Scientist explains ASAP research on impacts of population growth on local ecosystems
By Sean Tubbs
Monday, September 28, 2009
Trees capture carbon dioxide from the air. Open space helps filter groundwater to make it safer for drinking. These are two examples of “ecosystem services” that can be affected by population growth, but until now there has been no attempt to study what links there may be between the two.
Advocates for a Sustainable Albemarle Population
(ASAP) recently raised $112,000 to conduct a series of studies to establish an “optimal sustainable population size” for Charlottesville and Albemarle County.
The City contributed $11,000
County contributed $25,000
towards five studies, one of which was to analyze how different levels of population growth would affect the ability of the landscape to provide ecosystem services.
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ASAP hired Claire Jantz, a land use expert from Shippensburg University in Pennsylvania, to conduct the analysis into the area’s ecological carrying capacity. She was in Charlottesville this week to give briefings to the City Council, Albemarle County Board of Supervisors and the League of Women Voters of Charlottesville-Albemarle.
In her research, she first identified the current level of ecosystems services, then came up with several population scenarios for how population would grow. She then compared how population demands would affect the ability of the landscape to provide the services.
Her work began with a combined City-County population of 124,285 based upon the 2000 U.S. Census. She then used a program called CityGREEN that measures the environmental benefits of trees and green space, and cross-examined the effects on those benefits as population increases. The land cover data is from 2001.
Different sections of the community were assigned different “land-consumption” ratios based on different zoning and allowable densities. Each time a new theoretical person moves to the area, Jantz’s work assumes that a certain percentage of forest is cut down.
“For every new person that went into Charlottesville, we had to convert .16 acres of forest or open space into development,” Jantz said. People moving into rural areas used even more land per new person
Jantz’s research assumed that these densities would not change over the course of population build-out. She further assumed that when one area reached “build-out,” population would automatically spill over into neighboring areas.
According to Jantz, Charlottesville and Albemarle’s urban ring will reach a “build-out” with and added population of 111,882. She said the ability of rural areas to provide ecosystem services will deteriorate when population growth reaches 125% of current levels. However, her work does not offer any time horizons for when the development would occur. “I did not look at growth rates over time, and I’m actually not 100% sure what the growth rate is for the region,” Jantz said. “When the growth areas run out of space, that’s when we start to see a lot more development pressure in the rural areas,’ Jantz said.
And with that pressure would come more forests being lost to development, according to Jantz. At all three presentations, she demonstrated how that would reduce the ability of the land to sequester carbon, scrub carbon monoxide, protect from erosion, as well as other services.
“The rural areas are very important for maintaining ecosystem services for the whole study area, but what’s happening is the [growth areas] are the areas that experience the most loss of services up until we see growth pressure in the rural areas as well,” Jantz said.
Jantz said this baseline study provides a tool that can be adjusted as conditions and policies change. She stopped short of offering recommendations, but appeared to indicate that Albemarle County was moving in the right direction.
“The strategy of directing growth into the developing areas has the best chance of offsetting community wide impacts on ecosystems services,” Jantz said. She said the urban areas should work towards installing green roofs, implementing urban forestry management practices, and incorporating low-income development strategies. Both the City and County have begun installing green roofs on their administration buildings. The City recently announced it has attained a tree canopy of 45%.
However, Jantz said after the population reaches a certain point, the landscape’s ability to provide ecosystem services will degrade.
“Given what we found, that seems to happen at about 300,000 people,” Jantz said.
, a Republican candidate for the Board of Supervisors, asked if her analysis took into the amount of land that had been placed into conservation. Jantz responded that her study assumed that no additional lands would be placed into easements because otherwise it would have been too complex an analysis for this initial study.
“This is a first broad brush approach where we used the simplest assumptions that we could so we could move forward with the study,” Jantz said.
ASAP plans four more studies as part of the first phase of its project. The next to be released will look at what resources Albemarle County and Charlottesville are currently using, as well as projected demands as population grows. Additional studies include an air quality report, a report on stream health, and a report on how groundwater is affected by population growth.
A second phase, which will not be paid for with City and County money, will examine the socioeconomic issues related to growth, including a report from
opponent and ASAP Board member
on how the character of a community changes as it increases in size.