The level of biodiversity on a green roof will be dependant on a number of factors including the type of green roof installed.
In the past green roofs were designed with mainly engineering concerns at the top of the list such as storm water retention, energy consumption and overall building performance. However, while these are important factors, things have developed and now greater consideration is given over to ecological design and how green roofs can provide good habitats for a range of wildlife. This is particularly significant in towns and cities where natural habitats are few and often fragmented.
Due to their position, the fact remains that green roofs offer a stressed environment for would be colonizers, so it is important to accept that you are not going to be able to replicate ground level habitats. Furthermore, it is going to be a tougher journey for terrestrial wildlife to get to a roof top than it is for their more upwardly mobile cousins that may have the benefit of wings.
Green Roof Substrate
The type of roof substrate can also impact the type of plants that can be successful on a green roof. Generally speaking, crushed concrete is not good for retaining water or nutrients and is best avoided. Research has shown that sedum roof systems provide benefits to a number of invertebrates such as providing pollinators with foraging opportunities from the sedum flowers. The Riefa lightweight and organic green roof growing medium is ideal for a sedum roof. It is always worth considering the type of plants you choose for your green roof as some plants offer greater value to wildlife than others. Though appealing, we would not recommend that you choose the self-seeding method of greening your roof as you will probably end up with a terrible mess and a number of problematic plants such as buddleja whose root system will damage the materials it grows in.
Ecologically Designed Green Roofs
On extensive green roofs that have been ecologically designed, it is possible for ground nesting birds to nest or forage on the roof. Additionally, these sites offer a better level of security from predators. There have been a number of success stories from across Europe where birds such as black redstart, little ringed plovers and skylarks have all benefitted. It is generally accepted that where a suitable niche is provided on a green roof, plants and animals will establish new communities quickly. Compare this with the largely desolate conventional roof where the level of biodiversity is minimal.
The more features you have on a green roof then the more diverse range of habitats can be created that in turn will be more attractive to greater diversity of wildlife. It makes sense doesn’t it? You can use twig bundles, hollow logs, nesting boxes and rocks to add variety. It is best to plant a variety of species rather than a mono-culture alongside a varied substrate depth to really maximise biodiversity.
At Riefa, we appreciate that not all living roof projects are suitable for maximising biodiversity. For the small to medium sized projects a sedum roof with a high quality growing medium will create an excellent habitat for many an invertebrate and an excellent source of food for bees and butterflies.
What Next For Your Green Roofing Project?
To discuss your living roof project call us on 0844 057 0359. We’d be glad to give advice and can supply everything you’ll need for your green roof including a root resistant membrane, your sedum and importantly your lightweight and organic green roof growing medium.