Also long known to be high on the list of factors that increase ecosystem biodiversity is stability of environmental conditions (Sanders and Hessler, 1969; Fjeldsa and Lovett, 1997).  And now, in an impressive new study of how both of these factors, i.e., environmental stability and ecosystem productivity, influence the species richness of large animals in different parts of Kenya, Oindo (2002) presents evidence that provides compelling support for our contention that the ongoing rise in the air's CO2 content should be significantly stimulating this dynamic duo of biodiversity-enhancing factors throughout the entire world.

What Oindo did was compare regional patterns of large herbivore species richness in Kenya with remotely-sensed normalized difference vegetation index (NDVI) values derived from advanced very-high-resolution radiometer data that were obtained by U.S. National Oceanic and Atmospheric Administration satellites and processed by the Global Inventory Monitoring and Modeling Studies program of the U.S. National Aeronautics and Space Administration.  The 11-year (1982-1993) study focused on 25 large herbivores - including buffalo, elephant, gazelle, giraffe, hippopotamus, rhinoceros, wildebeest and zebra - found in 19 distinct rangeland districts in Kenya that were comprised primarily of game reserves, parks and private ranches.

In discussing the results of the study, Oindo remarks that our current understanding of the subject suggests that herbivore species richness should be higher in districts with higher interannual average NDVI, due to those districts' greater abundance of above-ground biomass, which is essentially what the NDVI measures, i.e., above-ground biomass.  And that relationship is precisely what was found.  In the words of the author, the study demonstrated that "the best predictor of species richness is interannual average NDVI."

With respect to the second concept investigated - the role of environmental stability in promoting ecosystem biodiversity - Oindo notes that "when the coefficient of variation of [the] NDVI over [the] 11-year period is considered, districts with [the] highest coefficient of variation have the lowest number of herbivore species."  This observation is also exactly what would be expected; for Oindo's study clearly demonstrated that "regions with a high coefficient of variation of NDVI have low above-ground biomass."

Oindo's verification of these two concepts - which is but the latest in a long string of such findings - bodes well for the biodiversity of the planet as the air's CO2 content continues to climb.  There is absolutely no question, for example, that higher concentrations of atmospheric CO2 lead to increased quantities of both above- and below-ground vegetative biomass in essentially all places where plants grow (see Plant Growth Data on our web site).  In addition, any warming that might possibly occur in the future - whether CO2-induced or otherwise - would likely enhance environmental stability (see Weather Extremes in our Subject Index).  Also, the rising CO2 content of the air would likely alleviate the deleterious effects of most environmental stresses (see Growth Response to CO2 with Other Variables in our Subject Index, as well as Idso and Idso, 1994), which should have the same biological effect as enhancing environmental stability.

Atmospheric CO2 enrichment also helps preserve the biodiversity of earth's natural ecosystems by enhancing the productivity and water use efficiency of agricultural crops.  By producing more food on the same amount of land with the same or a lesser amount of water per unit land area, for example, less land and water need be appropriated by humanity to feed itself, which leaves more land and water for the use of natural ecosystems (see our Editorials of 21 February 2001 and 2 May 2001, based on the studies of Wallace, 2000 and Tilman et al., 2001).  And with more land and water at its disposal, each species of plant and animal is better able to produce the "critical biomass" needed to maintain its existence.  Hence, it is clear that the ongoing rise in the air's CO2 content is a powerful force for helping earth's natural ecosystems preserve their biodiversity in the face of the many real-world pressures that are tending to reduce their species richness.

References
Fjeldsa, J. and Lovett, J.C.  1997.  Biodiversity and environmental stability.  Biodiversity and Conservation 6: 315-323.

Idso, K.E. and Idso, S.B.  1994.  Plant responses to atmospheric CO2 enrichment in the face of environmental constraints: A review of the past 10 years' research.  Agricultural and Forest Meteorology 69: 153-203.

Kassen, R., Buckling, A., Bell, G. and Rainey, P.B.  2000.  Diversity peaks at intermediate productivity in a laboratory microcosm.  Nature 406: 508-512.

Oindo, B.O.  2002.  Patterns of herbivore species richness in Kenya and current ecoclimatic stability.  Biodiversity and Conservation 11: 1205-1221.

Sanders, H.L. and Hessler, R.R.  1969.  Ecology of the deep sea benthos.  Science 163: 1419-1424.

Scheiner, S.M. and Rey-Benayas, J.M.  1994.  Global patterns of plant diversity.  Evolution and Ecology 8: 331-347.

Tilman, D., Fargione, J., Wolff, B., D'Antonio, C., Dobson, A., Howarth, R., Schindler, D., Schlesinger, W.H., Simberloff, D. and Swackhamer, D.  2001.  Forecasting agriculturally driven global environmental change.  Science 292: 281-284.

Waide, R.B., Willig, M.R., Steiner, C.F., Mittelbach, G., Gough, L., Dodson, S.I., Juday, G.P. and Parmenter, R.  2000.  The relationship between productivity and species richness.  Annual Review of Ecology and Systematics 30: 257-300.

Wallace, J.S.  2000.  Increasing agricultural water use efficiency to meet future food production.  Agriculture, Ecosystems & Environment 82: 105-119.