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Publication #WEC279

What Types of Urban Greenspace are Better for Carbon Dioxide Sequestration?1

Mark Hostetler and Francisco Escobedo2

Introduction

Figure 1. 

A representative school site that is dominated by turfgrass in Miami-Dade. Photo Credit: Francisco Escobedo


[Click thumbnail to enlarge.]

Meeting Florida House Bill 697 requirements to reduce Florida's carbon emissions will require a judicious look at how human-dominated landscapes are performing. It has been suggested that conserved urban greenspace could be used for carbon credit. But are all types of open spaces equal in terms of their ability to sequester carbon? Intuitively, this is not the case because we know that different types of vegetation (e.g., hammock vs. turf) and how they are managed will sequester different quantities of CO2. Using representative 400 m2 plot measurements (Zhao et al., 2010) and modeling of tree carbon sequestration (Escobedo et al., 2009) and estimates of lawn sequestration from various land use types in Florida, including their maintenance emissions, we calculated the source/sink potential of a 4 hectare (9.88 acres) site. Only above-ground vegetation values were calculated; soils and below ground organic matter were not included in the calculations.

The take home message is that highly maintained lawns and trees sequester much less CO2 than more natural areas with little maintenance (Table 1). With more lawn cover than tree canopy cover, the balance can actually shift to emitting CO2 (e.g., older residential areas in Miami-Dade). Of note is that we did not calculate the impact of built surfaces, just vegetative. The calculations were simplified as we did not add the carbon cost of making and maintaining the power equipment or the carbon cost of growing and transporting sod. In particular, we did not calculate the emission of nitrous oxide (N2O) from fertilization applications. Urban turfgrass typically emits N2O after fertilization and/or irrigation. N2O has a much worse global warming potential (GWP) as its heat-absorbing potential is approximately 300 times more than CO2. With these unmeasured factors, city parks with high maintenance regimes may have much larger impacts than reported here. Thus, urban open space that has a large amount of mowed, irrigated, fertilized lawns and pruned shrubs and trees can be a source of CO2 rather than a sink. These CO2 emissions are not trivial; for example, a 4-hectare greenspace in Miami-Dade with 85% of the land covered in lawn would emit over 11 tons of CO2 per year (Table 1).

Further, because below-ground soil carbon sequestration was not calculated, full carbon credit could not be assessed and these above-ground numbers reported should be regarded as a first look at the potential carbon value of urban greenspace. At this stage, natural greenspaces in and around urban areas, with little to no maintenance, seem to be the best option for CO2 sequestration. Natural urban greenspaces also have other benefits, such as biodiversity conservation, reduced stormwater runoff, and reduced fertilizer applications. Overall, the conservation of urban open space could play a role in reducing Florida's carbon footprint, but highly maintained urban greenspace could be regarded as a source of greenhouse gases. In relation to HB 697, these results indicate that if municipalities and developers are to use green spaces as CO2 sinks, they will have to justify the creation of such high-maintenance parks and may have to mitigate their effects.

Additional Resources

For additional information on conservation subdivisions, urban forestry, and conserving urban biodiversity, a variety of online guides, books and other publications exist.

Books and Scientific Publications

Jo, H. and G. E. McPherson, (1995). Carbon storage and flux in urban residential greenspace. Journal of Environmental Management 45: 109-133.

Nowak, D.J. and D.E. Crane, 2002. Carbon storage and sequestration by urban trees in the USA, Environmental Pollution 116, pp. 381–389

Schlesinger, W. H. 1999. Carbon sequestration in soils, Science, 284, 2095, doi:10.1126/science.284.5423.2095.

Thompson, J. W., and K. Sorvig. 2008. Sustainable Landscape Construction: A Guide to Green Building Outdoors 2nd edition. Island Press, Washington DC.

Townsend-Small, A. and C. I. Czimczik, (2010). Carbon sequestration and greenhouse gas emissions in urban turf. Geophysical Research Letters. 37, L02707, doi:10.1029/2009GL041675.

Zhao, M., F. Escobedo, and C. Staudhammer, 2010. Spatial patterns of a subtropical, coastal urban forest: Implications for land tenure, hurricanes, and invasives, Urban Forestry & Urban Greening, Accepted

