Arboriculture & Urban Forestry 38(2): March 2012 Arboriculture & Urban Forestry 2012. 38(2): 75–77 75 Letters The following letter was submitted as feedback to: Sydnor and Subburayalu. 2011. Should we consider expected environmental benefits when planting larger or smaller tree species? Arbori- culture & Urban Forestry 37(4):167–172. The author response follows the letter submission. To whom it may concern: There seems to be a growing interest in our industry to set values for the environmental benefits provided by trees and plants. Syd- nor and Subburayalu (2011) is another attempt at that paradigm. I applaud the authors’ effort to determine what may or may not have happened in the 46 years between the planting and their study, and also applaud their sincere attempt to select the 10 repre- sentative trees from the two planting sites. There are, in my opin- ion, a few points that may marginalize this article’s conclusions. The adjusted base for this study is the survival rates for haw- thorns (Crataegus × lavallei Hérincq ex. Lavallee) and honeylo- custs (Gleditsia triacanthos L. Sunburst) planted on two separate streets (Morton Avenue and Orchard Grove Avenue, both locat- ed in Brooklyn, Ohio, U.S.). The authors achieve this rate “by dividing the number of surviving trees by the (estimated num- ber)—my emphasis—of possible planting sites in 2007 and 2009. Obvious replacement trees and open sites were counted as miss- ing.” One is left to assume that “missing” equals did not survive. There is no data on why the estimated nine honeylo- custs and six hawthorns did not survive, which makes it extremely difficult to evaluate species/site suitability. There is no data on the soil at the two sites other than that they were different Urban Complexes of a “relatively recent geological origin.” Honeylocusts fix nitrogen. One might as- sume, therefore, this essential growth element to be more avail- able at the Morton Avenue site. Within the 46 growing seasons the hawthorns had reached a height of 7.4 m and the hon- eylocusts had reached a height of 15.3 m. Trees on both sites were pruned to ensure clearance for roadways and sidewalks. If the trees at both sites were crown raised to equal heights (data not available), then one would assume that the haw- thorns were pruned considerably more than the honeylocusts. At the end of 46 years, the DBH for the hawthorns was 34.5 cm and the honeylocusts 51.5 cm. Compari- son of benefits were based on these DBH measurements. Ten trees from each street were randomly selected, ana- lyzed, and given dollar values for their perceived envi- ronmental benefits in five categories (Table 2; Table 3). In each annual benefit category, the authors conclude that the larger honeylocusts have a greater dollar value than the hawthorns. In each of the following categories, I submit observations that seem to be in disagreement with the authors’ observa- tions, and if correct may alter the values reached by the authors. Energy Conservation. The authors conclude that prop- erly placed trees will save energy by shading, evapotranspira- tion, and reducing wind speed. At face value, most would agree that this is accurate. On a global scale, this assertion reverses. While the authors state that their values are “discounted” for biogenic volatile organic compounds (BVOC), there is no refer- ence to a BVOC “the smell of a pine forest,” which I assume to mean pinene. All trees release BVOC. Larger trees release higher amounts of BVOC. Trees release BVOC 365 days a year. BVOC emissions, like energy use, fluctuate with environmental conditions. I seriously doubt that the energy saved by the place- ment of trees near energy-using structures comes anywhere near mitigating the total global BVOC emission that contribute to global warming. But then again, I don’t have their discount data. Air Quality Improvement. The authors state that “air quality times greater for the honeylcousts than for hawthorns. All trees die. If they are disposed of similarly, the carbon released back into the atmosphere would be 3.5 times greater for the honeylocusts. The figures will wash. Any benefit would only be temporary. Stormwater Control. Stormwater interception is only partially based on canopy size and volume. Crown den- sity is significantly different (Figure 1). One would sus- pect that, by volume, the hawthorns might intercept more stormwater than the lacy honeylocust canopies. Property Values. There are many ways to place values on prop- erty by trees. Some, like the authors, use DHB in their calculations. It is inconsistent with the concept of value to assume that any tree contributes more to a property’s value than its individual value. The same tree can both increase and decrease a property’s value over time. If, however, a honeylocust delivers 15.6 times greater annual aesthetic benefit than a hawthorn, then it also holds that its loss to the property will be 15.6 times greater than a hawthorn. I would respectfully like to suggest that the authors did not sci- entifically validate their conclusion that, “Regardless of how it is viewed here there is a significant reduction in environmental ben- efits when using smaller statured trees compared with larger trees.” Regards, Norm Brady St. Michaels, Maryland, U.S. ©2012 International Society of Arboriculture savings include reduced ozone, nitrous and sulfur oxides, as well as particulate matter.” Actually, BVOC admitted by trees contrib- ute to the formation of tropospheric ozone (smog), which should not be confused with upper level ozone. The allergenicity of trees is well known. The National Institute of Allergy and Infectious Diseases is a good source for this information. Asthma related to tree pollen and particulate matter is rising. The contribu- tions of larger trees verses smaller trees are also well document. CO2 Benefits. The stored carbon in this study is listed as 3.5
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