Plant Performance Research 2 PLANT SPECIES ...

2R: Plant Performance Research 2 PLANT SPECIES FINDINGS FROM THREE WATER CONSERVING GREEN ROOFS IN TEXAS Bruce Dvorak1, Brooke Byerley 2, Astrid Volder3 Texas A&M Department of Landscape Architecture and Urban Planning / 2Botanical Research Institute of Texas (BRIT)/ 3Texas A&M Department of Horticultural Sciences

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Abstract Extensive green roofs are beginning to emerge across dry and warm climates that require water conservation practices. We report plant findings from green roof research in three different climates of Texas and report plant establishment findings. Experimental Green Roof #1 is a 20,000 s.f. green roof in Fort Worth, Texas, where twenty-five of thirty-eight native prairie species became established with 15.7 to 27.6 mm of irrigation per week the first growing season and limited irrigation thereafter. In Experimental Green Roof # 2, in south-central Texas, modular green roofs were used to examine establishment of 22 native and exotic species. Irrigation varied but ranged from no irrigation to 5.3 mm for the first 8 weeks. Four species had no mortality and seven species demonstrated varied degrees of establishment. Experimental Green Roof # 3 was a multi-level roof located in Houston and was planted with eight exotic species irrigated with 12.7 mm/wk from harvested rainwater. All species in Experimental Green Roof # 3 had survivors. In summary, forty-five candidate species are indentified for possible use on green roofs in Texas with water conservation practices. These findings will help create baseline expectations for sustainable green roofs in Texas. Introduction Texas is an emerging green roof market with much potential for growth (23.2 million urban residents in 2012 and 24.7 by 2015). According to the Texas Water Board, water as a resource will continue to become more scarce and costly in Texas due to urban growth and climate change [1]. Thus development of economically and environmentally sustainable green roofs in Texas is dependent upon knowledge of plant species performance and efficient use of water. Texas’ climate and geography are diverse. From east to west precipitation decreases from wet to dry with 1422 mm (56 inches) of precipitation per year along the eastern state boundary to 1 CitiesAlive!: 10th Annual Green Roof and Wall Conference 2012 Conference Proceedings

less than 254 mm (10 inches) along the western boundary [2]. The USDA cold hardiness ranges from zone 6b in the northwestern panhandle to zone 10a at the southern boundary near Mexico [3]. Topographic elevations range from mean sea level along the Gulf of Mexico where coastal plains and prairie typify the landscape, where the hill country region dominates the midsection of the state with prairie and savanna, and mountainous regions dominate the west with a high elevation of 3750 m in the Guadalupe Mountains where desert plant communities prevail. The climate of central Texas, unlike its more consistently dry western geography and wet eastern geography, is variable with reliably warm temperatures during the summer, but unreliable precipitation from year to year, which makes it a challenging environment for plant establishment and survival as variation seems to be its only constant [4]. Central Texas was historically dominated by oak savanna and tall grass prairie plant species. Many species of prairie vegetation persists through drought and heat stress with their deep fibrous roots or through dormancy. There are only a few succulent species of plants found growing in some prairie habitats. Materials and Methods This paper reports plant performance research findings from three different ecoregions in Texas (north, central and southern regions), each with different plant establishment methods and different approaches to watering including: no irrigation, restricted irrigation and frequent irrigation from harvested rainwater. The research methods varied per site, as did the size, and complexity of the green roofs. Climate norms and values are presented for each research site in Table 1. Overall, the regions were drier and warmer than normal for many months throughout the investigation periods. Experimental Green Roof #1-Fort Worth, Texas The 20,850 s.f. North Texas research site is located on top of a two-story building at the Botanical Research Institute of Texas. The overall roof design mimics a natural, thin-soiled, limestone prairie habitat that requires minimal inputs once established. The modular roof system is comprised of nearly 5,700 biodegradable coconut fiber trays (BioTray, Tremco Roofing). In July 2010, each 0.19 m2 (2 s.f.) tray was planted with six native Texas species (five 10-cm transplants and a sixth annual species from seed) from a list of 38 total test species. Test species were chosen based on their adaptation to thin, dry soils and their nativity to a specific local habitat, the Goodland Limestone Prairie Barrens. The trays held approximately 7.5 cm of growing media with another 5 cm of media below the trays. Media beneath the trays consisted of 1:1 calcareous sandy loam topsoil (CSL) and commercial aggregate media (LiteTop mix; American Hydrotech, Inc.). Media within the trays consisted of a lower 3.8-cm layer of 1:1 CSL and hadite; an upper 2.5-cm layer of 1:1:2 CSL, hadite, and biologically active Goodland Limestone topsoil harvested from a local prairie; and a 1.2-cm gravel mulch layer on top. Layered between the media and monolithic roof membrane were a fine mesh filter fabric, an aggregate-filled drainage layer (Gardendrain GR30 and LiteTop Aggregate; American Hydrotech, Inc.), polystyrene foam insulation, a drainage mat (Hydrodrain 300, American Hydrotech, Inc.), and a copper-based root protection sheet (Hydroflex RBII, American 2 CitiesAlive!: 10th Annual Green Roof and Wall Conference 2012 Conference Proceedings

