Where has all the carbon gone? Twenty five years of measurements show declining C in old-field forests

In the early 1980s quantitative measurements of soil carbon were made on reforested old-fields in New Hampshire. Using a chronosequence we projected that total soil carbon was increasing with forest regrowth and that it would take approximately 200 y to reach pre-disturbance levels. Others working in New England confirmed these results. Over the ensuing time we have repeated measurements at 12-year intervals at the original forest stands, the repeat measurements shows a very different pattern. Soil carbon is declining and offsetting much of the accumulating biomass in aboveground biomass. Mineral soil carbon has declined by 20% and total soil C has declined by an average of 10%. The net effect is that total ecosystem C has stopped increasing and in fact is declining in stands more than 80 years old. The sites examined are typical of the dominant land-use in New England and scaling these results regionally suggest that land-use is offsetting far less fossil fuel carbon emissions that previously thought.