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The Amazing Amazon Rainforest
Volume 12, Number 19: 13 May 2009

In a report published in the 6 March 2009 issue of Science, Oliver L. Phillips of the UK's University of Leeds and his 65 co-authors write that "old growth forests in Amazonia ... through photosynthesis and respiration ... process 18 petagrams [18 x 1015 grams] of carbon annually," which they say is "more than twice the rate of anthropogenic fossil fuel emissions." They also state that over the past quarter-century of intensive region-wide measurements, the productivity of the Amazon rainforest -- even in its extreme old age -- has been found to be "increasing with time," in support of which statement they cite the comprehensive observational studies of Phillips et al. (1998), Nemani et al. (2003), Baker et al. (2004), Lewis et al. (2004) and Ichii et al. (2005).

Against the backdrop of this very positive phenomenon, the goal of Phillips et al.'s new analysis was to determine what negative effect a severe drought might have on South America's surprisingly-spry-for-its-age tropical mega-forest, especially a drought of the type that the world's climate alarmists predict will occur if anthropogenic CO2 emissions are not significantly abated. What the international team of scientists wanted to know, essentially, was whether such a decline in the availability of water might wipe out the super ecosystem's biomass gains of prior decades, thereby fulfilling one of the climate alarmists' worst-case catastrophic scenarios.

Focusing their attention on the Amazonian drought of 2005, which they describe as "one of the most intense droughts of the past 100 years," as well as "a possible analog of future events," the 66 researchers (who had monitored a host of forest plots across the Amazon basin over the prior quarter-century) utilized tree diameter, wood density, and allometric models to compute the basin's woody biomass at each time of measurement, both before and after the drought, deriving the results that are plotted in the figure below.


The post-1980 cumulative biomass increase of Amazon trees >= 10 cm in diameter as a function of the mid-date of each forest-plot census interval, portrayed as a 50-interval moving mean. Adapted from Phillips et al. (2009).

As may readily be seen from these real-world measurement-based results, the great Amazonian drought of 2005 resulted in only a slight hiatus in the strong upward trend of tree biomass accumulation that was exhibited over the prior two decades, which had occurred, as Phillips et al. note, through a multi-decadal period spanning both wet and dry episodes, the latter of which are not even detectable in their wood biomass data. Hence, it would appear that although extremely severe drought conditions can indeed bring a halt to biomass accumulation in old growth tropical forests -- and sometimes even lead to minor reductions in biomass due to selective tree mortality -- the vast majority of the aged trees are able to regain their photosynthetic prowess and add to their prior store of biomass once the moisture stress subsides, thanks in large measure to the enhanced growth (Lin et al., 1998) and water use efficiency (Hietz et al., 2005) that are experienced by nearly all woody plants as the air's CO2 content rises.

Additional support for this attribution is provided by the work of Lloyd and Farquhar (2008), who concluded that "the magnitude and pattern of increases in forest dynamics across Amazonia observed over the last few decades are consistent with a CO2-induced stimulation of tree growth," while still more support for the premise comes from the work of Phillips et al. (2008), who concluded that the simplest explanation for the phenomenon is that "improved resource availability has increased net primary productivity, in turn increasing growth rates," and who further note that "the only change for which there is unambiguous evidence that the driver has widely changed and that such a change should accelerate forest growth is the increase in atmospheric CO2," because of "the undisputed long-term increase in [its] concentration, the key role of CO2 in photosynthesis, and the demonstrated effects of CO2 fertilization on plant growth rates."

So if the nations of the world are truly concerned about the health of "old growth forests in Amazonia" -- as they truly should be -- they had better not be in too great a hurry to drastically curtail anthropogenic CO2 emissions. In light of the overwhelming evidence for (1) no global warming over the past decade or so, and (2) the significant biological benefits provided by atmospheric CO2 enrichment, the climate-alarmist clamor to reduce fossil fuel use now -- and by whatever means deemed necessary -- makes no sense at all, especially when there is so much evidence for much warmer periods in our planet's past (such as the Medieval, Roman and Mid-Holocene Warm Periods), when there was so much less CO2 in the air than there is today.

World governments clearly have the time to analyze this subject much more carefully than they have done to date; and until they do so, they should not act upon demands for radical actions to reduce CO2 emissions that could greatly exacerbate the world's current economic crisis, as well as lead to a greater propensity for biological crises in unique and high-biodiversity places ... like the Amazon.

