Professor DuVivier wrote in response to "Deciduous trees have decidedly beneficial impact on air pollution" (Oct. 22, 2010). The deciduous trees story noted that a study conducted by the National Center for Atmospheric Research reported that "deciduous vegetation absorbs one-third more air pollution that previously believed -- tens of millions of metric tons worldwide."
However, the article also noted that not all trees are the same with respect to reducing the levels of air toxics. "The right trees include ash, apple, birch, hawthorn, hackberry, maple, pear, and peach. Wrong: poplar, eucalyptus and oak [because]...[t]hese species, NCAR scientists say, emit more volatile organize compounds [VOCs] than they absorb."
Professor DuVivier expanded on the deciduous trees article by identifying which trees that are "right" for absorbing VOCs are also "right" because they do not grow to heights that interfere with neighbors' use of the sun for passive solar heating or electricity generation through photovoltaic panels. Like the "wrong" trees with respect to the emission of VOCs, taller trees whose shading results in the need for more coal-fired power generation, contribute to the climate problem instead of helping it, she has noted.
In her letter, Professor DuVivier urged that planting the right types of trees in the right places is the best way to enlist trees in the climate change battle. Specifically, Professor DuVivier wrote:
"[The] article lauded trees for absorbing smog. Trees also mitigate O2 emissions. But not all trees are equally beneficial: some species emit more volatile organic compounds than they absorb.
"In urban environments, we need more restrictions to avoid negative impacts on those around us: e.g., wood burning or watering restrictions. Sunlight plays an increasing role in energy solutions — for solar energy and urban gardens. Trees that mature at over 70 feet can create shade pollution for neighbors up to three lots away. Several of the 'right trees' for smog absorption are also those that mature at lower heights: apple, hawthorn, pear and peach.
"Where we plant new trees in the city is also important. Branches of deciduous trees still block critical southern exposures catching the low winter sun. So, we should plant more trees, as long as they are the right trees in the right place."