Florida’s Coastal Dunes and Green Roof Design

Florida’s coastal sand dunes provide a wonderful opportunity to study native plants who may be suited for green roofs in hot, dry and windy climates.

We will be working with the Jacksonville Zoo and Gardens on a spectacular native plant green roof soon, I need some fresh, new plant perspectives and know where to go for inspiration.

The sunlight intensity of coastal dunes is intense, much like thousands of small shimmering mirrors reflecting and focusing bright, hot solar radiation across the ground.

Yet immediately leeward of the shoreline dune ridge lies acres of lush, beautiful vegetation growing with nature’s irrigation and without additional fertilizers added.

One of the hardiest dune plants is the pantropic Railroad vine, Ipomoea pes-caprae, a wonderful pollinator attractor for harsh ecosystems.  The flowers shown above are literally buzzing with a number of insects, many flowers fought over by multiple bees, wasps and other bugs.  Railroad vine, though frost tender can make a good addition to native plant green roofs, providing fast coverage and unmatched color.

A little on the weedy side (my style) but nevertheless a wonderful native plant for all type of wildlife, Painted leaf is a reliable native offering a muted poinsettia scheme and obviously adored by Lepidoptera.

Strikingly unique, Coral bean, Erythrina herbacea is one tough plant exhibiting C4 type forms of photosynthesis and growing directly under salt spray areas along the beach dune ridge.  Her berries possess dark and hypnotically inviting beauty, yet ingested she is curare-like paralyzing.

Of course the Poaceae family is always well represented along the dunes and preforms just as well on green roofs.  You may well see Spartina patens, Panicum amarulum and Uniola paniculata.  Poaceae also utilize water conserving photosynthesic traits, breaking the Calvin cycle down into reactions occurring embedded within vacuoles beneath the leaf epidermis, resisting desiccation.

We love to use native grasses on green roofs and the sand dunes are the perfect place to witness growth, habit and hardiness.

Though deciduous, Virginia creeper offers great summer greenery and vivid harvest season color.  Many consider the agressive growth patterns of Parthenocissus ‘weedy’. Here Virginia creeper was growing only meters away from the watermost dune ridge, a testimony to her salt tolerance and hardiness.

Virginia creeper’s fruit is sought out and devoured principally by many bird species especially on the green roofs!  However in ground level landscapes many small animals utilize the plant fruit for forage.  I’ve seen deer munching on ripe berries and leaves.

Passiflora incarnata is yet another great seashore plant we use in green roofs. Passion vine’s amazing flower opens with dawns first light, sharing royal hues of purple and bright whites with buzzing and crawling dune insects.  I actually pick the fruit pictured in the below photo for a tasty snack.

Passiflora combines fast, rambling growth, immense wildlife habitat value, strong evapotranspiration (roof and urban island cooling effects) and significant nutrient removal from stormwater on a green roof – in addition to her one of a kind mesmerizing form and iridescence.  Great ethnobotanical, food and flower plant for hot and dry living roofs.

Purslane grows where few other plants dare to grow, on the seashore and on the roof.  Often considered a CAM plant, purslane typically employs the C4 mechanisms of the Calvin cycle.  Similar in many ways, C4 processes moves CO2 into strategic spatial relations with RuBisCO whereas CAM plants react CO2 with the RuBisCO based on strategic time periods to prevent desiccation.  Purslane is edible and a reliable green roof plant – though she may be affected by extreme cold here in Florida.

Beach dunes speak to me of mass biodiversity at the plant family level (more biodiversity at higher taxa).  The few plants we’ve discussed today come from many families, including; Arecaceae, Aquifoliaceae, Convolvulaceae, Euphorbiaceae, Fabaceae, Poaceae, Vitaceae and more.

Simply put, the dune plants instruct in the same way the San Marcos de Castillo coquina walls teach.  Monocultures in genus levels do not exist in nature.  Green roofs fields of perennial peanut or sedum fight against nature’s plan and without RoundUp or 2,4D are doomed to accelerated spurge dominance.

To me, it is very simple to look and see nature’s complexity.  Dunes paint the canvas with complexity beyond my comprehension.

