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Soil carbon in urban parks important in fighting climate change, study shows

Trees by the side of streets in Brooklyn, U.S.

Trees by the side of streets in Brooklyn, U.S. Image by spurekar via Flickr (CC BY 2.0).

  • A recent study shows that urban parks and green spaces throughout the world have a similar amount of carbon stored in their soils as in natural regions close to cities, which means urban green spaces can be important to global carbon sequestration and mitigating the potential effects of climate change.
  • Soil microbes in urban green spaces play a vital role in carbon storage, but that carbon is also vulnerable to loss through microbial respiration in an increasingly warmer world; researchers emphasize the need for greater understanding of the soil microbiome in urban policies and planning.
  • For context, Suriname has 93% forest cover nationwide and is often referred to as the world’s “greenest” country — but the capital city, Paramaribo, lacks a structural approach to urban greenery.
  • Researchers conducted a project to promote a greener and more livable Paramaribo, with the aim of mitigating the effects of climate change and raising awareness among citizens.

Urban green spaces — parks, gardens and other green areas where people can go to enjoy some fresh air — are more than just pretty places to relax. New research shows they have a significant role in the fight against climate change through the sequestration of carbon.

The study, published in March in the journal Nature Climate Change, highlights the importance of parks in the context of climate change by showing that urban parks and green spaces throughout the world store similar amounts of carbon in their soil to natural regions close to cities. Even though, globally, the total area of urban green spaces is much smaller than that of natural ecosystems, the role of urban green spaces in carbon storage could help support the efforts of cities to mitigate their carbon footprint through natural climate solutions.

The soil in urban green spaces stores carbon in the ground, where it can remain for a long time and prevent it from returning to the atmosphere. So, by increasing the amount of green space, thereby increasing the amount of carbon in the soil, cities can help reduce the amount of carbon dioxide in the atmosphere and slow down the effects of climate change.

The researchers studied 56 areas of urban green spaces and natural ecosystems across 17 countries and a range of environmental gradients on six continents to look for potential natural solutions for mitigating climate change. They analyzed samples from surface soils beneath dominant vegetation in both green spaces and natural ecosystems. This is because the uppermost soil layer is usually the most biologically active.

In urban green spaces, the amount of carbon stored in the soil is mainly affected by tiny living soil microbes, while in natural areas, the amount of carbon stored is influenced by the growth of plants and the breakdown of dead plants and animals, Tadeo Sáez, a researcher from the Biodiversity and Ecosystem Functioning Laboratory, known as the BioFunLab, and a co-author of the study, explains in a press release. Since grass clippings, deadwood, leaf litter and other organic matter in urban green spaces are often removed, that can affect microbial activity and soil carbon, the authors note. If, for example, grass is mowed and left to decompose, it can enhance soil carbon. That means the way urban green spaces are managed is important — and important for city planners to take into account.

The Cultuurtuin (Culture Garden) is a park located on the northern side of Paramaribo, the capital of Suriname.
The Cultuurtuin (Culture Garden) is a park located on the northern side of Paramaribo, the capital of Suriname. The park is home to the Paramaribo Zoo, an animal shelter and four football fields. Running through the park is a trail where Surinamese people often take morning and late afternoon runs or jogs. The trail is also equipped with fitness equipment for exercise. Image courtesy of Sarah Jane, @sublimespecialty.

However, due to global warming, soil microbes are releasing more carbon back into the atmosphere, which reduces the amount of carbon stored in urban green spaces. So the researchers say it’s crucial to understand these complex systems and the role that soil microbes play in regulating carbon in city green areas, and to take steps to protect them so they can keep capturing carbon.

Furthermore, the study also found that the soil microbes are more sensitive to temperature in urban green spaces than in natural ecosystems. This means that urban green spaces may lose carbon more quickly as the climate warms up. “Warmer cities have lower soil carbon content in urban parks and natural ecosystems, which is not good news in our fight against climate change in a warmer world,” Manuel Delgado Baquerizo, director of the BioFunLab and the research’s lead author, states in a press release. According to the authors, these findings are especially important in an urbanizing world where, by 2050, it’s expected that 7 out of 10 people will live in cities. City green spaces are understudied resources that are often overlooked in research and urban planning.

Suriname can offer important context for these study findings: It’s sometimes dubbed the world’s “greenest” country, with 93% forest cover. However, more than half the population lives in and around the capital city, Paramaribo. And to this point, urban planners have not emphasized the potential environmental value of urban green spaces in the fight against climate change. The Surinamese government often speaks of supporting a green policy. However, the Planning Act of 1973 and the Urban Planning Act of 1972 have not been operationalized, and as a result, there is no structural approach to the design and development of urban areas.

Paramaribo is often described as “enchanting,” with its vibrant and colorful character. The heart of this city, a UNESCO World Heritage site, is a bustling melting pot of cultures, flavors and hues. The streets are lined with a blend of colonial and modern architecture. In the mornings and afternoons, they bustle with cars, buses, taxis and people going to and coming from work. At night, streetside restaurants and cafés come alive. A few streets have long rows of trees, some of them centuries old. But in many parts of this capital city in this “greenest” of nations, there is not much green to be seen. The Palmentuin “Garden of Palms” and Cultuurtuin “Culture Garden” include landscaped gardens and a zoo, while other public green spaces are limited to squares, playgrounds and sports fields with sparse vegetation.

