Arboriculture & Horticulture
Making a Case for Trees
The Story We Have to Share
Once upon a time trees were widely praised for their beauty and shade. Today’s hard-knocks economy requires a different look at the trees that are often planted and maintained with taxpayers’ dollars. While beauty and shade are still legitimate reasons to support trees and urban forestry, it currently makes more sense to look at their practical contributions. Fortunately, the data and facts are there to do the job.
The Danger of Deferred Maintenance
A study done years ago by the consulting firm ACRT compared tree values over time as affected by various levels of investment. As a benchmark, they began with an inventoried street tree value of $44 million. With no planting or maintenance, in five years there was a net loss in value of $14.5 million. At the maximum level of planting and maintenance, the city’s cost over five years was $3.7 million but the net gain in value was $22.7 million. Today, those values would be even higher than when the study was conducted.
Neglecting street and park trees is a sure way to increase the risk of limb breakage or entire tree failure. Not only does this compromise public safety, it raises liability and exposes the city to higher legal and compensatory costs.
Tree shade not only makes sidewalks, lawns and business districts more comfortable, it can save property owners money. In the Midwest, for example, trees can save as much as 56% of annual air conditioning costs and 25% of winter heating costs.
The cumulative energy savings provided by trees can reduce the need for expensive new power generating facilities - whether fueled by coal, gas or oil, wind, water or nuclear means.
Storm Water Retention
United States Department of Agriculture (USDA) Forest Service research shows that trees catch huge amounts of rainwater that would otherwise rush into the city’s storm water system. For example, each 100 mature trees in the Midwest catch about 539,000 gallons of rainwater annually; in the wetter Piedmont Region, the figure rises to 1.2 million gallons. In turn, trees reduce the need for larger, more costly pipes and catchment basins, especially as impervious pavement increases.
Trees not only slow the rush of stormwater, they help anchor soil and prevent erosion. This adds up to clean water supplies.
Air Pollution Control
Trees are called the low tech solution to high tech problems. For example, they are an important way to fight climate change. Researchers have found that in California’s inland valley communities, 100 trees remove 14 tons of carbon dioxide (CO2) each year and 235 pounds of pollutants, including 86 pounds of ozone and 84 pounds of dust and other particulate matter.
The ‘heat island’ effect of city structures serves as a catalyst for the creation of harmful air pollution. The cooling influence of trees can reduce this effect.
Healthy trees and landscaping add value to homes and businesses. This means more tax revenue and higher resale value. By contrast, no trees or trees in poor condition can lower property assessments and everyone loses.
Business & Social Factors
Research shows that the presence of trees entices shoppers to shop more frequently, stay longer, and spend more. Mounting volumes of research show that trees have a positive effect on reducing costly social problems such as workplace dissatisfaction, poor school performance, crime and domestic violence, and human health issues.
Green Infrastructure Grows in Value
Sewer and water pipes crack and break, bridges rust, street lights wear out and streets develop potholes. Most city infrastructure depreciates with time. The tree resource, on the other hand, is the one part of infrastructure that increases in service value over the span of its life.
When planting and pruning costs are spread over a longer period, these expenses become a smaller and smaller part of the cost-benefit ratio. On the positive side of the ledger, the so-called eco-services of trees increase with time and the size of the tree. Large-maturing species and trees with greater longevity improve the ratio even more. Forest Service studies have produced quantified models for various species and in all climate zones of the country. These studies also quantify the ‘pay back’ of planted trees after a set number of years.
For example, in the Pacific Northwest, 100 trees would accrue $84,000 in costs (if cared for) and yield $202,000 in measurable benefits after 40 years. This is a return of $118,000 and does not include the effects of jobs created or preserved, educational value for children, or the more traditional values of beautifying the city and bringing pleasure to its residents.