Paper Reviewed
Loehle, C., Idso, C. and Wigley, T.B. 2016. Physiological and ecological factors influencing recent trends in United States forest health responses to climate change. Forest Ecology and Management 363: 179-189.

In a review and analysis of pertinent scientific literature, Loehle et al. (2016) assess the likely growth trajectories of U.S. forests in response to potential environmental changes that many people believe will be driven by continued atmospheric CO2 enrichment, which phenomenon such believers further assume will be detrimental to forests growing everywhere. However, via their study of pertinent scientific literature, Loehle et al. found just the opposite to be the case.

In the event of significant future warming, for example, the three researchers report that "tree species have been shown to acclimate to changes in temperature," citing the work of Gunderson et al. (2010), who found that "warming treatments resulted in a shift in the temperature response curves for CO2 assimilation, such that tree leaves in warmer treatments had higher temperature optima." And to further support this positive tree response to warming, they cite the additional studies of Idso et al. (1989), Baker et al. (1992), Idso et al. (1995), Faria et al. (1996), Nijs and Impens (1996), Rowland-Bamford et al. (1996) and Vu et al. (1997). In addition, they note that "the optimum temperature for plant growth generally rises with atmospheric CO2 enrichment," citing the work of Berry and Bjorkman (1980), Jurik et al. (1984), and Taiz and Zeiger (1991).

As for the climate-alarmist contention that rising atmospheric CO2 concentrations will lead to more frequent and severe droughts that could have strong negative consequences for U.S. forests, Loehle et al. write that "the United States as a whole has not experienced any increase in drought over the past century, and has experienced actually the converse." In any event, they note that "elevated levels of atmospheric CO2 influence tree response to drought by increasing water use efficiency," citing the work of Feng (1999), Wyckoff and Bowers (2010), Brienen et al. (2011) and Keenan et al. (2013).

Air pollution is another phenomenon that can raise havoc with forest trees. But, again, the three researchers note that pertinent studies have documented "a reduction in detrimental effects of ozone with elevated CO2 on properties related to the growth and health of trees," citing Grams et al. (1999), Wustman et al. (2001), Percy et al. (2002), Peltonen et al. (2005) and Kostiainen et al. (2008). And in the cases of pests and pathogens, they cite still other studies that suggest that much the same holds true for them as well, i.e., that rising atmospheric CO2 concentrations also help trees to successfully deal with this latter pair of challenges.

And so it is that we begin to see a host of ways in which the ongoing rise of the air's CO2 content is helping to enhance the growth and development of forests throughout the United States. And what atmospheric CO2 enrichment can do for U.S. forests, it can do for the forests of the rest of the world as well.

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