The Value of Trees on The Greater Memphis Greenline

          As I am sure you are aware by now, global greenhouse gas emissions are rising, causing an increase in greenhouse gases (GG) in our atmosphere.  There are still a few people who feel that this is not manmade, because after all, look how high the sky is ! How could we possibly affect something that big ?  What they may not appreciate is that well over 95 % of all of the oxygen and carbon dioxide over our heads is in the troposphere, which extends a piddling 7 miles over our heads – roughly the distance from Highland Avenue to the Mississippi River, and yes, we can affect it. 

            There are many researchers and consultants who are working diligently to influence our choices to reduce our carbon footprint on the earth.  In general, efforts fall into a few major categories: use less or do less of something, or use less GG-producing

materials, or use more energy-efficient production and use methods, or lastly, carbon sequestration; that is, carbon capture.  One can attempt to limit the amount of carbon dioxide which escapes into the atmosphere from the burning of carbon fuels, for example, through either underground or ocean storage, or through use of excess carbon dioxide in other industrial processes, or else through mineral carbonation (such as seashells, or production of limestone). 

            There is one last method for carbon sequestration:  planting of trees.  Others have pointed out that tree planting and maintenance is aesthetically pleasing, of course, but is also very pricey – there are costs of planting, of pruning and maintenance, and naturally, in this day and age, there are potential legal liabilities.  In reality, though, it has been said that trees are the lungs of the earth.  Trees reduce air pollution and GG’s, and capture water (which reduces peak water flow during rainstorms and mitigates overflow and street flooding).  The water then evaporates and re-enters the atmosphere, rather than draining into sewer systems.  This tends to cool the surrounding areas, and reduces the amount of air conditioning one needs during the summer, and during the winter tends to shield buildings as well, reducing the amount of heating required.  Tree roots, of course, also filter and remove and use a considerable number of other pollutants – nitrogen, phosphorous, and potassium, to name a few. 

            Even more importantly however, trees sequester carbon and release oxygen.  Trees in urban forests, parks, and greenways capture in growth and development over 12 tons of carbon per acre.  A single mature tree can absorb up to 50 pounds of carbon dioxide per year, and release enough oxygen to support two people.

Trees also provide social benefits. Chicago, for example, recently spent over $10 million to plant 20,000 trees, mostly due to research which showed that in areas with trees, social service budgets were reduced, as were police budgets, since the number of domestic violence incidences were decreased, as were the incidences of child abuse.  Noise pollution was reduced by over 50 %, and residents who lived near trees were significantly healthier.  Trees also stimulate economic activity. People tend to linger and shop longer along tree-lined streets, and apartments and buildings rent more quickly.  Naturally, they also raise real estate values and attract tourists. 

Trees are a capital asset in and of themselves, and as such, need and deserve governmental support.  Entire societies through history have been shown to collapse when they did not manage their tree resources effectively.  Not meaning to scare anyone, but in the last 200 years, we have cut down over 50 % of the tree cover of the earth. In economic terms, over a 50-year lifetime, a single mature tree generates over $30,000 worth of oxygen, provides over $62,000 in pollution control, recycles over $37,000 of water, and controls over $30,000 in soil erosion, for a total pure added economic value of $159,000 per tree, or a little over $3,000 per tree per year .  Many cities have created a separate department to foster their trees, and have established a “tree budget” of $2 or more per citizen. 

The Greater Memphis Greenline (GMG) is a proposed multi-use urban park/trail on a former CSX railroad right-of-way from the intersection of Poplar/Walnut Grove/Union in Midtown Memphis to near Houston Levee in the suburbs of Shelby County. The GMG, when completed, will encompass 13.4 miles, 100-ft. wide; i.e., 160 acres.  Historically, with considerable variability, there are about 50 large trees per acre in urban forests, parks, and greenways in this region.  If we assume that about 25 % of the space will be botanic, then we estimate another 2000 large trees will be planted, which will capture an additional 480 tons of carbon as they grow and mature, and absorb an additional 50 tons of carbon dioxide per year.  At $3,000 per tree, the extra 2000 trees on the GMG will generate an additional $6,000,000 per year in pure economic value to Memphis and Shelby County.  Yes, that’s $6,000,000 per year. 

 

REFERENCES:

1. Minnesota Sustainable Communities Network : Value of Planting Trees Quantified

2. SF Environment: The Benefits of an Urban Forest

3. Benefits of Trees in Urban Areas

4. i-Tree : Tools for assessing and managing Community Forests

5. Collapse: How Societies Choos to Fail or Succeed. Jared Diamond, Penguin Books, 2005