodgrass & Snodgrass,

2006).

STATE OF THE ART

Hardy succulents are described by Snodgrass & Snodgrass (2006) as the “workhorses” of the green roof industry. Most succulents are extremely drought tolerant and utilize Crassulacean Acid

Metabolism, or CAM, photosynthesis which minimizes moisture loss through transpiration

(Snodgrass & Snodgrass, 2006). Commonly cultivated plants of this growth form include plants from the Sedum, Sempervivium, Talinum and Delosperma genera. Herbaceous perennials are sometimes used on extensive green roofs because they can provide aesthetic blooms, giving the roof texture and color, although many are not adequately drought tolerant for roof vegetation. Examples of useful herbaceous perennials include Petrohagia, Dianthus and Phlox (Snodgrass & Snodgrass,

2006).

Sedum species and South African Delosperma species are especially popular for living roofs.

Sedum species, or stonecrops, are found in “north temperate areas, tropical mountains,

Madagascar, and Mexico” (Diggs et al., 1999) and inhabit rocky slopes (Karahan et al., 2006) and cliffs in North America and Europe (Bunce, 1968; Holmen, 1965; Lundholm, 2006). Sedum provide dependable and attractive groundcover, displaying conspicuous flowers and changing colors with the seasons. They tolerate a wide range of soil moisture and texture, temperature and sun exposure. Furthermore, Sedum are readily available commercially and are popular for living roofs in much of Europe and northern and eastern United States. In a study from Michigan State University

(Van Woert et al., 2005), Sedum even outperformed native species in a living roof environment.

Delosperma are similar to Sedum in they are drought tolerant and produce showy flowers, but require slightly less moisture and are less cold tolerant (Snodgrass & Snodgrass, 2006).

Annuals and biennials should be used sparingly because of gaps left when they die; however, they quickly fill in gaps to provide color and texture. Portulaca and Phacelia are recommended, along with Townsendia. (Snodgrass & Snodgrass, 2006).

More research is needed for creating plant lists on living roofs. Ed Snodgrass, owner of green roof plant nursery Emory Knolls Farms, says “the American green roof market is still in its infancy.

True regional plant lists and reliable natives still elude us,” Werthmann (2007). Snodgrass (2006) suggests that grasses have not realized their full potential on living roofs and recommends genera

Festuca, Andropogon, Bouteloua, Carex (sedges), Sesleria and Sporobolis. Also, living roofs could support the growth of many educational, aromatherapeutic, culinary and medicinal herbs

(Snodgrass & Snodgrass, 2006).

Other factors to consider when planting a living roof include irrigation, fertilization and integration with other designed systems such as solar cells or water catchment. For reference, there is a new guide, E2400 from the American Society for Testing and Materials, or ASTM, which

“addresses performance characteristics for green roof systems with respect to the planting” (ASTM,

2006). The ASTM suggests developing plant lists by analyzing climate and microclimate, roof design intent, maintenance and budget, wildlife concerns, plant characteristics and growth medium. The only plant genera it recommends by name are Sedum (mentioned several times) and Sempervivum; however, it does advocate working with local botanists and naturalists for determining a plant list.

Cantor (2008) suggests several criteria to evaluate plants for a living roof (adapted below):

1. Avoid messy plants that shed leaf and twig litter. Plants requiring clean‐up increase

maintenance costs and can clog drains. A species that puts out excessive seed may gain

unwanted dominance on the roof.

2. Avoid large plants. Mature trees may exceed load limits. This is not typically a problem

with minimal soil because the restrictive growing conditions should stunt large species.

3. Avoid brittle plants. High winds on roofs can break brittle plants like Bradford Pears.

4. Avoid trite selections and research adaptability. Just because plants work well at

ground level does not mean they will work on a roof. Understand the plants you

choose, especially larger species or those that will be relied on to provide cover.

IV. FORT WORTH PRAIRIE BARRENS AND GLADES

INTRODUCTION

A key question in living roof design is whether living roof candidate species can be identified from native regional (Figure 4) vegetation? The answer starts by identifying regional plant communities in habitats that resemble the conditions of a roof. After consulting with Dr. Tony

Figure 4: Ecoregions of North Central Texas. Adapted from EPA Burgess of TCU and Mr. Robert O’Kennon of the Botanical Research Institute of Texas, BRIT, it was decided to focus on the limestone barrens and glades communities of the Fort Worth Prairie due to their thin soil profile, geographic placement and dry water regime (Figure 4).

The Fort Worth Prairie, also called Grand Prairie, is different from the Blackland Prairie. Lying to the west of the Blackland Prairie, the Fort Worth Prairie’s geology consists of layers of hard, weather‐resistant limestone with shallow soils. The Blackland Prairie’s limestone is softer, allowing it to form deep soil layers (Hill, 1887). The hard strata of the Fort Worth Prairie have been exposed by erosion, forming ridge tops and cuestas separated by valleys where softer rock has worn away.

Hill (1901) also says the Grand (Fort Worth) Prairie is flat, instead of undulated, and is the “hard lime‐rock country.” For this reason the Blackland Prairies were preferred for agriculture over the shallow, rocky Fort Worth Prairie (White, 2006).

Dyksterhuis (1946) has described the Fort Worth Prairie landscape as having bands of vegetation running along the topographic contours. Burgess (2007) describes at least three types of grassy vegetation, adapted below:

1) Low, open mixtures of short grasses, forbs, prickly pear, and yucca on shallow soils and limestone outcrops. These plant communities are influenced by recurring drought, especially during summer. These associations occur on higher slopes and ridgetops where erosion keeps the soils shallow and immature.

2) Grassy seeps are dominated by seep muhly (Muhlenbergia reverchonii). These are typically on middle or lower slopes where clayey marls outcrop. Seeping marl is often below fractured layers of hard limestone that allows downward percolation of water. Groundwater moves laterally just above the less permeable marl and resurfaces on slopes where erosion exposes the marl. These seeps may remain saturated for weeks after rain; but during longer dry spells they can also become completely dry. Thus the clayey soils alternate between complete saturation and desiccation. Such habitats have been called “hyperseasonal” (Sarmiento & Solbrig, 1984) and almost always support grassland. Muhly seeps are endemic to this region.

3) Mixed‐grass prairie on deeper soils. These soils often show as bands of little bluestem (Schizachyrium scoparium) on slopes. The deeper soils of footslopes and valleys that receive runoff from adjacent uplands may have stands of taller Indian grass (Sorghastrum nutans) and big bluestem (Andropogon gerardii).”

“The combination of these three types of vegetation reflects contrasting outcrops and the associated soils distinguishes the Fort Worth Prairie from other landscapes in the region. These diverse habitats support greater species richness than would occur in more uniform prairies.

“The Fort Worth Prairie, or Grand Prairie, lies at a peculiar place along a steep precipitation gradient that is usually too dry for large trees but wet enough (some years) for substantive growth. The local climate allows drought tolerant trees, such as plateau live oak (Quercus fusiformis) and mesquite (Prosopis glandulosa), to compete and perform well, and also allows numerous grasses and herbaceous forbs to coexist, (Diggs et al., 1999; Dyksterhuis, 1946; Hill, 1887, 1901).”

Fort Worth sits at an interesting confluence of differing ecosystems and environmental variables. About 225 miles to the west lay the high plains of the Texas panhandle and about 150 miles east are the piney woods and deciduous forests of east Texas. Burgess (2007) describes the

Fort Worth prairie as hugged by two arms of the Crosstimbers to the immediate east and west.

Here, at this junction of forest and grassland biomes, rainfall and soil substrate become the key variables which control the dominant vegetation cover. North/South bands of oak woodlands on sandy soils known as the Crosstimbers alternate with clay‐ soiled prairies. Except for riparian corridors, in a broad sense all smaller biomes in North Central Texas are a subset of either

Crosstimbers woodland or mixed‐grass prairie (T. Burgess et al., 2007). The deep, sandy‐ soiled

Crosstimbers do not closely resemble the conditions of a roof, therefore the plants of the thin soiled prairies were chosen as the template for this study. There is a broad set of limestone and shale controlled prairies bisected by the Dallas/Fort Worth Metroplex. Thin‐soiled prairies over hard limestone seem the viable choice for roofs, an ecosystem recognized as Barrens.

DEFINING BARRENS AND GLADES

Barrens have been described in a number of papers; however, nuances from region to region muddy the definition. The historical term used by settlers (Tyndall & Hull, 1999) refers to land with few, if any, timber‐sized trees. In 1911, Steele recognized that the shale barrens of the east have distinct vegetation and are caused in part by soil properties and processes (Steele, 1911). Many

16 barrens are described as xeric, or adapted to low moisture due to climate, and maintained by edaphic conditions, climate, fire and other factors that promote forbs and grasses and restrict woody growth (Baskin & Baskin, 1988; Borchert, 1950; Davis, 1977). The Fort Worth Prairie barrens are thin soiled ecosystems with rock outcroppings exhibiting distinct and stunted vegetation due to lack of resources for plant growth.

The Fort Worth Prairie barrens most closely resemble the eastern serpentine barrens, which are characterized by a distinct, and sometimes endemic, flora and substrate (Braunschweig et al.,

1999). The Fort Worth Prairie barrens exhibit characteristics described by Anderson et al. (1999) such as lack of timber‐sized trees, extremely thin and rocky soil with little or no organic layer or leaf litter, and containing distinct vegetation including some endemics (such as Yucca pallida and Dalea reverchonii). Plant species are adapted to periodic drought, shallow soil, and high insolation

(Heikens & Robertson, 1994; Packard & Mutel, 1997). Vegetation is stunted due to lack of soil nutrients and water. The barrens are distinguished from the rest of the Fort Worth Prairie in that there is more bare ground and a higher proportion of forbs and sub‐shrub succulents (Anderson et al., 1999; T. Burgess et al., 2007; Heikens & Robertson, 1994; Packard & Mutel, 1997).

This supports Baskin & Baskin (1988) who suggest rock outcrop communities (including barrens and glades) are known to harbor endemics. Although Kruckeberg defines the barrens of western America as “tracts of land almost devoid of vegetation” and “serpentine outcrops with scarcely any plant cover” (Kruckeberg, 1999), he acknowledges that those barrens do not corresponding to the eastern North American serpentine barrens. Braunschweig et al. (1999) describe the eastern shale barrens as having a shallow A and B soil horizon with a very rocky C horizon, with usually little or no organic soil horizon or leaf litter (Braunschweig et al., 1999) which most closely resembles the ecosystem of this study.

