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The Growth & Water Use Efficiency of Two Tree Species Since 1850

Paper Reviewed
Soulé, P.T. and Knapp, P.A. 2015. Analyses of intrinsic water-use efficiency indicate performance differences of ponderosa pine and Douglas-fir in response to CO2 enrichment. Journal of Biogeography 42: 144-155.

Working with locally co-occurring ponderosa pine (Pinus ponderosa var. ponderosa - PIPO) and Douglas fir (Pseudotsuga menziesii var. glauca - PSME) trees located within the U.S. Forest Service's Northern Rockies Region, Soulé and Knapp (2015) collected tree-ring data from 14 different locations, from which information they were able to determine yearly changes (from AD 1850 to the present) in basal area increment (BAI) and intrinsic water-use efficiency (iWUE), the latter of which parameters they derived from yearly stable carbon isotope ratios (δ13C) of the trees' annual layers of new-wood production.

As a result of this substantial effort, the two researchers determined that both PIPO and PSME trees experienced "exponentially increasing iWUE rates during AD 1850-present, suggesting either increased net photosynthesis or decreased stomatal conductance, or both" (see Figure 1, upper panel). And they add that "both species experienced above-average BAI in the latter half of the 20th century despite no favorable changes in climate" (see Figure 1, lower panel), further noting that "this response occurred at all sites, suggesting a pan-regional effect."

In light of these important and well-founded findings, it would appear that the "twin evils" of the climate-alarmist crowd (rising atmospheric CO2 and temperature) are actually twin blessings in disguise. In fact, however, they're not even "in disguise," for they are there for anyone to see, but only if they are willing to look.


Figure 1. Upper panel: Mean tree-ring δ13C-derived iWUE values over the period 1850-2005 for Douglas fir and Ponderosa Pine trees located in the U.S. Forest Service's Northern Rockies Region. Lower panel: Mean basal-area index values over the same time period and locations within the Northern Rockies Region. Adapted from Soulé and Knapp (2015).

Posted 7 April 2015