Grantee Research Project Results
Final Report: Creating Sustainability Indicators to Assess the Physical, Social, and Economic Values of Greening Cities - A Study of the Million Trees Initiatives in Los Angeles, CA
EPA Grant Number: R833364Title: Creating Sustainability Indicators to Assess the Physical, Social, and Economic Values of Greening Cities - A Study of the Million Trees Initiatives in Los Angeles, CA
Investigators: Saphores, Jean-Daniel , Gillespie, Thomas W , Pataki, Diane , Pincetl, Stephanie
Institution: University of California - Irvine , University of California - Los Angeles
EPA Project Officer: Hahn, Intaek
Project Period: March 1, 2007 through February 28, 2010 (Extended to February 28, 2012)
Project Amount: $299,985
RFA: Collaborative Science And Technology Network For Sustainability (2006) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities
Objective:
The overall goal of this project was to build sustainability indicators for urban forests with a focus on Los Angeles and to shed light on the social dynamics of implementing sustainability in large urban areas. We studied the Million Trees Initiative in Los Angeles, CA, using an integrated systems approach that combined biology, Earth system science, remote sensing, geography and economics. We set out to perform the following tasks:
1) Using remote sensing, map vegetation and its leaf area index (LAI) throughout Los Angeles over time;
2) Conduct in-situ measurements of urban tree function, and overlay meteorological data and concentrations of EPA criteria pollutants;
3) Integrate these data with housing and key urban characteristics in a GIS database;
4) Perform hedonic studies to quantify the impacts of urban forests on the housing market;
5) Define and calculate sustainability indicators for various neighborhoods, in cooperation with city agencies, NGOs, and the public; and
6) Document and disseminate our findings.
Summary/Accomplishments (Outputs/Outcomes):
When historic tree density reconstructions were examined for the 15 Los Angeles city council districts from the 1920s, 1950s and 2006, we found that most council districts experienced a significant increase in tree density, albeit with wide variations among city council districts. Trees densities have generally been higher on private land since the 1920s and this is still the case today. Results suggest the evolution of urban forests in Los Angeles mirrors the dynamics of urban forests in desert and grassland cities. Although there is still space to plant trees on public land, private land owners will need to be heavily involved to achieve the goals of Los Angeles’ Million Tree Initiative.
To evaluate the performance of trees and lawns in Los Angeles' urban environment, and to quantify environmental costs and benefits of different types of urban landscaping, we conducted three sets of studies. First, we focused on understanding the effects of pollution on urban plants, which is a-priori complex because of the interactions of multiple pollutants and local variations in the local climate. Our results showed (Wang and Pataki, 2010) that plant isotopes can be reliably used as indicators of exposure to pollutants. Our evaluation of the historical influence of pollution using climate records, pollution monitoring records, and measurements of tree rings in cores (Djuricin, et al., 2012a, 2012b) further showed that trees have responded to the reduction in atmospheric pollutant concentrations that occurred in Los Angeles following EPA regulations.
Second, we measured the water use of mature trees of many species grown throughout the study region, thus generating the first estimates of urban forest transpiration available in the literature. We found a strong sensitivity of forest transpiration to species in Los Angeles (Pataki, et al., 2011a). Using a novel approach involving the isotopic composition of water, we also found that many urban trees in Los Angeles are using a combination of irrigation water and groundwater for transpiration (Bijoor, et al., 2012).
Third, we examined tradeoffs between water loss and carbon fixation in trees using a Water Use Efficiency (WUE) measure defined as the ratio of carbon fixed to water lost. We used WUE as a proxy for urban ecosystem services because carbon fixation is a direct ecosystem service (through sequestration of CO2), and because it is indirectly related to canopy size, shading, and stormwater mitigation. Our results showed that WUE is related to the native habitat of the imported species considered (McCarthy, et al., 2010). An application of this approach to horticultural shrubs imported from different parts of the world showed that well-watered shrub species from arid environments could (surprisingly) have very high rates of transpiration and gas exchange, presumably as an adaptation to episodic availability of water following rain events in deserts (Goedhart, et al., 2012).
