April 2003, Volume 4, Issue 1

Joe R. McBride has a joint appointment as Professor of Forest Ecology and Urban Forestry in the College of Natural Resources and Professor of Landscape Ecology in the College of Environmental Design. He is also Chair of the Division of Forest Science in CNR. I became aware of his special interest in comparing urban forestry in cities around the world and asked him to describe what he has found so far.

Most people in the world live in cities and there is a growing need to plant trees to provide shade, reduce pollution, improve aesthetics, and provide other amenities. Joe’s study is aimed at evaluating what factors influence design of urban forests and to determine what can be learned through comparative analysis of their composition, structure, function, and management. To do this, Joe is taking the novel approach of comparing urban forests in the following cities located in each of the world’s 10 major biomes.

Cities in tundra or desert have sufficiently inclement climates that preclude the wide use of exotics. Joe found the city of Murmansk with its cold, harsh tundra climate in northern Russia, 125 miles north of the Arctic Circle, to be particularly interesting. Here, Joe was impressed that in the 1930s an arboretum was established 100 miles south of the city in which about 600 species of trees and shrubs were tested for their capacity to adapt to the climate. Of these, about 30 tree species were found to be potentially useful of which sixteen were ultimately capable of surviving and developing as urban trees in Murmansk. Joe says that the sight of trees in this challenging environment makes the city substantially more habitable.

Streetside canals in Tehran, Iran, planted with sycamores.

Teheran’s semi-arid climate also makes it difficult to establish urban trees. Shade trees were planted in two rows along the outer edges of the sidewalk in gravel-covered ‘canals’. An irrigation system enables the street trees to survive and the periodically running water provides additional aesthetic and cooling advantages.

Joe has had several visits to China where the cities, before the Cultural Revolution, had very little green cover—Beijing, for example only 2 percent. Since the Revolution there has been a rapid expansion of street tree planting. Often this has involved transplanting 3-m tall, severely pruned willow and cottonwood with very small root balls. These, surprisingly, have resulted in about 70 percent survival and many miles of ‘instant’ street trees providing shade over the sidewalks. The desire to beautify Beijing and ameliorate noise and smog for the 2008 Summer Olympics has provided added impetus to the street tree-planting program. I was especially interested to hear of Joe’s work in two other cities in China—Hefei (the Garden City) in Anhui Province and Ningbo just south of Shanghai—where Joe is using a model to test the effectiveness of street trees in reducing air pollution. Joe has demonstrated that, compared with 10 percent tree cover, having 30 percent cover with existing tree species and 30 percent cover using trees known for their enhanced capacity to reduce air pollution, should increase the monetary value to the city by three and four times, respectively. This information is of considerable interest to Chinese officials who are confronting the prospect of their cities doubling in population and increasing their ‘footprint’ by 70 percent within 12 years.

"Instant" street trees using large transplants in a redevelopment area, Shanghai, China.

Another of Joe’s interests is the concurrent aging of many large parks such as the Golden Gate Park and Presidio in San Francisco, Central Park in New York, and similar parks in London and Paris, all of which were established in the mid- to late-1800s. The trees in these urban parks are of the same age class and are maturing and declining in vigor. How to replace these trees while retaining the aesthetic appearance of the parks is of paramount concern to park managers. Residents are commonly anti-tree cutting and are not familiar with the concepts of stand dynamics and need for regeneration. The situation is particularly acute in Golden Gate Park and Presidio where the trees originally planted were predominantly relatively short-lived Monterey pines.

I asked Joe about the dynamics of urban forestry. Interestingly, he said that Europe is moving more aggressively than the U.S. in developing their urban forestry programs. For example, the European Union has urban forestry offices dedicated to developing needed research, programs, and funding.

We look forward to Joe’s book comparing urban forests of the world. I suspect that it will contribute greatly to developing a new sensitivity on how the composition and structure of urban forests could be made more compatible with native environments and lead to cities developing urban habitats having their own distinctive character.