By
Robert C. Balling, Jr.
Greening Earth Society Science Advisor

With the arrival of Spring, residents of and visitors to Our Nation’s Capital, enjoy the beauty of the cherry trees with their colorful blossoms. The cherry trees have a strong link to history in Washington, DC. They conjure up stories familiar to school children across the country of the deep-rooted honesty of one of our Founding Fathers and greatest leaders. I’m sure all elected officials look forward to a few photographs each year with those wonderful cherry blossoms in the background reminding folks of the importance of honesty in government.

How will the cherry trees fare in a world of increased atmospheric CO2? Imagine the horror of determining that our emissions of CO2 could harm these national treasures. Well, once again, relax. A recent two-part article sequence shows us that cherry trees, like so many other tree species around the world, may be crying out for more atmospheric CO2.

An international team of life scientists from Italy and Scotland recently reported the results of a two-year study on how elevated CO2 and drought could impact cherry seedlings. Centritto et al. planted seeds of cherry and grew the plants in open-top chambers in a glasshouse at the University of Edinburgh. Some of the plants grew in an environment of ambient atmospheric CO2 near 350 ppm while others grew in an atmosphere of 700 ppm CO2. Furthermore, the authors imposed various water deficiencies on some plants to simulate the effects of drought.

Among many other interesting findings, the team reported that elevated CO2 (1) significantly increased total dry-mass production of the cherry seedlings in both water regimes, (2) did not impact water loss from the plants for either the well-watered or drought-stressed plants, (3) significantly increased water-use efficiency (the ratio of total dry mass produced to total water consumption), (4) reduced stomatal conductance, especially for well-watered plants, (5) significantly increased the rate of photosynthesis, and (6) improved transpiration efficiency. In other words, the cherry seedlings in the elevated CO2 chambers were far better off than the plants growing in the ambient chambers.

We do not have information yet on how increased CO2 will impact the number and quality of cherries, but based on the results of Centritto et al., the cherry seedlings growing for a few years did not seem to complain a bit about a doubling of CO2. Imagine the sweet irony if a certain high-ranking public official chose to give one of his trademark greenhouse effect, global warming, Kyoto Protocol speeches using cherry trees alongside the Tidal Basin as his backdrop!

Not too far south from the wonderful cherry trees of the District of Columbia are Fraser fir and red spruce trees growing throughout Virginia and North Carolina. In a recent article in Forest Ecology and Management, Goelz et al. examined cross-sectional area and height data of these southern trees to identify possible long-term growth trends. They “harvested” (cut down) 45 red spruce trees and 13 Fraser firs ranging in age from 17 to 139 years. They analyzed the cross-sectional area patterns and heights using a variety of sophisticated numerical models and time series statistical procedures.

Cross-sectional area growth “provided no evidence of growth decline” and in fact, many cross-sectional disks “exhibited a steady increase throughout the series”. The authors noted, “These findings contradict other studies suggesting that a recent growth decline has occurred in red spruce in the southern Appalachians.” Where is the environmental press trumpeting this good news?

Could it be that increased CO2 in the atmosphere has made these trees more robust against the stresses of the Industrial Age? Experiments from throughout the world show us that virtually all trees are enhanced – not damaged – by exposure to elevated CO2 levels. These recent additions to the scientific literature add additional evidence to this claim.

If you Lorax-like “speak for the trees,” can you justify a policy that denies them the biological benefits of increased atmospheric concentrations of CO2?

Reference: 

Centritto, M., Lee, H.S.J., and Jarvis, P.G., 1999.  Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings. I. Growth, whole-plant water use efficiency and water loss. The New Phytologist, 141, 129-140.

Centritto, M., Magnani, F., Lee, H.S.J., and Jarvis, P.G., 1999.  Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings. II. Photosynthetic capacity and water relations. The New Phytologist, 141, 141-153.

Goelz, J.C.G., Burk, T.E., and Zedaker, S.M., 1999. Long-term growth trends of red spruce and Fraser fir at Mt. Rogers, Virginia and Mt. Mitchell, North Carolina. Forest Ecology And Management, 115, 49-59.

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