Impact of Climate Change and Land Use on the Southwestern United States

Impacts of climate change on life and ecosystems

This page is a discussion of
Assessment of Potential Future Vegetation Changes in the Southwestern United States

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

Ray --

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 ( 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.

References Cited:

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

Vegetation changes

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.

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