May 19, 2016 11:30AM # Old-Growth Forests of Southern Chile Are Experiencing Large and Unexpected Increases in Growth and Water-Use Efficiency By [Craig D. Idso](https://www.cato.org/people/craig-d-idso) --- SHARE Those who fear anthropogenerated climate change have long claimed that global warming will negatively impact Earth’s ecosystems, including old-growth forests, where it is hypothesized that these woodland titans of several hundred years age will suffer decreased growth and increased mortality as a consequence of predicted increases in temperature and drought. However, others see the situation as the *opposite* — one in which trees are *enhanced* by the aerial fertilization effect of rising atmospheric CO2 concentrations, which is expected to *increase* growth and make trees *less* susceptible to the deleterious effects of drought. So which vision of the future appears more likely to come about? According to the seven member research team of Urrutia-Jalabert *et al*. (2015), the much more optimistic future is not only coming, it is already here. Working in the Andean Cordilleras region of southern Chile, Urrutia-Jalabert *et al*. performed a series of analyses on tree ring cores they obtained from long-lived *Fitzroya cupressoides* stands, which they say “may be the slowest-growing and longest-lived high biomass forest stands in the world.” Focusing on two of the more pertinent findings of their study, as shown in Figure 1 below, both the basal area increment (a surrogate for aboveground woody biomass accumulation) and intrinsic water use efficiency (a measure of drought resistance) of *Fitzroya* dramatically increased over the past century. Commenting on these trends, the authors write “the sustained positive trend in tree growth is striking in this old stand, suggesting that the giant trees in this forest have been accumulating biomass at a faster rate since the beginning of the \[20th\] century.” And coupling that finding with the 32 percent increase in water use efficiency over the same time period, Urrutia-Jalabert *et al*. conclude the trees “are actually responding to environmental change.” Indeed they are. Magnificently. ![Figure 1. Basal area increment chronology (left panel, AD 1355-2010) and intrinsic water use efficiency (right panel, AD 1900-2010) of long-lived Fitzroya cupressoides trees in the Andean Cordilleras of southern Chile.](/sites/cato.org/files/styles/pubs_2x/public/wp-content/uploads/basalareaincrement.jpg?itok=pEpdmjDX) ***Figure 1.*** *Basal area increment chronology (left panel, AD 1355–2010) and intrinsic water use efficiency (right panel, AD 1900–2010) of long-lived Fitzroya cupressoides trees in the Andean Cordilleras of southern Chile.* With respect to the cause of these favorable developments, the researchers state “we believe that this increasing growth trend…has likely been driven by some combination of CO2 and/​or surface radiation increases,” adding that “pronounced changes in CO2 have occurred in parallel with changes in climate, making it difficult to distinguish between both effects.” Thus, it is clear that of the two views predicting the future of old-growth forests, the one most likely to occur (and which is actually occurring in the southern Chilean Andes) is the one in which the benefits of CO2 win out over model projections of climate-induced demise. **Reference** Urrutia-Jalabert, R., Malhi, Y., Barichivich, J., Lara, A., Delgado-Huertas, A., Rodríguez, C.G. and Cuq, E. 2015. Increased water use efficiency but contrasting tree growth patterns in *Fitzroya cupressoides* forests of southern Chile during recent decades. *Journal of Geophysical Research, Biogeosciences* **120**: 2505–2524. ##### Related Tags [Energy and Environment](https://www.cato.org/research/energy-environment) [![Creative Commons License](/build/cato_2020/images/creative-commons.svg)](http://creativecommons.org/licenses/by-nc-sa/4.0/) This work is licensed under a [Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License](https://creativecommons.org/licenses/by-nc-sa/4.0/).