An experiment that broached this unique subject was established in the spring of 1994 at the Cedar Creek Natural History Area in central Minnesota (USA), where a decade later Lambers et al. (2004) quantified the temporal evolution of the productivity and "staying power" of fourteen species of plants across an experimental grassland diversity gradient. Over the course of the long-term study, they learned that certain species were overyielders, i.e., plants that grow better and produce more biomass when grown in competition with other species than when grown by themselves. In this study there were six such species, including a C3 grass, three C4 grasses and two legumes; and the five researchers noted that these "overyielding species were either superior N competitors (C4 grasses) or N fixers (legumes)." On the other hand, underyielding species, of which there were five in this experiment (four of which were forbs), typically grow less robustly when in the presence of other species. Nevertheless, they determined that the "overyielding species [were] not displacing underyielding species over time."

In discussing their findings, Lambers et al. concluded that "diversity-promoting interactions also operate[d] in this experiment," and that "underyielding species appear to be buffered from extinction." How common is this phenomenon? No one knows; but its operation in this study suggests that earth's plants may be much better "buffered from extinction" than many have supposed. More research should thus be directed to better elucidate the various "diversity-promoting interactions" that maintain the existence of underyielding species in the face of what might logically be presumed to be significant competitive pressure from average and overyielding species. In addition, consideration should be given to how the phenomena responsible for enabling underyielding species to avoid extinction may be influenced by global warming and rising atmospheric CO2 concentrations, both of which phenomena could well prove helpful to them in this regard.

In another intriguing study, Stinson and Bazzaz (2006) grew well-watered stands of ragweed (Ambrosia artemisiifolia) out-of-doors in open-top-chambers maintained at either 360 or 720 ppm CO2 from seedling stage to the onset of senescence, after which the plants were harvested and the dry masses of their shoots, roots and reproductive structures determined, while prior to this time -- at 14, 33 and 52 days after the start of the experiment -- they also measured the heights and numbers of leaves of all the plants. This work revealed that doubling the atmosphere's CO2 concentration increased the mean stand-level biomass of the shoots of the ragweed plants by 44%, while it increased the biomass of their roots and reproductive structures by 46% and 94%, respectively, for a total CO2-induced biomass increase of 70%. Of perhaps even greater interest, however, was the researchers' finding that the extra CO2 "reduced the coefficients of variation for all aspects of plant growth, especially reproductive biomass," such that the CO2-induced growth enhancements were "more pronounced in small, rather than large plants." That is to say, as they rephrased their findings, "growth enhancements to smaller plants diminished the relative biomass advantages of larger plants in increasingly crowded conditions," or as they stated in yet another place in their paper, "CO2-induced growth gains of subordinate A. artemisiifolia plants minimize differences in the reproductive output of small and large plants."

The Harvard University scientists thus concluded that "more homogeneous reproduction between subordinates and dominants also implies that a larger number of individuals will contribute propagules to future generations," which phenomenon, in their words, "could in turn affect evolutionary and population dynamics." We agree, while wondering if what they found to be true for within-species subordinates and dominants might also be true for among-species subordinates and dominants. If it is, this preferential stimulation of growth responses to atmospheric CO2 enrichment in subordinate species, could well help those that are endangered to better withstand whatever forces might be pushing them towards extinction.

In another study that yielded some encouraging new insights, an international team of 33 researchers (Wills et al., 2006) analyzed seven tropical forest dynamics plots located throughout the New and Old World tropics that have a wide range of species richness and tree densities, and that had all been visited and "censused" more than once over the past few decades. The efforts of the team paid off handsomely, for they found that for all of the plots they studied, "rare species survive preferentially, which increases diversity as the ages of the individuals increase," or as they state for further clarity, "when species were rare in a local area, they had a higher survival rate than when they were common, resulting in enrichment for rare species and increasing diversity with age and size class in these complex ecosystems."

Why would that be? Some of the reasons the researchers give are that (1) "diversity should increase as a group of individuals ages, because more common species are selectively removed by pathogens and predators," especially those that are commonly associated with them, (2) "individuals compete more intensively with conspecifics than with individuals of other species," and (3) "diversity may increase if an individual facilitates (benefits) nearby nonconspecics," which facilitation "has the effect of making interspecific interactions more positive than intraspecific interactions and thus provides an advantage to locally rare species." Likewise, in a commentary on these important findings and the phenomena underpinning them, Pennisi (2006) wrote that "being closer together, common trees are more prone to deadly infections," and "they may also face stiffer competition for certain resources," while "rarer trees, by depending on slightly different sets of resources, may not have this problem."

Consequently, for whatever reason or reasons, and in the face of historical increases in air temperature and atmospheric CO2 concentration (which may or may not be as dramatic as climate alarmists claim them to be), the biodiversities of real-world tropical forests are increasing, and rare species are becoming more abundant, which is just the opposite of what climate alarmists continually claim is occurring. In addition, Pennisi quotes Scott Armbruster of the UK's University of Portsmouth as saying that the fact that "these patterns are found to be so consistent across so many distant tropical forests suggests to me that the conclusion may eventually be found to hold for other diverse ecosystems as well."

