Spatial variability of organic layer thickness and carbon stocks in mature boreal forest stands—implications and suggestions for sampling designs

Accurate field measurements from invento- ries across fine spatial scales are critical to improve sampling designs and to increase the precision of forest C cycling modeling. By studyingsoils undisturbed from active forest management, this paper gives a unique insight in the naturally occurring variability of organic layer C and provides valuable references against which subsequent and future sampling schemes can be evalu- ated. We found that the organic layer C stocks displayed great short-range variability with spatial autocorrelation distances ranging from 0.86 up to 2.85 m. When spatial autocorrelations are known,weshowthata minimum of 20 inventory samples separated by ∼5 m is needed to determine the organic layer C stock with a precision of ±0.5 kg C m −2 . Our data also demonstrates a strong relationship between the organic layer C stock and horizon thickness (R 2 ranging from 0.58 to 0.82). This relationship suggests that relatively inexpensive mea- surements of horizon thickness can supplement soil C sampling, by reducing the number of soil samples collected, or to enhance the spatial resolution of organic layer C mapping.