Redwood Reader

133. Forests (Old) – Summary
Co2 Science had this article several weeks ago summarizing previous articles and new results. This is extremely important because so much depends financially upon growth rates and returns. We can now see net production is higher with bigger trees, higher in elevated CO2, and there is no mention of soil exudates although at one point they do refer to forests as superorganisms and measure CO2 retention in the system, leaving a big hole as to where exactly this carbon went. Well, it obviously is going to the fungi in the soil. All of these studies support our claim that forests accumulate and use CO2 for a wide variety of reasons and that more CO2 will benefit most if not all living systems. The comparison of saving big trees to reforestation to control greenhouse gases is shown to be exactly opposite of most current thinking. What we need are FACE and glomalin surveys in a variety of forest age classes because this hard knowledge will allow us to quantify carbon sequestration in a realistic manner. We’d like to see this science discussed at any of the global warming conferences. We point out how the Papua-New Guineans have asked the UN to pay them to protect their big trees, an idea discussed here last year.
Really, how could smaller trees be more effective than a mature tree with an acre of greenery in its canopy producing miles of fungally infected roots running through the soil? And what about the aggregation properties that bind soil particles and prevent sedimentation? And who benefits from big trees- doesn’t this provide everything forest species could want in terms of habitat from shade and cover to water?
For us, then the trick is to protect long lived species and superorganisms from risk such as fire and insect attack. And again, we find trees use stored water to defend against these threats and do so successfully where the superorganism is allowed to thrive.
Forests (Old) -- Summary

The planting and preservation of forests has long been acknowledged to be an effective and environmentally-friendly (indeed, enhancing) means for slowing climate-model-predicted CO2-induced global warming. This prescription for moderating potential climate change is based on two well-established and very straightforward facts: (1) the carbon trees use to construct their tissues comes from the air, and (2) its extraction from the atmosphere slows the rate of rise of the air's CO2 content.
Although simple enough that a child can understand it, this potential partial solution to the putative global warming problem has been under attack for several years by people who seek to address the issue solely on the basis of forced reductions in anthropogenic CO2 emissions (Pearce, 1999). The tack they take in this campaign is to claim that carbon sequestration by forests is only viable when forests are young and growing vigorously. As forests age, say the regulatory-minded pundits, they gradually lose their carbon sequestering prowess, such that forests more than one hundred years old become essentially useless for removing CO2 from the air, as they claim such ancient and decrepit stands yearly loose as much CO2 via respiration as what they take in via photosynthesis.
Although demonstrably erroneous, with repeated telling the twisted tale actually begins to sound reasonable. After all, doesn't the metabolism of every living thing slow down as it gets older? We grudgingly admit that it does -- even with trees -- but some trees live a remarkably long time. In Panama (Condit et al., 1995), Brazil (Chambers et al., 1998; Laurance et al., 2004; Chambers et al., 2001), and many parts of the southwestern United States (Graybill and Idso, 1993), for example, individuals of a number of different species have been shown to live for nearly one and a half millennia. At a hundred years of age, these super-slurpers of CO2 are mere youngsters. And in their really old age, their appetite for the vital gas, though diminished, is not lost. In fact, Chambers et al. (1998) indicate that the long-lived trees of Brazil continue to experience protracted slow growth even at 1400 years of age. And protracted slow growth (evident in yearly increasing trunk diameters) of very old and large trees can absorb a huge amount of CO2 out of the air each year, especially when, as noted by Chanbers et al. (1998) with respect to the Brazilian forests in the central Amazon, about 50% of their above-ground biomass is contained in less than the largest 10% of their trees. Consequently, since the life span of these massive long-lived trees is considerably greater than the projected life span of the entire "Age of Fossil Fuels," their cultivation and preservation represents an essentially permanent partial solution to the perceived problem of the dreaded global warming that climate alarmists ascribe to anthropogenic CO2 emissions.
