forestation

Old-Growth Forests of Southern Chile Are Experiencing Large and Unexpected Increases in Growth and Water-Use Efficiency

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.

A Century of Forest Coverage Change on South Africa’s Cape Peninsula

The world’s forests provide a number of vital ecosystem services that benefit both society and nature alike. However, in recent years many have opined that the future of forests is in doubt. Deforestation, drought, fire, insect outbreaks and global warming represent only a handful of the many challenges that are claimed to be causing a near-term demise in forest health that is predicted to become only worse in the years and decades to come. But how valid are these fears? Are Earth’s forests truly on the eve of destruction?

Though there are indeed some locations that are suffering from a variety of maladies, there are many that are not. In fact, multiple studies reveal forests that are thriving, with many increasing in productivity and expanding their ranges (see, for example, the many reviews posted on the CO2 Science website under the heading Greening of the Earth and Forests). And they are typically accomplishing these things despite all the real and imagined assaults on Earth’s vegetation that have occurred over the past several decades. In fact, forests have more than compensated for any of the negative effects these phenomena may have inflicted upon them.

A recent example of this phenomenon is presented in the work of Poulsen and Hoffman (2015), who examined aerial and ground-based photographs to estimate long-term changes in the distribution of forests on the Cape Peninsula of South Africa. Specifically, the pair of researchers analyzed a series of forest-related characteristics from aerial photographs taken in 1944 and 2008, along with 50 historical ground-based repeat photographs that were initially imaged between 1888 and 1980 and then repeated in 2011 or 2012.

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