Anderson (1982) and Davis (1977) describe barrens as an ecotone between prairie and savanna, meaning a boundaries area where vegetation from prairie to savanna blurs resulting in indistinct plant and animal communities; however, the differently stratified plant make‐up from shallow soil suggests the barrens to be its own ecosystem type (Baskin & Baskin, 1988). The term savanna has also been used to describe barrens, but the term savanna describes an ecosystem that is more similar to a prairie and has a slightly deeper soil and less bare ground (Anderson et al., 1999;

Baskin & Baskin, 1988). Fort Worth’s Walnut limestone barrens are sometimes scattered mottes, commonly consisting of Quercus fusiformis, Fraxinus texensis, and Ulmus crassifolia, in a shortgrass barrens matrix, forming a savanna vegetation structure.

Though often similar, glades and barrens are differentiated by their surfaces. Glades are dominated by exposed rock outcrop, while the barrens are dominated by vegetation cover and soil with fewer bare outcrops (Baskin et al., 1995). Some differences in vegetation do occur, but most of the same species studied appeared in both ecosystems; therefore, both of these closely related ecosystems are included in this study.

Plants adapted to barrens and glades require high insolation and shallow soils less than 25‐cm deep. Barren and glade communities also harbor many rare and endemic species. The growth form spectrum of barrens vegetation seems to vary slightly with geography, but most barrens and glades contain many forbs, with some grasses, sedges, and only a few species of stem succulents and small shrubs. Lichens, mosses, and crytobiotic crusts also occupy these areas (Anderson et al., 1999;

Baskin & Baskin, 1988; T. Burgess et al., 2007; Heikens & Robertson, 1994; Wiser et al., 1996).

Local climate plays a role in plant selection for living roofs. The climate of north central Texas is described by Dyksterhuis as a “forest climate” (Dyksterhuis, 1946). More specifically, the National

Oceanic and Atmospheric Administration (NOAA) describes this area’s climate as a “humid subtropical with hot summers,” and is continental, with wide annual temperature fluctuations, and

18 with a wide range in precipitation, usually from below 20 inches to above 50 inches of rainfall annually. Rainfall usually occurs at night, and for only a day or two at a time. NOAA identifies the annual warm season at almost 250 days long, which equates to a long growing season (about mid

March to late November)(NOAA, 2008).

WALNUT LIMESTONE COMMUNITIES

This study focused on sites with Walnut Limestone, a Cretaceous formation from the (Figure

5). The Walnut is a hard limestone layer usually containing numerous hard fossils lying on top of a softer silty‐clay marl layer. After examining the fossiliferous, non‐chalky limestone, Dr. Arthur

Busby, TCU Geology professor, identified that the key fossil, Texigryphaea mucronata, which indicates the Walnut formation (Akers & Akers, 2002).

Figure 5: Walnut limestone glade, Inset: close‐up of Walnut surface For the barrens and glades, this formation of hard rock over softer marl presents the opportunity for plants to root deeply into cracks in the Walnut limestone layer, as witnessed in the field, especially in glade communities (Figure 5). Some plants, however, do not grow in cracks, but

rather exploit thin (sometimes less than 1in) layers of soil sitting on the impervious layer of

limestone (Figure 6).

Figure 6: Thin soil on Walnut barren.

Soils formed from the Walnut limestone formation are heavily influenced by carbonate

illuviation and sediment deposition. Soils are typically less than 1 meter deep with clay to clay‐loam

texture and high gravel content common (USDA, 1981). Though not technically a soil, the marl’s

texture is rich in clay and silt sized particles and are capable of storing moisture (Williams, 2008).

Dalea reverchonii, a Texas endemic and endangered species, only grows on the soils formed

from the Walnut limestone formation (Figure 7). D. reverchonii was thought to be extinct for a time,

until rediscovered by Bob O’Kennon from the Botanical Research Institute of Texas (O'Kennon,

2008).

Figure 7: Dalea reverchonii, a rare and endangered species. 20

V. PLANT PALETTE SELECTION AND INSTALLATION

DEFINING A HABITAT TEMPLATE

Two potential methodologies were considered for the plant selection of this project: the first focused on using a horticulture amalgam approach and the second, a habitat template approach.

The amalgam approach places many plant species from various areas and climates onto a roof environment. This requires a much broader plant palette selection, expecting mortality of unsuitable species. The habitat template approach, used in this study, focuses on searching for an analogous ecosystem and trying to mimic it, focusing plant selection and soil design on specific communities. This study uses a native regional ecosystem as its template.

Living roofs undergo stresses that halt or hamper plant growth, so it logically follows to use naturally adapted systems with a flora tailored to similar limiting factors. Suffering from sustained high winds (Lundholm, 2006; Werthmann & Associates, 2007), high amounts of solar radiation

(Werthmann & Associates, 2007) including ultraviolet radiation (Cantor, 2008), hail, ice, excessive drought (Cantor, 2008), episodic flooding (Lundholm, 2006; VanWoert et al., 2005; Werthmann &

Associates, 2007; Yocca et al., 2007) and temperatures in excess of 140°C in the summer (Barrio,

1998; K. Liu & Baskaran, 2003), roofs are at the mercy of their local climate. Roofs protect a building, so get little protection themselves (Cantor, 2008). Granted, simply adding appropriate growth medium will ameliorate many of these problems, but plants add benefit . This limits plant selection to species that can tolerate desiccation, sudden flooding, high temperatures, high winds, and survive in a thin, infertile growth medium (Cantor, 2008; KoÈhler et al., 2002).

In Germany, Reinhard Bornkamm noticed grasses, such as Canada bluegrass (Poa compressa) growing in the sand and gravel layer placed atop a tar surface of a roof, and decided to investigate

(Werthmann & Associates, 2007). The German Landscape Research, Development and Construction

Society (German: Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau or FLL), developed

21 criteria for living roofs, and considered Bornkamm’s studies as an extensive green roof (FLL, 2002;

Werthmann & Associates, 2007). Dr. Lundholm (2006) proposed Nova Scotia barrens as a template for green roof, noting similarities between urban surfaces and natural surfaces that resemble impervious concrete.

The habitat template seems an approach that many living roof professionals are using, but not explicitly stating (Baumann, 2006; Brenneisen, 2006; Oberndorfer et al., 2007). One of the roofs featured at GreenBuild 2007 was at the Peggy Notebaert Nature Museum in downtown Chicago

(Figure 8). That living roof design imitated many of the ecosystems in the Chicago area. A steep ecological gradient from shallow to deeper soil across a short length of roof allow several nearby habitats to serve as templates. This design contrasts with the roof of the American Society of

Landscape Architects (ASLA) headquarters, which mixes some native species with more commercially accepted green roof species (Werthmann & Associates, 2007). Even though the

Figure 8: Peggy Notebaert Nature Museum, Chicago IL.

ASLA’s roofs arranges plants adapted to appropriate soil depths and places more drought resistant

plants on the southern‐facing slope of the roof, there is no attempt to mimic any specific natural

ecosystem (Werthmann & Associates, 2007).

Although complete habitat reconstruction may not be possible, the habitat template

approach may produce an ecosystem similar enough to fulfill most of the functions performed by

the ecosystem being mimicked. It is naive to assume copying an ecosystem in every detail is

possible; however, the attempt of replication provides opportunity to learn about the ecosystem.

THE TEST MODULES

This study utilized a series of smaller scale modules for several reasons, including ease of

access, speed of construction, cost effectiveness, durability, and flexibility for monitoring the

hydrologic output of multiple treatments.

Figure 9: Test modules. Inset: Digital design of test module, courtesy David Williams.

Specifically, this study was carried out in fifteen test modules, constructed from treated

lumber, with inner dimensions of 1.2 x 1.2m (4ft by 4ft) by 15cm (6 inches) deep (Figure 9).

23 effects of ground temperatures and moisture and for ease of access for monitoring. The test modules were installed at approximately 2% slope to drain water from the front through a ¼ inch slit. Eight modules routed their output flow into a guttering system which led to rainfall gauges that measured the rate and quantity of outflow water from the module’s surface runoff and subsurface

Figure 10: View of aluminum water‐proofing in hydrologically monitored test modules. drainage. A specially constructed impervious box made from aluminum sheeting sat inside each of these eight modules (Figure 10). The impervious inner box had ¼ slit cut across the downward side, lining up with the wooden module’s drainage slit.

The other nine test modules, which were not hydrologically monitored, were constructed similarly but with less costly plastic sheeting in place of the aluminum sheeting.

TREATMENTS

The test modules each had a different treatment applied using either a native clay soil or a commercial growth medium as a substrate for plant growth.

Two different surface covers (and one bare‐soil control) were applied to native soil treatments, as well as to two treatments using commercial growth medium, totaling five treatments. Each test module treatment was applied in triplicate to provide redundancy. Table 2 details the treatments.

Table 2: Test module treatments

Treatment 1: Bare Surface Native Soil This treatment is comprised of lightly compacted native soil situated above a drainage mat, a common addition to living roofs (K. K. Y. Liu, 2002), which facilitates drainage of the substrate by providing separation between it and impervious layers. The native soil, used in treatments 1, 2, and 3 was obtained from property adjacent to the Fort Worth Nature Center and matched the plant palette and geology of the barrens studied. These act as a control for the other native soil treatments, as well as the purest system to benchmark against the commercial growth medium treatment.

Treatment 2: Barrens Soil with Gravel Mulch This treatment is similar to the bare native soil treatment, except for the addition of a one to two inch layer of fossiliferous gravel placed as mulch on the soil surface.

Treatment 3: Barrens Soil with Artificial Concrete Mulch Treatment 3 is similar to treatment 2, except the mulching layer is comprised of a rock‐like or tile mulch. This fabricated mulch performs many of the functions performed by the limestone rock surface of the glades, which served as its inspiration. Specifically, this rock mulch acts as a simple surface‐covering mulch, decreasing evaporation from the soil and increasing soil moisture. It restricts plant growth cracks in the limestone and through a central planting basin (Photo, right) which provides more available nutrients and water per plant. Cement tiles function as analogues to the lithified limestone observed in the natural systems.

Treatment 4: Commercial Living Roof Many commercial living roof systems are designed to be lightweight to facilitate green roof retrofits on existing structures not originally designed to hold the weight of natural soil. A commercial design that is well known and widely used in green roof projects around the United States was recommended by Dr. Steve Windhager, who is currently conducting living roof research at the Ladybird Johnson Wildflower Center in Austin, Texas. The commercial growth medium is a lightweight, proprietary mix of expanded clay, sand, and compost. This medium is installed above a filter fabric which rests upon a water retention tray filled with lightweight aggregate, providing additional water storage capability to the system as a whole. The combination of filter fabric and water storage layers takes the place of the drainage mat used in the native soil treatments.

