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Range Expansion (Herbaceous Plants) -- Summary
Climate alarmists have long contended that global warming will be so "fast and furious" that many species of plants will not be able to migrate either poleward in latitude or upward in altitude at rates sufficiently rapid to keep them within the geographically-shifting temperature regimes to which they have long been adapted, with the result that (1) many species will be driven to extinction and (2) the species richness of various ecosystems will be greatly reduced.

As an example of these contentions, Dyer (1995) wrote that "the magnitude of the projected warming is considerable," that "the rate at which it is predicted to occur is unprecedented," and, therefore, that "there is genuine reason for concern that the extent of range shifts will exceed the dispersal abilities of many plant species." Four years later, Malcolm and Markham (2000) similarly wrote that "rapid rates of global warming are likely to increase rates of habitat loss and species extinction," and that "many species may be unable to shift their ranges fast enough to keep up with global warming." Malcolm et al. (2002) added that "migration rates required by the warming are unprecedented by historical standards, raising the possibility of extensive, and in many cases, catastrophic, species loss." And in his 26 April 2007 testimony to the Select Committee of Energy Independence and Global Warming of the U.S. House of Representatives, NASA's James Hansen stated that "greenhouse gas emissions threaten many ecosystems," noting that "very little additional forcing is needed ... to cause the extermination of a large fraction of plant and animal species," while adding that "polar species can be pushed off the planet, as they have no place else to go," and stating that "life in alpine regions ... is similarly in danger of being pushed off the planet."

So what has been learned about the subject by scientists who have been making actual observations (as opposed to theoretical projections) in the real world of nature (as opposed to the virtual world of mathematical models), in order to see how earth's plants have responded to what climate alarmists routinely describe as the unprecedented warming of the past few decades?

An enlightening reality check is provided by Le Roux and McGeoch (2008), who examined patterns of altitudinal range changes in the totality of the native vascular flora of sub-Antarctic Marion Island (4654'S, 3745'E) in the southern Indian Ocean, which warmed by 1.2C between 1965 and 2003. The work of the South African researchers revealed that between 1966 and 2006, there was "a rapid expansion in altitudinal range," with species expanding their upper elevational boundaries by an average of 70 meters. And because, as they describe it, "the observed upslope expansion was not matched by a similar change in lower range boundaries," they emphasize the fact that "the flora of Marion Island has undergone range expansion rather than a range shift." In addition, they write that "the expansion of species distributions along their cooler boundaries in response to rising temperatures appears to be a consistent biological consequence of recent climate warming," citing references to several other studies that have observed the same type of response.

Another consequence of the stability of lower range boundaries and the extension of upper range boundaries of many plant species is that there is a greater overlapping of ranges, resulting in greater local species richness or biodiversity everywhere up and down altitudinal transects of the island, the theoretical basis for which outcome we have described in more detail in our special report The Specter of Species Extinction. And as a further consequence of this fact, le Roux and McGeoch indicate that "the present species composition of communities at higher altitudes is not an analogue of past community composition at lower altitudes, but rather constitutes a historically unique combination of species," or what we could truly call a "brave new world," which is significantly richer in diversity in many undisturbed locations than it was in the recent past.

Another concern was expressed by Wolfe-Bellin et al. (2006), who wrote that "nocturnal temperatures are predicted to increase more than diurnal temperatures" -- as was, in fact, observed to be the case over much of the 20th century -- and who speculated that "increased nocturnal temperature would increase dark respiration rate" and thereby "diminish the positive effects of elevated CO2 on whole-plant growth, as measured by total biomass." Subsequently, therefore, in an experiment they designed to explore this hypothesis, the three researchers grew the C3 forb Phytolacca americana from the four-leaf stage to maturity under well watered and fertilized conditions in containers filled with a general purpose growing medium within controlled-environment glass chambers maintained at either 370 or 740 ppm CO2 at diurnal/nocturnal temperatures of either 26/20C or 26/24C, during which time they periodically measured their light-saturated photosynthetic rates and whole-plant biomass production.

