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Air pollution and forest water use


Arising from T. F. Keenan et al. Nature 499, 324–327 (2013)10.1038/nature12291

Forests in North America and northern Europe increased their water-use efficiency (WUE)—the ratio of photosynthetic CO2 uptake to water loss through evapotranspiration—over the last two decades, according to a recent Letter1. Keenan et al. attribute the rising WUE to fertilization by increasing levels of atmospheric CO2 (ref. 1), although biosphere models predict this effect to be much smaller than the observed trend. Here, I show that falling concentrations of ozone and other phytotoxic air pollutants, which were not considered in ref. 1, may explain part of the WUE trend. Future efforts to reconcile biosphere models with field data should, therefore, use integrated modelling approaches that include both air quality and CO2 effects on forest growth and water use. There is a Reply to this Brief Communication Arising by Keenan, T. F. et al. Nature 507, (2014).

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Figure 1: Trends in ozone exposure metrics that correlate with tree injury.


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Correspondence to Christopher D. Holmes.

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Holmes, C. Air pollution and forest water use. Nature 507, E1–E2 (2014).

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