Treatment 5: Commercial Growth Medium in Coconut‐fiber Trays These trays are latex impregnated, coconut‐fiber trays used in living roof applications to provide ease of installation through a manageable, modular design, and biodegrade after installation to create a contiguous living roof such as the California Academy of Sciences. The coconut‐fiber trays were filled with the same commercial growth medium used in treatment 4, and were placed on a two‐ inch layer of additional growth medium above the same drainage mat used in the native soil treatments. However, we did not receive enough growth medium to fill in the area around the coconut‐fiber trays, so excess evaporation probably occurred around the sides of the trays through the course of the experiment.

PLANT PALETTE

The plant species chosen and the planting plan were the same for each template. The list of perennial species was based on field work conducted during the summer of 2007 on the Walnut

Prairie barrens at the Fort Worth Nature Center and Refuge. This barrens, which sits above the

Walnut Limestone, contains silty clay to clay soils (Williams, 2008). The plant species found are shown in Table 3. The vegetation resembled a savanna, with shorter grassland between deeper soiled mottes of plateau live oak (Quercus fusiformis), cedar elm (Ulmus crassifolia) and Texas ash

(Fraxinus texensis). Extremely thin soils were observed upon entering the site.

The species found were compiled into a list and grouped by growth form. After eliminating life forms unsuitable for living roofs, such as trees and shrubs, a growth form spectrum was made to

27 show species richness in each growth form category (Table 3). Entries without Latin or common names are those that were unidentifiable at the time of observation.

Table 3: 2007 Walnut barrens plant survey, nomenclature follows Diggs et al., 1999

Latin Name Common Name Growth Form Ambrosia artemisiifolia COMMON RAGWEED Annual Forb Baccharis neglecta ROOSEVELTWEED Annual Forb Bifora americana PRAIRIE‐BISHOP Annual Forb Chaetopappa asteroides ARKANSAS LEASTDAISY Annual Forb Croton monanthogynus DOVEWEED Annual Forb Daucus pusillus SOUTHWESTERN CARROT Annual Forb Erodium texanum STORK'S BILL Annual Forb Euphorbia dentata TOOTHED SPURGE Annual Forb Euphorbia longicruris WEDGELEAF SPURGE Annual Forb Evax prolifera BIG‐HEAD EVAX Annual Forb Gaillardia pulchella INDIAN BLANKET Annual Forb Galium sp. Annual Forb Gaura longiflora LONGFLOWER BEEBLOSSOM Annual Forb Glandularia pumila PINK MOCK VERVAIN Annual Forb Hedeoma hispida ROUGH FALSE PENNYROYAL Annual Forb Hedeoma reverchonii var. REVERCHON'S FALSE PENNYROYAL Annual Forb reverchonii Iva angustifolia NARROW LEAF SUMPWEED Annual Forb Lindheimera texana YELLOW TEXAS‐STAR Annual Forb Lotus unifoliolatus AMERICAN BIRD'S FOOT TREFOIL Annual Forb Lupinus texensis TEXAS BLUEBONNET Annual Forb Monarda citriodora HORSE MINT Annual Forb Oxalis stricta DILLEN'S OXALIS Annual Forb Palafoxia callosa SMALL PALAFOX Annual Forb Plantago patagonica BRISTLE‐BRACT PLAINTAIN Annual Forb Plantago rhodosperma RED‐SEED PLAINTAIN Annual Forb Rudbeckia sp. CONEFLOWER Annual Forb Scutellaria drummondii DRUMMUND'S SKULLCAP Annual Forb Spermolepis inermis REDRIVER SCALESEED Annual Forb Tetraneuris linearifolia FINELEAFED FOURNEURVED DAISY Annual Forb Thelosperma filifolium var. GREENTHREAD Annual Forb filifolium Torilis arvensis SPREADING HEDGEPARSELY Annual Forb ‐‐ Unidentified Species ‐‐ Annual Forb ‐‐ Unidentified Species ‐‐ Annual Forb Bromus japonicus JAPANESE CHESS Annual Grass

Limnodea arkansana OZARK GRASS Annual Grass Sporobolus ozarkanus OZARK DROPSEED Annual Grass ‐‐ Unidentified Species ‐‐ Annual Grass

Latin Name Common Name Growth Form ‐‐ Unidentified Species ‐‐ Annual Grass ‐‐ Unidentified Species ‐‐ Annual Grass ‐‐ Unidentified Species ‐‐ Annual Grass ‐‐ Unidentified Species ‐‐ Cryptobiotic Crust Aristida purpurea PURPLE THREEAWN Herbaceous Bunchgrass Bothriochloa barbinodis CANE BLUESTEM Herbaceous Bunchgrass Digitaria cognata subs. WESTERN WITCH GRASS Herbaceous Bunchgrass pubiflora Erioneuron pilosum HAIRY ERIONEURON Herbaceous Bunchgrass Muhlenbergia reverchonii SEEP MUHLY Herbaceous Bunchgrass Nassella leucotricha TEXAS NEEDLE GRASS Herbaceous Bunchgrass Panicum diffusum SPREADING PANICUM Herbaceous Bunchgrass Panicum hallii var. hallii HALL'S PANIC Herbaceous Bunchgrass Panicum oligosanthes SCRIBNER’S ROSETTE GRASS Herbaceous Bunchgrass Paspalum setaceum THIN PASPALUM Herbaceous Bunchgrass Schedonnardus TUMBLE GRASS Herbaceous Bunchgrass paniculatus Sporobolus cryptandrus COVERED‐SPIKE DROPSEED Herbaceous Bunchgrass Tridens albescens WHITE‐TOP TRIDENS Herbaceous Bunchgrass Tridens muticus var. ROUGH TRIDENS Herbaceous Bunchgrass elongatus ‐‐ Unidentified Species ‐‐ Herbaceous Bunchgrass ‐‐ Unidentified Species ‐‐ Herbaceous Bunchgrass ‐‐ Unidentified Species ‐‐ Herbaceous Bunchgrass ‐‐ Unidentified Species ‐‐ Moss Funastrum crispum WAVYLEAF TWINEVINE Perennial Climber Ibervillea lindheimeri LINDHEIMER'S GLOBEBERRY Perennial Climber Buchloe dactyloides BUFFALO GRASS Stoloniferous Grass Opuntia phaeacantha var. BROWN‐SPINE PRICKLY‐PEAR CACTUS Subshrub Prickly Pear major Abutilon fruticosum TEXAS INDIAN MALLOW Perennial Forb Asclepias asperula subsp. TRAILING MILKWEED Perennial Forb capricornu Cocculus carolinus CAROLINA SNAILSEED Perennial Forb Desmanthus leptolobus PRAIRIE‐MIMOSA Perennial Forb Glandularia bipinnitifida DAKOTA MOCK VERBAIN Perennial Forb Hybanthus verticillatus BABYSLIPPERS Perennial Forb Lactuca sp. LETTUCE Perennial Forb Ophioglossum LIMESTONE ADDERSTONGUE Perennial Forb engelmannii Phyllanthus polygonoides KNOTWEED LEAF‐FLOWER Perennial Forb Salvia texana TEXAS SAGE Perennial Forb Sida abutifolia SPREADING SIDA Perennial Forb Tragia ramosa NOSEBLEED Perennial Forb

Latin Name Common Name Growth Form Cuscuta pentagona var. DODDER Vascular Epiphytic glabrior Parasite

Figure 11 shows the proportional distribution of species richness among growth form categories within the Walnut barrens site. Annuals comprised 56% of the species found, while 44% were perennials. A little more than half of the perennials were grasses.

To reproduce this ecosystem in a roof module, the planting plan selected 11 perennial grass species (including one stoloniferous grass) and 5 perennial forbs species (including 1 subshrub prickly pear). To stimulate growth of annual species, the planting plan required bare soil be left open, except in the case of the gravel mulch and concrete tiles. The gravel mulch was limited to a depth of about 1 ‐1.5 inches so annual seed in the soil would be able to break the surface and establish. The transplanted perennial root balls were kept intact in the native soil treatments with the intent that any seeds housed in them might sprout.

The commercial growth medium was more challenging for annual plant growth since there was no seed bank in place, and for reasons discussed below in the transplanting section, the root balls had to be kept to a minimum. To introduce annuals we sprinkled native soil on the surface of the medium. This was moderately successful, and there were additional seeds in the perennial root balls that produced more annuals in modules with commercial growth medium as well.

The list of perennials selected for transplanting was created from the field work on the basis of their high frequency in the area of the study or their presence on other Walnut Limestone barrens sites. Table 4 lists sixteen perennial species we selected and planted, while Table 5 in the results section lists the annuals and perennials that germinated in the test modules.

Figure 11: Growth Form Spectrum, as proportion of species from 2007 study.

Table 4: Test module list of perennial species transplanted 2008, grouped by growth form.

Latin Name Common Name Growth Form Aristida purpurea PURPLE THREEAWN Herbaceous Bunchgrass Carex planostachys CEDAR SEDGE Herbaceous Bunchgrass Digitaria cognata subs. WESTERN WITCH GRASS Herbaceous Bunchgrass pubiflora Muhlenbergia reverchonii SEEP MUHLY Herbaceous Bunchgrass Nassella leucotricha TEXAS NEEDLE GRASS Herbaceous Bunchgrass Panicum hallii var. hallii HALL'S PANIC Herbaceous Bunchgrass Panicum oligosanthes SCRIBNER'S ROSETTE GRASS Herbaceous Bunchgrass Schizachyrium scoparium LITTLE BLUESTEM Herbaceous Bunchgrass Tridens albescens WHITE‐TOP TRIDENS Herbaceous Bunchgrass Tridens muticus var. ROUGH TRIDENS Herbaceous Bunchgrass elongatus Buchloe dactyloides BUFFALO GRASS Stoloniferous Grass Yucca pallida PALELEAF YUCCA Rosette Subshrub

Latin Name Common Name Growth Form Opuntia phaeacantha var. BROWN‐SPINE PRICKLY‐PEAR CACTUS Subshrub Prickly Pear major Glandularia bipinnatifida DAKOTA MOCK VERBAIN Perennial Forb Paronychia virginica YELLOW NAILWORT Perennial Forb Phyllanthus polygonoides KNOTWEED LEAF‐FLOWER Perennial Forb

TRANSPLANTING INTO ROOF MODULES

The planting plan called for three specimens of each perennial species (listed in Table 4) per test module. They were placed with one specimen in the top third of the module, one in the middle third, and one in the bottom third of the module in relation to the 2% slope (Figure 12). Effort was taken to stagger the plantings of the same species laterally to avoid any possible bias one side of the module might have over another side. This would leave adequate room for annuals to propagate, and with three specimens per test module there would be enough specimens to subject each species to all different moisture regimes possible along the slope gradient as well as gain statistical relevance.

Sixteen perennial species were selected for transplanting into a 16 ft2 test module, resulting in about three perennial species per square foot. Treatment 5 deviated from the above planting plan due to the reduced planting area outside the coconut‐fiber trays, so only two specimens of each species were transplanted. Treatment 5 placed a specimen of each species in one of the up‐slope trays and in one of the down‐slope trays. Figure 12 shows three planting plans, with different species represented by different colored shapes.

After the soils were in place, the test modules were planted. The modules with native soil and gravel mulch were left without their mulch until after the first round of planting so as to avoid mixing excess gravel into the soil itself. The planting plans for the modules with native soil and tile mulch were modified to accommodate the tiles. Plants were placed in the middle openings of the tiles, the cracks between tiles and the area between the tiles and the sides of the module.

Tile Mulch

Down‐slope Down‐slope

Coconut‐fiber Tray

Down‐slope

Figure 12: Planting diagrams. Top left clockwise: treatments 1,2 and 4; treatment 3; treatment 5

Most specimens were transplanted during cloudy weather with lower temperatures and high humidity (ideal conditions for this region). Modules with native soils were planted March 8, 2008, and modules with commercial medium were planted March 29, 2008. The cactus and yucca were planted shortly after so their spines would not be a hindrance.

For the transplanting, volunteers were split up into a field group and a module group. Target plants on the barrens were flagged by knowledgeable botanists in advance to insure proper

33 identification, which was difficult for some dormant grasses. The field crew split into smaller groups that focused on one or two dissimilar species at a time to promote identification control.

In the field, each plant was trimmed back close to the ground, and then the root ball was excavated. The specimen and the soil from the field were placed inside a 1‐gallon Zip‐Lock bag with a squirt of water. The bags were then filled with air and sealed, so that they would be cushioned during transport. Specimens were carefully labeled and placed in a large cooler. The crew at the modules sorted the specimens taken from the cooler, tallied the number of specimens of each species required at each test module, and reported the additional number needed. Bagged plants were delivered to the appropriate module.

Volunteers removed the plant plug from the bag, dug a hole, planted the plug, filled in any space between the plug and the edge of the hole, and watered the plug into place. Tags with a unique plant Identification number and species name were placed in the medium next to each specimen. These tags were used to track the specimens throughout the experiment.

Transplants going into the commercial growth medium had excess soil knocked off their root balls and were quickly submerged in water to eliminate as much soil from the roots as possible before being placed in the coarser growth medium. Because the root ball of native clayey soil had a lower infiltration rate than the commercial medium, there was concern that precipitation would not infiltrate the natural soil directly surrounding the roots sufficiently.

Opuntia phaeacantha were treated differently. Healthy pads of were cut and left in the shade for 10‐14 days in order for the wound to callus. Pads were planted vertically in the soil so that they would not receive too much light and heat; however, many pads were knocked over before they could properly root when vultures tried to land on them.

Transplanted specimens were closely watched for a week after the planting and were watered every other day to promote establishment and reduce shock. They continued to receive supplemental irrigation for a month after being transplanted.

VI. PLANT PERFORMANCE

MONITORING: PHENOLOGY AND GROWTH

Plants were monitored from April through September, 2008. Monitoring involved weekly photographic documentation, growth measurements four times during the study, and phenology tracking every two weeks. Phenology was monitored on the test modules, as well as on two separate field sites in order to ascertain the performance of the roof modules, both in relation to different media and to the barren and glade communities. This monitoring serves as a record of barrens and glades phenology; however, only the species that were planted or appeared in the roof modules were monitored on the field sites. Two field sites were located on the narrow band of

Walnut Limestone formation (Figure 13): one at the Fort Worth Nature Center and Refuge and a second just west of Rhome, Texas.

Plants in the test modules were monitored individually. Annual and perennial species established from seed were tagged with identification numbers only after they had been alive at least two weeks and were either over four inches tall or showing signs of sexual development

(production of blooms or seeds).

Phenology is the study of the timing of biological activity and the factors that trigger specific events, in this case, plants. Phenology and growth were recorded as a way to measure performance in the plants we tested. This was accomplished through observing the plants, and quantifying their development every two weeks according to variety of activity criteria involving survival, leaves, stems, blooms and fruit. Stress was assessed from plants showing senescing, insect damage, and/or dieback. To quantify development, this study used a phenology code adapted from Dr. Burgess

(Appendix A). Results were analyzed through the course of this study so a timeline or progression

(phenology) could be established.

Figure 13: Overview map showing field sites and Walnut Limestone geology. Adapted from Texas Natural Resources Information System, 2008.

Figures 14 and 15 depict the two field sites used in this study. The Rhome site, located at 33°

3' 27.82" N and 97° 29' 7.59" W, is just west of Rhome on Highway 114. This site features a long and narrow Walnut limestone glade with a Goodland limestone barren just upslope. The other field site, the Fort Worth Nature Center and Refuge, 32° 49' 44.08" N and 97° 28' 43.40" W, northwest of the Interstate 820 and Highway 199 (Jacksboro highway) intersection in northwest Fort Worth. The refuge is home to many ecosystems, but the barrens we studied lies north‐northeast of the entrance road and gatehouse. These sites lay on a ridgetop capped by the narrow strip of the Walnut

Limestone that runs north to south (Figure 13).

The phenology code was adapted to accommodate certain species:

• All grass species (family Poaceae): Stem growth was assumed if leaf growth was present.

The only exceptions were on species that had die‐back and the older growth had new

sprouts (such as regrowth exhibited by Buchloe dactyloides). Also, flower buds were not

noticed forming, so were marked as B0 when no blooms were present, B2 when anthers

and stigmas were exposed, and B3 when the flowering structures were still attached but

the anthers and stigmas were near abscission.

• Buchloe dactyloides: This often grows as a sod, making individuals difficult to separate

from one another for the purpose of measuring canopy extent. For this reason, canopy

dimensions were only recorded for the specimens planted in the roof modules.

• Moss: Height was not measured due to its very low life form; therefore only extent was

measured as a means of growth.

• Opuntia phaeacantha: Leaf growth only occurs for a short period following new pad

growth. As the pads are modified stems, the S0, S1 and S2 parts of the key were not

used, so L0‐L4 were used instead as follows. L0: not used. L1: New pad forming on

Figure 14: Rhome field site, aerial view. (Texas Natural Resources Information Systems, 2008)

Figure 15: Fort Worth Nature Center and Refuge field site, aerial view. (Texas Natural Resources Information Systems, 2008) 40

cactus. L1 used as long as the small vestigial leaves were present. After the vestigial

leaves fell off was L2 used as long as the specimen remained alive. L3: pad senesced. L4:

pad rotting or has insect damage.

• Salvia texana: Seeds never appeared to disperse, but instead remained in calyces

attached to the plant, so F3 represents abscission of the corolla.

• Yucca pallida and Carex planostachys: Rosette plant internodes were contracted and

stem growth was never apparent. Thus, S0, S1, and S2 were never used for these

species.

Dickenson and Dodd (1976) represent phenology in two different ways: as a series of lines and graphics representing stages and also as a progression graph with time on the x axis and phenologic progression on the y axis. Dickenson and Dodd, as well as Ahshapanek (1962), inspired how phenology is represented in this study (Figure 16). The x axis represents time in weeks, while the y axis represents the proportion of individual specimens showing each phenologic code with longer bars symbolizing more individuals. For example, Figure 16 shows, for Bouteloua rigidiseta, that most of the individuals observed in the field have mature fruits dispersing on June 1 and the highest mortality on July 13.

Plant growth was determined by measuring plant height and canopy extent. The term

“extent” is used here instead of “cover” because cover implies nearly 100% canopy, whereas extent is the measure of the furthest (non‐sexual) living above‐ground organ of the plant (Mueller‐Dombois

& Ellenberg, 1974). Height was measured from the base of the plant at ground level to the tallest non‐sexual, living extension of the plant. Cactus was measured to the top of the pads, not the spines. Grasses were measured to the top of the tallest leaf blade. Two axes measured extent: the longest possible and the shortest possible axis of the plant canopy (Figure 17). This was the simplest

Bouteloua rigidiseta Roof Module Average old fruits attached fruits mature/dispersing Fruits fruits growting/immature fruits absent flowers abscising flowers blooming buds flower buds growing flowers absent stems eaten back stems stems growing no stem growth leaves chewed/infected leaves senescing/abscissing leaves mature leaves leaves growing no leaves die‐back dead dying dead/dormant % Date 6/8 6/15 6/22 6/29 7/6 7/13 7/207/27 8/38/10 8/17 8/24 8/31 9/7 9/14 9/21 Figure 16: Average phenologic representation for Bouteloua rigidiseta found in test modules. Specimens of Bouteloua rigidiseta were most stressed on July 6 and September 7 and 21, 2008,

with moderate stress from July 27 through August 1. Note, stress can only be caused while plants are alive. Specimens experienced high mortality from July 27 through September 21. August 24 showed very little stress, indicating minor plant recovery though mortality increased. Rainfall results (not shown) increased in August, probably accounting for the lack of stress on August 24. Little flower development was observed in the test modules, but fruit development occurred numerous times through the study (June 8 and 22, July 27, and August 10 and 24) indicating there were at least two seasons for seed dispersal.

way to ensure reproducible data (Barbour et al., 1999; Kent & Coker, 1996; Mueller‐Dombois &

Ellenberg, 1974).

The perennial species were identified and tagged on the day of transplant, but during monitoring they were checked several times to verify their identity. Some species that closely resembled one another such as Panicum hallii and P. diffusum, as well as Tridens albescens and T. muticus, were very closely inspected. Identification involved studying the specimen, usually under a hand lens or microscope, and using the Flora of North Central Texas (Diggs et al., 1999).

Height Long axis Height

Short axis

CrossCross ‐sectionsection Top view

Figure 17: Simple growth axis diagram. Left, cross section; Right, top view.