This work revealed, in their words, that the plant's "photosynthetic rate was greater under elevated CO2 [+69% during the first part of the growing season], while dark respiration rate, predicted to increase under higher nocturnal temperatures, exhibited no response to the nocturnal temperature treatment." Hence, they acknowledged that in contrast to their expectation, the forb they studied "exhibited no diminishment of total plant size in response to elevated nocturnal temperature." In fact, they found that "time to flowering decreased" and that biomass allocation to reproduction actually "increased under conditions of elevated nocturnal temperatures." And as a result, Wolfe-Bellin et al. concluded that "since elevated CO2 increased total plant biomass and higher nocturnal temperatures increased allocation to reproduction, the results indicate that elevated CO2 and high nocturnal temperatures of the future could have a neutral or even positive effect on the growth of northern P. americana populations," even to the extent of "increasing population sizes, at least for plants growing at the northern edge of the species' range," which obviously would pave the way for their successful migration in that direction.

In another study germane to the issue, Holzinger et al. (2008) revisited areas of twelve mountains having summits located between elevations of 2844 and 3006 meters in the canton of Grisons, Switzerland, where in 2004 they had made complete inventories of vascular plant species, which they later compared with similar inventories made by other researchers in 1885, 1898, 1912, 1913 and 1958, following the ascension paths of the earlier investigators "as accurately as possible" in areas where mean summer temperature increased by at least 0.6C between the time of the first and their most recent study. This work revealed that the upward migration rates they detected were on the order of several meters per decade; and their data suggested that vascular plant species richness had increased by 11% per decade over the last 120 years on the mountain summits (defined as the upper 15 meters of the mountains) in the alpine-nival ecotone, which finding, in their words, "agrees well with other investigations from the Alps, where similar changes have been detected (Grabherr et al., 1994; Pauli et al., 2001; Camenisch, 2002; Walther, 2003; Walther et al., 2005)." With respect to the prediction of "the extinction of a considerable number of high-alpine species" within "the context of climate warming," therefore, Holzinger et al. concluded that this "outstanding threat for species to become out-competed 'beyond the summits' can neither be confirmed nor rejected with our data." Once again, therefore, the "outstanding threat" put forth by James Hansen to the U.S. House of Representatives was found to be unconfirmed by yet another study of the subject.

One year later, and noting that one of the predicted consequences of rising temperatures "is the migration of plant species from lower altitudes to higher elevations provoking consecutive displacements of alpine and nival plant species (i.e. 'biodiversity disasters')," Erschbamer et al. (2009) documented and analyzed changes (from 2001 to 2006) in plant species number, frequency and composition along an altitudinal gradient crossing four summits from the treeline ecotone to the subnival zone in the South Alps (Dolomites, Italy), where minimum temperatures increased by 1.1-2.0C during the past century with a marked rise over the last decades. And as they describe it, "after five years, a re-visitation of the summit areas revealed a considerable increase of species richness at the upper alpine and subnival zone (10% and 9%, respectively) and relatively modest increases at the lower alpine zone and the treeline ecotone (3% and 1%, respectively)." In addition, with respect to threats of extinction, they report that "during the last five years, the endemic species of the research area were hardly affected," while "at the highest summit, one endemic species was even among the newcomers." Consequently, the Austrian scientists concluded that "at least in short to medium time scales, the southern alpine endemics of the study area should not be seriously endangered." Moreover, they report that "the three higher summits of the study area have a pronounced relief providing potential surrogate habitats for these species," and that "recently published monitoring data from high altitudes indicate a consistent increase of species richness in the Alps," citing the work of Pauli et al. (2007) and Holzinger et al. (2008).