The Palmentuin (Palm Garden), a walking park and tourist attraction in Paramaribo.
The Palmentuin (Palm Garden), a walking park and tourist attraction in Paramaribo, is located behind the Presidential Palace. The garden is filled with royal palms and other trees and plants. It also features several statues, benches, huts and a playground. On holidays, various stalls are set up in the park. Due to falling branches, the park has been closed to the public from December 1, 2022, to September 2023 as part of the Paramaribo Urban Rehabilitation Program. Tree experts from Colombia and Ecuador will assess the condition of the trees during this period. Image courtesy of Sarah Jane, @sublimespecialty.

From January 2019 through December 2022, the environmental organization Tropenbos Suriname and the faculty of Geo-Information Science and Earth Observation of the University of Twente carried out the project Naar een Groen en Leefbaarder Paramaribo (Toward a Greener and More Livable Paramaribo) with the aim of promoting the ecosystem services of urban green spaces that contribute to a healthy and more livable environment for its inhabitants. The project spurred an array of research on the role of green spaces in society and the environment, and it spanned a variety of local activities: outdoor scavenger hunts, tree plantings, videos featuring local gardeners to inspire other residents to begin their own gardens. Additionally, the project led to the development of educational resources for schools that focus on the significance of urban green spaces in tropical regions, and it initiated a citizen science network of locals monitoring air temperature in urban green spaces. Crucial to the project was raising awareness among policymakers and society as a whole, both in terms of present circumstances and future implications.

Project coordinator Lisa Best says Paramaribo faces many challenges as the city develops. “Paramaribo is characterized by urban sprawl, as there is not yet any structural planning or zoning policy, and a policy for managing public green space is lacking, resulting in a trend of increased soil sealed surfaces and disappearing greenery.” This is a concern, given that climate change is a challenge for the city — and the potential mitigating effects of green spaces are underused and sometimes even unrecognized.

Paramaribo is the hub of economic activity and home to a significant portion of Suriname’s population. Located along the coast, it is not immune to the effects of climate change, being vulnerable to sea-level rise, extreme weather events and temperature increases.

As in many cities, Paramaribo endures the competing interests of urban green spaces, development projects and parking infrastructure. Meanwhile, the majority of the city’s “green” surface areas consist of grasses and low mixed vegetation, while trees cover only a small percentage. When trees disappear, so do the advantages they offer. According to Best, in Paramaribo, “There is no systematic effort to manage and add high-quality green spaces that can compensate for areas being developed.” Consequently, residents are missing out on the potential benefits of greater urban greenery.

Tropenbos Suriname and the University of Twente have also made data available for further research and policy development in the field of spatial planning and urban greenery. The data are openly accessible to anyone. The researchers acknowledge that additional studies are needed on urban green spaces in the tropics and their role in climate change mitigation.

The Vriendschapspark (Friendship Park) is dedicated to the Chinese immigration to Suriname.
The Vriendschapspark (Friendship Park) is dedicated to Chinese immigration to Suriname. The park is situated in an area with many schools and features a variety of trees, plants and benches. Within the park, there is a monument commemorating the first Chinese immigrants who arrived in Suriname. The park is particularly frequented by students. Additionally, after school hours, regular citizens also gather in the park. Image courtesy of Sarah Jane, @sublimespecialty.

While Tropenbos Suriname has not investigated urban green space soil carbon, the organization has researched soil carbon in Suriname’s forests. Suriname is considered a high forest, low deforestation (HFLD) country. The results of a 2009 study show that the main carbon stocks found in the forest exist in trees aboveground (trunks, branches, leaves), belowground (roots), in necromass (wood and litter) and soil organic material. The research also shows that the relative importance of different carbon compartments for the total amount of carbon stored in the forest is significantly influenced by soil type. The results also highlight that the largest carbon stocks are found in trees.

Other research has shown that Suriname’s forests store 1.5% of global forest carbon and are a significant contribution to combating climate change. Additionally, Suriname is a carbon-negative country, meaning it sequesters more CO2 than it emits.

Suriname confirms its commitment to remaining an HFLD country. In order to preserve its forests for the benefit of the world, Suriname seeks to qualify for carbon credits. The country has also joined the UN’s REDD+ Program, a mechanism for climate financing through carbon credits, which will allow reinvestment in sustainable economic alternatives.

But despite all this, the capital city has a long way to go to improve and expand its green spaces — and their potential benefits. There is also a need for further studies on soil carbon in urban green spaces and their role in climate change mitigation.

Banner image: Trees by the side of streets in Brooklyn, U.S. Image by spurekar via Flickr (CC BY 2.0).


Related reading: The key to averting environmental catastrophe is right beneath our feet


Citations:

Delgado-Baquerizo, M., García-Palacios, P., Bradford, M.A. et al. (2023). Biogenic factors explain soil carbon in paired urban and natural ecosystems worldwide, Nature Climate Change. doi:10.1038/s41558-023-01646-z

Seminar report: Towards a carbon balance for forests in Suriname. First results and recommendations for future monitoring. (2010). Retrieved from Tropenbos International Suriname website: https://www.tropenbos.sr/resources/publications/seminar+report:+towards+a+carbon+balance+for+forests+in+suriname.+first+results+and+recommendations+for+future+monitoring

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