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ASLA 2014 Annual Meeting and EXPO

Prairie Green Roofs: High Plains, Great Plains, and Beyond

Presenters Dr. Richard K. Sutton, FASLA, UN-Lincoln Peter MacDonagh, FASLA, Kestrel Design

Andy Creath, Green Roofs of Colorado


Prairie & Green Roof: Similarities & Differences

Great Plains vegetation is largely defined by water available after losses due to evapo-transpiration

Green Roof vegetation is largely defined by water available after losses due to evapo-transpiration


Learning Objectives 1.  Learning Objective #1 Examine key aspects of prairie plant

establishment and relate it to green roofs.

2.  Learning Objective #2 Understand the links between media and plant establishment, growth, and diversity.

3.  Learning Objective #3 Distinguish the advantages and disadvantages of diverse prairie plantings and sedum mono-generic cultures.

4.  Learning Objective #4 Describe the key elements of green roof maintenance.



•  Prairie Biomes –  Tall-grass (East) –  Mixed-grass –  Short-grass (West)

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These also stress green roof plantings: 1.  Negative Water Balance 2.  High Winds 3.  High Insolation 4.  High Summer Temperatures 5.  Low Winter Temperatures 6.  Diurnal & Seasonal Temperature Fluxes 7.  Long & Short-term Drought Oscillations



The main difference between prairie and green roof environments lies in the depth and composition of the rhizosphere.

No deep moisture is available in shallow green roof substrates.

Water holding clay fraction eliminated

Green roofs in drought need to be irrigated, just not heavily so.


Sedum vs. Diverse Native Prairie Plantings

Sedum Green Roof (Image Kestrel Design Group)

Prairie Green Roof (Image Kestrel Design Group)


• Glades with shallow soil • Sand prairies • Shortgrass prairies

Kimball Co., NE Thomas Co., NE Lancaster Co., Ne Shortgrass Prairie Sandhills Blowout Sandstone Prairie

Regional Templates

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Regional Influences on Species Selection

Bluff Bedrock Prairie Southern Minnesota


Every state or region has its own set of potenDal templates


Examples of prairie green roof

Municipal Building Commission, Minneapolis, Minnesota (Images © Kestrel Design Group)


M C L

P E E C M C L

M C L

Schizachyrium scoparium little bluestem

Frequency Abundance 100 19

East Central Minnesota Bedrock Bluff Prairies

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Green Roof Experiments, Trials and Observations in Nebraska

•  Substrate depth and quality •  Mychorrhizae, biomass, and fertility •  Planting propagule choice and

establishment time •  Seeding, recruitment, and cover •  Native grass seeding to reduce costs


Materials and Methods

•  Pioneers Park Nature Center: –  Native grasses & forbs planted in twelve, 1.83 m by

1.83 m (6’ X 6’) plots in an 3.1cm X 3.1cm (8” by 8”) grid of 64, 72 cells dibble boarded into the substrate


Results

Least Squares Means for Treatment Comparisons (Significant at P<0.05)

Effect trtmt trtmt Std. Est. Error DF t-Value P>tControl v Inoc 1 2 -0.1167 0.086 8 -1.36 0.2111Control v Gel 1 3 -0.3444 0.086 8 -4.01 0.0039Control v Inoc*Gel 1 4 -0.5556 0.086 8 -6.48 0.0002Inoc v Gel 2 3 -0.2278 0.086 8 -2.65 0.0291Inoc v Inoc*Gel 2 4 -0.4389 0.086 8 -5.12 0.0009Gel v Inoc*Gel 3 4 -0.2111 0.086 8 -2.46 0.0393


•  Obvious visual differences in robustness and color between control and interaction Control

Inoc*Gel Interaction

Discussion

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Seeding, Recruitment, and Cover

•  Arbor Day Foundation Ultra-Extensive G. R.: –  37.2 m2 (400 ft2) with 5 cm (2 inches) of Carlisle

lightweight extensive over a moisture retention pad

20’ X 20’ Plot Area in sea of Sedum spp.


Results


Propagule Choice, Size & Timing

•  Sandhills Publishing G. R. •  185.8 m2 (2000 ft2) with Semi-intensive 15.8 cm (6-in) of

custom substrate blend; hand irrigated as needed

Native Plant Trial Garden

Native Grass Seeding Plots Trial Garden


Objectives

•  Seeding density study for 5 native grasses

•  Study time to

cover: Four months from seed!!

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Results


Native seeding to Reduce Costs

•  Larson Building-Parkhouse Apartments G. R. •  557 m2 (6000 ft2) variable depth 10-15.8 cm (4-6-in) of

Midwest Trading Extensive substrate; irrigated as needed


Objectives

•  Seeding but not by hand

•  Compare cost and coverage of seeding to Sedum


Maintenance to the Design Intent •  Necessity •  Installation: Delivery to planting •  Establishment: Coverage time •  After Establishment

– Weeding, clean-up, and drainage – Annual fertility testing and application –  Irrigation

•  Documentation

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Maintenance to the Design Intent •  Necessity •  Designing for Maintenance •  Installation: Delivery to

planting •  Establishment: Coverage

time •  Post-Establishment •  Documentation


Necessity • There is no such thing as a maintenance-

free roof • Ensures that the design intent is fulfilled

and plants are healthy • Saves long-term costs in repairs and re-

roofings


Necessity • To comply with manufacturer warranties • To maintain aesthetic appeal of roof

• To help comply with voluntary standards, local regulations/incentives, building codes, and insurance requirements


Challenges

• No maintenance plan • Lack of budget • Belief that a green roof is maintenance-free • Designed without regard to maintenance • Improperly trained maintenance staff

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Designing for Maintenance •  Safety •  Roof Access •  Water

Access •  Plant

Selection


Designing for Maintenance

•  Maintenance requirements at each stage

•  All parties involved consider impact on maintenance

•  Identify owner expectations early and design to it

•  The type and design intent play a major role in maintenance requirements and cost


Installation: Delivery to planting •  Ensure plant

health at arrival

•  Verify water access if necessary

•  Stockpile in shady area until planting


Establishment •  Visit at higher

frequencies •  Ensure healthy plant

development •  Verify proper drain

function •  Check and adjust

irrigation •  Weed, prune, and

remove debris •  Check for disease

and pests

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Post-Establishment •  Visit less frequently

•  Ensure healthy plants •  Test for annual fertility and

apply amendments if necessary

•  Verify proper drain function •  Check and adjust irrigation •  Weed, prune, and remove

debris •  Check for disease and pests


Documentation Site visitation documentation should include the following information:

•  Date and time of visit •  Maintenance performed •  Overall health of green roof •  Time spent on roof •  Testing that was performed •  Amendments used/applied •  Weather conditions (current and recent) •  Photographic documentation


Summary

•  Native prairie plantings can make it on extensive green roofs (Peter)

•  Flammability issue (Richard) •  Reduced costs (Richard) •  Establishment and plant selection is

critical (Andy) •  Minimal yet informed maintenance (Andy)

Documents

Prairie & Green Roof: Similarities & Differences Prairie ... · PDF file20’ X 20’ Plot Area in sea of ... • Stockpile in shady ... ASLA_2014_Ed_Session_AO1_DRAFT2.2.ppt Author: