Shedding Light in the Forest: Climate Change's Effects on Timber

The effect of climate change on some trees harvested for paper and wood may not be quite as severe as expected, according to U.S. Department of Agriculture (USDA) scientists in Auburn, Ala.

Climate change is expected to increase levels of carbon dioxide (CO₂) in the atmosphere. A key question is whether rising CO₂ levels will increase the severity of tree diseases.

Agricultural Research Service (ARS) plant pathologist Brett Runion and his colleagues at the agency's National Soil Dynamics Laboratory in Auburn exposed loblolly pine and red oak seedlings to twice the normal levels of CO₂ in open-top field chambers for six weeks, then inoculated them with the fungal pathogens that cause pitch canker and fusiform rust, two common tree diseases. They then placed the seedlings back in the chambers to grow for seven months.

Results showed that both types of seedlings grown under elevated CO₂ were larger in diameter, height and weight than seedlings grown under normal CO₂ levels. The researchers expected to see fusiform rust increase under elevated CO₂ levels because the added biomass would give the pathogen more tissue for infection. They also expected to see reduced levels of pitch canker because the trees would be healthier and better able to defend themselves against the disease. Instead, they found that the incidence of both diseases declined under elevated CO₂, while disease severity was unaffected.

Higher CO₂ levels may have caused the trees to produce higher levels of tannins and phenols, which can help plants fight off infections, according to Runion. The higher CO₂ also altered the timing of the fusiform rust reproductive cycle in a beneficial way. Fusiform rust moves from red oak to pine trees by way of spore dispersal. Pine tissues don't stay highly susceptible for long, and it's possible a delay in spore formation on the oaks, caused by higher CO₂, means spores were dispersed after the pine tissues had hardened and were less susceptible.

The research was published in the journal New Forests.

Read more about this research in the September 2013 issue of Agricultural Research magazine.

ARS is the USDA's principal intramural scientific research agency, and the research supports the USDA priority of responding to climate change.