Green Roofs plants should be selected with care.
Once a green roof plant is installed, the species becomes a significant contributor of plant DNA to the surrounding environment.
A green roof plant is perched high above most other local plant species, subject to seed dispersal by wind, rain and wildlife much more so than plants on the ground.
The proposed Gainesville, Florida's Regional Utilities Building Green Roof planting list contains species listed warned against by the University of Florida's Center for Invasive and Aquatic Plants.
|Heavenly Bamboo, Nandina domestica, Invasive Plant|
According to the University of Florida's Center for Invasive and Aquatic Plants website, Heavenly Bamboo, Nandina is not only rapidly spread through seed dispersion from wildlife foraging but "it also spreads vegetatively via suckers and rhizomes. Nandina has the habit of forming dense thickets that displace native vegetation."
The Gainesville Regional Utility's Heavenly Bamboo will be easier for birds to see and access, being planted on the roof and not hidden by ground shrubs and trees. This will facilitate the spread of the seeds to surrounding natural areas even quicker.
Importantly, the nursery industry realizes Nandina's seeds, spread by wildlife quickly sprout, displace native vegetation. According to the University of Florida's Center for Invasive and Aquatic Plants website, the nursery industry is working on developing Nandina cultivars that do not produce seed.
However Nandina also colonizes areas by thick and matted rhizome spread and regardless of seed producing or non-seed producing varieties, Heavenly Bamboo should not be used as a green roof plant in Florida.
I can recall our hikes through Indian Head Acres in Tallahassee, just south of Florida's Capitol, with the family and seeing Nandina and Ardesia taking over as the dominant groundcover shrub in what was once a Beech - Magnolia forest.
We have posted several articles about the importance of working with a botanist or landscape designer who understands native plant species when designing a green roof. The Gainesville Regional utility Center is situated only a few miles north of the important Paynes Prairie Preserve, a Florida State Park.
Allowing Nandina to spread possibly into Paynes Prairie would further compound invasive species problems in the State Park. Chinese tallow, Sapium sebiferum control has been a costly pest species for Florida to control in Paynes Prairie.
The Paynes Prairie Sweetwater Preserve Management Plan details the concerns about Nandina or Heavenly Bamboo, particularly within the Floodplain Forest areas surrounding the Prairie and indicating the targeting for eradication of invasive species as a priority.
Interestingly, the Center for Invasive Species and Ecosystem Health at the University of Georgia has developed a Google Earth-based exotic and invasive species mapping system called EDDMaps - Early Distribution and Mapping System. EDDMaps offers a fascinating insight into Heavenly Bamboo distribution across the Southeast. Heavenly Bamboo occurrences are clustered around the Gainesville area - NOTE: This link requires Google Earth .
Finally, the USDA's Forest Service, in their publication entitled Silent Invaders of Our Southern Forests references Nandina and suggests "non-native invasive plants may interrupt native succession and eventually displace an entire native ecosystem."
Planting invasive species and providing a seed source atop a building near Central Florida's springs and natural areas is easily avoidable and the planting schedule should be changed to use Florida Friendly plants species of Florida native plant species.
The Florida Friendly Landscape program, an effort of the University of Florida and Florida's Water Management Districts, offers a concise and effective website for designing with ecologically friendly water conservation and ecological concerns. Moreover, the website offers an interactive online design program to assist in selecting eco-friendly landscape plants.
Additionally, the Florida Native Plant Society offers many resources focused on preserving native ecosystems and plant communities. Their Education and Outreach webpage makes available an example list of public gardens and natural areas using native plants for landscaping.
I called the green roof design firm and spoke to a designer this morning. She indicated Nandina had been successfully used on other projects around Gainesville and they had not seen a problem with the plant and would speak with the project's landscape architect and get back in touch.
We hope the plant will be replaced with another, Florida Friendly green roof plant. I have not received a response from the landscape architect about the Nandina at the time of this blog posting. They did however ask us not to use their company name in the blog post.
However, as we've indicated before, Florida green roofs are hostile places for plants - and must take into account at a minimum, the 5 H's - hurricanes, humidity, high desiccating winds, hard freezes, horrible heat and more.
The green roof plant schedule requires some plant species well equipped for survival on the green roof, such as the Yucca filamentosa and the native Muhlenbergia grass. In fact, the design calls for no additional irrigation, an exemplary design criteria, especially as Florida is faced with a crushing water crisis.
Moreover, an irrigation system is supposedly being included in the final construction as the green roof plan also includes water dependent plant species such as Camellias, Fan Palms and Windmill Palms. We might suggest substituting Florida's native Saw Palmetto or Bluestem, Serenoa spp. for the Fan and Windmill Palms.
Ultimately, green roof design must be approached with consideration for many factors most of us do not consider, such as;
- Native or exotic invasive qualities
- Drought resistance
- Wildlife value
- Fire fuel contributor (high volatile oil content - remember how dry xmas trees burn!)
- the 5 H's and much more.
- Cleaning of nutrients from stormwater runoff (if the roof and stock plants are non-fertilized)
- Providing much needed vertical green habitat to Urban Core wildlife (such as the green Florida anole - which in turn provides superb integrated pest management)
- Creating beauty for people
- Sequestering Carbon and CO2 and providing fresh oxygen as a result of photosynthesis, and more.
As always, email us with your questions and comments here.
Happy Green Roofing!