PHOTOGRAPHIC DOCUMENTATION

The modules were documented throughout the project by taking standard photographs of each module from an overhead view approximately five feet from the top of the substrate. A mount with four legs was built to fit into the corners of the test modules, with a Canon PowerShot SD1100‐

IS attached to the “quad‐pod.” The Canon was set to super‐fine resolution and largest size.

Overhead pictures were taken once a week, usually around noon. These pictures were then grouped into a progression for each test module. Figure 18 shows three photos of the Native soil with tiles treatment. Appendix B contains the full set of photos.

Figure 18: Test module 11, left to right, April 24, transplants established; August 26, post drought; October 2, after resurrection and germination.

For the scope of this thesis, the photo documentation gave a sensible impression of the

results from the other monitoring techniques. These pictures could be scaled and used to calculate

actual percent cover over time using the appropriate image processing software.

RESULTS: GROWTH FORMS

The planting plan combined with annual germination produced a similar growth form

spectrum as initially studied in 2007 on the Walnut barrens. Table 5 lists the species which

germinated in the test modules between April and September, 2008. These species, along with

those transplanted, produce a growth form spectrum for the test modules (Figure 19, top).

Table 5: Test module list of germinated annual and perennial species 2008

Latin Name Common Name Growth Form Croton monanthogynus DOVEWEED Annual Forb Erodium texanum STORK'S BILL Annual Forb Gaillardia pulchella INDIAN BLANKET Annual Forb Galium sp. Annual Forb Gutierrezia texana BROOMWEED Annual Forb Heliotropium tenellum PASTURE HELIOTROPE Annual Forb Iva angustifolia NARROW LEAF SUMPWEED Annual Forb Lupinus texensis TEXAS BLUEBONNET Annual Forb Oxalis stricta DILLEN'S OXALIS Annual Forb Palafoxia callosa SMALL PALAFOX Annual Forb Plantago sp. PLAINTAIN Annual Forb

Latin Name Common Name Growth Form Scutellaria drummondii DROMMUND'S SKULLCAP Annual Forb Tetraneuris linearifolia FINELEAFED FOURNEURVED DAISY Annual Forb Thelesperma filifolium var. GREENTHREAD Annual Forb filifolium Bromus japonicus JAPANESE CHESS Annual Grass Limnodea arkansana OZARK GRASS Annual Grass Bothriocloa ishaemum KING RANCH BLUESTEM Herbaceous Bunchgrass Bouteloua rigidiseta TEXAS GRAMA Herbaceous Bunchgrass Erioneuron pilosum HAIRY ERIONEURON Herbaceous Bunchgrass Paspalum setaceum THIN PASPALUM Herbaceous Bunchgrass Sorghum halepense JOHNSON GRASS Herbaceous Bunchgrass Sporobolus ozarkanus OZARK DROPSEED Herbaceous Bunchgrass Sida abutifolia SPREADING SIDA Perennial Forb Sisyrinchium campestre BLUE‐EYED GRASS Perennial Forb Tragia ramosa NOSEBLEED Perennial Forb Cuscuta pentagona var. DODDER Vascular Epiphytic Parasite glabrior

Of the plants found in the test modules, 48% of the species found were annuals while 52% were perennials. This spectrum closely resembles the spectrum found in the 2007 Walnut barrens study (Figure 19, bottom). Noticeable differences include a higher ratio of annuals to perennials in the 2007 Walnut barrens study, and a higher proportion of herbaceous bunchgrasses in the test modules. The species richness (the total number of different species) in the test modules was 48, while the 2007 Walnut barrens study had a species richness of 70.

RESULTS: SURVIVORSHIP

The survival rates among the treatments produced trends between the commercial growth medium treatment and the native soil treatments. Figure 20 shows test module survivorship by treatment against time.

Figure 20 illustrates fundamental differences between commercial growth medium and native soils. Treatments using commercial growth medium suffered losses immediately following

Figure 19: Growth form spectra as proportion of species found, top, 2008 test modules; bottom, 2007 Walnut barrens study.

46 transplanting, while the native soil treatments kept most of their vegetation, although, the bare native soil treatment suffered some losses early on. The commercial growth medium’s survival rate continuously declined, yet stayed constant enough to maintain the highest survival rate by the study’s end, despite an aggressive 15% increase from resurrection and germination in the native soil with tile mulch treatment. Initial die‐off during the week after transplant (April 20‐26) is evident, especially in the commercial growth medium treatments (Figure 20). The commercial media had less than a 75% survival rate while the native soil with gravel mulch treatment was 95%. Regrowth

Figure 20: Survival rates among living roof treatments over time showing standard deviation. Survival rates were averaged for each test module from all the species populating that test module. The average survival rate of each treatment was calculated from the averages of the test modules of that particular treatment. The error bars on the data set represent standard deviation. For example, on June 8, 2008, the Native Soil with Gravel Mulch treatment averaged a 56.2% survival with a standard deviation of 0.07%.

47 during and after the August rains was significant in the native soil treatments. The standard deviation of the commercial growth medium data is less than 10%, while the native soil treatments vary widely with standard deviations from <1% to 30%.

Figure 20 shows survival as a percentage; however, it should be noted that even though the commercial media treatment has a survival rate exceeding all the other treatments by the study’s end there were 20 – 25% fewer specimens in the commercial media test modules than in any of the native soil treatments. This means that the commercial media may not necessarily support Walnut barrens plants better than native soil in which they are found.

Figure 21 shows the total extent of measured live plant cover by treatment. The native soil with tile mulch treatment exhibits much more cover than the other treatments tested. Also, Figure

21 does not show dead or dormant plant cover, which can still provide ecological benefit to a greenroof (Cantor, 2008), showing credibility to the native soil treatments as a green roof medium despite lower survival rates.

Figure 21: Total Vegetated Canopy Extent among Living Roof Treatments over Time.

Survival trends suggest relative stability and predictability using the commercial growth medium, while the native soil treatments suggests resiliency. This debate is examined further in the

Discussions section.

RESULTS: PHENOLOGY AND GROWTH

The phenological results from the plants in the field sites and in the test modules were similar. Figure 22 shows the average phenologies of the test modules and the field sites. The differences in sexual progression between field and test modules may be attributed, in part, to transplant stress reducing reproductive activity in perennials. For instance, some perennial species would not be expected to bloom, such as Yucca pallida, Dalea reverchonii and Opuntia phaeacantha, and others such as Aristida purpurea and Carex planostachys, could have bloomed and fruited had they not suffered transplant shock.

There was some dissimilarity between the phenologies of individual species in the field versus the test modules. Annuals in the test modules that sprouted before the drought and died out either did not revive at all or not in time to produce inflorescences; however, the specimens in the field did revitalize. This was the case with Croton monanthogynus, Salvia texana (weak perennial, but from seed), and Scutellaria drummondii. Erodium texanum germinated in the test modules in late September, but in the field E. texanum seedlings were rarely discovered. Some species, such as

Carex planostachys, Liatris mucron ata, and Paronychia virginica, died in the test modules without reviving or germinating, while specimens in the field survived. Other species, such as Asclepias asperula var. capricornu, Bromus japonicus and Lupinus texensis died off or entered dormancy in the test modules and the field sites at similar times.

Indications of stress were observed on specimens in the field and in the test modules; however, the stress was often prolonged and/or led to mortality in the test modules while many

Test Module Average old fruits attached fruits mature/dispersing Fruits fruits growting/immature fruits absent flowers abscising flowers blooming buds flower buds growing flowers absent Date ‐ Weeks 1‐23‐45‐6 7‐89‐11 12‐13 14‐15 16‐17 18‐19 Field Average old fruits attached fruits mature/dispersing Fruits fruits growting/immature fruits absent flowers abscising flowers blooming buds flower buds growing flowers absent Figure 22: Test Modules’ and Field Sites’ Phenology Represented by Length of Horizontal Bar. Proportionately, more specimens in the field sites bloomed and fruited, which was expected since the test module transplants were establishing. For example, during weeks 18 and 19, almost half of the living plants in the field sites showed some sort of fruit development, while those in the test modules showed very little fruit development. specimens in the field recovered. Qualitatively, the field specimens did not seem to suffer stress to the same degree as the test module specimens, though more research could clarify the degree to which the stress differed.

Phenologic response to rain was quicker in the field than in the test modules. Glandularia bipinnitifida and Palafoxia callosa both bloomed in the field within a few days to a week after rain; however, in the test modules there was either no response or it occurred after several inches had fallen (such as in early summer and early fall). Specimens in the test modules continually showed more signs of stress than specimens in the field.

The field sites, as a whole, showed very similar phenologies; however, there were a few notable differences. Muhlenbergia reverchonii bloomed almost a month later at the Rhome field site (Site B, August 3, 2008), than at the Fort Worth Nature Center and Refuge Barren Site on (Site A,

August 31, 2008) (Figure 23). This discrepancy may be due to available moisture or temperature differences between a glade and a barren or possibly geographic precipitation difference.

Muhlenbergia reverchonii Field A Average old fruits attached fruits mature/dispersing Fruits fruits growting/immature fruits absent flowers abscising flowers blooming buds flower buds growing flowers absent Date 7/6 7/13 7/20 7/27 8/3 8/10 8/17 8/24 8/31 9/7 9/14 9/21 Muhlenbergia reverchonii Field B Average old fruits attached fruits mature/dispersing Fruits fruits growting/immature fruits absent flowers abscising flowers blooming buds flower buds growing flowers absent Figure 23: View of sexual development of field phenologies of Muhlenbergia reverchonii

Through the course of the study, the bare native soil and native soil with tile mulch treatments had the greatest average height at about 15 cm. The lowest average height was observed in the commercial medium with Biotrays at about 4 cm (Figure 24). The test modules with native soil and tile mulch also showed the largest average extent of any treatment, at 10.4‐cm2, though the other treatments had similar average extents (about 9.6‐cm2), with the exception of the

Biotrays at 7.1‐cm2. Average extent was used in place of total extent because extent was measured by recording the longest and shortest axis the plant extended, which oftentimes was due to thin extensions and not canopy coverage thereby giving misleading data. Total extent would also be misleading when comparing treatments because the Biotray treatment planting plan did not include as many total species planted as the other treatments.

The height and growth show huge scatter. Measured height stayed consistent across treatments (Figure 24) and between the two field sites; however, the standard deviation of the dataset was typically one‐third to one‐half of the mean. Measured cover was even more

51 unpredictable with the standard deviation often 75% or more of the calculated mean. This suggests it is more informative to evaluate growth performance on a species by species basis.