To quantify the impact of Los Angeles’ urban forests on the housing market, we performed two hedonic studies that rely on state-of-the-art econometric techniques. First, we analyzed 20,660 transactions of single family detached houses sold in 2003 and 2004 in Los Angeles, CA, to estimate the value of urban trees, irrigated grass, and non-irrigated grass areas (Saphores and Li, 2012). To deal with spatial autocorrelation and unobserved neighborhood characteristics, we contrasted two models: a geographically weighted regression model, and a Cliff-Ord model with spatial lags in the dependent variable, the exogenous variables, and the disturbances as well as submarket fixed effects and an extensive set of covariates. We found that Angelenos like lawns: more than 88 percent of the properties examined would gain value with additional irrigated grass on their parcel or in their neighborhood. However, additional parcel trees would decrease the value of almost 40 percent of the properties examined and they would have only a small positive impact on most of the others. By contrast, additional neighborhood trees would slightly increase the value of more than 97 percent of the properties analyzed. This suggests that while Angelenos may want more trees, they are unwilling to pay for them.
In a second study, we estimated how urban green spaces (tree canopy cover and grassy areas) impact the value of multifamily buildings based on 1,197 multifamily buildings sold in 2003-2004 in Los Angeles. To assess the robustness of our results, we contrasted a spatial Durbin model with a geographically weighted regression model and conducted an extensive sensitivity analysis. We found that increases in grassy areas either on the parcels of multifamily buildings or in their vicinity (200 meters outward of each parcel boundary) would typically not enhance their value, and neither would more parcel tree canopy cover (TCC), possibly because additional space for trees would decrease space for parking; by contrast, most multifamily properties would benefit from an increase in neighborhood tree canopy cover.
These results have implications for urban tree planting programs that rely primarily on private property owners, such as Los Angeles’ tree planting program.
The last component of our project encountered the most difficulties because creating local environmental indicators in Los Angeles had a strong political dimension that had the potential for stoking fears in parts of the city, so we had to abandon the creation of environmental indicators at the council district level to focus instead on environmental indicators at the city level. For more than a year, we worked closely with the Bureau of Public Works to propose a comprehensive set of environmental indicators, including indicators of urban green spaces. However, because of the severity of the economic crisis, the city restructured a number of its departments and centralized the creation of environmental indicators in the Mayor’s office. In 2010, we started working with the person in charge of sustainability in the Mayor’s office to create city-wide environmental indicators with some indicators dealing with urban green spaces. Overall, we found that environmental quality in Los Angeles is improving. The City is a recycling and waste management leader, and it has made substantial efforts to reduce its water consumption (partially because of the recent regional drought) and to use energy more efficiently thanks to a number of programs. Air quality also is improving slowly, although air pollution is a regional problem. Regarding urban green spaces, Los Angeles has been creating additional parks (although it remains park-poor compared to other large U.S. cities) and it has been planting approximately 60,000 trees per year on average since the start of its tree planting program. Although this number is substantial, it is below initial expectations, partly because of the economic crisis but also for institutional reasons. Because this part of our work was completed only recently, there was no time to get feedback from non-governmental organizations or from the public. We will attempt to obtain feedback after these environmental indicators have been made public.
Conclusions:
This study made several contributions. First, it reconstructed the temporal evolution of urban forests in Los Angeles over several decades and showed that tree density has been higher on private lands. Second, it showed that plant isotopes can be reliably used as indicators of exposure to pollutants; it also presented a novel way to study water use by urban trees and illustrated that water use by urban trees differs from similar species in non-urban environments. Third, we found that urban trees do not necessarily increase property values, as is often assumed in the urban planning/landscaping literature that relies on benefits transfers, especially for multi-family buildings. Our analyses also underscore the importance of institutions for executing ambitious tree planting programs in urban environments. Finally, although we encountered difficulties in creating local environmental indicators for Los Angeles, we worked with the City of Los Angeles to create a set of city-wide environmental indicators that also provide some useful information about green space in Los Angeles. Findings from this project should be useful to other large cities with Mediterranean climates, for large urban tree planting programs, and more generally for implementing urban sustainability.
