BIODIVERSITY ON GREEN ROOFS

From tiny soil-dwelling insects to large birds of prey, a diverse array of wildlife finds food and shelter on urban green roofs. 

 

Green roofs are wildlife habitats, 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 close 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 pass through 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.

Common questions

Are there bats in NYC?


Five bat species are found in NYC and all of them have been recorded using green roofs. While bats have been recorded over NYC green roofs throughout the entire year, peak bat activity occurs during the spring and fall bat migration. Bats use green roofs to forage and are more likely to be on a green roof when their most common food, moths, are abundant.




Is it safe to have bats feeding on my green roof?


Yes. The bats over your green roof would be passing through the city anyway. If your green roof wasn’t there providing food, they would likely be at street level. Bats are harmless animals that help keep insect populations under control.




When can I find bats on my green roof?


Most bats use green roofs during spring and fall migration. In NYC we generally see peak bat activity from the end of August through mid-October.





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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

Are there bats in NYC?


Five bat species are found in NYC and all of them have been recorded using green roofs. While bats have been recorded over NYC green roofs throughout the entire year, peak bat activity occurs during the spring and fall bat migration. Bats use green roofs to forage and are more likely to be on a green roof when their most common food, moths, are abundant.




Is it safe to have bats feeding on my green roof?


Yes. The bats over your green roof would be passing through the city anyway. If your green roof wasn’t there providing food, they would likely be at street level. Bats are harmless animals that help keep insect populations under control.




When can I find bats on my green roof?


Most bats use green roofs during spring and fall migration. In NYC we generally see peak bat activity from the end of August through mid-October.





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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

Are honeybees good for biodiversity on green roofs?


Honeybees are beneficial for pollinating crops and producing honey, and they are a great education tool. However, honeybees are not native to NYC and can outcompete native species. Honeybees should be thought of as a type of livestock and not a form of arthropod conservation.




Will having a green roof cause an indoor pest infestation?


No. Pests that infest homes are going into the home for some sort of resource, such as food or wood. The living green space on your roof is not a useful habitat for indoor pest species.




How do I encourage native arthropods?


Plant a diversity of native plants with a variety of bloom times and canopy heights. Consider introducing a rock or a log to a portion of your green roof to create shelter. Ask your neighbors to install a green roof or a garden in their backyard to increase connectivity.





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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.





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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.





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 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 that may have shaped fungal assemblages.

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