Background
One of the major scare stories promulgated by climate alarmists is that of massive extinctions of species due to CO2-induced global warming. Thomas et al. (2004), for example, have suggested that ecosystem biodiversity will decline, and many endangered plants will disappear altogether, as a result of continued unprecedented increases in air temperature, calculating that 15-37% of the species of plants scattered throughout many regions of the earth will be "committed to extinction" by the year 2050.

What was done
In a study that employed a wealth of data pertinent to this horrific claim, 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 have all been visited and "censused" more than once over the past few decades.

What was learned
The group of 34 international researchers 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) writes 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."

What it means
For whatever reason or reasons, and in the face of increases in air temperature and CO2 concentration that 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."

References
Pennisi, E. 2006. Rare tree species thrive in local neighborhoods. Science 311: 452-453.

Thomas, C.D., Cameron, A., Green, R.E., Bakkenes, M., Beaumont, L.J., Collingham, Y.C., Barend, F., Erasmus, N., Ferreira de Siqueira, M., Grainger, A., Hannah, L., Hughes, L., Huntley, B., van Jaarsveld, A.S., Midgley, G.F., Miles, L., Ortega-Huerta, M.A., Peterson, A.T., Phillips, O.L. and Williams, S.E. 2004. Extinction risk from climate change. Nature 427: 145-148.