Trees and Shrubs Benefit from Higher Atmospheric CO2
The basic growth response of woody plants (trees and shrubs) to atmospheric CO2 enrichment has been extensively studied. Ceulemans & Mousseau (1994), for example, tabulated the results of 95 separate experimental investigations related to this topic; while the review of Poorter (1993) includes 41 additional sets of pertinent results, and the two reviews of Wullschleger et al. (1995, 1997) contain 40 other sets of applicable data. When averaged together, these 176 individual woody plant experiments reveal a mean growth enhancement on the order of 50% for an approximate doubling of the air's CO2 content, which is about one and a half times as much as the response of non-woody herbaceous plants.
It is possible, however, that this larger result is still an underestimate of the capacity of trees and shrubs to respond to atmospheric CO2 enrichment; for the mean duration of the 176 woody plant experiments described above was only five months, which may not have been sufficient for the long-term equilibrium effects of the CO2 enrichment of the air to be manifest. In the world's longest such experiment, for example, Idso and Kimball (1997) also observed a 50% growth stimulation at the five-month point of their landmark study of sour orange trees; but the response continued to increase to well over 100% during the following year and a half, finally leveling out after about nine years at a value on the order of 70%). Likewise, studies of Eldarica pine trees conducted at the same location have revealed a similarly increasing growth response over the same length of time (Idso and Kimball, 1994).
Poorter, H. 1993. Interspecific variation in the growth response of plants to an elevated ambient CO2 concentration. Vegetatio 104-105: 77-97.
Wullschleger, S.D., Post, W.M. and King, A.W. 1995. On the potential for a CO2 fertilization effect in forests: Estimates of the biotic growth factor based on 58 controlled-exposure studies. In: Woodwell, G.M. and Mackenzie, F.T. (eds) Biotic feedbacks in the global climatic system. Oxford University Press, Oxford, p 85-107.
Wullschleger, S.D., Norby, R.J. and Gunderson, C.A. 1997. Forest trees and their response to atmospheric CO2 enrichment: A compilation of results. In: Allen, L.H., Jr., Kirkham, M.B., Olszyk, D.M. and Whitman, C.E. (eds) Advances in carbon dioxide effects research. American Society of Agronomy, Madison, p 79-100.