Drought and its long term effects: What could it mean for BC’s forests?

Image by Alan Grinberg | flickr.com

Image by Alan Grinberg | flickr.com

Although forests are a critical part of the carbon cycle, as they store carbon dioxide in the process of growth and decay, the extent of their influence may need to be re-evaluated. 

A recent study from the University of Utah challenges the assumption that forests are able to store up to one-quarter of the carbon produced by humans, particularly throughout periods of drought.  While climate modeling assumes that forests rebound quickly after extended periods of drought, researchers found that trunk growth took an average of two to four years to return to their normal rates.

The growth rates of forests are essential in maintaining a carbon balance – the difference between human generated carbon emissions and carbon uptake by earth systems.  The progression of climate change may be underestimated if this carbon balance has been miscalculated, since forests are unable to store as much carbon dioxide as predicted. 

Researchers measured tree stem growth and recovery since 1948 at 1,300 forest sites around the planet after severe droughts.  The data was collected from records at the International Tree Ring Data Bank.  A few regions, such as California and the Mediterranean, showed higher than predicted growth; however, most of the Earth’s forests showed negative effects after drought.

It is not certain why drought correlates with inconsistencies in the carbon balance, though it may be related to a loss of foliage and carbohydrate stores, which affects growth, or perhaps the accumulation of pests during dry periods.

These findings are significant because, “droughts are supposed to increase in frequency and severity due to climate change,” says author and assistant professor of biology, William Anderegg.  The study also found that in dry forests such as pines, the effects of drought were most persistent. 

Recently, several areas in BC (such as South Thompson, Similkameen, Skagit, and Kettle) recently declared a Level 4 drought.  As a result, we may need to reconsider our methods of global climate modeling to account for these, and other similar real-life scenarios.  These areas lie in the Southern Interior of British Columbia, an area consisting predominantly of dry forests that often include lodgepole pine.  A decrease in the growth rate of these forests as a result of drought could have long-term effects on climate change

It is evident that we must reconsider the methods we use to predict different climate variables, especially if we are minimizing the potential for climate change.  If forests are not as effective at taking up carbon as predicted, climate change may be an even greater threat than anticipated.