Trees and Their Impact on Economic Development

1 02 2010

Hill Center Green Hills, Nashville, TN

A discussion was started on the ASLA LinkedIn group last week regarding street trees’ impact on retail districts. The discussion centered on Professor Kathleen Wolf’’s research. Professor Wolf is a Research Social Scientist in the University of Washington’s College of Forest Resources Department. She has been at the forefront of the research being conducted in this area. Like the landscape architect who started the conversation, I have also been wondering if anyone has taken her research a step further. Professor Wolf’s research relies on user surveys that include both visual preference surveys and traditional questionnaires that ask respondents to rate environments and/or their willingness to pay more for a product.

In an Arborist News article published last year, Dr. Wolf reported on the work she has been doing. In the article, she reports that across all categories, places rated steadily higher with the increased presence of trees. Larger trees rated higher than smaller trees. Her surveys that looked at product pricing within districts with trees indicated that customers are willing to pay 9 percent more in smaller cities and 12 percent more in larger cities.

In her response to an emailed question posted on LinkedIn, she explains that she does not suggest that trees are the panacea for other business challenges and that there is not a simple casual link between having trees and increased revenues. Street trees and streetscapes are positive reinforcement of the “atmospherics” that market researchers consider to have influence on consumer’s buying habits.

I agree that street trees and streetscapes do add a considerable amount to the ambiance and character of place that people enjoy. Anecdotally, I think most people can understand the impact trees have on how we feel in a space/district. However, since retail success can be very sensitive to location and surrounding demographics, it can be difficult to make a clear connection between retail sales and trees. I hope that research continues to make the case, and like the sophisticated interior research done by market researchers, we can continue to increase our understanding of this relationship.

The article in Arborist News also offered some guidelines on street trees in retail districts such as the proper tree species, size, maintenance, and providing signage that contrasts with the trees’ foliage. I would add that tree placement along the street and their relationships to the doors, windows, and dividing walls between businesses are also important to consider.

The reports on Professor Wolf’s website Human Dimensions of Urban Forestry and Urban Greening are worth checking out.

-Brian Phelps


Comments : Comments Off on Trees and Their Impact on Economic Development
Tags: , , ,
Categories : Streetscape, Sustainable Site Strategies

Trees Please

11 12 2009

Street Trees at Hill Center Green Hills

This year many cities in the Southeast have already exceeded their average rainfall by over 20%. As a result, we’ve heard many stories about flooding and 500 year flood events in the Atlanta area and elsewhere. I wondered about the ability of tree planting to affect stormwater. I have seen various reports referring to the benefits of trees based on their ability to reduce stormwater through evaporation of rainwater which lands on its leaves and branches back into the atmosphere, and through the infiltration of rainwater into the ground reducing the total amount of runoff and also affecting the peak flows by making slight reductions to the volume of stormwater runoff.

Over the past few decades, American Forests has developed an analysis that they refer to as an Urban Ecosystem Analysis (UEA) in over 40 metro areas in the U.S. These reports quantify a number of benefits provided by trees especially relating to stormwater benefits , air pollution reduction and carbon sequestration. The assessment is based on specific GIS modeling of tree canopy for regional and site specific areas within each municipality it studies. The GIS studies also show that impervious surfaces have increased by 20% over the past 2 decades in urban areas. American Forests has developed tree canopy goals for various areas in the United States, with the following recommended generally for cities east of the Mississippi.

AMERICAN FORESTS’ General Tree Canopy Goals
40% tree canopy overall
50% tree canopy in suburban residential
25% tree canopy in urban residential
15% tree canopy in central business districts

I noted that several southeastern cities had had an Urban Ecosystem Analysis including nearby Chattanooga and Knoxville. I also found some data for Charlotte/Mecklenburg County. One of the critical items that the UEA measures is loss of tree canopy. Some of the losses noted are staggering.

Between 1984 and 2001, Mecklenburg County (Charlotte, NC) lost over 22% of its tree cover and 22% of its open space. Over that same time period, the county’s impervious surfaces increased by 127%. By comparison between 1974 to 1996 Chattanooga and its nearby neighbor, Atlanta, both lost 17% of its regional tree cover.

Even with the dramatic percentage of loss noted in Mecklenburg Co, the 2002 UEA still noted that Charlotte, whose city limits are within Mecklenburg County, still exceeds the Tree Canopy Goals mentioned above at 49% Tree Canopy. The city’s tree canopy is valued of $398 million dollars based on a total stormwater retention capacity of Charlotte’s existing urban forest of more than 199 million cubic feet. This translates into a value of approximately $398 million dollars (based on construction costs estimated at $2 per cubic foot to build equivalent retention facilities). Chattanooga comparatively achieved a Tree Canopy Goal of 22.5%.

In a ten year period from 1989 to 1999, Knox County (Knoxville, TN) lost a less dramatic 2.2% of its regional tree cover. Knoxville’s tree canopy measured at 40% of the total land area just met the 40% American Forest Tree Canopy Goal. This was assessed by the UEA to have a value equal to $280 million dollars.. This value is based on a total stormwater retention capacity and related construction costs to build equivalent retention facilities noted in the above Charlotte example. UEA also quantified that the tree cover in Knoxville sequesters more than 2.3 million pounds of pollutants from the air, with a value of more than $5.9 million.

As we consider the goal of increasing our Tree Canopy cover and, especially, the American Forests recommendation of 15% Tree Canopy cover for central business districts, consider that the Knoxville UEA study and The Green Build-out Model: Quantifying the Stormwater Benefits of Trees and Green Roofs in Washington, D.C . completed in 2007, noted a difference in a tree’s stormwater benefit based on whether it was over a pervious or impervious surface. The D.C. report modeled that trees over impervious areas, such as a sidewalk or parking lot, provided a stormwater benefit that was over 5 times that of a tree over a pervious surface such as grass or planting beds. The Knoxville report further noted that it requires ten or more newly planted trees to equal a single large mature tree’s ecological value.

-Kim Hawkins


Comments : Comments Off on Trees Please
Tags: , , , , , ,
Categories : Plans and studies, Sustainable Site Strategies