A diverse array of wildlife, from tiny soil-dwelling insects to large birds of prey, find food and shelter on urban green roofs. Green roofs can also increase local native plant populations if native plants are part of the design or allowed to establish on their own.
Green roofs are wildlife habitat, so keep wildlife in mind when designing them. Try to use native plants when possible and avoid using pesticides. Avoid allowing pet cats out on the green roof, especially during migration. Importantly, avoid large windows in close proximity to vegetation or install bird-friendly glass treatments so that you can avoid causing bird collisions.
Birds on Green Roofs
Birds use New York City in all seasons of the year. Some birds breed in NYC, some spend their winters here, and others just pass through during spring or fall migration. In many parts of NYC, birds don’t have access to enough green space to find the food and shelter they need. Green roofs can provide habitat in areas where birds may not otherwise be able to survive.
Over 48 bird species have been recorded using green roofs in NYC. The majority use green roofs during spring and fall migration. During migration, birds travel long distances, but they need to refuel from time to time. Green roofs act as stopover sites, where birds forage on the abundant insect community found there. Many of the birds using green roofs during the migration would not usually be found in the city outside of parks.
Common questions
What birds use green roofs other than pigeons and sparrows?
If I build a green roof will I attract pigeons?
There is no evidence to date that pigeons are attracted to green roofs. Along with House Sparrows and European Starlings, pigeons are common city birds that are invasive urban dweller species and do well in a built environment. Creating green space is not likely to benefit them.
How do I attract birds to my green roof?
The best thing you can do to have birds safely use your green roof is to make sure all of the windows overlooking it have a bird-friendly covering. Also create a diverse assemblage of plants that attract insects (bird food), and don’t deadhead flowers in the fall since the seeds can also be food for birds. An additional element that allows birds to use green roofs is a simple perch.
Credit: American Natural History Museum Bats in Central Park
Bats on Green Roofs
Bats are an important component of ecosystems and help protect people by keeping pest insect populations under control. In North America, many bat species are imperiled due to white-nose syndrome or habitat loss. Green roofs provide habitat for bats in the city.
Common Questions
Should I weed plants that arrive on my green roof?
Try to identify the plant first to see if it can survive on a green roof in NYC. Many colonizing plants provide benefits for wildlife.
Should I deadhead (remove) flowers after they bloom?
No. Flowers go to seed after they bloom. These seeds, especially from native plants, provide an important food source for migratory birds in the fall.
Is it ok to just have a Sedum green roof?
Absolutely! Sedum species capture stormwater and provide wildlife habitat. If possible, add a few planters or a semi-intensive row to increase habitat quality and plant diversity.
Arthropods on Green Roofs
Arthropods are invertebrates with exoskeletons, including bees, true bugs, spiders, and ants. Arthropods provide food for other wildlife, pollinate plants, control pest species, decomposing plant material, and cycle the soil.
The area surrounding a green roof and the connectivity of a green roof influences which arthropods are found, as does green roof design. Green roofs in NYC host a higher arthropod richness and abundance than non-green conventional roofs and can play an important role in increasing arthropod diversity across the city.
Common Questions
What birds use green roofs other than pigeons and sparrows?
If I build a green roof will I attract pigeons?
There is no evidence to date that pigeons are attracted to green roofs. Along with House Sparrows and European Starlings, pigeons are common city birds that are invasive urban dweller species and do well in a built environment. Creating green space is not likely to benefit them.
How do I attract birds to my green roof?
The best thing you can do to have birds safely use your green roof is to make sure all of the windows overlooking it have a bird-friendly covering. Also create a diverse assemblage of plants that attract insects (bird food), and don’t deadhead flowers in the fall since the seeds can also be food for birds. An additional element that allows birds to use green roofs is a simple perch.
Plants on Green Roofs
Plant diversity on green roofs is determined by the depth of the growing medium. In NYC, several native plant species are known to survive on green roofs of varying depths, and more are being tested by researchers. In addition to what is planted intentionally, new plant species will colonize green roofs, increasing plant diversity.
Introducing plants on a previously impervious roof surface creates habitat for microbes, fungi, arthropods, birds, and bats. At ground level sites, native plants provide a better habitat for native wildlife and the same is likely true for green roofs. However, more research is needed on which native plants can survive on green roofs in NYC.
Common questions
Should I weed plants that arrive on my green roof?
Try to identify the plant first to see if it can survive on a green roof in NYC. Many colonizing plants provide benefits for wildlife.
Should I deadhead (remove) flowers after they bloom?
No. Flowers go to seed after they bloom. These seeds, especially from native plants, provide an important food source for migratory birds in the fall.
Is it ok to just have a Sedum green roof?
Absolutely! Sedum species capture stormwater and provide wildlife habitat. If possible, add a few planters or a semi-intensive row to increase habitat quality and plant diversity.
Microbes on Green Roofs
Several groups of microbes, including mycorrhizal fungi, decomposer fungi, N-fixing bacteria, and pathogens, are important for the functioning of non-constructed ecosystems, and likely have implications for green roof design and maintenance. These functional groups interact with certain plant taxa and soil properties in complex ways. The bacterial and fungal communities are different on green roofs with mixed vegetation (wildflowers, grasses, and succulents) than on single-genus (Sedum) green roofs. There is a higher proportion of mycorrhizal fungi on mixed-vegetation roofs. Sedum roofs have higher pathogen loads.
The fungal communities of green roofs are compositionally distinct from those in city parks, and only 54 percent of the green roof microbial taxa were found in park soils. Across the city's green roofs, fungal communities are geographically clustered, indicating that local factors such as edaphic variations, wind patterns, and dispersal from proximate parks may have shaped fungal assemblages.
common questions
How can I manage my green roof media for diverse, healthy microbial assemblages?
Due to the intricate link between plant and soil microbial communities, planting green roofs with diverse native plant communities will provide habitat for diverse microbial assemblages. Green roofs offer opportunities to construct and recreate habitats native to NYC. When selecting species, consider plant communities native to the NYC region.
What types of soil amendments are best to use?
We are still in the early phases of research about how to amend or inoculate microbes on green roofs. While we cannot give specific advice on this question yet, we hope that additional research will allow us to provide green roof soil management recommendations specifically related to microbes. Review microbial functional groups that likely play critical roles in green roof ecosystem health.
Additional Resources
Urban green roofs provide habitat for migrating and breeding birds and their arthropod prey
The impact of free-ranging domestic cats on wildlife of the United States
Native plants improve breeding and foraging habitat for an insectivorous bird
Bats in the Bronx: Acoustic Monitoring of Bats in New York City
Green roofs provide habitat for urban bats
Conserving honey bees does not help wildlife
Habitat connectivity shapes urban arthropod communities: the key role of green roofs
Worldwide decline of the entomofauna: A review of its drivers
Plant Colonization of Green Roofs Is Affected by Composition of Established Native Plant Communities
Digging the New York City Skyline: Soil Fungal Communities in Green Roofs and City Park
Bacteria and Fungi in Green Roof Ecosystems