Background
The authors write that "warmer climates induced by elevated atmospheric CO2 are expected to increase damaging bark beetle activity in pine forests," yet they say that "the effect of elevated CO2 on resin production - the tree's primary defense against beetle attack - remains largely unknown." What is known, however, is that "resin physically ejects or entombs attacking beetles and, when volatile components of resin have evaporated, seals wounds in the bark," as revealed by the studies of Ruel et al. (1998) and Wilkens et al. (1998). But any potential role of elevated CO2 in this eternal battle has remained unknown ... up until now.

What was done
In an experiment intended to help fill this important knowledge void, Novick et al. assessed the effect of elevated CO2 on resin production of dominant-and-unfertilized 27-year-old loblolly pine (Pinus taeda L.) trees growing under both ambient and elevated (ambient + 200 ppm) atmospheric CO2 concentrations in the Duke Forest of North Carolina (USA) over the period March to October of 2009.

What was learned
The four researchers report that the elevated CO2 treatment significantly increased resin flow by a whopping 140% in dominant trees growing in unfertilized subplots; and they say that this CO2-induced resin flow enhancement "persisted throughout the growing season."

What it means
Novick et al. conclude that "forests with low- to mid-range fertility" - which, in their words, "currently represent the majority of southern pine forests (Fox et al., 2007)" - "may become increasingly protected from bark beetle attacks in an elevated CO2 climate." And the validity of this conclusion is further supported by the fact, as they note, that "previous studies have shown that even more modest increases in resin flow (i.e., enhancements less than or equal to 100%) significantly increase the survival probability of pine trees experiencing bark beetle attack," as demonstrated by the studies of Reeve et al. (1995) and Strom et al. (2002).

References
Fox, T.R., Jokela, E.J. and Allen, H.L. 2007. The development of pine plantation silviculture in the southern United States. Journal of Forestry 105: 337-347.

Reeve, J.D., Ayres, M.P., Lorio Jr., P.L. Cappuccino, N. and Price, P.W. 1995. Host suitability, predation, and bark beetle population dynamics. In: Cappuccino, N. and Price, P.W. (Eds.). Population Dynamics: New Approaches and Synthesis. Academic Press, San Diego, California, USA, pp. 339-357.

Ruel, J.J., Ayres, M.P. and Lorio, P.L. 1998. Loblolly pine responds to mechanical wounding with increased resin flow. Canadian Journal of Forest Research 28: 596-602.

Strom, B.L., Goyer, R.A., Ingram Jr., L.L., Boyd, G.D.L. and Lott, L.H. 2002. Oleoresin characteristics of progeny of loblolly pines that escaped attack by the southern pine beetle. Forest Ecology and Management 157: 169-178.

Wilkens, R.T., Ayres, M.P., Lorio Jr., P.L. and Hodges, J.D. 1998. Environmental effects on pine tree carbon budgets and resistance to bark beetles. In: Mickler, R.A. and Fox, S. (Eds.). The Productivity and Sustainability of Southern Forest Ecosystems in a Changing Environment. Springer, New York, New York, USA, pp. 591-616.