Figure 24: Average heights across treatments over time (with standard deviation)

Height and canopy extent, both individually and represented as a ratio, were compared to survival; however, there did not appear to be any relationship between any measured growth and survival, possibly due to drought conditions, or lack of statistical confidence in growth measurements. Except for the commercial growth medium, the treatments showed a significant drop in average plant extent as rainfall decreased significantly from the end of June through July

(Figure 21). This drop is mostly due to plants dying off or going dormant (meaning their extents were not recorded). Growth measurments showed the plants in the native soil treatments having a fast response to drought (Figures 21 and 24), but the response to rain after drought was slower than the response from plants growing in the field sites (Figure 22). Two of the treatments, native soil with gravel mulch and native soil with tile mulch, showed increases in both average extent and survival rates after the drought was ended by August rains. These growth trends further supports

52 the idea of stabile performance from plants in the commercial growth medium treatments and resilient performance from plants in the native soil treatments.

FALL RESURRECTION DATA

The scope of this study did not involve tracking the growth and resurrection that occurred in late September through November 2008; however, the following observations were made.

Resurrection in the test modules using native soil occurred in Glandularia bipinnitifida, Buchloe dactyloides, Muhlenbergia reverchonii, Panicum hallii and P. diffusum, Digitaria cognata, Tridens muticus var. elongatus and T. albescens, and Phyllanthus polygonoides. Furthermore, Panicum oligosanthes and Paspalum setaceum germinated all over the native soil test modules. Many annual species also germinated from the seedbank including Erodium texanum, Gaillardia pulchella, and

Lupinus texensis. No resurrection was noticed in the commercial media test modules.

This resurrection and regrowth is promising for several reasons: many of the perennial species are capable of going dormant and resprouting; with diversity in plantings and an active seedbank, fall plant cover is very attainable; germination of cool season annuals can be expected in the winter and spring with an active seedbank present.

RESULTS: PHOTOGRAPHIC PROGRESSION

The photographic progression (Appendix C) shows a basic time‐lapse of the test modules through the study and document the phenologic and growth monitoring. The photographic progressions are important for two reasons. First, they give people not directly involved with the study accessibility to the research. Secondly, the photographs give another perspective of the test modules in addition to the quantitative data collected. For example, the phenology code used in

53 this experiment did not have a scale to the degree a plant may be senesced. Quantitatively, senescing is a sign of stress no matter the extent, but aesthetically and visually this may be a factor taken into consideration in developing living roofs.

The photographic progressions, however, do not generally show substantial differences from start to finish, a seven month period. Most test modules started out with low cover, showed initial growth, died back, and then showed growth again after the rains. The lack of substantial visual change, however, should have been expected because that is consistent with this vegetation type, although three events were quite apparent from the photos: initial die‐off just after transplantation; die‐off during the drought in July; and regrowth during and after the August rains.

VII. SPECIES ACCOUNTS

Four species studied in this project show promise as candidates for living roofs in north central Texas: Buchloe dactyloides, Muhlenbergia reverchonii, Opuntia phaeacantha and Yucca pallida. These species outperformed others in terms of survival, growth and stress response.

The following accounts may provide designers with useful information that combines scholarship with what was learned during this research.

Buchloe dactyloides (Nutt.) Engelm.

Synonyms: Bouteloua dactyloides (Nutt.) J.T. Columbus (N. USDA, 2008) Vernacular names: buffalo grass (Diggs et al., 1999) Life form: Stoloniferous hemicryptophyte, low‐growing grass (Quinn & Engel, 1986) Root form and behavior: Fibrous root systems, establishes at each node on stolons (Webb, 1941) Propagation type: Seeds and stolons (Quinn & Engel, 1986) Duration: Perennial (Diggs et al., 1999) Sexuality: Mostly dioecious, but occasionally monoecious (Diggs et al., 1999) USDA symbol: BUDA or BODA2 (N. USDA, 2008) USDA hardiness zone: 4 (N. USDA, 2008) Horticultural attributes: Used by settlers for sod houses, recently used as low maintenance, drought resistant yard grass (Diggs et al., 1999) Flowers: Light brown flowers (Snodgrass & Snodgrass, 2006) Federal status: Native (N. USDA, 2008) Distribution and occurrence: Canada (Manitoba and Saskatchewan) south to Texas, from Nevada east to Virginia (N. USDA, 2008) Sun/Shade: prefers sun, but somewhat shade tolerant (Beetle, 1950). Shade tolerant commercial strains are available (Saphire, 2007; Smith, 2008) Grazing: Poor on the Fort Worth Prairie. Buchloe increases under severe grazing because it is less desired by livestock (Dyksterhuis, 1946) though it is good grazing in Kansas (Webb, 1941)

Disturbed Site Rehabilitation Value: Exceptional erosion control, especially from wind, and recommended for mine spoil sites because it will establish on bentonite and coal spoils (Webb, 1941) Attracts: Nectar source for butterflies, is a larval host and/or nectar source for the Green Skipper butterfly, Hesperia viridis (Opler et al., 2006) pH: 6‐8.5 (Baker, 2004) Seed germination requirements: Light required. Pre‐chilling the seeds at 41 to 50˚ F (5‐10˚C), drying seeds for 6 to 48 hours at 104˚ to 158˚F (40˚ to 70˚C), or soaking seeds 1 to 72 hours in sodium hypochlorite greatly increased germination (Ahring & Todd, 1977; U.S. Forest Service & USDA, 2008) Growth Rate: Establishes quickly, spreads stolons quickly (Quinn & Engel, 1986) Phenology: Growth in late spring through summer. Flowers April to June (and later). Seeds from early summer to late fall (Webb, 1941). Soil Requirement: Fibrous roots up to 6 feet deep (Weaver & Darland, 1949) Wetland Indicator: Facultative upland where occurring (USDA NRCS, 2008) Successional Stage: Early to mid‐stage secondary succession (U.S. Forest Service & USDA, 2008) Fire Ecology: More prevalent in fire managed sites (Clements, 1934; Quinn, 1987)

Buchloe dactyloides is a sod‐forming, perennial grass that grows through the bread belt of the

United States, from Montana east to Minnesota and south to Arizona, Texas, eastern Louisiana and into Mexico (USDA NRCS, 2008),It is usually 4‐5 inches tall (Weaver & Darland, 1949) and can be grazed, and also mown. B. dactyloides is a co‐dominant component in shortgrass prairies, with

Bouteloua gracilis, and a minor component in tallgrass prairies. It grows in all soils, but is most commonly found on alkaline clays with a high water‐holding capacity and most rarely on sandy soils.

It is grazed all seasons by livestock. B. dactyloides is increasingly used as a native, low water requirement lawn (Van Auken & Bush, 1987; Diggs et al., 1999; Gruntman et al., 2004; Huff & Wu,

1992; Quinn & Engel, 1986).

Webb (1941) studied buffalo grass as a way to recover from the Dustbowl because it spreads rapidly, establishes good hold on the soil through fast growing root systems and quickly spreads through stolons. Webb described buffalo grass as a more drought tolerant species, and he foresaw it being used more in urban and suburban areas (Webb, 1941). In 1941, Webb recognized Buffalo grass as a possible solution to topsoil erosion, probably the biggest environmental problem in

Kansas at that time (Quinn, 1998). Now, buffalo grass could be used in living roofs to help mitigate global warming (Getter & Rowe, 2006) because of the same characteristics Webb identified 70 years ago.

Gould (1975) referred to Buchloe dactyloides as monoecious. It was believed that the male and female parts were separate species for a time (Quinn, 1991), but Shinner’s and Mahler's

Illustrated Flora of North Central Texas describes it as mostly dioecious (Diggs et al., 1999). Huff and

Wu (1992) studied eight plots of buffalo grass in Texas, Kansas and New Mexico and found both monoecious and dioecious populations. Huff and Wu observed reduced germination rates in monoecious populations possibly caused by inbreeding in the monoecious populations. Based on this information, it would be prudent to gather seed for propagation from a known dioecious population to promote more seed viability (Ortmann et al., 1998; Quinn, 1991; Quinn & Engel,

1986).

In the Fort Worth Prairie, Buchloe dactyloides may form thick mats with few other plants growing up within them or grow as scattered small colonies. The bigger colonies on Walnut barrens appear in partial shade. It occurs on both the Walnut and Goodland formations, as well as other geological contexts.

A study by Qui, et al. (1996) indicates that buffalo grass can absorb toxic compounds from the soil which suggests a role in ameliorating urban pollution.

Buchloe dactyloides can be competitive (Gruntman et al., 2004) which indicates possible problems with establishment of other species if B. dactyloides gained dominance on a living roof.

However, the living roof environment in hotter and drier climates will probably require plants such as B. dactyloides which are competitive and able to survive. Buffalo grass is not a dominant grass on the barrens and glades suggesting it would not be the dominant plant on a properly designed living roof.

Buchloe dactyloides is a fine candidate for living roofs in north central Texas. In test modules, only one species, Opuntia phaeacantha, held a higher survival rate and showed less signs of stress.

B. dactyloides withstood drought, and most specimens revived after irrigation or precipitation.

According to Qian & Fry (1997), B. dactyloides grows well in both wet and dry soils. Its stolons quickly spread and established new clumps, so it providing fast growing and effective ground cover

(Gruntman et al., 2004) which could stabilize steeply sloping roofs. Commercial buffalograss sod could be directly applied to a living roof.

Buchloe dactyloides is commercially available in a wide variety of strains, including varieties claiming shade tolerance (Smith, 2008), resistance to wear, rolled edges which are softer on skin

(Saphire, 2007), and shorter plant and leaf height with deeper rooting characteristics (The Arizona

Board of Regents on behalf of the University of Arizona, 1995).

Muhlenbergia reverchonii Vasey & Scribn.

