Tuesday, October 26, 2010

Preventing Green Roofs and Green Roof Plants from Becoming Vectors of Exotic Invasives Species

Green Roofs provide many benefits.  We have mentioned many of the positive facets of green roofs in past blogs, in presentations and in our passion to see Green Roofs become a part of every sustainable and green project.

Our motto - "Restoring Volumetric Green to the Urban Core'" reflects our beliefs plants need to be in our homes, buildings and cities.  Green Roofs and Living Walls clean stormwater, provide wildlife with habitat, they create a sense of place for people, sequester carbon, uptake CO2, pump oxygen into our atmosphere, remove pollutants, prevent and cure cancers, provide food and the list goes on and on.

Plants are living organisms with many purposes!  They eat sunshine and convert the sun's energy into a host of benefits for our world.

These are some of the reasons we love Green Roofs and Living Walls.

With passion comes responsibility too.  As a certified arborist I hear the phrase - 'Right Tree, Right Place' and 'Right Plant, Right Place' many times a week.

The same slogan should hold true for Green Roofs and Living Walls.  In our rush to install volumetric green in the Urban Core we should not forget to remember some plants are considered aggressive and invasive in certain locations.

Florida, for instance has designated certain plant species to be exotic and invasive.  Typically those plant species are so aggressive they out compete native species - and can form monoculture stands.  For more information on Florida's Exotic and Invasive Plants click here.

I am working with a University here on installing a small green roof and a series of living walls and the University Botanist and Natural Area curator expressed concern about the selection of species to be used on both the roof and walls.

The University policy specifies using only native species or Florida Friendly Species that are not aggressive.  This holds especially true when working near the conservation and natural areas on the campus.

Seed source potential was another question addressed.

Green roof plants with tiny, lightweight seeds will serve as seed sources to surrounding areas with wind and bird dispersal.

Planting a non-native plant on a green roof almost always guarantees the plant will eventually spread into adjacent areas.  Of course the heavier the seed the less likely and slower the spread potential becomes.

It is possible some of the more popular non-native, drought tolerant ground covers could potentially become a nuisance in natural areas.

In our rush to grow green everywhere, let's make sure the plants we are using are compatible with surrounding environments.  Plant selection should always be coordinated with an area conservation botanist to ensure compatibility.

The below photo shows an Allium species on a Florida Green Roof with dried seed ready to drop.   The seeds are large and heavy enough to prevent wind from scattering them about the adjacent areas.  When they do fall from the dried flower stems, they will drop to the green roof and hopefully germinate with spring rains.

Green Roof Seeds - Allium
Choosing native species and non-invasive species is an important part of designing a successful green-roof.

As always - email us with your questions!

Happy Green Roofing!


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