As important as are these facts about trees, however, there's an even more important fact that comes into play in the case of forests and their ability to sequester carbon over long periods of time. This little-acknowledged piece of information is the fact that it is the forest itself -- conceptualized as a huge super-organism, if you will -- that is the unit of primary importance when it comes to determining the ultimate amount of carbon that can be sequestered on a unit area of land. And it when it comes to elucidating this concept, it seems that a lot of climate alarmists and political opportunists can't seem to see the forest for the trees that comprise it.
That this difference in perspective can have enormous consequences has been clearly demonstrated by Cary et al. (2001), who note that most models of forest carbon sequestration wrongly assume that "age-related growth trends of individual trees and even-aged, monospecific stands can be extended to natural forests." When they compared the predictions of such models against real-world data they gathered from northern Rocky Mountain subalpine forests that ranged in age from 67 to 458 years, for example, they found that aboveground net primary productivity in 200-year-old natural stands was almost twice as great as that of modeled stands, and that the difference between the two increased linearly throughout the entire sampled age range.
So what's the explanation for the huge discrepancy? Cary et al. suggest that long-term recruitment and the periodic appearance of additional late-successional species (increasing biodiversity) may have significant effects on stand productivity, infusing the primary unit of concern, i.e., the ever-evolving forest super-organism, with greater vitality than would have been projected on the basis of characteristics possessed by the unit earlier in its life. They also note that by not including effects of size- or age-dependent decreases in stem and branch respiration per unit of sapwood volume in models of forest growth, respiration in older stands can be over-estimated by a factor of two to five.
How serious are these model shortcomings? For the real-world forests studied by Cary et al., they produce predictions of carbon sequestration that are only a little over half as large as what is observed in nature for 200-year-old forests; while for 400-year-old forests they produce results that are only about a third as large as what is characteristic of the real world. And as the forests grow older still, the difference between reality and model projections grows right along with them.
Another study relevant to the suitability of forests to act as long-term carbon sinks was conducted by Lou et al. (2003), who analyzed data obtained from the Duke Forest FACE experiment, in which three 30-meter-diamerer plots within a 13-year old forest (composed primarily of loblolly pines with sweetgum and yellow poplar trees as sub-dominants, together with numerous other trees, shrubs and vines that occupy still smaller niches) began to be enriched with an extra 200 ppm of CO2 in August of 1996, while three similar plots were maintained at the ambient atmospheric CO2 concentration. A number of papers describing different facets of this still-ongoing long-term study have been published; and as recounted by Lou et al., they have revealed the existence of a CO2-induced "sustained photosynthetic stimulation at leaf and canopy levels [Myers et al., 1999; Ellsworth, 2000; Luo et al., 2001; Lai et al., 2002], which resulted in sustained stimulation of wood biomass increment [Hamilton et al., 2002] and a larger carbon accumulation in the forest floor at elevated CO2 than at ambient CO2 [Schlesinger and Lichter, 2001]."
Based upon these findings and what they imply about rates of carbon removal from the atmosphere and its different residence times in plant, litter and soil carbon pools, Luo et al. developed a model for studying the sustainability of forest carbon sequestration. Applying this model to a situation where the atmospheric CO2 concentration gradually rises from a value of 378 ppm in 2000 to a value of 710 ppm in 2100, they calculated that the carbon sequestration rate of the Duke Forest would rise from an initial value of 69 g m-2 yr-1 to a final value of 201 g m-2 yr-1, which is a far, far cry from the sad scenario promulgated by the cadre of climate alarmists that have long claimed earth's forests will have released much of the carbon they had previously absorbed as early as the year 2050 (Pearce, 1999).
Another study that supports the long-term viability of carbon sequestration by forests was conducted by Paw U et al. (2004), who also note that old-growth forests have generally been considered to "represent carbon sources or are neutral (Odum, 1963, 1965)," stating that "it is generally assumed that forests reach maximum productivity at an intermediate age and productivity declines in mature and old-growth stands (Franklin, 1988), presumably as dead woody debris and other respiratory demands increase." More particularly, they report that a number of articles have suggested that "old-growth conifer forests are at equilibrium with respect to net ecosystem productivity or net ecosystem exchange (DeBell and Franklin, 1987; Franklin and DeBell, 1988; Schulze et al., 1999), as an age-class end point of ecosystem development."