Sherwood, Keith and Craig Idso

References
Baker, T.R., Phillips, O.L., Malhi, Y., Almeida, S., Arroyo, L., Di Fiore, A., Erwin, T., Higuchi, N., Killeen, T.J., Laurance, S.G., Laurance, W.F., Lewis, S.L., Monteagudo, A., Neill, D.A., Núñez Vargas, P., Pitman, N.C.A., Silva, J.N.M. and Vásquez Martínez, R. 2004. Increasing biomass in Amazonian forest plots. Philosophical Transactions of the Royal Society of London Series B - Biological Sciences 359: 353-365.

Hietz, P., Wanek, W. and Dunisch, O. 2005. Long-term trends in cellulose δ13C and water-use efficiency of tropical Cedrela and Swietenia from Brazil. Tree Physiology 25: 745-752.

Ichii, K., Hashimoto, H., Nemani, R. and White, M. 2005. Modeling the interannual variability and trends in gross and net primary productivity of tropical forests from 1982 to 1999. Global and Planetary Change 48: 274-286.

Lewis, S.L., Phillips, O.L., Baker, T.R., Lloyd, J., Malhi, Y., Almeida, S., Higuchi, N., Laurance, W.F., Neill, D.A., Silva, J.N.M., Terborgh, J., Lezama, A.T., Vásquez Martinez, R., Brown, S., Chave, J., Kuebler, C., Núñez Vargas, P. and Vinceti, B. 2004. Concerted changes in tropical forest structure and dynamics: evidence from 50 South American long-term plots. Philosophical Transactions of the Royal Society of London Series B - Biological Sciences 359: 421-436.

Lin, G., Marino, B.D.V., Wei, Y., Adams, J., Tubiello, F. and Berry, J.A. 1998. An experimental and modeling study of responses in ecosystems carbon exchanges to increasing CO2 concentrations using a tropical rainforest mesocosm. Australian Journal of Plant Physiology 25: 547-556.

Lloyd, J. and Farquhar, G.D. 2008. Effects of rising temperatures and [CO2] on the physiology of tropical forest trees. Philosophical Transactions of the Royal Society B 363: 1811-1817.

Nemani, R.R., Keeling, C.D., Hashimoto, H., Jolly, W.M., Piper, S.C., Tucker, C.J., Myneni, R.B. and Running. S.W. 2003. Climate-driven increases in global terrestrial net primary production from 1982 to 1999. Science 300: 1560-1563.

Phillips, O.L., Aragao, L.E.O.C., Lewis, S.L., Fisher, J.B., Lloyd, J., Lopez-Gonzalez, G., Malhi, Y., Monteagudo, A., Peacock, J., Quesada, C.A., van der Heijden G., Almeida, S., Amaral, I., Arroyo, L., Aymard, G., Baker, T.R., Banki, O., Blanc, L., Bonal, D., Brando, P., Chave, J., de Oliveira, A.C.A., Cardozo, N.D., Czimczik, C.I., Feldpausch, T.R., Freitas, M.A., Gloor, E., Higuchi, N., Jimenez, E., Lloyd, G., Meir, P., Mendoza, C., Morel, A., Neill, D.A., Nepstad, D., Patino, S., Penuela, M.C., Prieto, A., Ramirez, F., Schwarz, M., Silva, J., Silveira, M., Thomas, A.S., ter Steege, H., Stropp, J., Vasquez, R., Zelazowski, P., Davila, E.A., Andelman, S., Andrade, A., Chao, K.-J., Erwin, T., Di Fiore, A., Honorio C., E., Keeling, H., Killeen, T.J., Laurance, W.F., Cruz, A.P., Pitman, N.C.A., Vargas, P.N., Ramirez-Angulo, H., Rudas, A., Salamao, R., Silva, N., Terborgh, J. and Torres-Lezama, A. 2009. Drought sensitivity of the Amazon rainforest. Science 323: 1344-1347.

Phillips, O.L., Lewis, S.L., Baker, T.R., Chao, K.-J. and Higuchi, N. 2008. The changing Amazon forest. Philosophical Transactions of the Royal Society B 363: 1819-1827.

Phillips, O.L., Malhi, Y., Higuchi, N., Laurance, W.F., Nunez, P.V., Vasquez, R.M., Laurance, S.G., Ferreira, L.V., Stern, M., Brown, S. and Grace, J. 1998. Changes in the carbon balance of tropical forests: Evidence from long-term plots. Science 282: 439-442.