76 Author Response I am pleased that Mr. Brady noted the increased interest by re- searchers and practitioners alike in trying to define environ- mental benefits. One frustration for me over fifty years is that I have often been told that the customer could not afford to plant trees because while everyone knows that trees are attrac- tive, attractiveness cannot be quantified and does not affect site functionality. Both are inaccurate and now we begin to have the tools needed to address these questions. I will try to ad- dress some of the questions he raised in no particular order. Site Conditions. Of the 97 sites originally identified for inclu- sion in the OSTEP city plantings, these two sites had the least site restrictions and were most similar where both a large and smaller growing tree had been planted. Both sites had large tree lawns (~3 m), similar homes with similar setbacks, similar maintenance guidelines and the same crews, similar socio-economic circum- stances, lack of overhead wires, and no canopy trees nearby at planting. Further, no major construction activity resulting in plant losses had been noted since planting. Trees were similar in size at planting. In our judgment, sites were not particularly limiting for urban sites and the resulting growth over 46 years would be rep- resentative of the growth of larger and smaller growing trees that might be expected in a desirable urban site in the northeastern U.S. Survival Rates. Survival rates were based on possible plant- ing sites available in 1964 rather than at the time data was col- lected. Neither site had seen construction activity. Where present, sidewalk cuts appeared to be the same age as the streets and side- walks. Curbs had not been replaced in the 46 years since plant- ing. This was based on a site inspection, earlier data collections, and conversation with a former city employee who remembered planting the trees in both sites and lived on Morton Avenue. Estimated Losses. We evaluated losses from all causes. Missing or obvious replacements were considered as a loss. This was consistent between sites. Survival of hawthorns on Orchard Grove (65%) was quite high relative to the other eight sites that were planted with hawthorn in the early OSTEP city plantings. The mean hawthorn survival across nine sites was 35% survival and the mode was 0% survival. Survival of hon- eylocusts on Morton was similar to other honeylocust plant- ings. If there is an error in losses it would suggest that hawthorn survival was lower than reported. This would have reduced the environmental benefits relative to a larger growing tree with higher survival rates. Thus the differences in environmental benefits reported are conservative in that errors would favor exaggerating benefits for hawthorns rather than honeylocusts. A variety of losses that were not tree related were discov- ered in the 97 community sites in the OSTEP plantings. Some losses eliminated, minimized, or not considered through site selection but seen in the 97 sites in the OSTEP city plant- ings included airport expansion, installation of a school bus landing area, chances in design requirements, freeway or roadway construction, and resident preference for other trees or no trees. These losses are significant but in the au- thor’s judgment not part of this study and thus not discussed. Urban Soils. Urban soils are complexes and highly variable. Where the term urban is first, as in Urban land-Elnora com- plex (UeA), more than half of the material is disturbed. Where the term urban is second, as in Hornell-Urban land complex (HsC), 30%–50% of the material is disturbed. Soil conditions may vary significantly in urban soils within a few feet but this ©2012 International Society of Arboriculture Letters to the Editor is the growing media in which most urban trees survive. These two urban soil complexes were similar as stated in the pa- per and not growth limiting for either species in our judgment. Nitrogen Fixation. Honeylocust is a non-nodulating legume and does not fix nitrogen. Approximately 10% of legumes fix ni- trogen, including major agricultural crops such as soybeans, peas, beans, and alfalfa, thus we often extrapolate this characteristic to the family. Some trees, such as alder, do fix nitrogen, but it is not a legume and black locust is a nodulating legume and fixes nitrogen. In any event, nitrogen fixation rates are low relative to recommend- ed rates for lawn fertilization in urban areas. Lawn quality varied in both sites, although tree growth rates were similar within a site. Trees were selected randomly in part to deal with this concern. Pruning. No pruning except crown lifting for head space was noted. No overhead wires were present such that trees heights were limited by species characteristics not pruning saws. Since the hawthorns did not extend beyond street-side parking and above the roadway, there was no need to lift them to gain headspace for larger vehicles. Surely the hawthorns would have been limbed lower if they had been used for screening, such as in a fence row rather than for street tree use. In my experience, canopy volumes of the trees on Orchard Grove were similar to Lavalle hawthorns of similar age on the campus of The Ohio State University (Columbus, Ohio, U.S.), although these trees have died over the last ten years. Urban foresters suggest to me that smaller growing trees require a reduced pruning cycle, but pruning is fine pruning while pruning on larger trees tends to be coarser or safety pruning. Thus pruning costs may be similar over time assuming that the trees are not armed. Lavalle hawthorn is lightly armed and was considered as unarmed in this example. Energy Conservation. Annual rates for a given year were as stated and noted by Mr. Brady. Thus we are comparing the impact of a 34.5 cm tree with a 51.5 cm tree in 2009. No at- tempt was made to draw conclusions regarding global events. BVOC. Yes, plants contribute BVOC and utilize or remove BVOC. The question is net balance. The Midwest Tree Guide published by McPherson et al. (2006) is a good place to be- gin to understand discounting for BVOC and was referenced to assist understanding this issue for those interested. The numbers presented were estimates of annual air quality ben- efits of the trees studied less BVOC emitted during the same year by those same trees. The result was the net positive im- pact of those trees on air quality where they grew. No attempt was made to extrapolate to Brooklyn Ohio’s or global BVOC emissions. This study does suggest that trees may be more likely to have a positive impact on air quality than an activity, such as adding a manufacturing business in Brooklyn might. CO2 Benefits. Yes, a 3.5 times larger tree would give off 3.5 times the CO2 if disposed of in the same manner, especially when viewed in a geological time scale. In this study we compared the carbon sequestered by ten 51.5 cm honeylocusts in 2009 and compared it with carbon sequestered by ten 34.5 cm hawthorns in 2009. We found that the larger trees sequestered 3.5 times as much carbon in that period of time. What we do with the car- bon once stored was not addressed. Mulch might deteriorate in a year, furniture might last another hundred years, and if the tree was landfilled, then it might store its carbon for millennia. Storm Water. Yes, stormwater interception is based on a host of factors in addition to foliar opacity in a photograph. The hawthorn does allow water to penetrate its canopy as does the
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