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Responses of Tree Species to Global Warming
Volume 11, Number 37: 10 September 2008

Looking through a pile of old papers the other day, we came across the study of Gunter et al. (2000), which was all "marked up," as if we were ready to write something about it but for some reason had never gotten around to it. Hence, we decided "better late than never," so here is the paper's write-up in the form of this week's editorial ... a mere eight years behind the times (but still amazingly relevant).

The four scientists -- all associated with the Environmental Sciences Division of the Oak Ridge National Laboratory in Tennessee (USA) at the time of their paper's publication -- introduced their study by noting that many models of actual or attempted range shifts in response to global warming lack a thorough understanding of "the role that acclimation and genetic adaptation may have in a species' response to predicted climate regimes," while stating that if populations "have a greater capacity for adjustment to higher temperatures, and if they are not constrained by complete genetic isolation from other populations, then the effects of global warming will probably be less severe than what may be predicted from a simple temperature-response curve applied without regard to spatial or temporal genetic variation."

In exploring this possibility, Gunter et al. employed random amplified polymorphic DNA markers to evaluate population-level genetic structure as an indirect indicator of the capacity for response to environmental change by sugar maple (Acer saccharum Marsh.) trees from three geographical locations representing a north-south gradient of the species' current distribution. This work revealed, as they describe it, that "genetic diversity, as indicated by estimates of percent polymorphic loci, expected heterozygosity, fixation coefficients, and genetic distance, is greatest in the southern region, which consists of populations with the maximum potential risk due to climate change effects," and that "the high degree of variation within sugar maple implies that it may contain genetic mechanisms for adaptation."

In discussing their findings, Gunter et al. note that the sugar maple range shift potentials derived by the Goddard Institute for Space Studies (Hansen et al., 1983) and Geophysical Fluid Dynamics Laboratory (Manabe and Wetherald, 1987) -- as described by Davis and Zabinski (1992) -- "assume that a species grows only in a climate with temperature and precipitation identical to its current range." In a rebuff of those studies and their alarmist implications, however, they state that existing "high levels of genetic variation among families indicate that vegetational models designed to predict species' response to global-scale environmental change may need to consider the degree and hierarchial structure of genetic variation when making large-scale inferences." And when the latter approach is taken, it is clear that the ability of a species to adapt to the changing environment may be far greater than what is presumed by the outdated climate envelope approach, as may also be ascertained by perusing other materials we have archived over the years in under the headings of Biodiversity (Among Genotypes) and Evolution (Terrestrial Plants - Natural Vegetation) in our Subject Index.

Sherwood, Keith and Craig Idso

References
Davis, M.B. and Zabinski, C. 1992. Changes in geographical range resulting from greenhouse warming: Effects on biodiversity of forests. In: Global Warming and Biological Diversity, Peters, R.L. (Ed.), Yale University Press, New Haven, Connecticut, USA, pp. 297-308.

Gunter, L.E., Tuskan, G.A., Gunderson, C.A. and Norby, R.J. 2008. Genetic variation and spatial structure in sugar maple (Acer saccharum Marsh.) and implications for predicted global-scale environmental change. Global Change Biology 6: 335-344.

Hansen, J., Russell, G., Rind, D., Stone, P., Lacis, A., Lebedeff, S., Ruedy, R. and Travis, L. 1983. Efficient three-dimensional global models for climate studies: Models I and II. Monthly Weather Review 111: 609-662.

Manabe, S. and Wetherald, R.T. 1987. Large-scale changes in soil wetness induced by an increase in carbon dioxide. Journal of Atmospheric Sciences 44: 1211-1235.