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Green Roofs in the Urban Environment
With today’s ever-growing population and rapid urbanization of municipalities and cities across the globe brings increased stress to the environment and causes of increased climate change. To combat these issues environmentalist and conservationist minded people alike have come up with many new innovative ideas and solutions.Finding space on the ground for trees to be planted and grown in ground-based soil is becoming an ever increasing challenge. This drove foresters to look up to rooftops as an option, and what is known as Green Roofs has become the next frontier in Urban Forestry practices.

This article focuses on the use of “Green Roofs” and the benefits they provide and how they are implemented and managed properly. A green roof can be described as a living soil and plant layer ranging from as shallow as Two centimeters known as “extensive” to over three feet deep known as an “intensive” roof.(1) The main difference between the two is the depth of the soil or “medium” on the roof that the green infrastructure is rooted in. Each type is successful in providing ecosystem and financial benefits to the area they are being used in. These benefits include a greater diversity of plant species, increased shade which can lower energy cost for heating and cooling, and higher carbon capture or sequestration which is becoming a huge priority in all Urban forest settings.(4) Along with the benefits they provide there are liabilities that must be noted such as the weight placed on the infrastructure the green roof is being implemented on, litter that may come from the vegetation growing, and the overall cost of building, planting, and maintaining the green infrastructure.

In comparison of the two types of green roofs, Intensive green roof applications are more successful in their ability to lower energy cost, mitigate stormwater runoff, and in having a higher plant diversity.(1) Intensive green roofs do require more maintenance which requires good accessibility to the roof and being larger than an extensive style roof they usually cost more to implement and maintain. Extensive green roofs can be a good choice when funding is low, accessibility is hard, or when an older building is being redeveloped and maybe the infrastructure can’t support the weight and necessities of an intensive application. (5)

Here you can see a great example of a Green Roof installment being used in an urban setting.

As stated above and in several articles on Wikipedia, Green Roofs can provide many benefits and ecosystem service. However, they’re not a build it and forget about it system. For a green roof to be successful they require regular maintenance and upkeep just like any other green infrastructure found in an urban area. The first to fifth year a green roof is installed is the most crucial time to provide the proper care and maintenance to achieve a successful installation.(1) In many cases it is recommended that when writing a contract to provide funding for a green roof that the first five years of maintenance cost be included. Commonly after the fifth year of use, the green roof has successfully established itself and can ward off issues from invasive species, changes in rainfall, and have reached an age where most or all bare soil is covered.

After the green roof either intensive or extensive has successfully established itself the level of maintenance needed usually lowers but can fluctuate due to factors such as; the overall goal of the project, location, weed sources/influences, irrigation functions, and overall aesthetics of the green roof.(6)(1) Common maintenance practices include weeding 2-5 times a year, plant replacement due to unavoidable plant mortality, Irrigation, Fertilization, and even soil tests to monitor levels of nitrogen and phosphorus in the soil to maximize plant growth. (2)(3)

When proper implementation and maintenance is followed the benefits to humans, wildlife, and the environment are widely recognized and being improved upon in each new Green Roof application.

Sources

1)	Minnesota Pollution Control Agency. (n.d.). Operation and maintenance of green roofs operation and maintenance of green roofs. Operation and maintenance of green roofs - Minnesota Stormwater Manual. Retrieved May 5, 2022, from https://stormwater.pca.state.mn.us/index.php/Operation_and_maintenance_of_green_roofs

2)	U.S. Department of the Interior. (n.d.). Green roof benefits-technical preservation services, National Park Service. National Parks Service. Retrieved May 5, 2022, from https://www.nps.gov/tps/sustainability/new-technology/green-roofs/benefits.htm

3)	Green roofs. Virginia Association of Soil and Water Conservation Districts. (n.d.). Retrieved May 5, 2022, from https://vaswcd.org/green-roofs

4)	 Francis, L. F. M., & Jensen, M. B. (2017). Benefits of green roofs: A systematic review of the evidence for three ecosystem services. Urban forestry & urban greening, 28, 167-176.

5)	Oberndorfer, E., Lundholm, J., Bass, B., Coffman, R. R., Doshi, H., Dunnett, N., ... & Rowe, B. (2007). Green roofs as urban ecosystems: ecological structures, functions, and services. BioScience, 57(10), 823-833.

6)	Contributor), J. S. (G. (2021, December 17). Green roofs provide many benefits as cities densify. The Urbanist. Retrieved May 5, 2022, from https://www.theurbanist.org/2021/12/17/green-roofs-provide-many-benefits-as-cities-densify