To see if these claims had any merit, Paw U et al. used an eddy covariance technique to estimate the CO2 exchange rate of the oldest forest ecosystem (500 years old) in the AmeriFlux network of carbon-flux measurement stations -- the Wind River old-growth forest in southwestern Washington, USA, which is composed mainly of Douglas-fir and western Hemlock -- over a period of 16 months, from May 1998 to August 1999. Throughout this period, the fourteen scientists report "there were no monthly averages with net release of CO2," and that the cumulative net ecosystem exchange showed "remarkable sequestration of carbon, comparable to many younger forests." Hence, they concluded that "in contrast to frequently stated opinions, old-growth forests can be significant carbon sinks," noting that "the old-growth forests of the Pacific Northwest can contribute to optimizing carbon sequestration strategies while continuing to provide ecosystem services essential to supporting biodiversity."
Yet another study to ask and address the question "Do old forests gain or lose carbon?" was that of Binkley et al. (2004), who revisited an aging aspen forest in the Tesuque watershed of northern New Mexico, USA -- which between 1971 and 1976 (when it was between 90 and 96 years old) was thought to have had a negative net ecosystem production rate of -2.0 Mg ha-1 yr-1 -- and measured the basal diameters of all trees in the central 0.01 ha of each of 27 plots arrayed across the watershed, after which they used the same regression equations employed in the earlier study to calculate live tree biomass as of 2003.
"Contrary to expectation," as they describe it, Binkley et al. report that "live tree mass in 2003 [186 Mg ha-1] was significantly greater than in 1976 [149 Mg ha-1] (P = 0.02), refuting the hypothesis that live tree mass declined." In fact, they found that the annual net increment of live tree mass was about 1.37 Mg ha-1 yr-1 from age 96 to age 123 years, which is only 12% less than the mean annual increment of live tree mass experienced over the forest's initial 96 years of existence (149 Mg ha-1 / 96 yr = 1.55 Mg ha-1 yr-1). Consequently, in response to the question they posed when embarking on their study -- "Do old forests gain or lose carbon?" -- Binkley et al. concluded that "old aspen forests continue to accrue live stem mass well into their second century, despite declining current annual increments," which, we might add, are not all that much smaller than those the forests exhibited in their younger years.
In our Editorial of 9 Jun 2004, we note that 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 these 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 observations about forests are remarkably similar to recent findings regarding humans, i.e., that nongenetic interventions, even late in life, can 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 significant amounts of carbon in their old age, when past theory (which was obviously based on past observations) decreed they should be in a state of no-net-growth or even negative 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," as Klingons might phrase it, would appear to be the aerial fertilization effect produced by the flooding of the air with CO2 that resulted from the Industrial Revolution and is being maintained by its ever-expanding aftermath (Idso, 1995).
Based on these many observations, as well as the results of the study of Greenep et al. (2003), which strongly suggest, in their words, that "the capacity for enhanced photosynthesis in trees growing in elevated CO2 is unlikely to be lost in subsequent generations," it would appear that earth's forests will remain strong sinks for atmospheric carbon far beyond the date at which the world's climate alarmists have long proclaimed they would have given back to the atmosphere most of the carbon they had removed from it over their existence to that point in time.
References
Binkley, D., White, C.S. and Gosz, J.R. 2004. Tree biomass and net increment in an old aspen forest in New Mexico. Forest Ecology and Management 203: 407-410.
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.
Chambers, J.Q., Higuchi, N. and Schimel, J.P. 1998. Ancient trees in Amazonia. Nature 391: 135-136.
Chambers, J.Q., Van Eldik, T., Southon, J., Higuchi, N. 2001. Tree age structure in tropical forests of central Amazonia. In: Bierregaard, R.O., Gascon, C., Lovejoy, T., and Mesquita, R. (Eds.). Lessons from Amazonia: Ecology and Conservation of a Fragmented Forest. Yale University Press, New Haven, CT, USA, pp. 68-78.
