Wednesday, January 18, 2012

Florida Green Roofs and a Terrible Drought! Looking to Poaceae

Here in Northeast Florida we continue to suffer from extreme drought.  Strange, because four hundred miles west lies the city of Pensacola with an abundance of rain.  But here in Jacksonville, a harsh, dry, period of time marked with a significant lack of water is stressing and killing plants and contributing to wildfires.

Selecting those native plant species adapted to drought survival is important for green roof designers.

Poaceae is a good place to start.

Poaceae is the family of grasses, referred to previously as Graminaceae.  According to Wikipedia, Poaceae contains about 600 genera and around 10,000 species of grasses.

Grasses comprise from 20-25% of all the herbaceous vegetation covering the earth.

Wikipedia, as other sources also suggest the Poaceae is the single most economically important family of plants in the world to humans, containing many food, grain and cereal crops, such as corn, rice, wheat and barley.

Poaceae grasses contain both C3 grasses and C4 grasses, referring to the much discussed in this blog 'photosynthesis process' type.  The above link also contains a list of commonly known C4 plants.

C4 plants have evolved a process to survive drought.  They protect compounds in their leaves, crucial to photosynthesis, from dessiccation and loss through a variety of means, including; timed stomata openings, storage of photosynthesis compounds in vacuoles and separation of photosynthesis reactions into differentiated cells.

This means they can make an excellent green roof plant or rooftop garden species.

As does corn.

Corn growing on Rooftop Garden, Sudan, photo by S. Newman

Sudan is dry.  Corn, Periwinkle and Mango thrive. Photo by S. Newman.

As you can see from the above photos, Sudan is a dry and arid place, hostile to most plants.

However corn, a Poaceae family member thrives on a hot, dry, windy roof.

MetroVerde also grows corn on roofs, and the plants will grow well in places most others would wilt in a matter of days.

Other grasses too, members of the Poaceae family adapted to drought make excellent green roof plants.  many are perennial and evergreen species, affording year in and year out color and texture, supporting biodiversity with food and communal shelter, providing beauty, cleaning stormwater and reducing heat island effect.

Purple muhly grass, Muhlenbergia capillaris, is another of my favorite green roof Poaceae.

Green Roof Muhly Grass, photo by C. Burkee.
Purple muhly gras, excellent C4 green roof grass.
There are many other grasses available and suitable for green roofs.  Preferring to use native species, I consult with local nurseries in an area to see what they recommend for drought tolerance.

Your local native plant society is also a good resource for grasses recommendations.

The beauty of the Poaceae family is that they have been around a long time on this earth and survive in the most inhospitable of places.

Try Poaceae on your next green roof!

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