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Biodiversity, Productivity and CO2
Volume 3, Number 30: 8 November 2000

"Diversity peaks at intermediate productivity in a laboratory microcosm."  So states the title of the recent paper of Kassen et al. (2000).  But, as the authors of this clever treatise readily admit in the first paragraph of their text, "at continental scales, the diversity of plants and animals usually increases monotonically with productivity."

Such was also determined to be the case in a recent massive review of the subject by Waide et al. (1999) - see our Journal Review Productivity and Species RichnessProductivity and Species Richness.  In fact, in the concluding paragraph of their experimental microcosm paper, Kassen et al. state that "at larger spatial scales it has been observed that diversity tends to increase linearly [our italics] with productivity."

From another field of research comes a second important fact - abundantly documented on our website (see Growth Response to CO2 in our Subject Index) - namely, that atmospheric CO2 enrichment tends to increase the productivity of almost all plants (Kimball, 1983; Poorter, 1993), and that it does so under almost all environmental conditions (Idso and Idso, 1994).  Pulling these two observations together, we conclude that one of the best things we could possibly do to preserve the biodiversity or species richness of the planet is let the carbon dioxide content of the air continue to rise, rejecting all overt attempts to curtail anthropogenic CO2 emissions via Kyoto-style interventions.

This is also the conclusion of a new review of the subject by Idso et al. (2000) - see our Journal Review Ecosystem Biodiversity and CO2).  In addition to the biodiversity-benefiting impact of the CO2-induced increase in plant productivity, however - for which we cite a number of supporting studies - our analysis considers several other important effects of the ongoing rise in the air's CO2 content.

First, there is the tendency for higher concentrations of atmospheric CO2 to counter the deleterious effects of heat stress in plants.  This phenomenon allows different species of plants to maintain the high-temperature boundaries of their ranges while extending their low-temperature boundaries in response to rising temperatures.  The consequent increases in the sizes of their ranges thus leads to more over-lapping of the territories they inhabit, producing increases in the species richness of plants in discrete geographical areas.

This CO2-and-temperature-driven increase in plant species richness is subsequently felt throughout all higher levels of the many food chains of nature; and we cite several real-world examples of this phenomenon.  Included in this discussion is the enhanced overlapping of the ranges of more than half a hundred species of butterflies that has been observed over the past century of modest warming in Europe, as well as the overlapping of the ranges of an equally large number of bird species that has been observed throughout Britain over the past few decades.

Another biodiversity-enhancing effect of the ongoing rise in the air's CO2 content that is discussed in our review derives from the well-established fact that atmospheric CO2 enrichment tends to promote greater root growth and consequent exudation of nutrients and carbon compounds into the soil, which in turn increases microbial activities there and leads to increased root colonization by various fungi, which promotes the development of intricate mycelial networks that connect the root systems of neighboring plants.  The enhanced nutrient transfers that consequently occur among these interconnected plants ultimately result in a sharing of resources among differing species that, in the words of Read (1997), "would be expected to reduce dominance of aggressive species, so promoting coexistence and greater biodiversity."

It has also been demonstrated that higher-plant species richness is sometimes directly dependent upon the diversity of soil fungi.  Hence, with more CO2 in the air, enabling plants to pump more carbohydrates into the soil, there is a greater resource base for supporting a greater diversity of such fungi, which may thereby provide yet another impetus for an increase in the diversity of higher-plant life.

Clearly, there are a number of different ways in which the rising CO2 content of earth's atmosphere tends to enhance biodiversity across the face of the planet, both on land and in fresh and marine waters.  Let us not, therefore, bite the hand that helps sustain our fellow passengers on spaceship earth, which hand, incidentally, is our own.

So, keep those CO2 emissions going, derail Kyoto, and burn, burn, burn those fossil fuels.  But do it as cleanly as possible.  The developed nations will ultimately thank you, the developing nations will thank you even sooner, and the biosphere will thank you immediately, boosting its productivity and increasing the critical biomass required by every species to maintain its unique identity.

Dr. Craig D. Idso
Dr. Keith E. Idso
Vice President

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.

Idso, K.E., Idso, S.B. and Idso, C.D.  2000.  Atmospheric CO2 enrichment: Implications for ecosystem biodiversity.  Technology 7S: 57-69.

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

Kimball, B.A.  1983.  Carbon dioxide and agricultural yield: An assemblage and analysis of 430 prior observations.  Agronomy Journal 75: 779-788.

Poorter, H.  1993.  Interspecific variation in the growth response of plants to an elevated ambient CO2 concentration.  Vegetatio 104-105: 77-97.

Read, D.  1997.  The ties that bind.  Nature 388: 517-518.

Waide, R.B., Willig, M.R., Steiner, C.F., Mittelbach, G., Gough, L., Dodson, S.I., Juday, G.P. and Parmenter, R.  1999.  The relationship between productivity and species richness.  Annual Review of Ecology and Systematics 30: 257-300.