Volume 7, Number 23: 9 June 2004
Dietary restriction is known to increase lifespan in organisms ranging from yeast to mammals, presumably, in the words of Mair et al. (2003), "by slowing the accumulation of aging-related damage." In stark contrast, however, their studies of Drosophila (the common fruit fly) indicate that "dietary restriction extends lifespan entirely by reducing the short-term risk of death." So powerful is this phenomenon, in fact, they report that only "two days after the application of dietary restriction at any age for the first time, previously fully fed flies are no more likely to die than flies of the same age that have been subjected to long-term dietary restriction."
In an accompanying article entitled "It's Never Too Late," Vaupel et al. (2003) indicate that a similar phenomenon operates in humans. Following the unification of East and West Germany, for example, they note that "mortality in the East declined toward prevailing levels in the West, especially among the elderly." After citing a number of other studies that confirm the operation of this phenomenon, they report that long-held "evolutionary theories of aging, which emphasize that senescence is inevitable," are gradually giving way to the realization that "aging is plastic," and that "survival can be substantially extended by various genetic changes and nongenetic interventions," noting that "interventions even late in life [our italics] can switch death rates to a lower, healthier trajectory."
The situation with perennial plants, such as trees, is proving to be very similar. Long-held theory, according to Knohl et al. (2003), maintains that assimilation is "balanced by respiration as a forest stand reaches an 'advanced' stage of development." Quite to the contrary, however, a number of newer studies are finding this supposition to be as poor a representation of reality as were the early evolutionary theories of aging in animals.
In a recent biomass inventory, for example, Cary et al. (2001) found much larger than expected net primary production in multi-species subalpine forest stands ranging in age from 67 to 458 years, while similar results have been obtained by Hollinger et al. (1994) for a 300-year-old Nothofagus site in New Zealand, by Law et al. (2001) for a 250-year-old ponderosa pine site in the northwestern United States, by Falk et al. (2002) for a 450-year-old Douglas fir/western hemlock site in the same general area, and by Knohl et al. (2003) for a 250-year-old deciduous forest in Germany.
In commenting on their findings, the latter investigators say they found "unexpectedly high carbon uptake rates during 2 years for an unmanaged 'advanced' beech forest, which is in contrast to the widely spread hypothesis that 'advanced' forests are insignificant as carbon sinks." For the forest they studied, as they describe it, "assimilation is clearly not balanced by respiration, although this site shows typical characteristics of an 'advanced' forest at a comparatively late stage of development."
These recent observations about trees are remarkably reminiscent of the recent findings of demographers regarding humans, i.e., nongenetic interventions, even late in life, put one on a healthier trajectory that extends productive lifespan. So what is the global "intervention" that has put the planet's trees on the healthier trajectory of being able to sequester carbon when past theory, which was obviously based on past observations, decreed they should be in a state of no net growth?
The answer, to us, seems rather simple. For any tree of age 250 years or more, the greater portion of its life (at least two-thirds of it) has been spent in an atmosphere of much-reduced CO2 content. Up until 1920, for example, the air's CO2 concentration had never been above 300 ppm throughout the entire lives of such trees, whereas it is currently 375 ppm or 25% higher. And for older trees, even greater portions of their lives have been spent in air of even lower CO2 concentration. Hence, the "intervention" that has given new life to old trees and allows them to "live long and prosper," in clear contradiction of previous perceived wisdom, would appear to be the flooding of the atmosphere with CO2 that was produced by the Industrial Revolution and is maintained by its ever-expanding aftermath (Idso, 1995).
| Sherwood, Keith and Craig Idso |
References
Carey, E.V., Sala, A., Keane, R. and Callaway, R.M. 2001. Are old forests underestimated as global carbon sinks? Global Change Biology 7: 339-344.
Falk, M., Paw, U.K.T., Schroeder, M. 2002. Interannual variability of carbon and energy fluxes for an old-growth rainforest. In: Proceedings of the 25th Conference on Agricultural and Forest Meteorology. American Meteorological Society, Boston, Massachusetts, USA.
Hollinger, D.Y., Kelliher, F.M., Byers, J.N., Hunt, J.E., McSeveny, T.M. and Weir, P.L. 1994. Carbon dioxide exchange between an undisturbed old-growth temperate forest and the atmosphere. Ecology 75: 143-150.
Idso, S.B. 1995. CO2 and the Biosphere: The Incredible Legacy of the Industrial Revolution. Department of Soil, Water and Climate, University of Minnesota, St. Paul, Minnesota, USA.
Knohl, A., Schulze, E.-D., Kolle, O. and Buchmann, N. 2003. Large carbon uptake by an unmanaged 250-year-old deciduous forest in Central Germany. Agricultural and Forest Meteorology 118: 151-167.
Law, B.E., Goldstein, A.H., Anthoni, P.M., Unsworth, M.H., Panek, J.A., Bauer, M.R., Fracheboud, J.M. and Hultman, N. 2001. Carbon dioxide and water vapor exchange by young and old ponderosa pine ecosystems during a dry summer. Tree Physiology 21: 299-308.
Mair, W., Goymer, P., Pletcher, S.D. and Partridge, L. 2003. Demography of dietary restriction and death in Drosophila. Science 301: 1731-1733.
Vaupel, J.W., Carey, J.R. and Christensen, K. 2003. It's never too late. Science 301: 1679-1681.