Hydrotech, Inc.). The drainage system was designed to retain 7.6 l/m2 with a flow rate of 479 l/min/m. One hundred percent non-potable irrigation was achieved by using harvested stormwater and an on-site underground spring. In addition to natural rainfall, all plants received approximately 15.7 mm/wk supplemental, dry-season irrigation (May–Sept) during the first 12 months of establishment (Aug 2010–Aug 2011), with additional irrigation during extreme drought conditions in June-July 2011. At the end of the growing season, irrigation tapered to 7.85mm/wk for two weeks and then ceased completely until the beginning of the following dry season (May 2012). Plant survival was assessed 18–22 months after initial planting during March-June 2012 using centralized replicate sampling of 0.25 m2 roof plots whereby every species in a plot was identified and documented. Plot size was chosen based on species accumulation curves created in the native prairies the roof was designed to mimic. Experimental Green Roof #2-College Station, Texas The College Station research is located on top of a four-story building at Texas A&M University. Twenty-one 11.2-cm-deep modular green roof trays were planted over three growing seasons. The 0.37 m2 (4 s.f.) plastic trays (TectaAmerica Corp, Skokie, IL) each contained a 8.9 cm depth of FLL compliant growing media for extensive green roofs (Rooflite®drain, Skyland USA LLC), a non-woven moisture retention geotextile, thirty-six 2.5 cm deep drainage retention cups filled with expanded shale, and various species were planted in the modules from April 2009 to April 2012. Drainage for each tray is facilitated from twelve 0.95 cm (diameter) holes located about 2 cm above the bottom of the drainage retention cups. Water holding capacity is rated at 24.38 mm depth of water if the water retention cells are left void. The trays were designed to retain precipitation to both retain moisture for plants and reduce stormwater runoff. Trays were irrigated with 5.3 mm of tap water once a week as needed during the first two to eight weeks of plant establishment. Experimental Green Roof #3-Friendswood, Texas The experiment in Friendswood, Texas, was located on a one-story building. An existing green roof was replanted with eight drought resistant plants produced by Ozbreed Ltd, an Australian based plant breeding company [5]. The plugs were planted in groups of six into existing green roof media that was 15 cm deep and composed of expanded shale (60%), leaf mold compost (30%) and enriched loam (10%), as well as some fertilizer [5]. Plants were planted on January 15, 2009 and watered with on-site recycled water three times per week at 4.2 mm per irrigation (12.7 mm per week) until July 19, 2009. During this period a total of 619 mm in rainfall was recorded. On July 19, half of the surviving plants stopped receiving irrigation, while the other half received 25.4 mm drip irrigation per day (daily complete saturation of the growth media, as practiced by the building owner on other areas of the roof).

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Table 1. Climate characteristics for Fort Worth, College Station, and Houston, Texas (Friendswood). Monthly means and annual means are presented regarding precipitation (mm), maximum and minimum temperatures (°C) compared to study period summaries. Bolded numbers indicate a 10% or greater deviation from the monthly or annual mean. Forth Worth, TX

Jan

Feb

March

April

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Annual

Mean precipitation (mm)

54.10

67.56

88.14

76.96

124.46

97.54

54.86

48.51

64.77

106.83

68.83

65.28

918.21

2011-2012 mean (mm)

40.64

23.37

1.78

62.48

201.93

72.14

2.29

24.38

16.76

79.25

21.84

110.49

657.35

Mean max. temp. (°C)

13.6

15.8

20.2

24.6

28.7

33.0

35.4

35.7

31.4

25.7

19.4

14.0

24.8

2011-2012 mea (°C)

12.1

16.1

22.5

27.9

28.6

36.4

38.7

40.2

33.6

26.6

20.2

13.5

26.4

Mean min. temp. (°C)

1.9

4.1

8.3

12.6

17.9

21.9

23.9

23.9

19.8

13.8

7.9

2.8

13.2

2011-2012 mean (°C)

