Gunter et al. (2000) introduced their study of the subject 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," 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 trees from three geographical locations representing a north-south gradient of that 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 significant 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that the ability of a species to adapt to the changing environment may be far greater than what is presumed by the outdated climate envelope approach.

In another intriguing paper, Jump et al. (2006) introduce their study of potential tree responses to global warming by noting that "one of the basic assumptions in the study of plant adaptation to environment (genecology) is that natural selection in different environments generates genetic clines that correlate with environmental clines." Within this context, they further state that "temperature is of major importance as a selective agent causing population differentiation over altitudinal and latitudinal clines (Saxe et al., 2001)," and that "temporal changes in gene frequency that result from global warming should therefore mirror spatial changes observed with decreasing altitude and latitude," which changes are typically manifest in particular alleles that "may be confined to, or occur preferentially in, different sites with contrasting environmental conditions."

As a test of this hypothesis, Jump et al. say they "combined population genomic and correlative approaches to identify adaptive genetic differentiation linked to temperature within a natural population of the tree species Fagus sylvatica L. [European beech] in the Montseny Mountains of Catalonia, northeastern Spain," concentrating on three areas: the upper treeline (high Fagus limit, HFL), the lower limit of F. sylvatica forest (low Fagus limit, LFL), and an area of the forest interior.

With respect to the temperature differential between the HFL and LFL locations, the researchers note that the 648-meter altitudinal difference that separates them "equates to a mean temperature difference of 3°C ... based on the altitudinal lapse rate of 0.51°C per 100 meters reported by Penuelas and Boada (2003) for Montseny." Likewise, with respect to the change in temperature due to the region's manifestation of 20th-century global warming, they report that "by 2003, temperatures had increased by approximately 1.65°C when compared with the 1952-1975 mean," which temperature change, as they see it, "is likely to represent a strong selection pressure."

Numerous tests conducted by Jump et al. on the data they collected reveal that the frequency of a particular F. sylvatica allele showed a predictable response to both altitudinal and temporal variations in temperature, with a declining frequency and probability of presence at the HFL site that the Spanish research team determined to be "in parallel with rising temperatures in the region over the last half-century." As a result, they say their work "demonstrates that adaptive climatic differentiation occurs between individuals within populations, not just between populations throughout a species geographic range," which further suggests, in their words, that "some genotypes in a population may be 'pre-adapted' to warmer temperatures (Davis and Shaw, 2001)."

The researchers also went on to contend that "the increase in frequency of these genotypes," which occurred in their study in parallel with rising temperatures, "shows that current climatic changes are now imposing directional selection pressure on the population," and that "the change in allele frequency that has occurred in response to this selection pressure also demonstrates that a significant evolutionary response can occur on the same timescale as current changes in climate (Davis et al., 2005; Jump and Penuelas, 2005; Thomas, 2005)."

In concluding, Jump et al. suggest that an evolutionary response to global warming of the type they describe is likely already "underway," which further suggests -- to us, at least -- that many species of plants likely will not be forced to migrate either poleward in latitude or upward in altitude in response to global warming, as climate alarmists adamantly claim they will be forced to do. Rather, they will have the opportunity to so adjust their ranges (i.e., expand them) at the cold-limited boundaries of their ranges, but they may not be forced to make any major changes at the heat-limited boundaries of their ranges, due in part to the phenomenon elucidated by Jump et al.

Considered in their entirety, these observations suggest that earth's plants may be much better prepared to meet whatever climatic challenges the future may pose for them than what almost everyone once believed.

References
Davis, M.B. and Shaw, R.G. 2001. Range shifts and adaptive responses to Quaternary climate change. Science 292: 673-679.

Davis, M.B., Shaw, R.G. and Etterson, J.R. 2005. Evolutionary responses to changing climate. Ecology 86: 1704-1714.

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. 2000. 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.

Jump, A.S., Hunt, J.M., Martinez-Izquierdo, J.A. and Penuelas, J. 2006. Natural selection and climate change: temperature-linked spatial and temporal trends in gene frequency in Fagus sylvatica. Molecular Ecology 15: 3469-3480.

Jump, A.S. and Penuelas, J. 2005. Running to stand still: adaptation and the response of plants to rapid climate change. Ecology Letters 8: 1010-1020.

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.

Penuelas, J. and Boada, M. 2003. A global change-induced biome shift in the Montseny Mountains (NE Spain). Global Change Biology 9: 131-140.

Saxe, H., Cannell, M.G.R., Johnsen, B., Ryan, M.G. and Vourlitis, G. 2001. Tree and forest functioning in response to global warming. New Phytologist 149: 369-399.

Thomas, C.D. 2005. Recent evolutionary effects of climate change. In: Lovejoy, T.E. and Hannah, L. (Eds.), Climate Change and Biodiversity, Yale University Press, New Haven, Connecticut, USA, pp. 75-88.