Vernacular names: Seep Muhly, Reverchon’s Muhly (Diggs et al., 1999) Life form: Perennial bunchgrass (Barkworth et al., 2007) Root form and behavior: Fibrous root systems (Barkworth et al., 2007) Propagation type: Seeds (Ladybird Johnson Wildflower Center, 2008) Duration: Perennial (Diggs et al., 1999) USDA symbol: MURE2(N. USDA, 2008)

USDA hardiness zone: 6 (Snowden, 2006) Horticultural attributes: Conservation plant on steep, highly erodible soils (USDA NRCS, 2008) Flowers: strikingly red (Diggs et al., 1999), straw or mauve (Snowden, 2006) to purple or pink or brown (Ladybird Johnson Wildflower Center, 2008) Federal status: Native (USDA NRCS, 2008) Distribution and occurrence: Texas and Oklahoma (USDA NRCS, 2008) Sun/shade: Full sun (Snowden, 2006) Seed germination requirements: Collect seed in November (Ladybird Johnson Wildflower Center, 2008) Phenology: Warm season (Snowden, 2006), blooms August to November (USDA NRCS, 2008) Soil requirement: Dry, gravelly soils. Calcareous, limestone‐based rocky, clay, clay loam (Ladybird Johnson Wildflower Center, 2008) Wetland indicator: Facultative where occurring (USDA NRCS, 2008) Fire ecology: Withstands frequent burning (USDA NRCS, 2008) Elevation range: 150‐650m above sea level (Barkworth et al., 2007)

Muhlenbergia reverchonii is a perennial bunchgrass that grows only in Texas and Oklahoma

(USDA NRCS, 2008), usually 2‐3.5 feet tall. M. reverchonii may become semi‐dormant in drought conditions, but will revive and start new growth in the fall (USDA NRCS, 2008). It grows as nearly pure, dense stands (USDA NRCS, 2008). on limestone and marl rock outcrops and rocky slopes

(Barkworth et al., 2007) often on seeps (USDA NRCS, 2008). M. reverchonii has a long ligule, 2‐9 mm and is very apparent in bloom (Figure 25), making it easily distinguishable in the field (Barkworth et al., 2007). It closely resembles M. capillaris, but while M. capillaris has dull, scabrous lemmas, M. reverchonii has smooth and shiny lemmas (Barkworth et al., 2007). It also resembles M. setifolia, but M. setifolia has narrower panicles and ranges from New Mexico to west Texas (Barkworth et al.,

2007).

Muhlenbergia reverchonii is well suited for living roofs in north central

Texas. It can thrive in moist conditions, as evidenced by frequently occupying seeps, as well as withstand drought

(USDA NRCS, 2008). It was present in both the barrens and glades. In test modules, M. reverchonii showed less Figure 25: Muhlenbergia reverchonii in September stress than other species and survived bloom, Fort Worth Nature Center and Refuge longer in the native soil treatments than most species tested. M. reverchonii readily grew in commercial growth medium and developed sexually in commercial growth medium earlier than in native soil treatments. It can be propagated by seed (Ladybird Johnson Wildflower Center, 2008) and can provide green cover for much of the year, especially if dormancy is avoided. Aesthetically, it has an attractive bloom as viewed in proximity and from a distance, and is “neater and more formal in appearance than Gulf [Muhlenbergia filipes]or Hairyawn Muhly [Muhlenbergia capillaris], but equally delicate” (Snowden, 2006).

Opuntia phaeacantha Engelm. var. major Engelm.

Vernacular names: Brown Spine Prickly‐Pear, Engelmann’s Prickly‐Pear (Diggs et al., 1999) Life form: Shrub (USDA NRCS, 2008) Propagation type: Seeds and cut pads (Ladybird Johnson Wildflower Center, 2008) Duration: Perennial (Diggs et al., 1999) USDA symbol: OPPHM (USDA NRCS, 2008) Horticultural attributes: Drought resistant ornamental (Ladybird Johnson Wildflower Center, 2008) Flowers: Yellow petals with red bases (USDA NRCS, 2008)

Federal status: Native USDA NRCS, 2008) Distribution and occurrence: Southwest U.S., California east to Texas and Kansas, South Dakota (USDA, 2008) Sun/shade: Part shade (Ladybird Johnson Wildflower Center, 2008) to full sun (Diggs et al., 1999) Attracts: Numerous invertebrates (Kingsley, 1998) Phenology: Flowers [April] May to June [July] (N. USDA, 2008)[(Ladybird Johnson Wildflower Center, 2008)] Soil Requirement: Rocky soils, from sandy to clay (Diggs et al., 1999) Fire ecology: Can cause mortality. Burned but resprouted specimens are often more susceptible to insect and rodent damage (Bunting et al., 1980; McLaughlin & Bowers, 1982).

Opuntia phaeacantha is a large sprawling perennial prickly‐pear cactus (Diggs et al., 1999) growing 30‐60cm wide (Pinkava & McLeod, 1971) and rarely almost 2.5m tall (Ladybird Johnson

Wildflower Center, 2008). They form dense thickets up to 10 feet across (Ladybird Johnson

Wildflower Center, 2008). The pads are 12.5‐25cm long and 10‐20cm broad. O. phaeacantha hybridizes with O. engelmannii, which was thought to be O. phaeacantha var. discata until major dissimilarities were recognized (Grant & Grant, 1979). It also hybridizes with O. aureispina (forming

O. spinosibacca), O. ficus‐indica, and O. littoralis (Song, 1999). It is adapts to heat and low moisture

(Ladybird Johnson Wildflower Center, 2008), and, like all cacti, utilizes Crassulacean Acid

Metabolism (CAM) photosynthesis.

Opuntia phaeacantha var. major grows spines on the upper one third to one half of the pad, differing from var. camanchica which has spines all over its pad, and in Texas is found mainly in the panhandle (Diggs et al., 1999). O. phaeacantha’s flowers open around 8:00 a.m. and close eight hours later (Parfitt & Pickett, 1980) and each flower lasts one day (Turner et al., 1995).

Opuntia phaeacantha var. major attracts and feeds a number of invertebrates. Its purple‐red fruits, 31‐62mm long (Diggs et al., 1999), are edible and served as a dependable source of food for

Native Americans as well as bears (Theimer & Bateman, 1992; Turner et al., 1995). The seeds get

61 eaten and passed by animals, including coyote (Shreve, 1935) and taste a similar to beet, but more acidic. Invertebrates, including solitary bees (Anthophoridae, Halictidae, and Megachilidae) and sap beetles (Nitidulidae) pollinate O. phaeacantha (Parfitt & Pickett, 1980; Turner et al., 1995). The homopteran Dactylopius confusus causes severe damage to the pads (Gilreath & Smith, 1988).

Furthermore, Kingsley (1998) found the following invertebrates on O. phaeacantha in Arizona:

Coleoptera Bruchidae Mimosestes amicus (Horn)

Coleoptera Buprestidae Acmaeodera cuneata Fall

Coleoptera Cerambycidae Dendrobias mandibularis Audinet‐Serville

Coleoptera Melyridae Trichochrous indutus Casey

Coleoptera Nitidulidae Carpophilus pallidipennis (Say)

Coleoptera Rhipiphoridae unidentified

Diptera Stratiomyidae unidentified

Diptera Tephritidae Euaresta bellula Snow

Diptera Tephritidae Tomoplagia cressoni Aczel

Herniptera Coreidae Chelinidea vittiger Uhler

Hemiptera Coreidae Leptoglossus oppositus (Say)

Hemiptera Coreidae Narnia femorata Stal

Hymenoptera Anthophoridae Centris pallida (Fox)

Hymenoptera Anthophoridae unidentified

Hymenoptera Apidae Apis mellifera Linnaeus

Hymenoptera Megachilidae Lithurge apicalis (Cress.)

Opuntia phaeacantha var. major could be a successful candidate for living roofs in north central Texas as it was the only species of the 42 studied that sustained 100% survival. It established

62 and grew quickly and showed little stress. Although it did not produce fruit this first year of study, it spread through abscising pads rooting into place where they fell. It showed tremendous growth, often growing one or two pads, and sometimes three. During this study, vultures disturbed the pad during establishment, and since they had not grown sturdy roots, many came out of the soil. Even so, the pads rooted where they fell and established themselves. Cut pads were planted with the cut side in the soil; they readily grew roots from the scarred cut on the bottom of the pad. Pads lain horizontally, rather than planted vertically, showed senescing and shriveling in the heat of summer, probably stress due to too much direct sunlight during the hottest part of the day.

Yucca pallida McKelvy

Vernacular names: Pale Yucca, Pale‐leaf Yucca (Diggs et al., 1999), Life form: Rosette Subshrub, Tuft chamaephyte with thick rhizomes (N. USDA, 2008) Height: 0.3 ‐0.6m (Ladybird Johnson Wildflower Center, 2008) and 1.3‐2.5m with inflorescence (Diggs et al., 1999) Propagation type: Seeds, rhizomes and cuttings (Ladybird Johnson Wildflower Center, 2008) Duration: Perennial (Diggs et al., 1999) USDA symbol: YUPA (N. USDA, 2008) Flowers: Greenish center with white edges (Diggs et al., 1999) to white (Ladybird Johnson Wildflower Center, 2008) Federal status: Native (N. USDA, 2008) Distribution and occurrence: Endemic to north central Texas Sun/shade: Sun, will grow in partial shade, but blooms may be less showy (Ladybird Johnson Wildflower Center, 2008) Attracts: Nectar source for butterflies (Ladybird Johnson Wildflower Center, 2008) and moths, such as Prodoxus quinquepunctellus (Althoff, 2001) Phenology: Evergreen, flowers May to June (Diggs et al., 1999) Seed germination requirements: Germinates from seed held over winter if stored in the refrigerator in a sealed container of moist sand (Ladybird Johnson Wildflower Center, 2008)

Soil requirement: Good drainage, clay (Ladybird Johnson Wildflower Center, 2008) Habitat: Limestone outcrops and rocky prairies, Grand (Fort Worth) and Blackland Prairie. (Diggs et al., 1999) Elevation: 100‐400m (Song, 1999)

Yucca pallida is one of the smaller Yuccas in Texas (Ladybird Johnson Wildflower Center,

2008) and forms colonies 10‐30 rosettes (Song, 1999). It is used as an ornamental in the area, and can be purchased commercially (Cain, 2008). Research indicated that smaller individuals could be successfully transplanted due to smaller rhizomes than on the bigger specimens.

Originally thought to be Yucca rupicola (Webber, 1953), McKelvy proposed it hybridizes with

Yucca arkansana to produce a entire‐margin variety Yucca pallida var. edenta (Song, 1999).

Yucca pallida deserves more inquiry as a candidate for living roofs in north central Texas as it has a regional aesthetic, and could be hardy enough to withstand the roof environment. It is commonly used in landscaping, specifically for low moisture and full sun applications (Cain, 2008;

Ladybird Johnson Wildflower Center, 2008). Rhizomes did not seem to be very deep; rather the fibrous roots growing from the taproots went downward. None of the transplants showed signs of flowering during the first season of this study.