-0.1

3.4

10.1

15.1

16.7

24.4

27.2

28.1

19.7

13.6

8.6

3.8

14.2


80.52

69.85

81.03

64.52

114.81

110.50

55.12

68.33

84.33

124.21

78.99

79.50

1016.3

2010-2011 mean (mm)

75.18

42.91

41.91

13.97

68.07

150.36

16.00

7.87

101.6

11.94

41.91

53.85

625.57


16.17

18.22

22.11

26.11

29.89

33.22

34.94

35.61

32.56

27.50

21.72

16.94

26.3

2010-2011 mean (°C)

15.22

16.09

23.08

28.66

31.97

35.05

36.11

39.08

34.38

29.13

23.22

17.88

27.49


4.78

6.61

10.22

14.17

18.94

22.28

23.33

23.33

20.44

15.39

10.00

5.44

14.6

2010-2011 mean (°C)

3.66

4.66

10.44

16.05

19.08

24.08

24.91

25.41

21.69

14.58

10.22

6.72

15.13


85.85

81.03

86.61

84.07

129.29

150.62

96.27

95.50

104.65

144.53

-

-

-

2009 mean (mm)

12.44

38.60

103.63

263.65

9.65

6.85

72.14

53.59

118.87

334.26


17.11

19.0

22.72

26.38

30.2

33.0

34.3

34.7

32.1

27.26

-

-

-

2009 mean (°C)

19.16

22.44

22.88

25.88

30.88

35.94

36.00

35.77

30.55

26.83


5.8

7.7

11.0

14.9

19.8

22.9

23.9

23.8

21.0

15.7

-

-

-

College Station, TX

Houston, TX

10.00 2009 mean (°C) 5.22 11.38 14.77 20.38 23.66 25.5 24.44 21.66 16.5 Note: Above data is from NOAA Online Weather Data, NOWData 1981-2010. http://www.srh.noaa.gov/hgx/?n=climate_cll. Data not collected at Houston research site during November to December 2009.


Findings From these green roof studies, forty-five candidate species have been identified for potential use on extensive green roofs in Texas (Table 2). These results are from a limited data set and short-term establishment periods. Actual performance in similar climates may vary depending upon green roof substrate design, irrigation regimes, maintenance practices and departure from the climate norms during establishment. Candidate species are species with evidence of survival of at least 20% during the experimental periods or evidence of the species establishing from seed (Table 2). Species in the unsuccessful list are those with less than 20% survival and were observed to not perform well.

Experimental Green Roof #1-Fort Worth, Texas Twenty-five candidate species were identified at the North Texas research site. These include 13 forbs, 8 graminoids, and 4 succulents. Five species did not survive in the form of the original transplants, but they did germinate and become established from latent seeds that came in with the native prairie topsoil. These species are differentiated in Table 2. The four most successful species in terms of speed of establishment, overall growth, and spread were Bouteloua curtipendula var. curtipendula, Bouteloua dactyloides, Dyschoriste linearis, and Opuntia phaeacantha. Several unsuccessful species, such as Asclepias asperula, Convolvulus equitans, and Oenothera macrocarpa, may have failed due to poor quality of transplants or transplant shock while other species, such as Callirhoe involucrata and Carex planostachys likely failed because they could not tolerate the calcareous soil. Experimental Green Roof #2-College Station, Texas Twelve candidate species were identified for south-central Texas. Five species had no losses and are likely to survive without irrigation including Graptopetalum paraguayense, Malephora lutea, Manfreda maculosa, Portiluca pilosa and Talinum calycinum. Seven species demonstrated survivors including Bulbine frutescens, Delosperma cooperi, Lampranthus spectabilis ‘Red Shift’, Lupinus texensis, Sedum album f. ‘Murale’, Sedum kamtschaticum, and Stipa tenuissima but may need some irrigation to thrive. Nine species had no surviving plants including Allium senescens ‘Glaucum’, Delosperma nubigenum ‘Basutoland’, Delosperma ‘Psfave’ Dichondra argentea, Stemodia lanata, Myoporum parvifolium, Sedum mexicanum, Sedum moranense, Sedum moranense ‘Grandiflorum’, and Sedum tetractinum. Experimental Green Roof #3-Friendswood, Texas During initial establishment of Dianella caerulea ‘Cassa Blue’, Dianella revoluta ‘Baby Bliss’, Dianella revoluta ‘Big Rev’, Dianella revoluta ‘Little Rev’, Dianella tasmanica ‘Tasred’, Lomandra hystrix ‘Tropic Belle’, Lomandra longifolia ‘Breeze’,and Lomandra longifolia ‘Katrinus Deluxe’ only four cultivars showed some mortality. Lomandra longifolia ‘Katrinus Deluxe’ performed the 5 CitiesAlive!: 10th Annual Green Roof and Wall Conference 2012 Conference Proceedings