Online

Hostetler, M. E., G. Klowden, S. Webb, S. W. Miller, and K. N. Youngentob. 2003. Landscaping backyards for wildlife: top ten tips for success.
http://edis.ifas.ufl.edu/UW175
Department of Wildlife Ecology and Conservation Extension
http://www.wec.ufl.edu/extension/
Escobedo, F., J. Seitz, and W. Zipperer, 2009. Carbon sequestration and storage by Gainesville's urban forest. University of Florida- IFAS, EDIS FOR 210.
http://edis.ifas.ufl.edu/document_fr272
Florida Fish and Wildlife Conservation Commission – Planting a Refuge for Wildlife
http://myfwc.com/viewing/adventures/wildlife-viewing-at-home/refuge/
Florida's Urban and Urbanizing Forests Program
http://www.sfrc.ufl.edu/urbanforestry/
Lawn Fertilization Recommendation
http://hort.ifas.ufl.edu/yourfloridalawn/
Living Green
http://www.livinggreen.ifas.ufl.edu
Program for Resource Efficient Communities
http://www.buildgreen.ufl.edu
Sustainable Site Initiative
http://www.sustainablesites.org/
DelValle, T. B., J. Bradshaw, B. Larson, and K. C. Ruppert. 2008. Energy Efficient Homes: Landscaping
http://edis.ifas.ufl.edu/fy1050
USDA Forest Service, Urban forests and climate change resource center:
http://www.fs.fed.us/ccrc/topics/urban-forests/

Tables

Table 1. 

Annual carbon sequestration by trees and lawns in different types of Florida urban greenspaces.

Greenspace type

Tree cover

(m2)

Lawn cover

(m2)

Tree seq.

Lawn seq.

CO2 emitted - lawn

CO2 emitted - tree

Net annual (CO2 kg/yr) sequestration for a 4 hectare site

Miami-Dade

Tree/lawn cover per 400 m2 plot

Tree/lawn CO2 sequestration per 400 m2 plot (kg CO2/yr)*

CO2 emissions- tree/lawn maintenance per 400m2 plot (CO2kg/yr)T

(CO2 kg/yr)

Hammock

380

0

4653

0

0

0

465,330

Pine Rockland

120

0

70

0

0

0

6,980

Mangrove

400

0

3031

0

0

0

303,060

Commercial

72

8

247

0.3

3

6

23,860

Residential old

280

380

25

16

153

23

-13,570

Residential new

180

52

7

2

21

15

-2,640

Park/school

20

340

17

14

137

2

-10,800

Gainesville

             

Pine hardwood

240

0

699

0

0

0

69,910

Swamp cypress

300

0

904

0

0

0

90,360

Plantation

200

0

162

0

0

16

14,570

Commercial

200

0

237

0

0

16

22,050

Residential old

360

100

428

4

36

29

36,660

Residential new

100

260

124

11

93

8

3,350

Park/school

0

88

0

4

32

0

-2,800

Orlando

             

Pine palmetto

260

0

445

0

0

0

44,520

Oak pine

360

0

102

0

0

0

10,240

Cypress dome

320

0

1102

0

0

0

110,170

Commercial

40

80

39

3

29

3

1,020

Residential old

340

140

442

6

50

28

36,960

Residential new

60

80

63

3

29

5

3,280

Park/school

0

284

0

12

102

0

-9,050

*Lawn sequestration rate (grass stubble only)1 is 48.1 g CO2 m-2 yr -1

**Lawn maintenance numbers are from three sources of carbon: fuel to maintenance equipment (122 g CO2 m-2 yr -1)2, energy for irrigation (193 g CO2 m-2 yr -1)3, and fuel inputs to manufacture fertilizer (1.436 moles of C per mole of N produced)5. Tree maintenance2 is 81 g CO2 m-2 yr -1.

TLow fertilization rate recommended by IFAS for St. Augustine grass in south Florida4 - 4lbs 1000 ft-2 yr -1

TLow fertilization rate recommended by IFAS for St. Augustine grass in central Florida5 - 2lbs 1000 ft-2 yr-1

1Jo, H. and McPherson, G.E. (1995). Carbon storage and flux in urban residential greenspace. Journal of Environmental Management 45: 109-133.

2Townsend-Small, A. and Czimczik, C. I. (2010). Carbon sequestration and greenhouse gas emissions in urban turf. Geophysical Research Letters. 37, L02707, doi:10.1029/2009GL041675.

3Schlesinger, W. H. (1999). Carbon sequestration in soils, Science, 284, 2095, doi:10.1126/science.284.5423.2095.

4http://hort.ifas.ufl.edu/yourfloridalawn/

5http://hort.ifas.ufl.edu/yourfloridalawn/

Footnotes

1.

This document is WEC279, one of a series of the Wildlife Ecology and Conservation Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date March 2010. Revised January 2013. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Mark Hostetler, associate professor and Extension specialist, Department of Wildlife Ecology and Conservation, University of Florida, P.O. Box 110430, Gainesville, FL 32611-0430; and Francisco Escobedo, assistant professor, School of Forest Resources and Conservation, P.O. Box 110806, University of Florida, Gainesville, FL 32611-0806


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.