The American Heritage Scientific Dictionary describes biodiversity as, “the number, variety, and variation of different organisms found within a specific geographic region.”
A bio-diverse environment can have both native and introduced species. A mono-culture of a native species can be just as detrimental as having a monoculture of an invasive species. The key word in a bio-diverse environment is diversity. For an environment to thrive there must be competition and prey predator relationships to strengthen the key players within that ecology.
On ground level, efforts to promote biodiversity are typically geared toward enhancing or restoring the surrounding to preexisting environment. Preexisting elements such as soil and accessibility play a critical role in what species can thrive there.
As a result of development, there exists a lot of fragmented habitat creating connectivity and migration challenges. Some creative ways that connections can be made between severed environments are wildlife bridges, tunnels, and green corridors. Wildlife bridges and tunnels serve not only as key instruments allowing safe passage from one environment to the next, they also cut down on traffic accidents. Green corridors are often areas around streams left wooded in heavily developed area or around fields in intense used agriculture. These areas serve as a haven for bird and mammal migration.
While green roofs can provide habitat for biodiversity to exist they typically have a similar challenge of disconnect for non-aerial fauna. To create access to a green roof one option would be to design the building so that it is built into a hill or create a ramp which wraps up the side of the building to the roof. Terraced landings or steps can also be used to promote access to the roof. Species and size of fauna depending, green walls consisting of vines can also be a method of access.
Creating biodiversity on a green roof or green wall is significantly different than restoring it on ground level. On a rooftop there is no preexisting ecology to enhance; everything is from scratch. In most cases the growing media is drastically different from the soil down below which in turn dictates what ecology can be supported. Beside accessibility, high winds, more temperature extremes and proximity to the sun can also be very challenging issues for organisms.
Studies show that plant
selection and depth of growing media have a greater influence on the
biodiversity of a green roof than the height of the building. In the translation of
research covering the biodiversity of green roofs, “Where the Beetles are Crawling and the Honeybees are Humming,” (Mann / Breuning) the biodiversity found on green roofs as tall as 400 feet were comparable to that of lower green roofs.
Tray or modular green roof systems create the visual impression of a green roof by placing a series of planters close together. With these planters multiple organisms can be already introduced - wanted or unwanted. The history of German tray systems, introduced in 1978, show that in most cases the performance of pre-planted boxes fail to meet performance and maintenance expectations. The composition of a modular system simply does not provide the right set-up to reliably enjoy the 30 to 50 year lifespan expected from a built-up or in-place equivalent green roof system. Additionally there tends to be amounts of species die back during the first 5 years creating a sparsely vegetated monoculture setting. These factors create a very poor and unreliable environment for biodiversity to take place. The higher costs of planters have no advantage for biodiversity.
Intensive green roofs with great media depth and plant selection offer ample opportunities for biodiversity. Ramps or tiered levels offer roof access to non-aerial fauna setting the stage for the introduction and interaction of the surrounding ecology. Just because a large animal such as a bear or moose may inhabit the local area does not mean that the intensive green roof must attract it to make the biodiversity effort a success. Creating an environment which supports a variety of green roof plants and fauna on the lower levels of the food chain benefit the entire food web for the surrounding area. Smart green roof designs on intensive green roofs allow combinations for recreational use combined with biodiversity. can Intensive green roofs often used for
Rooftop farming has the allure of self-reliance in a world of food uncertainties. Rooftop farming is a very seasonal business and without extensive knowledge or the availability of winter crops there might be no vegetation and zero diversity for almost 6 months every year. At the end it all depends on crop selections and the intensity of maintenance performed by the farmers. Organic farming typically allows a higher diversity and can provide habitat for several pollinators. All farms also provide food and shelter for many unwanted plants, insects, birds, and small mammals. A rooftop farm can offer a diverse environment or a monoculture stage for chemical warfare between man and nature.
They say variety is the spice of life and this indeed tends to be the case when creating a green roof to promote biodiversity. Green roofs with both intensive and extensive portions have been found to support the highest amount of biodiversity. The combination of Sedum meadow, grasses, and shrubs provides not just food but shelter for several species. More information covering biodiversity on semi-intensive green roofs can be found on our case studies page in "Where the Beetles are Crawling and the Honey Bees are Humming."
Despite issues of limited growing media depth and access an extensive green roof still offers a lot of potential for creating biodiversity. The shallow system is capable of supporting a variety of drought tolerant herbaceous plants, succulents and grasses providing food and shelter year round. Many insects and birds have found their way onto this type of green roof orchestrating ecological webs and food chains. The limited accessibility of the green roof to terrestrial animals also offers sanctuary to ground nesting birds. Some examples of Green Roof Service LLC green roofs which provide these benefits are Hamerschlag Hall and Resource Conservation Technology Ice House.
The desperate run for LEED credits didn't stop at green roofs. LEED professionals are inexperienced and they typically count the amount of different species not understanding their interaction with the green roof system and among the plants. Many LEED projects with focus on diversity are going to fail in less than 5 years or their maintenance is not affordable. LEED is counter productive for diverse and successful green roof implementation.
Green Roof Service LLC was the first green roof engineering and green roof design firm in Northern America that consistently implemented advanced green roof solutions to enhanced biodiversity of flora and fauna. With a wide range of natural breeding and housing options for insects, spiders and mammals installed in the ground, at the building or as a stand-alone many species were introduced and discovered on roofs. Temporary nursing plants, seasonal plantings from seeds combined with reliable succulents go far beyond the wide spread picture in America of a "European Style" green roof.