2.4.2.3. Soil and Litter
2.4.2.3.1. Woody debris
Coarse and fine woody debris on the forest floor often accounts for about 20
percent as much carbon as living biomass. The amount of woody debris may increase
markedly immediately following forest harvest, which typically leaves a large
amount of organic debris on the soil surface (Covington, 1981). These residues
will decompose within a few years following harvest, although there is little
information on the carbon content of different types of litter. Sampling the
volume of woody debris is as straightforward as it is for live trees, but assessing
its mass is more problematic because decay affects wood density dramatically.
2.4.2.3.2. Litter
The litter layer-also known as the L and O horizons-is the layer of dead plant
material that lies on top of the mineral soil. During forest regrowth, the litter
layer may accumulate rapidly, so changes in its carbon content are an important
component of a total carbon inventory in ecosystems (Richter and Markewitz,
1996). During a cycle of forest harvest followed immediately by regrowth, however,
there is usually little overall change in carbon storage in the forest floor
(Johnson, 1992).
Litter quantities change dramatically with the seasons. As a result, remeasurements
must be made at the same time of the year as initial measurements. If litter
were to be sampled together with the top layer of mineral soil, temporal variability
in the standing crop of litter could confound detection of changes in soil carbon.
Typically, dividing litter from mineral soil when sampling is not difficult.
The number of samples necessary to estimate the accumulation of surface litter
will differ greatly between ecosystems. In some forests, as few as 10-15 randomly
located samples may provide an accurate estimate of changes in the mass of the
forest floor over large areas (e.g., Schiffman and Johnson, 1988); in shrub
deserts, where the spatial variability of soils is enormous, it is often necessary
to take a larger number of random samples in locations that are stratified by
plant cover (e.g., Conant et al., 1998). In any particular location,
some preliminary sampling is probably required to determine the number of forest
floor samples that is necessary to estimate the total mass to the desired level
of accuracy.
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