In one final paper dealing with plants, Londre and Schnitzer (2006) write that all around the globe, woody vines or lianas are "competing intensely with trees and reducing tree growth, establishment, fecundity, and survivorship," possibly because "increasing levels of CO2 may enhance growth and proliferation of temperate lianas more than of competing growth forms (e.g., trees)," and possibly because "warmer winter temperatures may also increase the abundance and distribution of temperate lianas, which are limited in their distribution by their vulnerability to freezing-induced xylem embolism in cold climates." Consequently, the two researchers decided to see if these phenomena had impacted liana abundance and distribution over the prior 45 years in 14 temperate deciduous forests of southern Wisconsin (USA), during which time (1959-1960 to 2004-2005) the atmosphere's CO2 concentration rose by some 65 ppm, mean annual air temperature in the study region rose by 0.94°C, mean winter air temperature rose by 2.40°C, but mean annual precipitation (another important growth-altering factor) did not change.

So what did the Wisconsin scientists find?

As they describe it, and contrary to their initial hypothesis, "liana abundance and diameter did not increase in the interiors of Wisconsin (USA) forests over the last 45 years." In fact, they report that Toxicodendron radicans -- a liana popularly known as poison ivy, which they say "grew markedly better under experimentally elevated CO2 conditions than did competing trees (Mohan et al., 2006)" -- actually decreased in abundance over this period, and did so significantly.

But how did it happen that what had seemed to be so logical turned out to be so wrong?

Londre and Schnitzer write that "the lack of change in overall liana abundance and diameter distribution in [their] study suggests that lianas are limited in the interiors of deciduous forests of Wisconsin by factors other than increased levels of CO2," and in this regard they suggest it is likely that the interior-forest lianas were limited by the historical increase in atmospheric CO2 via the enhanced tree growth provided by the CO2 increase, which likely resulted in the trees becoming more competitive with the vines because of CO2-induced increases in tree leaf numbers, area and thickness, all of which factors would have led to less light being transmitted to the lianas growing beneath the forest canopy, which phenomenon likely negated the enhanced propensity for growth that likely was provided the vines by the historical increase in the atmosphere's CO2 concentration.

Support for this net-zero competing effects hypothesis is provided by Londre and Schnitzer's finding that "compared to the forest interior, lianas were >4 times more abundant within 15 m of the forest edge and >6 times more abundant within 5 m of the forest edge," which "strong gradient in liana abundance from forest edge to interior," in the words of the two researchers, "was probably due to light availability." In addition, they say their results "are similar to findings in tropical forests, where liana abundance is significantly higher along fragmented forest edges and within tree fall gaps," and, we might add, where the interior tropical trees have also not suffered what some have claimed would be the negative consequences of CO2-induced increases in liana growth, as we describe in our review of the study of Phillips et al. (2002).

In commenting on the significance of their findings, Londre and Schnitzer write that because "forest fragmentation (and thus edge creation) has increased significantly over the last half-century, particularly in the northeastern and midwestern United States (e.g., Ritters and Wickham, 2003; Radeloff et al., 2005), liana abundance has likely increased in temperate forests due to forest fragmentation." Consequently, they say that "as forest fragmentation continues, liana abundance will also likely continue to increase, and the effects of lianas on temperate forests, such as intense competition with trees (Schnitzer et al., 2005), reduced tree growth rates and biomass sequestration (Laurance et al., 2001), and the incidence of arrested gap-phase regeneration (Schnitzer et al., 2000) may become even more pronounced."

In light of these latter observations, it is clear that it is not rising CO2 concentrations that are to be feared in this regard, it is the encroachment of man upon the world of nature (Waggoner, 1995; Tilman et al., 2001, 2002; Raven, 2002); for it is this phenomenon that is destined to desecrate the globe's forests and drive innumerable species of both plants and animals to extinction, unless we can dramatically increase the water use efficiency of our crop plants, so we are not forced to encroach further upon the forests of the world to obtain the additional land and water resources (Wallace, 2000) we will otherwise need to grow the greater quantities of food that will be required to sustain our larger projected population at the midpoint of the current century.

Clearly, the most effective means of ensuring that the needed increase in plant water use efficiency actually comes to pass (in contrast to the grandiose schemes of men that promise much but produce little, especially where it is really needed) is to allow the atmosphere's CO2 concentration to continue its natural upward course, which will truly give crops throughout the world the productivity boost they will need to supply us with the food we will require but a few short decades from now without usurping further land and water resources from "wild nature," which should thereby preserve for future generations what yet remains of the world's forests and the great profusion of lifeforms they shelter and sustain (Idso and Idso, 2000).

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