Saturday, September 28, 2013

Nature's Living Wall, Fifty Species in Coquina Stone, Castillo de San Marco

Native plants play an important role in supporting worldwide biodiversity heritage, and offer an awesome opportunity to explore history.  Weaving history into present green roof technology is one of the most exciting aspects of touring historic places like St. Augustine, Florida.

I always love exploring the Castillo de San Marcos structure on the banks of St. Augustine inlet, just north of the Bridge of Lions.

Though not what you would expect, one of the many ways to learn about native plants on the fort park property is to 'look up'.  This week I spent several hours walking in the moat of the old Spanish Fort in St. Augustine.  Plants grow all over the rough coquina shell stone wall.

In my opinion the National Park Service has it backwards - they charge for going inside the fort but allow you to walk for free in the moat and around the grounds.  The moat is where you can see many, many native and other plants species growing in the coquina walls!

Castillo de San Marco, St. Augustine

As you can see in the above photo, most plants grow underneath the downspouts on the walls. Though the downspouts provide water primarily when it rains, they also collect dew and fog from surrounding areas and funnel the water to the plants.

Interestingly, learning about green roof and living walls plants from the fort offers insight into those plants that not only do well under the hot Florida sun and with no additional irrigation, but also the plants shed light on soil media composition.

Coquina shell and the limestome mortar have a quite high pH level.  High pH is usually one of the toughest issues to work with on green roofs and living walls.

If you are looking for native plant species that thrive and survive under harsh conditions such as; relentless sun exposure, salt spray, hot desiccating winds, heavy frosts, hurricanes without irrigation other than rainfall, then plan a trip to Castillo de San Marcos, or other similar stone structure.

It is amazing just how many different species can be found growing vertically, forming amazing living walls.  Park staff have identified over fifty different plant species growing in the coquina stone walls!  What an awesome living wall created by nature!

Samolus valerandi
Pteris vittata & 2 Cuban anoles
Wildlife seeks out plants, especially those providing resource benefit such as food or nectar or shelter.  Native plants are best suited at providing the most optimum level of ecological benefit to those wildlife endemic to an area.

In otherwords, planting native plants on green roofs and living walls encourages and supports native populations of insects, birds, reptiles, amphibians and other wildlife.

Many popular landscape plants used on green roofs may not offer the same level of resource benefit.

Learning about your local native plants broadens design capabilities for both green roofs and living walls.

Limestone & Coquina Walls are Harsh Ecosystems

Friday, September 13, 2013

Green Roofs, Many Times the Last Defense for Water Quality!

Green and living roofs are so very important to our water quality, sometimes being the last line of defense for removing pollutants before runoff enters our ecologically sensitive and important waterways.

Green roofs slow down stormwater, cleaning and sequestering pollutants 
Even small green roofs can provide a significant benefit to reducing peak runoff amounts and reducing loadings on creeks, rivers and ponds by removing nutrients such as nitrogen and phosphorous.
Blue Hole, Ichetucknee Springs
Once stormwater hits a roof and flows to the street below it may only be a matter of minutes before the water and any contaminants picked up as the volume flows across streets, drives and roads enters Florida's drinking water supply. Green roofs also moderate and attenuate the volume of stormwater leaving a building footprint.

Floating wetlands, Gainesville, Florida - greenroof on a pond
Storm drain allows pollutants to enter waterways
Florida has a unique geology across many parts of the state called Karst.  Karst formations are typified by limerock with caves, tunnels and holes throughout the  formation.  Once stormwater runoff enters the limerock above drinking aquifers the flow to the pools of underground water can be very quick.

Many times storm drains are a direct connect to water supply aquifers
Green roofs, living walls, floating wetlands and other best management practices can help keep water clean by slowing the runoff and removing contaminants from the water.

Wekiwa Springs, Florida - higher in nitrogen and algae
Wekiwa Springs, located just north of Orlando, Florida and shown above is surrounded by houses, streets, roads and commercial development.  Though many good best management practices are in place to contain nutrients and runoff, the springs still suffer from high nutrient contents such as nitrogen and phosphorous.
Salt Springs, Ocala National Forest, not as impacted by development
Salt Springs in the Ocala National Forest on the other hand, though threatened by development, does not have all the septic tanks, stormwater runoff and as you can see, the water is much clearer, contains less nitrogen and other nutrients and is so much more healthy.

Installing a green roof on your commercial or residential building is just one small contribution you can make in the Urban Core to help protect clean water supplies and ensure a healthy Florida for future generations.

Wednesday, September 4, 2013

Florida Green Roofs and Allelopathy

Allelopathy is the little referenced yet extremely important green roof secondary design principle of the bio-chemical influences certain plants and trees have on other plants and in this instance - on green roof plants.  A recent Green Roof we completed had a planting area surrounded on three sides by tall trees. Some of these trees are deciduous and loose their leaves during the winter, others like the laurel oaks keep leaf cover most of the year.


