Pines v. Kyoto

In mid-May, 1999, newspapers around the world carried a story about an article that had just appeared in Science magazine (possibly the most prestigious journal in the world) dealing with the impact of elevated CO2 on a pine forest in North Carolina. The results suggested that the increase in forest productivity caused by increased CO2 could “fix about 50 percent of the anthropogenic carbon dioxide projected to be released into the atmosphere in the year 2050.” Fantastic – the forests of the world would do more for stabilizing CO2 than dozens of Kyoto Protocols!

The stories concern research conducted by DeLucia et al. in a 13-year-old loblolly pine forest in the Piedmont region of North Carolina. The scientists recognized that many other experiments on tree saplings and seedlings using growth chambers, greenhouses, and open-top chambers have revealed a near 54 percent increase in photosynthesis and an approximate 31 percent increase in biomass as atmospheric CO2 is doubled. These scientists were interested in how this may translate into an actual forest in a “natural” state. They selected this particular North Carolina pine forest and managed to artificially increase atmospheric CO2 from 360 ppm to 560 ppm for two years. They found that the elevated CO2 increased the growth rate and total net primary production of the trees by about 25 percent. If these findings from a standing 13-year-old forest translate to other forests around the world, the total carbon uptake could approach half of the total anthropogenic emission by 2050. Their relatively fast-growing, young forest may produce an upper limit on this uptake. Only time will tell.

While the Science article stole the headlines, pines were being featured in other important recent papers dealing with the impact of elevated CO2. Consider these entries:

(1) Janssens et al. grew Scots pine seedlings in open-top chambers with ambient and doubled atmospheric CO2 levels with an eye on the impact on the root systems. After six months, the plants in elevated CO2 showed a doubling of both root length and total biomass. They reported that “This increased root length may have led to a more intensive soil exploration.” That’s hardly bad news for a tree that must rely on its roots for survival.

(2) Roberntz enclosed branches of 30-year-old Norway spruce in transparent plastic bags with ambient and ambient plus 340 ppm CO2. Among many other interesting findings, this Swedish scientist reported that photosynthesis was an average of 56 percent higher in the elevated CO2 conditions.

(3) Turnbull et al. grew pine seedlings in open-top chambers in New Zealand for four years at ambient (360 ppm) and elevated atmospheric CO2 levels (650 ppm). The elevated CO2 increased photosynthesis by 63 percent in the youngest plants and by 31 percent in older plants. The impact on photosynthesis declined with age, but nonetheless remained significant, irrespective of age.

(4) Kainulainen et al. surrounded 20-year-old Scots pines with open-top chambers, and they introduced not only a doubling of atmospheric CO2, but also a doubling of atmospheric ozone (O3) levels. Their primary goal was to explore the interactive effects of CO2 and O3 on starch production of these pines. Near the end of the third year of the experiment, the scientists had found a significant increase in starch levels in the needles of trees receiving elevated CO2. This starch can be used by the trees to ultimately increase the overall biomass of the plants. Interestingly, they did not find such an increase until the third year of the study. This result reminds us all that experiments conducted for a short time on long-lived tree species may not uncover the benefits that show-up later in the life of the plants.

These studies, whether in the headlines or lost in the current periodicals section of major libraries, provide us with limited evidence of how these forest will respond in a future world with elevated CO2 levels and other changes to atmospheric composition and climate. All of these recent findings suggest that pines will experience more biological benefits than costs, and it is tempting to argue that elevated CO2 is a blessing and not a curse for pines throughout the world.

But rather than pound on that theme, another lesson comes from these efforts as well. It was the theme that took the DeLucia team to the lofty pages of Science and newspapers worldwide. We commonly assume that our emissions of CO2 will pile-up in the atmosphere and rapidly increase atmospheric CO2 levels in future years. But we clearly have a lot to learn. The findings from North Carolina stimulated a discussion on what will happen to half of the global emission of CO2 by the year 2050. This represents a very large uncertainty on where we are headed in terms of CO2 buildup in the atmosphere. The magnitude of the number dwarfs the projected savings from the Kyoto Protocol.

We often hear scientists pleading for more research funding to answer basic questions regarding global warming and the greenhouse effect. I suspect more than a few folks wonder if the scientific community’s advice isn’t a bit self-serving. It should be obvious that conducting biological research can provide some important information of potential use to the policy debate. The highly-trumpeted research in North Carolina was funded by the U.S. Department of Energy, NASA, the Electric Power Research Institute, and the National Science Foundation – not Big Carbon. Let’s hope they keep up the good work and keep the good news in the headlines everywhere!

DeLucia, E.H., Hamilton, J.G., Naidu, S., Thomas, R.B., Andrews, J.A., Finzi, A., Lavine, M., Matamala, R., Mohan, J.E., Hendrey, G.R., Schlesinger, W.H. 1999. Net primary production of a forest ecosystem with experimental CO2 enrichment.  cience, 284, 1177-1179.

Janssens, I.A., Crookshanks, M., Taylor, G., Ceulemans, R. 1998. Elevated atmospheric CO₂ increases fine root production, respiration, rhizosphere and soil CO2 efflux in Scots pine seedlings. Global Change Biology, 4, 871-878.

Kainulainen, P., Holopainen, J.K. and Holopainen, T. 1998. The influence of elevated CO2 and O3 concentrations on Scots pine needles: Changes in starch and secondary metabolites over three exposure years. Oecologia, 114, 455-460.

Roberntz, P. 1999. Effects of long-term CO2 enrichment and nutrient availability in Norway spruce. I. Phenology and morphology of branches. Trees, 13, 188-198.

Turnbull, M.H., Tissue, D.T., Griffin, K.L., Rogers, G.N.D. and Whitehead, D. 1998. Photosynthetic acclimation to long-term exposure to elevated CO2 concentration in Pinus radiata D. Don. is related to age of needles. Plant, Cell and Environment, 21, 1019-1028.

Robert C. Balling, Jr., is Director of the Laboratory of Climatology at Arizona State University and contributing editor of World Climate Report. He earned his Ph.D. in geography from the University of Oklahoma in 1979.