Journal Articles on this Report : 16 Displayed | Download in RIS Format
Other project views: | All 23 publications | 16 publications in selected types | All 16 journal articles |
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Bijoor NS, McCarthy HR, Zhang D, Pataki DE. Water sources of urban trees in the Los Angeles metropolitan area. Urban Ecosystems 2012;15(1):195-214. |
R833364 (2007) R833364 (Final) |
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Djuricin S, Xu X, Pataki D. The radiocarbon composition of tree rings as a tracer of local fossil fuel emissions in the Los Angeles basin:1980–2008. Journal of Geophysical Research 2012;117:D12302. |
R833364 (Final) |
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Gillespie TW, Pincetl S, Brossard S, Smith J, Saatchi S, Pataki D, Saphores J-D. A time series of urban forestry in Los Angeles. Urban Ecosystems 2012;15(1):233-246. |
R833364 (Final) |
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Goedhart CM, Pataki DE. Do arid species use less water than mesic species in an irrigated common garden? Urban Ecosystems 2012;15(1):215-232. |
R833364 (Final) |
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Li W, Saphores J-D. A spatial hedonic analysis of the value of urban land cover in the multifamily housing market in Los Angeles, CA. Urban Studies 2012;49(12):2597-2615. |
R833364 (Final) |
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Litvak E, McCarthy HR, Pataki DE. Water relations of coast redwood planted in the semi-arid climate of southern California. Plant, Cell & Environment 2011;24(8):1384-1400. |
R833364 (Final) |
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Litvak E, McCarthy HR, Pataki DE. Transpiration sensitivity of urban trees in a semi-arid climate is constrained by xylem vulnerability to cavitation. Tree Physiology 2012;32(4):373-388. |
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McCarthy HR, Pataki DE. Drivers of variability in water use of native and non-native urban trees in the greater Los Angeles area. Urban Ecosystems 2010;13(4):393-414. |
R833364 (Final) |
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McCarthy HR, Pataki DE, Jenerette GD. Plant water-use efficiency as a metric of urban ecosystem services. Ecological Applications 2011;21(8):3115-3127. |
R833364 (Final) |
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Pataki DE, McCarthy HR, Litvak E, Pincetl S. Transpiration of urban forests in the Los Angeles metropolitan area. Ecological Applications 2011;21(3):661-677. |
R833364 (Final) |
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Pataki DE, Carreiro MM, Cherrier J, Grulke NE, Jennings V, Pincetl S, Pouyat RV, Whitlow TH, Zipperer WC. Coupling biogeochemical cycles in urban environments: ecosystem services, green solutions, and misconceptions. Frontiers in Ecology and the Environment 2011;9(1):27-36. |
R833364 (Final) |
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Pataki DE, Boone CG, Hogue TS, Jenerette GD, McFadden JP, Pincetl S. Socio-ecohydrology and the urban water challenge. Ecohydrology 2011;4(2):341-347. |
R833364 (Final) |
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Pincetl S. Implementing municipal tree planting: Los Angeles million-tree initiative. Environmental Management 2010;45(2):227-238. |
R833364 (Final) |
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Pincetl S, Gillespie T, Pataki DE, Saatchi S, Saphores J-D. Urban tree planting programs, function or fashion? Los Angeles and urban tree planting campaigns. GeoJournal 2012;doi:10.1007/s10708-012-9446-x. |
R833364 (Final) |
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Saphores J-D, Li W. Estimating the value of urban green areas: a hedonic pricing analysis of the single family housing market in Los Angeles, CA. Landscape and Urban Planning 2012;104(3-4):373–387. |
R833364 (2007) R833364 (Final) |
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Wang W, Pataki DE. Drivers of spatial variability in urban plant and soil isotopic composition in the Los Angeles basin. Plant and Soil 2012;350(1-2):323-338. |
R833364 (Final) |
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Supplemental Keywords:
Sustainability indicators, sustainable development, land use, urban forest, GIS, conservation, ecosystem management, water supply, RFA, Scientific Discipline, Sustainable Industry/Business, Sustainable Environment, Technology for Sustainable Environment, Environmental Monitoring, Ecology and Ecosystems, green design, ecological design, environmental sustainability, alternative infrastructure design, sustainable urban environment, economic input output, environmental education, million trees initiativeRelevant Websites:
http://www.geog.ucla.edu/latree/ Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.