Direct effects of 2xC02
A comment by Raymond Watts
Vegetation will not only respond to the climate changes that will accompany CO2 doubling, but also to the CO2 doubling itself. Do we have any research yet that indicates the direct effect of CO2 doubling on these species or, even more to the point, the combined effect of doubling CO2 and simultaneously changing climate?
Effects of increased atmospheric CO2 on plant growth
A comment by Robert S. Thompson
There have been many studies of the effects of changes in carbon dioxide concentration on plant growth. The Carbon Dioxide Information Analysis Center sponsored by the Department of Energy provides an excellent bibliography of such studies at: http://cdiac.ESD.ORNL.GOV/ftp/bibliography.
In the western United States, the study by LaMarche and others (1984) has been followed by new investigations of the effects of increased atmospheric CO2 on tree growth at high elevations in the southwestern United States. Graybill (1987) concluded that increased CO2 levels could not be ruled out as a contributing factor to enhanced tree growth at high elevation in the Great Basin. On the other hand, Graumilch (1991) found that increased rates of tree growth among three tree species at high elevation in the Sierra Nevada did not necessarily support the hypothesis advanced by LaMarche and others that increased CO2 concentrations were having a fertilizing effect on high-elevation trees.
Van de Water and others (1994) studied limber pine needles from ancient packrat middens and found that the stomatal density of these needles changed as atmospheric carbon dioxide increased after the Last Glacial Maxium into the Holocene. These western trees are thus undergoing physiological changes due to changes in CO2 that will influence their reactions to climate change. The VEMAP (Vegetation/Ecosystem Modeling and Analysis Project) project (http://www.cgd.ucar.edu/vemap/) is conducting an intensive integrated study of the potential future changes in plant growth in the United States due to climatic changes and changes in atmospheric chemistry.
Graumlich, L.J. (1991). Subalpine Tree Growth, Climate, and Increasing CO2: An Assessment of Recent Growth Trends. Ecology 72:1-11.
Graybill, D.A. (1987). A Network of High Elevation Conifers in the Western U.S. for Detection of Tree-Ring Growth Response to Increasing Atmospheric Carbon Dioxide. IN: Proceedings of the International Symposium on Ecological Aspects of Tree-Ring Analysis. U.S. Dept. of Energy Conference Report; DOE/CONF-8608144 (G.C. Jacoby and J.W. Hornbeck, eds.), NTIS, Springfield, Virginia, pp. 463-474.
LaMarche, V.C. Jr. et al. (1984) "Increasing atmospheric carbon dioxide: Tree-ring evidence for growth enhancement in natural vegetation." Science 225, 1019-21
Van de Water, P.K., S.W. Leavitt, and J.L. Betancourt (1994). Trends in stomatal density and13C/12C ratios of Pinus flexilis needles during the last glacial-interglacial cycle. Science, v. 264, pp. 239-243
A comment by Craig Brunstein
Your paper sheds light on the fascinating and scary potential effects of climatic change on our agricultural capability. It is also fascinating to think that the present distribution of flora and fauna could (will) change radically. It would be quite interesting to drive through West Texas and see Saguaro! The evidence for vegetation changes (tree injury during severe frost-ring years, treeline changes, and variation of tree growth forms with altitude and time) over the past 2,000 years at some of the bristlecone pine sites I've visited in Colorado makes me wonder, as do you, about the rapidity as well as severity and duration of past and future climatic change. Thanks for an interesting paper.