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August 2007 Issue

Research Design Connections
Studies examine the retail value of trees, psychological effects of roadside plantings, and not driving in national parks.

By Sally Augustin and Jean Marie Cackowski-Campbell, ASLA

Rsearch Design Connections William Brown

Studies examine the retail value of trees, psychological effects of roadside plantings, and not driving in national parks.

By Sally Augustin and Jean Marie Cackowski-Campbell, ASLA

Landscape Architecture, in partnership with the web-based newsletter and daily blog Research Design Connections, uses this column to report current research of interest to landscape architects from a wide array of disciplines. We welcome your comments, suggestions about future topics, and studies you have encountered in your own practice.

Trees Earn Their Keep

Recent research by Kathleen Wolf builds on previous studies that show the positive effects of trees on judgments of visual quality and, in particular, on consumer behavior. Two studies by Wolf, reported together, indicate that trees increase people’s positive perceptions of central business districts in cities and towns of various sizes, generate shopping activity, and enhance perceptions of product pricing. Wolf says she was motivated to conduct her survey-based research because few marketing studies “have looked beyond the door of the store to assess the consequences of streetscape character and shopping response.”

Wolf presented study participants with images of business districts with varying numbers of trees. The responses revealed that:

  • Participants consistently valued the presence of trees in images presented to them. “Image categories depicting business district settings having tidy sidewalks and quality buildings but no trees were at the low end of the preference ratings. Images having well-tended large trees received the highest preference ratings, even though plants obscured other elements (such as historic buildings) that often are the targets of business-improvement programs.” 

  • Participants valued both openly pruned and densely canopied trees, which indicates that trimming trees for better visibility of buildings or storefronts doesn’t diminish shoppers’ positive responses to the trees.

From these responses, Wolf concludes that “limbing up” and thinning the canopies of large trees “is a better management strategy for visual quality enhancements than topping [trees] at sign levels or planting smaller trees [whose] mature canopy height is the same as business windows and signage.” The study also linked the presence of trees to more positive conjectures about in-store experiences. “Judgments of products and merchants were more positive in forested places as were inferences about product value, product quality, and merchant responsiveness,” Wolf notes. “Respondents infer that the green streetscape has more positive atmosphere, image, and comfort level and would be a more favorable place to visit and dine out.”

Participants reported that once drawn to sylvan streetscapes, they would be willing to pay more for parking, goods, and services in areas with trees. These increased parking fees, along with the increased store revenue that can reasonably be associated with the longer time periods that people indicated they would spend in areas with trees, may provide the needed financial support for tree planting in shopping districts.


  • “Business District Streetscapes, Trees, and Consumer Response,” by Kathleen Wolf; Journal of Forestry, vol. 103, no. 8, 2005.

  • “Trees in the Small City Retail Business District: Comparing Resident and Visitor Perceptions,” by Kathleen Wolf, Journal of Forestry, vol. 103, no. 8, 2005.

Landscape Improves Road Safety

Is the roadside landscape a stress buster or a fender bender? Environmental psychologists have argued the first point, while transportation researchers have often argued the second, because of the seriousness of vehicle/tree collisions and the potential for designed roadside landscape to distract drivers. Recent research in Texas allows environmental psychologists to chalk up a point for their position.

The study, by Jeong-Hun Mok, Harlow Landphair, ASLA, and Jody Naden, reports that along 10 test sections of road, planted roadside landscape was linked with a significant decrease in crash rates. The researchers chose study sites in eight different cities. Eight of the study locations were on interstate or major arterials, and two were on city streets. The authors analyzed data collected by state agencies on 5,874 crashes during the three- to five-year periods before and after the landscape changes took place. The analyses included all types of crashes that occurred along these sections of road, although the researchers eliminated crashes during the year the landscape plantings were made, because the landscape had not yet assumed its final form.

The authors say that “the results show that there was a significant decrease in crash rates after landscape improvements,” and “the calculated reduction factor of tree collisions shows a decrease of about 70.83 percent on tree collisions after landscape treatments at 10 study locations.”