An alleopathic tree usually exerts negative influence on adjacent vegetation via a number of different processes including;
  • Fog & dew drip
  • Leaf litter
  • Volatilization 
  • Sap drip
  • Pollen
  • Other biological processes
Trees impacting the recent green roof include;
  • Triadica sebifera, Chinese tallow - western border of green roof
  • Quercus laurifolia, Laurel Oak - northwestern corner and eastern side of green roof
  • Platanus occidentalis, American sycamore - southeastern and southwestern corners of green roof

According to the University of Georgia, School of Forestry Resources , there are a number of significant allelopathic trees requiring attention when planting other plants nearby.  They include;

Strong Potential for Allelopathic Impacts 
Acacia spp
Acer saccharum
Ailanthus altissima
Celtis laevigata
Celtis occidentalis
Eucalyptus camaldulensis
Eucalyptus globulus
Eucalyptus spp 
Juglans cinerea
Juglans nigra
Leucaena spp
Myrica cerifera
Picea engelmannii
Platanus occidentalis 
Populus deltoides
Prosopis juliflora
Prunus cornuta
Prunus serotina leaf 
Quercus falcata leaf 
Quercus marilandica
Quercus rubra
Quercus stellata
Robinia pseudoacacia
Sassafras albidum
Ulmus americana


Moderate Potential for Allelopathic Impacts
Abies amabilis
Abies balsamea
Abies grandis
Acer circinatum
Acer negundo
Acer platanoides
Acer pseudoplatanus
Acer saccharinum
Aesculus glabra
Aesculus hippocastanum
Aesculus octandra
Arbutus menziesii
Carya illinoensis
Carya ovate
Corylus spp
Crataegus spp
Fraxinus excelsior
Ginkgo biloba
Gleditsia triacanthos
Juniperus monosperma
Juniperus scopulorum
Kalmia spp
Picea spp
Pinus banksiana
Pinus contorta
Pinus densiflora
Pinus edulis
Pinus elliotii
Pinus monophylla
Pinus ponderosa
Pinus sylvestris
Prunus pumila
Quercus alba
Quercus borealis
Quercus douglasii
Quercus gambelii
Quercus michauxii
Quercus shumardii
Rhododendron maximum
Rhus copallina 
Sorbus sitchensis
Tsuga canadensi



Slight Potential for Allelopathic Impacts
Abies concolor
Aesculus spp
Betula pendula
Carpinus spp
Casuarina spp
Cupressus macrocarpa
Fagus spp
Fraxinus spp
Larix decidua
Picea excelso
Pinus palustris
Pinus spp
Populus spp
Pseudotsuga menziesii
Quercus petraea
Quercus robur
Quercus rubra
Salix pellita
Sambucus racemosa
Sequoia sempervirens
Taxus brevifolia
Thuja plicata
Tilia americana
Tilia cordata
Tilia planifolia
Ulmus laevis
Ulmus parvifolia
Umbellularia californica

As mentioned, a recently completed Green Roof will be adjacent Chinese tallow trees, Laurel Oaks and American Sycamores.

Quercus laurifolia, Laurel oak - although literature suggests laurel oak does not possess allelopathic qualities, care should be given to potential impacts of pollen and flower litter.  The laurel oak adjacent the northwest corner of the green roof has stained the white TPO and covered the roofing material with a layer of leaf and pollen litter.  Though laurel oak may not exhibit direct allelopathic influence on the green roof plants, potential for covering the plants with litter exists.  Continued site inspection will be required to confirm any impacts on the green roof plantings.

Triadica sebifera, Chinese tallow - one medium height tree exists adjacent the western border of the BGC green roof.  Chinese tallow has been the subject of numerous allelopathic studies and research.  Interestingly, research exists to support the theory of Chinese tallow leaf litter and fog drip may actually support germination and shoot growth on adjacent plants.  In fact, Chinese tallow was shown to actually improve germination and growth rates in Little Bluestem, Schizachyrium


Importantly, the American Sycamores, Platanus occidentalis located in the southeastern and southwestern corners of the green roof have the potential to exert significant negative influence over the green roof plants.   As indicated in the above list, American sycamore produces strong allelopathic effects.  Data exists showing the active ingredients, scopoletin and chlorogenic acid found in the sycamore leaf may interfere with the ability of stomata on certain plant's leaves to malfunction,  interrupting the vital processes of photosynthesis and either stunting plant growth or killing the plant.  Close observation will be required on the effects of the American sycamore on the entire green roof planting area and in particular, the southeast and southwest corner plantings.  Pruning of sycamore limbs away from the green roof may be necessary.


Finally, good green roof design incorporates the effects of adjacent trees and other vegetation and allelopathic effect possibilities.  Recognizing and dealing with a potential allelopathic problem is much easier and more cost-effective up front.  Know the basics of adjacent tree and plant allelopathism and how your green roof design integrates into a site with pre-existing trees.


One of the related positive issues of anti-allelopathism and green roof adjacent trees is a benefit derived from leaf micro-nutrient content.