Why someone would plant perennial peanut or exotic sedum as a monoculture on a roof is easy to understand.  It is cheap and requires minimal creativity.  The below photo is of a Carlisle Roof Garden system on the aloft motel in Jacksonville.  The roof was originally planted with a monoculture of sedum who lasted three months.  The contractor remediated the roof on the recommendation of a local Jacksonville landscape company with peanut.

Monocultures do not work unless regular maintenance is applied to prevent nature from reverting to biodiversity at higher taxa as we see in the sand dunes. Unfortunately now the Pensacola bahia and other pioneer species are strangling out the peanut.  Bahia and crabgrass are impossible to pull out of a green roof mat so they will be there forever unless the herbicides are used.  Being tort aware from law school experiences, I frown thinking of the liability issues associated with spraying herbicides above the adjacent swimming pool.

The really problematic part of this roof is the fact that now there are countless grass and spurge seeds embedded in the roof system.  This weed problem will end up costing much more than a thoughtful initial native plant install.

Anecdotally, while taking the below photo today, I could see insects and birds hitting bahia and complex system of emerging ‘weeds’ yet none foraging about the peanut.   I suspect the same ‘none foraging’ would happen if sedum would live here.

Old school landscape companies and old school green roof companies though roil with disdain when talk of their monoculture practices of the past are rapidly supplanted by native plant society influenced projects.  But activism against monocultures is essential, now more than ever.   You must always speak against projects based in one genus.

Native plant groups need to rally other environmentally focused organizations like Audubon and Sierra to fight local monoculture projects, no matter how much of a green facade they may be disguised within.

Finally, listening and watching nature is the best education for an inspiring green roof designer.

What I find delightful is when still and quiet I see and hear what most do not.

The sand dune community is full of life.

Most think beach expanses are for horse flies and sand gnats.

Yet on my beach excursion to study green roof plants I witness more insects, birds and wildlife than I ever thought possible across the wind swept, hot and dry barrens. Though this trip plant identification was the focus, next time I’ll be attempting to understand animal inhabitants.

I’ve been going to the beach here in Florida for most of my 54 years.  Yet just now are my eyes opening to the extreme diversity at higher taxa levels.

Overwhelmed I sit in the sand.  The pitiful sedum and peanut monocultures and stupid exotic landscapes I become aggravated over quickly fade from my temporary reality.

Nature’s complexity swirls across the brown sands in helical patterns of elaborateness.  The gentle,whispering ocean waves each come ashore with individually different tones and metre.

Light breezes buffet infinite grains of sand, no two alike.

Infinitesimally tall cumulous clouds paint the deep blue with shapes not lasting a breath before taking new form.

Calls of Tringa semipalmata and Calidris alpina strike chords of complex and irrational meter.

Monocultures are so temporal.  They are a capitalistic driven flash of futility.

Her sand dunes speak to me what I need to hear of designs for my Jacksonville Zoo green roof.

I can only hope to come close to the most basic of Her complex interwoven individuality in my green roof designs.

But it is later in my life than I wish that I can see these things. I feel I learn this day more than I learned in my botany studies in undergrad and subsequently in law school.

Turning to the incoming tide I sit in the wet sand.

Every green roof I do in the future will be filled with extreme plant biodiversity.

Each landscape or permaculture project I work on will grow under new eyes fashioned with purposeful plant family multiplicity.

This day at the dunes I see things I never realized were manifest.

To me the sea is La Mar, even though the proper structure would be El Mar.  She is La Mar because to me she is like a woman, the mother of life.

Today La Mar, she has another gift for me, an offering, a token of nature’s complexity.  Island glass lizard,  Ophisaurus compressus swims up out of the breaking surf onto the coquina shell sand.

I have practically lived on the beaches of Florida yet never seen Ophisaurus swim up out of the surf onto the sand, though her cousin used to frequent our kava.

With my Canon raised, she slithers to my feet, pushed gently forward by the waves.

I know she is no sea-snake or other venomous creature.

The digital camer’s shutter mechanism is rapidly and arrogantly firing, a testimony to my immature inability to sit and experience.

La Mar brings an omen this day.

I know what she says.

She says she desires to be impetuously complex.

My future green roofs will be as intricately woven.

 

 

 

 

 

 

 

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