Urban Rooftops and Native Plant Preservation

Recently I shared my thoughts about how green roofs in the city can provide important habitat to endangered native plants with The Nature of Cities.

While there are many other contributors on the TNOC website with wonderful articles, my thoughts are posted below (as well as within the TNOC site).  And while some may brush aside green roofs as insignificant with respect to native plants, the majority of green roofs today are unfortunately being vegetated with exotic and sometimes invasive species, for it is the most aggressive monster plants that ultimately are easier to design for installation on the rooftop.

Urban rooftops are positioned as prime vectors of plant DNA for they are high up in the seed and root spreading wind (especially during storms) and first to be swept away to adjacent locales during a downpour.  Invasive on the rooftop are indeed a serious threat to pre-Columbian species preservation.

In fact, several weeks ago I was asked by a green roof company who is currently installing a Florida green roof if I could recommend plants that would do well (this is their first Florida green roof).  After short consideration of the native species I proposed, the green roof contractor indicated they’d rather go with several hardy exotic species including one aggressive exotic that is presently listed on the Florida Exotic Pest Plant Council watch list.  When I mentioned the potential benefits of native plant use and partnering with the local native plant organizations their reply was discouraging.  “I am not worried about native plant organizations in Florida.  Those groups tend to self destruct through all the bickering and in-fighting amongst themselves.  They are really just a non-issue.”

Yet despite all the obstacles, I still truly hold hope that our cities, our urban rooftops can be a refuge for native wildflowers and plants.  The benefits are numerously important.  Native plants are drought tolerant; they clean stormwater through particulate filtration; produce oxygen; attract local pollinators vital for urban agriculture so much better than exotic invasives; they provide wildlife habitat; and create economy and community, and so much more.

Here are my thoughts:

Lightweight residential green roof with Dune Daisy, Helianthus debilis by Kevin

Today, many native wildlife and plant species struggle to compete with exotic,  invasive horticultural and anthropogenically related non-native species for survival.  Aggressive species with no natural predators are in many areas replacing native plants and animals at an alarming rate.  Although change across our planet has always occurred, today’s rate of pre-columbian ecosystems change has accelerated to the point where mass extinctions may soon be unavoidable.

Species extinction issues involve great risks to humans, including loss of potential medicines, important economics, longstanding traditions and more.  Unfortunately, invasive species colonization and native displacement is hard to control across most urbanscapes, except perhaps on green roofs.

We may never fully win the battle of preserving all pre-columbian ecosystem component species.  Over time humankind will continue to lose critically important species to monocultures of aggressive plants and swarms of unnatural predator species, most brought on by our own anthropogenic activities.

Noxious species roots and seeds will cover the landscape, transported by roads, stormwater ditches and urban runoff.  Native flower blooms may be relegated to specimens in a museum or photos in a library book.

Yet green roofs, be they on a shed, garage, house, commercial building, apartment complex or bus stop can truly make the difference between death and survival for many of our native plants and wildlife.  With the health of the human species so closely related to successful functioning of those ecosystems around us, ensuring native plant and animal survival benefits humankind.

Yes, there are many sustainability oriented reasons to require green roofs on new buildings, from urban heat island effect reduction to cleaning and attenuating stormwater to sequestering carbon.  I suggest too, that many of our native species, both plants and animals, may find last corners of uninvaded habitat on our city rooftops.

While ground level landscapes can quickly fall prey to invasion of nuisance plant monocultures, green roofs have boundaries.  Yes, maintenance on a green roof maybe just as cost and labor intense as ground level exotic plant control.  Green roofs however have clearly defined borders, usually free of an unrelenting and uncontrolled neighboring invasive grass, shrub or tree patch.

Many threatened native plants thrive on green roofs.  Case studies across the world have highlighted endangered plant colony survival successes in green and brown rooftop habitat.

Importantly, imperiled wildlife will seek out green roofs.  We have seen the progression after installation of vegetated roofs of the arrival of smaller creatures, lizards, anoles, tree frogs, insects and and dragonflies, butterflies and moths, each establishing their community throughout native vegetation on green roofs.

Here in Florida, as the first generation of smaller wildlife species become established on green roofs additional populations of larger birds and reptiles begin to appear.  Snakes soon forage through green roof plants for lizards and frogs, maintaining population control.

Following snakes come birds of prey tracking snakes and smaller birds, squirrels and other green roof species.

Owls, red-tailed hawks, peregrine falcons, swallow-tail kites, osprey and a pair of eagles regularly visit our green roofs, choosing perches in nearby trees and often taking the opportunity to feed on a ground mouse running through the neighborhood streets and yards below.

Green roofs are important sanctuaries in the concrete jungle for wildlife, especially those species endangered because of habitat loss.  Green roofs should be considered necessary infrastructure, required for all new development for many reasons, but especially with respect to habitat for threatened and endangered species conservation.

It may well be future generation archaeological and paleontological expeditions will find many pre-columbian plant and animal species made their last stand atop our urban core rooftops.

© 2015, Kevin Songer. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. We have received many requests to reprint our work. Our policy is that you are free to use a short excerpt which must give proper credit to the author, and must include a link back to the original post on our site. Please use the contact form above if you have any questions.