Condit, R., Hubbell, S.P. and Foster, R.B. 1995. Mortality-rates of 205 neotropical tree and shrub species and the impact of a severe drought. Ecological Monographs 65: 419-439.
DeBell, D.S. and Franklin, J.S. 1987. Old-growth Douglas-fir and western hemlock: a 36-year record of growth and mortality. Western Journal of Applied Forestry 2: 111-114.
Ellsworth, D.S. 2000. Seasonal CO2 assimilation and stomatal limitations in a Pinus taeda canopy with varying climate. Tree Physiology 20: 435-444.
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.
Franklin, J.F. 1988. Pacific Northwest Forests. In: Barbour, M.G. and Billings, W.D. (Eds.) North American Terrestrial Vegetation. Cambridge University Press, New York, New York, USA, pp. 104-131.
Franklin, J.F. and DeBell, D.S. 1988. Thirty-six years of tree population change in an old-growth Pseudotsuga-Tsuga forest. Canadian Journal of Forest Research 18: 633-639.
Graybill, D.A. and Idso, S.B. 1993. Detecting the aerial fertilization effect of atmospheric CO2 enrichment in tree-ring chronologies. Global Biogeochemical Cycles 7: 81-95.
Greenep, H., Turnbull, M.H. and Whitehead, D. 2003. Response of photosynthesis in second-generation Pinus radiata trees to long-term exposure to elevated carbon dioxide partial pressure. Tree Physiology 23: 569-576.
Hamilton, J.G., DeLucia, E.H., George, K., Naidu, S.L., Finzi, A.C. and Schlesinger, W.H. 2002. Forest carbon balance under elevated CO2. Oecologia 10.1007/s00442-002-0884-x.
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.
Lai, C.T., Katul, G., Butnor, J., Ellsworth, D. and Oren, R. 2002. Modeling nighttime ecosystem respiration by a constrained source optimization method. Global Change Biology 8: 124-141.
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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.
Luo, Y., Medlyn, B., Hui, D., Ellsworth, D., Reynolds, J. and Katul, G. 2001. Gross primary productivity in the Duke Forest: Modeling synthesis of the free-air CO2 enrichment experiment and eddy-covariance measurements. Ecological Applications 11: 239-252.
Luo, Y., White, L.W., Canadell, J.G., DeLucia, E.H., Ellsworth, D.S., Finzi, A., Lichter, J. and Schlesinger, W.H. 2003. Sustainability of terrestrial carbon sequestration: A case study in Duke Forest with inversion approach. Global Biogeochemical Cycles 17: 10.1029/2002GB001923.
Myers, D.A., Thomas, R.B. and DeLucia, E.H. 1999. Photosynthetic capacity of loblolly pine (Pinus taeda L.) trees during the first year of carbon dioxide enrichment in a forest ecosystem. Plant, Cell and Environment 22: 473-481.
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Paw U, K.T., Falk, M., Suchanek, T.H., Ustin, S.L., Chen, J., Park, Y.-S., Winner, W.E., Thomas, S.C., Hsiao, T.C., Shaw, R.H., King, T.S., Pyles, R.D., Schroeder, M. and Matista, A.A. 2004. Carbon dioxide exchange between an old-growth forest and the atmosphere. Ecosystems 7: 513-524.
Pearce, F. 1999. That sinking feeling. New Scientist 164 (2209): 20-21.
Schlesinger, W.H. and Lichter, J. 2001. Limited carbon storage in soil and litter of experimental forest plots under increased atmospheric CO2. Nature 411: 466-469.
Schulze, E.-D., Lloyd, J., Kelliher, F.M., Wirth, C., Rebmann, C., Luhker, B., Mund, M., Knohl, A., Milyuokova, I.M. and Schulze, W. 1999. Productivity of forests in the Eurosiberian boreal region and their potential to act as a carbon sink: a synthesis. Global Change Biology 5: 703-722.
Last updated 11 May 2005