R. D. Yanaia*, M.A. Arthurb, T. G. Siccamac and
* Corresponding author. Tel.: +1-315-470-6955; fax: +1-315-470-6954; e-mail: email@example.com
ACCURATE ESTIMATES of the retention of carbon in forest soils following forest disturbance are essential to predictions of global carbon cycling. The belief that 50% of soil carbon is lost in the first 20 years after clearcutting is largely based on a chronosequence of forest floors in New Hampshire northern hardwoods. We resampled forest floors in 13 stands from the original chronosequence after an interval of 15 years. The three youngest stands, which were predicted to lose organic matter over this time, did not exhibit the 40 to 50% losses predicted by the model. Young stands had significantly less organic mass than older stands, but this pattern could be explained equally well by historical changes in the nature of forest harvest as by the age of the stands. For example, advances in mechanized logging probably caused more mechanical disturbance to the forest floor than horse logging, burying more organic matter in the mineral soil. Markets for forest products and the intensity of harvest removals have also changed over time, possibly contributing to lower organic matter in young stands. In any chronosequence study, change in the nature of the treatment over time can easily be mistaken for change with time since treatment. Repeated sampling of the chronosequence controls for some of these effects. In the case of forest floor organic matter, however, high spatial variation makes it difficult to detect subtle differences between predicted responses. Because of the large amounts of carbon involved, small changes in rates of soil organic matter storage may be quite important in global climate change, but they will remain difficult to detect, even with very intensive sampling.
Forest floor organic matter as a function of stand age. The curve is that fit by Covington to stands measured in 1976 by Covingtion (1981). Stands measured in 1979-1980 are those reported by Federer (1984), reanalyzed by this study. Lines show the change over 15 years predicted by Covington's equation applied to stands measured by Federer.
Covington, W.W. 1981. Changes in the forest floor organic matter and nutrient content following clear cutting in northiern hardwoods. Ecology. 62: 41-48.
Federer, C.A. 1984. Organic matter and nitrogen content of the forest floor in even-aged northern hardwoods. Can. J. For. Res. 14: 763-767.