Mok and his colleagues conclude that “the use of roadside plantings is having a positive effect on overall performance and can be used as a tool to improve the safety performance of urban streets.” The authors also recommend that “when developing urban corridors, consideration should be given to the development of the landscape as an integral part of the safety management within the corridor. The landscape not only contributes to greater aesthetic compatibility between the urban environment and the highway but may contribute to a safer street.”


  • “The Landscape Improvement Impacts on Roadside Safety in Texas,” by Jeong-Hun Mok, Harlow Landphair, ASLA, and Jody Naden; Landscape and Urban Planning, vol. 78, 2006.

Over the Hills and Through the Woods—in Yosemite

Automobile-based transportation has traditionally reigned supreme within the national park system and has always been the primary mode of transportation to the parks. Within the parks, this has “contributed to traffic congestion, parking shortages, visitor crowding, localized air pollution, noise pollution, wildlife impacts, and roadside vegetation disturbance,” researcher Dave White notes. This has led Congress to allocate funds to encourage alternative modes of transportation within the national park system. Several national parks, including Yosemite, have promoted walking and bicycling and introduced alternative transportation systems such as buses, trams, and other group transportation. Although White reports some details of these options in other parks, his research focuses on the system in Yosemite, which promotes buses, bicycling, and walking.

Under the right conditions, Americans visiting national parks are amenable to using alternative transportation rather than their own vehicles while in the park. According to White, some of the influences on the use of alternative transportation in Yosemite National Park included previous experiences in the park and with public transportation (in other national parks or outside them), features of the transportation system, and the length of their visit. This research, he writes, begins to “suggest approaches for shaping the way Americans visit and experience their national parks to encourage environmental sustainability.”

White used in-park interviews with 160 visitors to collect the data for this study. The interviews revealed that a host of individual psychological factors as well as situational influences affect whether visitors choose alternative transportation. The interview method allows the researcher to probe, interactively, topics of interest with interviewees, which is not possible with a static, written survey. 

White’s comprehensive study found:

  • Interviewees linked use of their private automobile within the park to convenience, scheduling freedom, control, and unique access to park features. Nearly all of those interviewed linked car use with convenience

  • Visitors also related private automobile use to traffic, crowding, and getting lost. Visitors did not generally view these problems as very important or as detracting from their enjoyment of Yosemite.

  • Visitors see the Yosemite bus shuttle as eliminating problems related to traffic, parking, and getting lost. People chose to use the shuttle when they experienced traffic and parking issues. Their criticisms of the shuttle generally related to crowding, wait times, scheduling, and routes.

  • Visitors reported that walking and bicycling within the park allowed them “to take their time, focus on their immediate surroundings, move at their own pace, and connect to the park and its natural and cultural features in an environmentally friendly way.” They viewed bicycles, in particular, as a faster, freer, and more environmentally friendly way to travel between two points than either buses or cars.

  • Interviewees were most likely to be walking or riding bicycles when their most significant or memorable park experiences took place. 

  • More than half of the people who participated in this study felt that alternative transportation should be encouraged within Yosemite, particularly as these modes are environmentally responsible, reduce crowding, alleviate traffic and parking problems, and encourage meaningful experiences. They positively viewed alternative transportation both within the park and to the park.

  • The research indicated that if visitors had had positive experiences with other alternative transportation in national parks, they would have a more positive response to Yosemite’s alternative transportation.

White concludes the article by suggesting that park managers maximize the convenience, accessibility, and flexibility of park shuttles and communicate to visitors that alternative transportation is the more environmentally friendly choice. Also, visitors should be made aware of the connection between walking and bicycling and meaningful park experiences.


  • "An Interpretive Study of Yosemite National Park Visitors’ Perspectives Toward Alternative Transportation in Yosemite Valley," by Dave White; Environmental Management, vol. 39, 2007.

Sally Augustin, RDC’s senior editor, is an environmental psychologist. Jean Marie Cackowski-Campbell, ASLA, is the publisher of Research Design Connections and has an MLA degree from Ohio State University. 

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