worst with only 50% establishment, while Dianella revoluta ‘Baby Bliss’ had a 67% establishment rate and Lomandra hystrix ‘Tropic Belle’ and Lomandra longifolia ‘Katrinus Deluxe’ had an 83% establishment rate [5]. Surprisingly, after initial establishment (January 15 July 19, 2009) no more plants were lost between then and October 30, 2009, regardless of irrigation. Plants received an additional 575 mm in rainfall between July 19 and October 30, 2009. Overall quality rating at the end of the summer (October 30, 2009) was highest for Dianella caerulea ‘Cassa Blue’, Dianella revoluta ‘Big Rev’, and Dianella revoluta ‘Little Rev’, which were also cultivars that had a 100% survival rate throughout the trial. Quality ratings were not affected by irrigation treatment. [5] Conclusions Our investigation demonstrates the effectiveness of forty-five candidate species for extensive green roofs in three different climates in Texas. Three different watering approaches were used to test the species varying from no irrigation to irrigation applied multiple times per week with harvested rainwater. We conclude that irrigation is likely an important component of establishing extensive green roofs in Texas; however, it may be possible to maintain green roofs with little to no supplemental watering once vegetation is established. One key component of implementing a water conservation approach to plant establishment is communication of maintenance and watering practices to owners and managers of green roofs. These findings help establish baseline expectations for sustainable green roofs in Texas.

References 1. 2. 3. 4. 5.

Pittman R., et al., Water for Texas 2007, 2007, Texas Water Development Board: Austin, TX. p. 44. Larkin, J.T. and W.G. Bomar, Climatic Atlas of Texas, 1983, Texas Department of Water Resources: Austin. p. 157. USDA Agricultural Research Service, USDA Plant Hardiness Zone Map, 2012, 2012, U.S. Department of Agriculture: Washington D.C. Arnold, M.A., Landscape Plants for Texas and Environs. Second ed. 2002, Champaign, IL: Stipes Publishing. 1088. Camerino, A.W., C.S. Brouwer, and A. Volder, Evaluation of Landscape Plants for Use on Green Roofs in the Texas Gulf Coast Area, in SNA Research Conference, D.N. Gawel, Editor 2011, Southern Nursery Association. p. 10.


Table 2. Extensive green roof plant species establishment findings for three Texas research sites. Candidate species are those with an estimated 20% or greater survival, or successfully established from seed. Genera Species Nativity USDA Cold Life-form Irrigation Irrigation Hardiness Rate Duration Zone Fort Worth Candidate Species Bouteloua curtipendula var. Texas 3-9 graminoid 15.7 mm/wk 12 mo* curtipendula Bouteloua dactyloides Texas 3-10 graminoid 15.7 mm/wk 12 mo* Dichanthelium oligosanthes var. Texas 3-9 graminoid 15.7 mm/wk 12 mo* scribnerianum Digitaria cognata Texas 4-10 graminoid 15.7 mm/wk 12 mo* Dyschoriste linearis Texas 7-10 forb 15.7 mm/wk 12 mo* Erioneuron pilosum Texas 6-9 graminoid 15.7 mm/wk 12 mo* Escobaria missouriensis Texas 4-10 succulent 15.7 mm/wk 12 mo* Gaillardia pulchella Texas 3-10 forb 15.7 mm/wk 12 mo* Hedeoma reverchonii Texas 7-10 forb 15.7 mm/wk 12 mo* Heliotropium tenellum Texas 6-9 forb 15.7 mm/wk 12 mo* Liatris aestivalis Texas 7b-8 forb 15.7 mm/wk 12 mo* Lupinus texensis Texas 3-8 forb 15.7 mm/wk 12 mo* Marshallia caespitosa Texas 5-9a forb 15.7 mm/wk 12 mo* Minuartia michauxii Texas 3-8 forb 15.7 mm/wk 12 mo* Muhlenbergia reverchonii Texas 6-10 graminoid 15.7 mm/wk 12 mo* Opuntia phaeacantha Texas 5-10 succulent 15.7 mm/wk 12 mo* Phemeranthus calycinus/calcaricus Texas 5-9 succulent 15.7 mm/wk 12 mo* (Talinum) Phyla nodiflora Texas 6b-13 forb 15.7 mm/wk 12 mo* 7 CitiesAlive!: 10th Annual Green Roof and Wall Conference 2012 Conference Proceedings

