Saturday, February 5, 2011

Learning Green Roof Plants from the Glade

What is a Glade and why is an understanding of Glades important to Green Roof Design and development?  Native glade habitat plants can make great extensive living and green roof native plantings!

Florida Natural Areas Inventory, more commonly known as FNAI defines a glade habitat as 'a largely herbaceous community with woody inclusions that occurs on thin soils over limestone outcrops on steep topography'.

Echinacea spp. Upland Glade Plant

Glade habitats are not just restricted to Florida.  In fact there are few examples of upland glades in Florida.  Yet from Alabama to Tennessee to Wisconsin to Canada, upland glades are found across outcroppings of siltstone, sandstone, limerock, granite and other stone.

Glades can be either wet like the Everglades or quite dry as in upland glades.

Upland glades can also be found across Europe, South Africa, West Indies, Mexico and other global regions.

Blanket Flower, Gaillardia spp. Upland Glade Plant

Extensive living and green roofs possess many similar characteristics as those found in nature within upland glade habitats.  Some of these similarities include;
  • Thin soil layers
  • Herbaceous plants comprising the main vegetated component
  • No additional nutrient input other than nature provided (no fertilization)
  • Limited native hydrology
    • Some upland glades contain 'seep' hydrology, while most
    • Are subject to rain, fog or dew as water sources
  • Subject to severe fluctuations in water availability
  • Have significantly alkaline soil components
  • Are subject to moderate to high sunlight exposure due to lack of a dense forest canopy
  • Due to exposure both may experience wider and harsher temperature fluctuations
  • And others
Bidens mitis, Upland Glade Plant

A glade for instance may have soil pH of 7 to 8 while garden top soil may have a pH of 4.5 to 6.  Green Roof soil media many times has a much higher pH because of the use of expanded clay from brick or other heat treated and expanded stone.

Additionally, soils depths on extensive green roofs are normally approximately 4" in depth.  According to the FNAI data, the average soil depths of glade upland communities are similarly shallow.

Finally, without consistent groundwater supply available, glades are usually either soggy during the late rainy part of the year or extremely dry during periods of drought, typically late summer to autumn.  Living roofs, too are limited to rainfall amounts as well as other water vapor such as dew and fog (unless they are irrigated).

Many beautiful, hardy plants have adapted themselves to the relative harsher climates of upland glades.  It is these plants worth studying for inclusion in living and green roof designs.

There are many benefits of using native species such as those found in upland glades on green roofs (and of course in ground level landscaping).  Most native species typical of upland glades provide significant food value in the form of seeds and leaves for wildlife.  In fact, studies show native plants can provide more nutritional value and help support native wildlife more so than hybrid type landscape plants.  The Florida Fish and Wildlife Conservation Commission list a number of native species suitable for landscape plants, some of which are very important to wildlife as a food source.

Importantly though, when designing a green roof with glade plants it is important to specify the original native varieties and take caution with some hybrid varieties.

Glade habitats are home to some of the most beautiful and stunning wildflowers.  Echinacea (Coneflowers), for example, is a glade plant.  Because of their attractiveness and visual appeal some species are protected by Federal law from collection in the wild.  Moreover, Echinacea has long possesses important ethnobotanical qualities and is sought out, like ginseng for medicinal properties.

Even though stunning in their natural forms, some in the industrial horticultural community have taken three species of the upland glade plant Echinacea, purple coneflower (Echinacea purpurea), yellow coneflower (Echinacea paradoxa), and blacksamson coneflower (Echinacea angustifolia) and interbred to produce even brighter hybrids.  There is considerable data showing many hybrids may be sterile and not be able to deliver the same high quality food and other wildlife, bird and pollinator value as do the original varieties.   'Planting for Wildlife, Don't Go Coneflower Crazy' offers good insight into the Echinacea hybrids.

In addition to Echinacea, glade plants include;
As research points more towards the value of native plants species for pollinators, birds and wildlife and as more green roofs are established, glade habitat may well provide us with a wealth of information for green and living roof native plant design.

Sometimes nature provides obvious answers.

You may be surprised and how many parks and conservation areas in your locale contain rock outcroppings and glade type environments.  It is worth an afternoon trip with the camera and plant field guide.  You will be pleasantly surprised at what you see - flowers in the spring, summer and autumn and interesting structure.

Understanding upland glade habitats will provide the extensive, nature irrigated living roof designer with a wealth of green roof options contributing to the ultimate success of a beautiful, biodiverse and truly sustainable living roof.

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