Also publishing in the same year were Kuparinen et al. (2009), who -- with the help of real-world micrometeorological data measured during the vegetative growth period (May-September) of ten consecutive years (1998-2007) in a boreal forest of southern Finland -- investigated the effects of a warming-induced increase in local convective turbulence (caused by a postulated 3C increase in local temperature) on the long-distance dispersal (LDD) of seeds and pollen based on mechanistic models of wind dispersal (Kuparinen et al., 2007) and population spread (Clark et al., 2001). This work revealed that for light-seeded herbs, spread rates increased by 35-42 m/yr (6.3-9.2%), while for heavy-seeded herbs the increase was 0.01-0.06 m/yr (1.9-6.7%). Somewhat analogously, they found that light-seeded trees increased their spread rates by 27-39 m/yr (3.5-6.2%), while for heavy-seeded trees the increase was 0.2-0.5 m/yr (4.0-8.5%). And in this regard they note that "climate change driven advancements of flowering and fruiting phenology can increase spread rates of plant populations because wind conditions in spring tend to produce higher spread rates than wind conditions later in the year."

As for the significance of their findings, the four researchers write that -- in addition to the obvious benefits of greater LLD (being better able to move towards a more hospitable part of the planet) -- the increased wind dispersal of seeds and pollen may "promote gene flow between populations, thus increasing their genetic diversity and decreasing the risk of inbreeding depression," citing the work of Ellstrand (1992) and Aguilar et al. (2008), while further noting that "increased gene flow between neighboring populations can accelerate adaptation to environmental change," citing the work of Davis and Shaw (2001) and Savolainen et al. (2007), which phenomena are all very positive developments. In fact, they report that the "dispersal and spread of populations are widely viewed as a means by which species can buffer negative effects of climate change."

Last of all, De Frenne et al. (2010) collected seeds of Anemone nemorosa -- a model species for slow-colonizing herbaceous forest plants -- found in populations growing along a 2400-km latitudinal gradient stretching from northern France to northern Sweden during three separate growing seasons (2005, 2006 and 2008), after which they conducted sowing trials in incubators, a greenhouse, and under field conditions in a forest, where they measured the effects of different temperature treatments (Growing Degree Hours or GDH) on various seed and seedling traits. As a result of this work, they found that "seed mass, germination percentage, germinable seed output and seedling mass all showed a positive response to increased GDH experienced by the parent plant," noting that seed and seedling mass increased by 9.7% and 10.4%, respectively, for every 1000 C-hours increase in GDH, which they say is equivalent to a 1C increase in temperature over a 42-day period. Based on these findings, the nineteen researchers -- hailing from Belgium, Estonia, France, Germany and Sweden -- thus concluded that "if climate warms, this will have a pronounced positive impact on the reproduction of A. nemorosa, especially in terms of seed mass, germination percentage and seedling mass," because "if more seeds germinate and resulting seedlings show higher fitness, more individuals may be recruited to the adult stage." In addition, they indicate that since "rhizome growth also is likely to benefit from higher winter temperatures (Philipp and Petersen, 2007), it can be hypothesized that the migration potential of A. nemorosa may increase as the climate in NW-Europe becomes warmer in the coming decades."

In light of these several positive findings, it would appear that earth's plants will be able to migrate either poleward in latitude or upward in altitude at rates sufficiently rapid to keep them within the geographically-shifting temperature regimes to which they have long been adapted, with the result that (1) many species will not be driven to extinction and (2) the species richness of various ecosystems will be greatly enhanced, which is essentially just the opposite of what the world's climate alarmists typically contend.

References
Aguilar, R., Quesada, M., Ashworth, L., Herrerias-Diego, Y. and Lobo, J. 2008. Genetic consequences of habitat fragmentation in plant populations: susceptible signals in plant traits and methodological approaches. Molecular Ecology 17: 5177-5188.

Camenisch, M. 2002. Veranderungen der Gipfelflora im Bereich des Schweizerischen Nationalparks: Ein Vergleich uber die letzen 80 Jahre. Jahresber nat forsch Ges Graubunden 111: 27-37.

