Esthetic Perceptions of The Urban Forest: A Utility Perspective

Basic benefits of urban trees

Research on human response to landscapes has consistently shown that environments with natural elements such as trees are highly preferred to urban scenes lacking vegetation (12, 13). The presence of natural features in urban environments can increase residents' overall satisfaction with their living conditions (3, 5).

When people are asked to describe in their own words what kinds of experiences they have in environments with natural vegetation, the most frequent responses are beauty and tranquility (7). The calming quality of vegetation can also be measured physiologically. Pulse rate, blood pressure, and brain wave recordings show that a person viewing a vegetated landscape is more relaxed than a person viewing an urban scene without vegetation (12), and that vegetation promotes recovery from stress (14). Thus trees can provide a partial remedy for the stress and ugliness that are too often associated with urban living. It is not surprising that people often become upset when their trees are removed or severely pruned.

Attitudes towards street trees and their management

Survey research has helped us find out how people attach priority to trees and their management, and some specific sources of satisfaction and annoyance with particular trees. A survey in a Chicago suburb found that 99 percent of the respondents thought parkway trees were an asset to the community (8). Detroit residents ranked park and street trees second only to education programs in priority for receiving additional funding, and they rated trees on streets as more important than trees in yards, parks, and wooded areas (2).

People also attach importance to the maintenance of trees. Schroeder and Appelt (8) found that removing hazardous trees and controlling insect and disease problems rated higher in importance than planting new trees. In this survey, 84 percent of the people said they thought maintenance of parkway trees was adequate, but in a survey of California communities that had suffered budget cuts from a tax reduction initiative, only 14 percent said that tree maintenance was good or excellent (11).

The most important benefits that urbanites receive from street trees are visual esthetics and shade (2, 11). With respect to preference for types of trees, in Detroit 63 percent of survey respondents said they preferred a combination of large shade trees and small flowering trees, 24 percent preferred just large shade trees, and 11 percent preferred just small flowering trees (2). In California, small Immature trees received lower evaluations from residents than larger trees, apparently because they were less esthetic and provided less shade. Flower parts dropping from trees annoyed residents and detracted from their preference for flowering species. Most of the people in this survey said that they would not want to have their current tree removed and replaced with another tree, but that they would have preferred the city to have planted a different tree originally (11).

Visual preferences for street trees

We have conducted a series of studies on how trees influence the visual quality of residential streets, as seen in the view along the street (e.g. from a motorist’s perspective). Our general technique was to take photographs representing a variety of street scenes in one or more communities, show them to groups of people, and ask the people to evaluate the visual quality of the scenes by rating them or rank-ordering them. Preference scores calculated from the viewers' evaluations were then statistically related to measurements of the amount and kind of vegetation on the streets.

In one study (9) we photographed randomly chosen streets in 10 towns in northern and central Ohio and took an inventory of the trees located on those streets. The inventory included the species and size of each tree. We also recorded the visual prominence of a variety of vegetative and manmade features visible in the photographs.

We showed the photographs of the streets to university students in Chicago and Urbana- Champaign, Illinois, who rated each scene on a 10-po¡nt scale of attractiveness. From the ratings we calculated scale values for the visual quality of each scene. We also showed slides to several local groups in one of the Ohio towns we photographed and found a very high correlation between the local groups' ratings and the university students' ratings.

Our analyses indicated that street trees were the strongest positive influence on visual quality and that vegetation in yards was the next strongest. Large street trees had a much greater influence than small ones. Overhead wires, cars, and buildings had substantial negative impacts on visual quality.

Studies of visual quality of streets in Dearborn and Ann Arbor, Michigan, have produced similar results (1,4). The strongest contributors to visual quality in these studies were the amount of deciduous crown visible in the scene, and the average size of the trees. Lien and Buhyoff (4) found that preference increases rapidly with increasing tree size up to about 10 inches in diameter, after which the rate of increase begins to slow.

A later study that compared the roles of street and yard trees in visual quality showed that a street tree contributed about 8 times as much to the visual quality of the view along a street as did a yard tree. The positive influence of street trees decreases, however, as the number and size of yard trees increase (10).

Orland (6) analyzed people’s responses to the spatial characteristics of street tree plantings and found that the highest preference was for plantings of tall trees that created an enclosed space, with the tree crowns meeting above the street. The more open the space between and beneath the trees, and the wider the gap between the crowns of trees on the two sides of the street, the lower was the rated preference.