sweet gum

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Joined: Wed Jan 13, 2010 11:52 am

sweet gum

Post by jhoward » Wed Jan 13, 2010 11:55 am

Why do the sweet gum trees cause a loss under the heading "Air Quality" on the benefits of public trees table generated by STRATUM?
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Sweetgum BVOC effects

Post by azelaya » Wed Jan 13, 2010 3:35 pm

The model takes into account negative impacts on air quality created by the emmision of biogenic volatile organic compounds (BVOCs) by certain species. I have copied a section from the Tree Guide for the South Climate region which has a good explanation starting on page 19. Hope this helps. Al

Trees may also adversely affect air quality. Most trees emit biogenic volatile organic compounds (BVOCs) such as isoprenes and monoterpenes that can contribute to O3 formation. The contribution of BVOC emissions from city trees to O3 formation depends on complex geographic and atmospheric interactions that have not been studied in most cities. Some complicating factors include variations with temperature and atmospheric levels of NO2. As well, the ozone-forming potential of different tree species varies considerably (Benjamin and Winer 1998). Genera emitting the greatest relative amount of BVOCs are sweetgum (Liquidambar spp.), blackgum (Nyssa spp.), sycamore (Platanus spp.), poplar (Populus spp.), and oak (Quercus spp.) (Nowak 2000).

A computer simulation study for Atlanta suggested that it would be very difficult to meet EPA ozone standards in the region using trees because of the high BVOC emissions from native pines and other vegetation (Chameides et al. 1988). Although removing trees reduced BVOC emissions, this effect was overwhelmed by increased hydrocarbon emissions from natural and anthropogenic sources due to the increased air temperatures associated with tree removal (Cardelino and Chameides 1990).

A similar finding was reported for the Houston-Galveston Area, where deforestation associated with urbanization from 1992–2000 increased surface temperatures. Despite the decrease in BVOC emissions, ozone concentrations increased due to the enhanced urban heat island effect during simulated episodes (Kim et al. 2005). In another study in the Los Angeles basin, increased United States, however, found that species mix had no detectable effects on O3 concentrations (Nowak et al. 2000). Any potentially negative effects of trees on one kind of air pollution must be considered in light of their great benefit in other areas such as absorption of other pollutants.

The USFS Community Tree Guides can be accessed from the Resources - Archives page http://www.itreetools.org/resources/archives.php under the i-Tree Streets Reference City Tree Guides tab
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