Extension 17.7: Planting Trees

Energy, Ch. 17, extension 7 Planting trees 14
emitting more nitrous oxide. (778) Aye et al. consider these effects to be arising at different
urban scales, (778)
[O]ur results support three hypothetical links between human decisions and
biogeochemistry at multiple scales. At the regional scale, our data suggest that
bio-geochemical fluxes depend on which land-cover types are converted to
urban use. The conversion of grasslands to urban use (increasing N 2 O,
decreasing CH 4 ) will have a much different effect than conversion of corn to
urban use (moderate decrease in N 2 O, no change in CH 4 ). At the landscape or
neighborhood scale, we hypothesize that effects of urbanization depend on
landscape architecture, especially the proportion of the landscape that is
lawns vs. impervious surfaces. At the household scale, we hypothesize that
individual management decisions (irrigation and fertilization levels) are
important determinants of biogeochemical fluxes.
Additionally, Nemitz et al. find that urban traffic, particularly at rush hour, releases CO 2
and heat directly into the city and affects local climate. (779) Similarly, Grimmond et al.
find their “observations at a single suburban site in Chicago show significant diurnal
variations in CO 2 concentrations. The CO 2 concentrations are elevated relative to global
background values” at ground level, but not as much at higher elevations. (780) Grimmond
et al. also find that carbon dioxide is being removed from the air in leafy neighborhoods.
As a result of all this research, it is clear that land-use change is an important cause of
regional—and global—climate change.
This agrees with the IPCC and other studies. However, it seems to be the direct opposite
of what has been found by others. Computer models of forest growth on the Great
Planins shows that the opposite occurs. (781) Climate change with increased temperatures
leads to changes in composition, but little change in diversity. As research has shown the
effect of warming is not in increased daytime temperatures, but in increases in the
nighttime temperatures. (322) The so-called diurnal temperature range has gotten smaller.