Green Spaces

Introduction

The implementation of increased urban green spaces holds significant potential for mitigating the harmful effects of climate change, in addition to other social and environmental benefits. “Green spaces” refer to urbanized areas hospitable to tree growth, including parks, greenways, gardens, and paths. Green space tackles all three climate threats identified as affecting coastal communities by Mission 2021– heat rise, rising sea levels, and severe weather– in addition to contributing to our preventative plan by counteracting carbon emissions.

Investment in green space along coastal regions of Cambridge and bordering concentrated transportation routes presents a viable, multifaceted solution adddressing several climate risks. As it specifically pertains to sea level rise and inland flood threat, increased green space provides more plant life for water absorption and retention, providing alternate paths for flowing water to enter other than into city streets, buildings, and subway stations. In an October 2017 interview with a Mission 2021 representative, MBTA Climate Change Resiliency Specialist Marybeth Gilbert stated that increased green space along coastal areas of the city can also provide a buffer in case of unavoidable rising waters. If sea levels surpass shores, flood barriers or dams, installing greenways and trees to absorb incoming waters results in reduced risks to people and city infrastructure. Increasing tree canopy also addresses the issue of high temperatures concentrated in small, specific areas, formally known as “urban heat islands.” The City of Cambridge’s 2015 Climate Change Vulnerability Assessment (CCVA) plotted temperature vs. tree canopy in a simple linear regression, indicating a direct correlation between the two as illustrated in the graph below.^[1] The regression slope of -0.1157 indicates that for every percent increase in tree canopy there correlates a localized temperature decrease of approximately 0.12 degrees Fahrenheit. While increasing tree canopy in Cambridge may have negligible impact on the rising global average temperature, the city can feel significant, concentrated positive effects as a result of its implementation.

Increased green spaces improve air quality by counteracting carbon emissions, especially within concentrated urban communities such as Cambridge. In a 2002 report sponsored by the USDA Forest Service, researchers studying carbon storage and sequestration claimed that “urban trees currently store 700 million tons of carbon, with an annual sequestration rate of 22.8 million tons.” Urban tree cover veritably reduces ambient concentrations of ozone, particulates, and other dangerous pollutants to maintain high air quality in even the most concentrated populations. While implementing this solution focuses primarily on climate adaptation to mitigate threatening effects and its measurable economic feasibility, the positive social and environmental externalities of urban tree coveralso contribute to the appeal and of the solution.

 

Solutions

Increasing green space on public lands and encouraging private citizens to participate as well provides a financially and physically feasible solution to addressing the risks associated with the threats of heat rise, severe weather, and sea level rise. This solution addresses several of Mission 2021’s identified climate change risks, in addition to providing social, public health, and aesthetic benefits. When considering this solution, municipal bodies will most likely contend two predominant issues: finding both the ideal space and the necessary funding for planting new trees. Fortunately for climate risk mitigation plans, these concerns taper with higher understanding of site-specifics and economic valuations.

In A Report on the City of Cambridge’s Existing and Possible Tree Canopy, researchers from the municipal government published data comparing existing tree canopy to areas with potential for increased coverage.^[2]

As illustrated in the righthand graph provided in the report, the MIT/Area 2 displayed a high percentage for possible tree coverage relative to other areas of Cambridge, attributing its ability to support new canopy to its diverse mix of surface vegetation and areas lacking impervious infrastructure, such as roads and buildings. Relocating the current occupants, commonly parking lots and recreational fields, of areas showing potential for tree coverage presents the primary obstacle in establishing more canopies. Residential neighborhoods display the highest existing tree coverage percentages, which accounts for the lower potential percentages for central Cambridge. Accounting for the research obtained from the tree canopy report, one optimal method of increasing green space for the region would be to focus on the MIT/Area 2 neighborhood itself to increase its existing tree coverage to the 41%-45% category by 2050.

In a report utilizing a cost-benefit analysis of investment in urban tree planting and maintenance developed by the US Forest Service Center for Urban Forest Research, analysts calculated the economic benefits achieved per dollar spent in eight U.S. cities.^[3] This analysis took into account all significant quantifiable factors affecting the financials of urban tree coverage investment. Measurable benefits include lowered costs for stormwater treatment, energy savings for heating and cooling, carbon sequestration, air quality improvement, and increased property values.

Calculated costs of planting and maintaining urban trees include pruning, tree and stump removal, pest and disease control, irrigation, infrastructure damage repair, litter cleanup, litigation and settlements for tree-related claims, and program administration. Results, displayed in the table below, indicated that not only did the financial benefits of urban planting match the initial one dollar investment, but that in all eight analyzed cities this solution resulted in significant net-positive returns ranging from just under $1.50 per dollar spent in Berkeley, CA to $3.25 in Charlotte, NC.Beyond the returns given by measured analysis, tree cover provides innumerable social, community, public health, and aesthetic benefits to any urban community.

 

By Jen Fox

 

References

1. Kleinfelder. (2015). Appendix D – Urban Heat Island Protocol. CCVA. Retrieved from https://www.cambridgema.gov/cdd/projects/climate/~/media/007A3255079540399C25A78038B961A9.ashx
2. A Report on the City of Cambridge’s Existing and Possible Tree Canopy. (2012, June 1). University of Vermont. Retrieved from https://www.fs.fed.us/nrs/utc/reports/UTC_Report_Cambridge.pdf
3. Raciti, S., et al. (2006). Urban Tree Canopy Goal Setting – Chesapeake Bay Program. United States Department of Agriculture. Retrieved fromwww.chesapeakebay.net/documents/UTC_Guide_Final.pdf