VIII. DISCUSSION AND CONCLUSIONS

Between the two field sites subtle contrasts were noticed between the barrens and the glades. Plant selection for this study focused on the Walnut Barrens (and more specifically those at the Fort Worth Nature Center) and did not address additional species found in the glades. Talinum calycinum is a native member of the Portulaca family growing as a perennial in north central Texas

(Diggs et al., 1999) on the glades site and, though not included in this study, is suggested by Ed and

Lucie Snodgrass (2006) as a viable, self‐sowing annual (which it may be to their native Maryland area) for living roofs. Sites were chosen from a geology that has a longitudinal range from just south of the Red River almost to Austin. Dalea reverchonii is endemic to only Parker and Wise counties

(Diggs et al., 1999), and glades and barrens are known for harboring endemics (Braunschweig et al.,

1999; Kruckeberg, 1999; Tyndall & Hull, 1999). This study has discovered only a small part of the potential for living roof plants in north central Texas.

The idea of a “living roof” can be further refined to fulfill conservation purposes such as creating habitat for endangered species, for example, Dalea reverchonii. These “conservation roofs” will challenge the current aesthetic; the Fort Worth Prairie barrens and glades offer a look and feel far different from the traditional lawn or garden. Barrens are low growing and anything but lush.

The predominant color seen in the winter is grey or brown, although the wildflower displays in spring and summer showcase brilliant reds, violets, yellows, blues and oranges. However, the conservation implications make this form of roof stunning by eliminating the hot black tar surface that contributes to environmental degradation and installing a functioning ecosystem into the areas in which they belong. Living roofs can become an asset for local biodiversity and conservation through restoration.

The Botanical Research Institute of Texas is currently pursuing a conservation design for their living roof rather than the traditional Sedum roof. This is not a decision made lightly. The designers,

Balmori Associates, are taking a risk because a conservation roof counters the aesthetic currently held. They recognize the attractiveness of restoration and which gives the roof meaning through function and sense of place.

Observations of plants’ performance suggest the argument of stability versus resilience.

Holling (1973) explains stability as the “ability of a system to return to an equilibrium state after a temporary disturbance” and resilience as “a measure of the persistence of systems and of their ability to absorb change and disturbance and still maintain the same relationships between populations or state variables.” While this study does not have multiple oscillations of disturbance, the preliminary results show characteristics of Holling’s argument through plant performance in commercial growth medium versus plant performance in native soils. Plants in the commercial growth medium treatments suffered mortality after transplant, but then showed only minor changes in growth, phenology and survival, fitting Holling’s description of a stable system. Plants in the native soil treatments suffered little mortality after transplant, grew vigorously, suffered great losses and showed stress during drought, but grew vigorously again after the drought, following

Holling’s explanation of resilience.

Holling (1973) goes on to say that the stability view emphasizes equilibrium, among other things, and that it tries to sustain similar conditions lest a chance event reduce resiliency and undermine the whole system, while “a management approach based on resilience, would be not the presumption of sufficient knowledge, but the recognition of our ignorance; not the assumption that future events are expected, but that they will be unexpected. The resilience framework can accommodate this shift of perspective, for it does not require a precise capacity to predict the future, but only a qualitative capacity to devise systems that can absorb and accommodate future events in whatever unexpected form they may take.” Lest we claim to know the intricacies of the ecosystems we are so crudely mimicking, stable behavior may not be the best option for greenroof

66 planning. A more humble resilience planning strategy might be accomplished through the use of planting natives in a native soil medium with an active seedbank.

Substrate choice effected plant‐water relations which governed plant survival during transplant and establishment. Native soil shocked the plants less than the commercial growth medium because the commercial growth medium does not hold as much water as the native soils.

While commercial growth medium is coarse in texture (Williams, 2008) to avoid clogging drainage mats with silt and clay particles (Lundsford, 2008), a coarser native soil, such as the Aquilla sands

(Soil Survey Staff, 2001), would be compatible with existing drainage mats while still potentially providing an active seedbank. More research is warranted to investigate whether the native soil provides more invertebrate and avian food and habitat, a reduction in urban heat island and pollutants, and increased production of annuals over commercial growth medium.

Observed microtopography appeared to encourage survival when plants’ surface features attracted water to the base of a plant and increased mortality when surface water was deflected away from the plant. Many of the grass clumps that died out were slightly raised above the soil surface of the test modules. Clumps were transplanted at grade, but the soil around the transplant settled while the roots of the clump prevented settling. Therefore, the transplants should be planted as deeply as possible to maximize the hydrologic benefits of microtopography. On a wide scale, planting most plants in low areas while saving the most drought tolerant species for the high areas would increase survival during establishment. Also, microtopography can increase biodiversity and habitat (Catling & Brownell, 1995) for colonizing small organisms by harboring moisture and providing shelter from the sun (Larson et al., 2000).

The transplanted perennial species which died, specifically the dead grass clumps, served ecologic function by providing germination sites for annuals. Even the commercial growth medium, which had no seedbank, produced annuals from dead clumps. Liatris mucronata only germinated

67 from Carex planostachys clumps. Paspalum setaceum only germinated from clumps of the Panicum genus (P. oligosanthes, P. hallii and P. diffusum). Transplanting large grass clumps, even if dead, may be a viable strategy for incorporating annuals into a planting plan. Dead clumps would leave more resources and reduce competition while holding the substrate in place for annual germination.

More research is warranted to investigate dead clump planting as an avenue to establish annuals in commercial growth medium.

The planting plan and annual germination produced a similar growth form spectrum as initially studied in 2007 on the Walnut barrens (Figure 19). The assumption was that the invertebrates and avian life would follow if the natural environment was closely mimicked. Casual observation noted some invertebrate and avian presence in the test modules. Further research would provide more meaningful results. Also, the convergence of similar growth form spectra in vegetation structure was initially celebrated as an indicator that the planting plan was well guided because of the similarities between growth form spectra; however, more research should be done to ascertain what further species will be noticed over time, and whether or not abundance should be taken into account as an indicator of a well mimicked restoration attempt.

The succulents tested, Opuntia phaeacantha and Yucca pallida, both lived through the experiment and showed little stress in the test modules, indicating research with other succulent species is promising. The succulents studied did not bloom this first year, so the inclusion of plants with showy blooms would be attractive additions. These two species, along with Buchloe dactyloides and Muhlenbergia reverchonii, are native species which should survive well on a living roof in north central Texas. Several others may do very well including Panicum oligosanthes, Panicum hallii,

Panicum diffusum, and Phyllanthus polygonoides.

The field sites chosen match each other well in terms of phenology of the same species, but noticeable deviances were seen in Muhlenbergia reverchonii, Liatris mucronata, Schizachyrium

68 scoparium, and Tridens albescens. These species phenologies either did not match timing or progression. This may be due to differences in site drainage (sites received similar rainfall amounts) but could also be because one is a barren while the other is a glade.

Further research is warranted in many areas. First, investigating more regional barrens and glades is needed before a suitable list of ecosystems to use as habitat templates can be compiled.

The Guadeloupe Mountains, or even the Chihuahuan Desert, would probably yield several ecosystems and numerous plant species suitable for greenroofs in north central Texas.

Furthermore, species related to those examined may prove successful as green roof species. These species might include Opuntia humifusa, Yucca rupicola or species from the Agave family. Another species to consider is Nostoc commune, a photosynthetic alga known for drought and cold tolerances, could provide valuable ecological function through fixing nitrogen (Dodd et al., 1995).

This research indicates that the Walnut barrens and glades are appropriate ecosystems to mimic as a template. Identifying four viable species, Buchloe dactyloides, Muhlenbergia reverchonii,

Opuntia phaeacantha, and Yucca pallida, is a step towards establishing a regional plant list of living roof performers. Native soil and commercial growth medium both have their place in living roof design and more innovation and research will provide better solutions to finding a suitable substrate maximizing the positive potentials of both types.

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VITA

Jonathan (Jon) William Kinder was born September 19, 1983, in Tulsa, Oklahoma. He is the Son of

Gerald and Shelley Kinder. Jonathan (Jon) graduated from Tulsa Booker T. Washington High School in 2002. His love of the outdoors and experiences as a Boy Scout and Explorer Scout led Jon to pursue a Bachelor of Science degree from Texas Christian University in Fort Worth, Texas. He graduated in 2006 with a major in Environmental Science and a minor in Computer Science.

During his undergraduate study at TCU, Jon co‐founded and served as president of the environmental science club, Aduco Viridis (to lead green). He is an active rock climber and outdoor enthusiast. Jon worked for several companies in the environmental field: as an Air Tester at Air

Hygiene Inc., Environmental Contractor at Environmental Trainers Inc., and an Environmental

Scientist at Dunaway Associates, L.P.

Jon pursed his Masters of Science in Environmental Science at Texas Christian University from 2006 to 2009 under the tutelage of Dr. Tony Burgess and Dr. Michael Slattery of TCU, as well as botanist

Robert O’Kennon of the Botanical Research Institute of Texas. As a Graduate Teaching Assistant, he taught five semesters of Principles of Environmental Science course, and with a fellow grad student

Dave Williams, formed Prairie Designs, LLC.

Jon and his wife Kathryn currently reside in Fort Worth, Worth, Texas and have no children. Jon recently founded Prairie Designs, a firm providing consulting and product development for living roofs in the southwest, with friend and business partner Dave Williams.

ABSTRACT

APPROPRIATE DESIGN ELEMENTS AND NATIVE PLANT SELECTION FOR GREEN ROOFS IN NORTH CENTRAL TEXAS

By Jonathan William Kinder, B.S., 2006 Department of Environmental Science Texas Christian University

Thesis Advisors: Michael Slattery, Ph.D, Professor of Environmental Science, Department Chair

Tony Burgess, Ph.D, Professor of Professional Practice, Environmental Science

Bob O’Kennon, Botanist, Botanical Research Institute of Texas

Living roofs, or green roofs, provide ecosystem function to rooftops. Plant selection for living roofs in North America has been dominated by members of the Sedum genus and other rocky ecosystem plants. This paper investigates the Walnut Limestone barrens and glades communities as an appropriate ecosystem from which to choose plant species for use on living roofs in north central

Texas. This study presents plant performance data from six months of monitoring five test module treatments and two field sites. Performance data suggests the Walnut barrens and glades are viable ecosystems to use as a template for plant selection. First growing season results indicate commercial growth medium substrate provides stability and predictability, while a native soil substrate provides resilience and an active seedbank for annual germination. Four species were identified as viable living roof candidates for north central Texas: Buchloe dactyloides, Muhlenbergia reverchonii, Opuntia phaeacantha var. major, and Yucca pallida.