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The Greening of Earth's Arid and Semi-Arid Lands
Volume 14, Number 21: 25 May 2011

Nearly three decades ago, when the air's CO2 concentration was approximately 340 ppm (up from a pre-industrial value on the order of 280 ppm), Idso (1982) wrote in a small self-published book (Carbon Dioxide: Friend or Foe?) that if the air's CO2 content continued its upward climb, it would ultimately enhance plant growth and water use efficiency to the point that semi-arid lands not then suitable for cultivation "could be brought into profitable production," further opining that "the deserts themselves could 'blossom as the rose'."

Four years later, the research physicist advanced essentially the same thesis -- this time in the pages of Nature (Idso, 1986) -- in a brief paper provocatively entitled: "Industrial Age Leading to the Greening of the Earth?" Much subsequent research answered Idso's pseudo-query in the affirmative (see Deserts (Expanding or Shrinking?) and Greening of the Earth in our Subject Index); but the welcome and still-ongoing transformation of the planet has had a lot of help along the way from a number of things that were stimulated to occur as a result of the growth-promoting impact of the historical increase in the air's CO2 content, several of which are highlighted in the recent report of Yang et al. (2011).

Working in the semi-arid Loess Plateau of northwestern Shanxi, China, the five researchers studied characteristics of Caragana microphylla plantations that had been established there five, ten, twenty, thirty and forty years previously, in efforts to combat desertification, which in the 1960s had claimed 48.5% of the region's surface area. These perennial leguminous and sand-binding shrubs were chosen for the task because they have well-developed stems with many clustered branches and large root systems capable of adapting to poor nutrient conditions; and they were thus positioned in groups to act as sand barriers and windbreaks. So what did Yang et al. learn by scrutinizing the different-aged plants' environments?

The establishment and development of the C. microphylla shrubs, in the words of the Chinese scientists, "improved soil texture, enhanced soil organic matter (SOM), total nitrogen (TN), and cation exchange capacity (CEC)." In addition, they report that "SOM, TN, and CEC were significantly higher at the center than at the outside of the shrub canopies and were higher at the 0-5 cm depth than at the 5-10 cm depth." Moreover, they state that "the differences in SOM, TN, and CEC from the center to the outside of shrub canopies were greater under 30- and 40-year-old shrubs than under 10- and 5-year-old shrubs." And they even discovered that the spatiotemporal heterogeneity of the soil properties "facilitated the development of herbaceous species diversity and the restoration of the [region's] natural ecosystem," which had previously been lost to desertification.

Clearly, once the photosynthesis-promoting and transpiration-reducing impacts of atmospheric CO2 enrichment kick-in, so to speak, and shrubs begin to grow in arid and semi-arid lands -- even without being planted there by man -- a whole host of additional beneficial phenomena begin to operate, hastening the ongoing greening of the earth that is currently in process of transforming the terrestrial surface of the planet.

Sherwood, Keith and Craig Idso

References
Idso, S.B. 1982. Carbon Dioxide: Friend or Foe? IBR Press, Tempe, Arizona, USA.

Idso, S.B. 1986. Industrial age leading to the greening of the Earth? Nature 320: 22.

Yang, Z.P., Zhang, Q., Wang, Y.L., Zhang, J.J. and Chen, M.C. 2011. Spatial and temporal variability of soil properties under Caragana microphylla shrubs in the northwestern Shanxi Loess Plateau, China. Journal of Arid Environments 75: 538-544.