Clark, J.S., Lewis, M. and Hovarth, L. 2001. Invasion by extremes; population spread with variation in dispersal and reproduction. American Naturalist 157: 537-544.

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

De Frenne, P., Graae, J.J., Kolb, A., Brunet, J., Chabrerie, O., Cousins, S.A.O., Decocq, G., Dhondt, R., Diekmann, M., Eriksson, O., Heinken, T., Hermy, M., Jogar, U., Saguez, R., Shevtsova, A., Stanton, S., Zindel, R., Zobel, M. and Verheyen, K. 2010. Significant effects of temperature on the reproductive output of the forest herb Anemone nemorosa L. Forest Ecology and Management 259: 809-817.

Dyer, J.M. 1995. Assessment of climatic warming using a model of forest species migration. Ecological Modelling 79: 199-219.

Ellstrand, N.C. 1992. Gene flow by pollen: Implications for plant conservation genetics. Oikos 63: 77-86.

Erschbamer, B., Kiebacher, T., Mallaun, M. and Unterluggauer, P. 2009. Short-term signals of climate change along an altitudinal gradient in the South Alps. Plant Ecology 202: 79-89.

Grabherr, G, Gottfried, M. and Pauli, H. 1994. Climate effects on mountain plants. Nature 369: 448.

Holzinger, B., Hulber, K., Camenisch, M. and Grabherr, G. 2008. Changes in plant species richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects and migration rates. Plant Ecology 195: 179-196.

Kuparinen, A., Katul, G., Nathan, R. and Schurr, F.M. 2009. Increases in air temperature can promote wind-driven dispersal and spread of plants. Proceedings of the Royal Society B 276: 3081-3087.

Le Roux, P.C. and McGeoch, M.A. 2008. Rapid range expansion and community reorganization in response to warming. Global Change Biology 14: 2950-2962.

Malcolm, J.R., Liu, C., Miller, L.B., Allnutt, T. and Hansen, L. 2002. Habitats at Risk: Global Warming and Species Loss in Globally Significant Terrestrial Ecosystems. World Wide Fund for Nature, Gland, Switzerland.

Malcolm, J.R. and Markham, A. 2000. Global Warming and Terrestrial Biodiversity Decline. World Wide Fund for Nature, Gland, Switzerland.

Pauli, H., Gottfried, M. and Grabherr, G. 2001. High summits of the Alps in a changing climate. The oldest observation series on high mountain plant diversity in Europe. In: Walther, G.R., Burga, C.A. and Edwards, P.J. (Eds.) Fingerprints of Climate Change - Adapted Behaviour and Shifting Species Ranges. Kluwer Academic Publisher, New York, New York, USA, pp. 139-149.

Pauli, H., Gottfried, M., Reiter, K., Klettner, C. and Grabherr, G. 2007. Signals of range expansions and contractions of vascular plants in the high Alps: observations (1994-2004) at the GLORIA master site Schrankogel, Tyrol, Austria. Global Change Biology 13: 147-156.

Philipp, M. and Petersen, P.M. 2007. Long-term study of dry matter allocation and rhizome growth in Anemone nemorosa. Plant Species Biology 22: 23-31.

Savolainen, O., Pyhajarvi, T. and Knurr, T. 2007. Gene flow and local adaptation in trees. Annual Review of Ecology, Evolution and Systematics 38: 595-619.

Walther, G.R. 2003. Plants in a warmer world. Perspectives in Plant Ecology, Evolution and Systematics 6: 169-185.

Walther G.R., Beissner, S. and Burga, C.A. 2005. Trends in the upward shift of alpine plants. Journal of Vegetation Science 16: 541-548.

Wolfe-Bellin, K.S., He, J.-S. and Bazzaz, F.A. 2006. Leaf-level physiology, biomass, and reproduction of Phytolacca americana under conditions of elevated carbon dioxide and increased nocturnal temperature. International Journal of Plant Science 167: 1011-1020.

Last updated 31 March 2010