Old-growth forests are assumed to be in equilibrium with respect to carbon
exchange. The standing biomass has reached a maximum and as the canopy trees
progressively die coarse woody debris is formed, which after an initial increase also
reaches an equilibrium. This notion of equilibrium contradicts additional carbon
sequestration during the old-growth stage. However, in old-growth forests the
turnover of carbon in the ecosystem is highest which could result in higher carbon
export rates to the soil system. Residual carbon storage in the soils would help to
close the gap between flux and inventory based estimate of ecosystem carbon
storage. Unfortunately, such a build-up in in soil carbon stocks during the old-growth
stage are difficult to detect, because soil carbon is very heterogeneously distributed.
Here we used a paired sampling design to overcome these problems and to measure
the changes in the carbon content of soils in an old growth forest at the National
Park Hainich, Germany. We found a decrease of carbon in the upper horizons, which
was probably due to the heat-induced carbon release during the extreme year 2003.
However, these losses were overcompensated by an increase of soil carbon in deeper
horizons and there was thus a significant carbon accumulation in the total soil
column of the old-growth forest Our results suggest that old-growth forests are not
in equilibrium with respect to carbon exchange and that these vanishing should be
protected, because not only do they store large amounts of carbon but also continue
to accumulate carbon.
http://www.bgc-jena.mpg.de/bgc-systems/workshops/eds/Abstract_compilation.pdf