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O, Christmas Tree

By Robert C. Balling Jr., Ph.D.
Arizona State University

Aliens observing my household would certainly wonder about our behavior this time of year. After receiving the proper paperwork from our government, we then drove 100 miles to northern Arizona, cut down one carefully selected pine tree, transported it to our home in the desert, decorated it with lights, balls, angels, and a star, set up a miniature bullet train around its base, and then stood around the thing getting pictures taken with a dog. This tree gets more attention than many children, and for the time it stays in our home, it is literally part of the family. Neighbors even stop by to tell us how beautiful our latest family member is.

At this time of year, it’s natural to wonder if these precious evergreens will reap any significant biological benefits from the continued increase in atmospheric carbon dioxide.

Ample evidence exists to tell us that future Christmas trees will in fact be better off than the one in the living room this holiday season. A past Greening Up column reviewed an article by Tissue and colleagues showing that loblolly pines in CO2-enriched air grew taller and had thicker trunks, more extensive root systems, more primary branches, more secondary branches, and more efficient use of water and nitrogen.

In evergreen forests in Finland, Kellomäki and colleagues concluded, "The establishment of a seedling stand was substantially improved under the combined elevation of temperature and CO2 in such a way that the temperature increased the number of mature seeds and enhanced germination of seeds and CO2 increased seedling growth."

Similarly, Walker and researchers showed that the magnificent ponderosa pines of the great western forests were enhanced by elevated CO2 in terms of seedling heights, stem diameters, shoot weights, coarse root weights, and total root length. Later, we reviewed an article by Talkkari, who concluded that any warming in Finland would cause evergreen growth rates and harvest volumes to increase significantly.

All of these articles were published in 1997 or 1998, and they only build on an already extensive literature on this subject.

Now, ’tis the season of glad tidings, the more the merrier and all that. So it’s fortunate that another article has appeared recently regarding the future of our favorite trees. Roberntz and Stockfors examined the effect of doubled atmospheric CO2 concentrations on the new foliage of 30-year-old Norway spruce trees. They found that a) elevated CO2 produced a 50 percent increase in the net photosynthesis rate, which is a measure of growth; and b) the doubled CO2 level had no effect on the new growth’s stomatal conductance, a measure of water use efficiency. These two findings show us that as CO2 rises, the spruce trees will increase their growth rate, but because of the lack of an effect on stomatal conductance, the transpiration losses per unit area will remain the same, and the trees will use water more efficiently.

So we put it all together and find that future evergreens in the next century will grow faster and bigger, expand their range, become more water-efficient, and, should some warming take place in the future, will be even better off than they are now.

The world’s evergreens cannot expect a greater Christmas gift from us than more and more atmospheric CO2. Unlike human beings, they don’t need Santa Claus.

References:

Kellomäki, S., et al., 1997, Model computations on the effects of elevating temperature and atmospheric CO2 on the regeneration of Scots pine at the timber line in Finland. Climatic Change, 37, 683–708.

Roberntz, P., and J. Stockfors, 1998, Effects of elevated CO2 concentration and nutrition on net photosynthesis, stomatal conductance and needle respiration of field-grown Norway spruce trees. Tree Physiology, 18, 233–241.

Talkkari, A., 1998. The development of forest resources and potential wood yield in Finland under changing climatic conditions. Forest Ecology and Management, 106, 97–106.

Tissue D.T., et al., 1997, Atmospheric CO2 enrichment increases growth and photosynthesis of Pinus taeda: A 4-year experiment in the field. Plant, Cell and Environment, 20, 1123–1134.

Walker, R.F., et al., 1998, Atmospheric CO2 enrichment and soil N fertility effects on juvenile ponderosa pine: Growth, ectomycorrhizal development, and xylem water potential. Forest Ecology and Management, 102, 33–44.