by Justin Morgenroth – Urban Forester, MFC

London is affectionately known as the “ Forest City”, but unfortunately, the City is following a predictable pattern, duplicated by many urban locales in North America. As populations grow, development inevitably increases and green space is lost; with this, trees are removed or growing environments become too inhospitable and existing trees succumb to mortality. London’s canopy cover deficiencies are most evident in the downtown core, but are spreading outward as urban sprawl advances.

London’s canopy cover is susceptible to two types of threats, categorized by the magnitude of their effect. The first threat involves large-scale tree loss, the solution to which is complex and often involves policy change, sustainable planning, and social change. Examples of this type of loss are woodlot harvesting to provide land for future development, or tree removal for road-widening projects and utility corridors. Other large scale threats to the urban forest are:

• Air pollution: airborne particulates can cover leaves (like dust) limiting photosynthesis, while ozone produces yellow and brown spots on leaves, which eventually leads to premature leaf loss.
• Pests and disease: Asian long-horn beetle, Dutch elm disease, and many others have been responsible for the loss of millions of trees nationally.
• Poor soil conditions: Excessive salt use on roadways or acid rain can affect tree roots’ ability to absorb water and nutrients from the soil.
• Age distribution: A high proportion of older trees dying at approximately the same time can leave the urban forest in poor condition.

These large scale problems generally result from poor municipal policy, climate change, and insufficient funding. With respects to poor policy, some municipalities enforce “One for One” policies, such that the number of trees removed equals the number of trees planted. London does not have such a policy, which when combined with inadequate funding results in the planting of only a single tree for every one and a half trees removed. Consequently, there is a three year backlog for tree replacement. This guarantees that canopy cover will continue to diminish, especially in high-density areas where tree loss is proportionally higher.

The second category of threats to London’s canopy cover can often be resolved by individual citizens or community groups. For instance, water or nutrient deficiencies can be alleviated by watering or fertilizing a declining tree. This is especially important during droughts or for newly planted trees. While these two stresses are the most significant ones 1, a multitude of others challenge the health of the urban forest:

London’s “Forest City” reputation bears with it a responsibility to be a leader in urban forest management. In order to maintain this status, the challenges detailed above must be addressed. With this mandate, ReForest London was formed to help by engaging the community to support tree planting in their neighbourhood yards, streets and parks.

What Have Trees Done for Me Lately?

Trees are frequently referred to as the lungs of a city due to their ability to provide oxygen, while decreasing air pollution through the uptake of airborne pollutants including carbon dioxide, sulfur dioxide, and ozone 2. However, numerous other ecological, social and economic benefits result from enhanced tree cover.

Ecological benefits include the reduction of water pollution by minimizing fertilizer and pesticide runoff into sewer systems 3. Furthermore, tree cover reduces scorching summer temperatures and minimizes the impact of the ‘Urban Heat Island” effect 4. Tree cover also provides habitat for urban-based, as well as, migrating wildlife species 5. With respect to social benefits, natural vegetation improves aesthetic values, while providing community meeting spaces. Finally, the economic benefits offered by tree cover can be realized at the individual home level 6. First of all, well-located trees can reduce energy costs by providing shade for homes during the summer while deciduous species can act as windbreak during the winter months. Additionally, tree cover and open spaces have been associated with increases in property value between 10-25% 7. Hence tree cover has a positive impact on ecological, social, and economic dynamics.

While trees provide these benefits throughout their lifecycle, large trees deliver the greatest benefits 8 . So, while it is essential to plant new trees to increase canopy cover, it is equally important to ensure their health and continued growth. So, a commitment to tree planting and maintenance can guarantee increased ecological, social, and economic benefits.

Considering the strong link between trees and these benefits, it is unacceptable to concede tree cover decline as an unavoidable truth. Instead it is necessary to educate and engage community groups such that they undertake tree maintenance and planting. It is equally important to work alongside the City of London to improve current policy and planning. This bilateral approach will guarantee a healthy urban forest for current and future generations.

References

1. Gilbertson, P. and A. Bradshaw. 1985. Tree survival in cities: the extent and nature of the problem. Arboric. J. 9: 131-142.

2. Heckel, P.F. 2004. Using trees to mitigate pollution. Proceedings of the Air and Waste Management Association’s Annual Meeting and Exhibition. pp 4019-4031.

3. Xiao, Q., E.G. McPherson, J.R. Simpson, S.L. Ustin. 1998. Rainfall interception by Sacramento ’s urban forest . J. Arboric. 24: 235-243.

4. Long-Sheng Mao, Yong Gao, and Wen-Quan Sun. 1993. Influences of street tree systems on summer micro-climate and noise attenuation in Nanjing City, China. Arboricultural Journal 17: 239-251.

5. Dunster, J.A. 1998. The role of arborists in providing wildlife habitat and landscape linkages throughout the urban forest. J. Arboric. 24: 160-167.

6. McPherson, E.G. 1994. Using urban forests for energy efficiency and carbon storage. Journal of Forestry 92: 36-41.

7. Anton, P.A. 2005. The Economic Value of Open Space. Embrace Open Space.

8. Nowak, D.J., 1994. Urban forest structure, the state of Chicago's urban forest, in: Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project, (E.G. McPherson, D.J. Nowak, and R.A. Rowntree, eds.) Gen. Tech. Rep. NE-186, USDA Forest Service, Northeastern Forest Experiment Station, Radnor, PA, pp. 3-18; 140-164.

Justin Morgenroth is a consulting urban forester formerlystationed in London, Ontario. He received his Master’s degree from the University of Toronto’s Faculty of Forestry. Justin’s work is motivated by the belief that trees have crucial aesthetic and cultural values, and that their systematic elimination from densely populated urban areas is an avoidable disaster. He can be reached for comment at justin.morgenroth@utoronto.ca.