Genera

Species

Nativity

Schizachyrium Scutellaria Stenaria Tetraneuris Thelesperma Tridens Yucca

scoparium drummondii nigricans scaposa filifolium muticus var. elongatus pallida

Fort Worth Unsuccessful Species Aristida purpurea Asclepias asperula Callirhoe involucrata Carex planostachys Convolvulus equitans Glandularia bipinnatifida Hymenopappus tenuifolius Oenothera macrocarpa Panicum hallii Salvia engelmannii Salvia texana Senna roemeriana Setaria reverchonii

Life-form

Irrigation Rate

Irrigation Duration

Texas Texas Texas Texas Texas Texas Texas

USDA Cold Hardiness Zone 3-10 7-10 5-10 4-9 5-11 6-8 7b-8

graminoid forb forb forb forb graminoid succulent

15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk

12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo*

Texas Texas Texas Texas Texas Texas Texas Texas Texas Texas Texas Texas Texas

3-10 6-9a 4-10 7-9 5-10 4-10 3-9 4-8 6-10 7-9a 7-10 8-10 7b-10

graminoid forb forb graminoid forb forb forb forb graminoid forb forb forb graminoid

15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk 15.7 mm/wk

12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 12 mo* 8

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Genera

Species

College Station Candidate Species Bulbine frutescens Delosperma cooperi Graptopetalum paraguayense Lampranthus spectabilis ‘Red Shift’ Lupinus texensis Malephora lutea Manfreda maculosa Nassella tenuissima Sedum album f. ‘Murale’ Sedum kamtschaticum Phemeranthus calycinus (Talinum) Portulaca pilosa College Station Unsuccessful Species Allium senescens ‘Glaucum’ Delosperma ‘Psfave’ (Lavender Ice) Delosperma nubigenum ‘Basutoland’ Dichondra argentea Myoporum parvifolium

Nativity

USDA Cold Hardiness Zone

Life-form

Irrigation Rate

Irrigation Duration

S. Africa S. Africa Mexico S. Africa Texas S. Africa Texas Texas Asia Asia Texas

8b-11 6 8b-11 8a-10b 3-8 8-11 7 6 3-11 4 6

succulent succulent succulent succulent forb succulent subshrub/forb graminoid succulent succulent succulent

5.3 mm/wk 5.3 mm/wk 5.3 mm/wk 5.3 mm/wk 5.3 mm/wk 5.3 mm/wk 5.3 mm/wk 5.3 mm/wk 5.3 mm/wk 5.3 mm/wk 5.3 mm/wk

2 wks 2 wks 2 mo 2 mo 2 mo 2 mo 2 mo 2 mo 2 wks 2 mo 2 wks

S. USA

6-10

succulent

5.3 mm/wk

2 wks

Europe S. Africa S. Africa

4-8 4-9 5

bulb succulent succulent

5.3 mm/wk 5.3 mm/wk 5.3 mm/wk

2 wks 2 wks 2 wks

S. USA Australia

10-12 9-10

forb creeping

5.3 mm/wk 5.3 mm/wk

2 mo 2 mo 9

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Genera

Species

Nativity

USDA Cold Hardiness Zone

Sedum Sedum Sedum

mexicanum moranense moranense ‘Grandiflorum’ tetractinum lanata

C. America Mexico Mexico

8 8 8

China Texas

7 8a-11

Sedum Stemodia

Houston Candidate Species Dianella caerulea ‘Cassa Blue’ Dianella revoluta ‘Baby Bliss’ Dianella revoluta ‘Big Rev’ Dianella revoluta ‘Little Rev’ Dianella ‘Tasred’ hystrix Lomandra ‘Tropic Belle’ Lomandra longifolia ‘Breeze’ Lomandra longifolia ‘Katrinus Deluxe’

Australia Australia Australia Australia Australia Australia Australia Australia

Life-form

Irrigation Rate

Irrigation Duration

shrub succulent succulent succulent

5.3 mm/wk 5.3 mm/wk 5.3 mm/wk

2 mo 2 wks 2 wks

succulent forb

5.3 mm/wk 5.3 mm/wk

2 wks 2 mo

forb forb forb forb forb forb forb forb

12.7 mm/wk 12.7 mm/wk 12.7 mm/wk 12.7 mm/wk 12.7 mm/wk 12.7 mm/wk 12.7 mm/wk 12.7 mm/wk

5 mo. 5 mo. 5 mo. 5 mo. 5 mo. 5 mo. 5 mo. 5 mo.

*Irrigation was suspended during the cool season within the first 12 months (August–August).
