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Effects of an Urban-Rural CO2/Temperature Gradient on Plant Productivity
Ziska, L.H., Bunce, J.A. and Goins, E.W.  2004.  Characterization of an urban-rural CO2/temperature gradient and associated changes in initial plant productivity during secondary succession.  Oecologia 139: 454-458.

What was done
Working within and around Baltimore, Maryland, USA, the authors characterized the gradual changes that occur in a number of environmental variables as one moves from a rural location (a farm approximately 50 km from the city center) to a suburban location (a park approximately 10 km from the city center) to an urban location (the Baltimore Science Center approximately 0.5 km from the city center).  At each of these locations, four 2 x 2 m plots were excavated to a depth of about 1.1 m, after which they were filled with identical soils, the top layers of which contained seeds of naturally-occurring plants of the general area.  These seeds sprouted in the spring of the year, and the plants they produced were allowed to grow until they senesced in the fall, after which all of them were cut at ground level, removed, dried and weighed.

What was learned
Ziska et al. report that along the rural to suburban to urban transect, the only consistent differences in the environmental variables they measured were a rural to urban increase of 21% in average daytime atmospheric CO2 concentration and increases of 1.6 and 3.3C in maximum (daytime) and minimum (nighttime) daily temperatures, respectively, which changes, in their words, "were consistent with most short-term (~50 year) global change scenarios regarding CO2 concentration and air temperature."  In addition, they determined that "productivity, determined as final above-ground biomass, and maximum plant height were positively affected by daytime and soil temperatures as well as enhanced CO2, increasing 60 and 115% for the suburban and urban sites, respectively, relative to the rural site."

What it means
The three researchers say their results suggest that "urban environments may act as a reasonable surrogate for investigating future climatic change in vegetative communities," and those results indicate that the twin evils of the radical environmentalist movement (rising air temperatures and CO2 concentrations) tend to produce dramatic increases in the productivity of the natural ecosystems typical of the greater Baltimore area and, by inference, probably those of many other areas as well.

Reviewed 8 February 2006