KE4 2021 2.4 BodemC 2021 NAPRO (BO-43.10-005-014, BO-43-126-010, BO-53-001-037)

In 1996, the project "Landelijke Steekproef Kaartbladen" (LSK)  project made carbon determinations of soils, stratified by soil type and groundwater level. The data here have been used to set standard soil stocks per soil type and land use, for use in the LULUCF reports. These points were sampled again in 2018-2019 and the C stock determined in project CC-NL from the climate envelope Slim Landgebruik. This re-uptake shows no significant change in the amount of land under a given land use. This can be affected by a too low number of sample points and differences in the exact sample location. Specifically for forest, that there are no additional data collected to explain patterns, such as tree species and traces of tillage.

For the LULUCF reports it is mandatory to report on the amount of carbon in litter, and how this changes over time. For the situation in 1990, the start of the report series, use is made of four datasets of studies from that time. For the Meetnet Functievervulling (MFV, Function Fulfillment Monitoring Network), the predecessor of the Sixth National Forest Inventory (NBI-6), the protocol has been added to measure the thickness of the litter layer. As a result, a thickness of the litter layer was measured for approximately half of the MFV points, in 2004 and 2005. During the NBI-6 (2012-2013), the thickness of the litter layer was measured at all points. In the NBI-7 (2017-2021), thickness is measured at 3 points at each NFI-plot, instead of a single measurement in previous inventories. The measured litter thicknesses are converted into estimates of the amount of carbon, based on relationships derived from the studies around 1990 and a smaller study from 2008 by Schulp et al. Documentation of the underlying methods is available, but never published. It is not known how reliable this method is, or whether the relations from 1990 are still valid. For safety's sake, carbon in litter is not currently listed as a carbon sink because the uncertainty in the figures is considered too great to be able to report properly. If measures have an effect on carbon in the litter, as proposed in the climate envelopes, this will not be registered by the current LULUCF system. Therefore, with this project proposal, we are making progress towards better relationships that have an impact on LULUCF.

In 2020, in the context of the climate envelopes, soils were sampled at 142 points of the NBI, for the tree species Scots pine, Douglas, oak and birch on poor to moderately rich sandy soils and dry to wet. This provides interesting insights. For example, there are some clear differences between tree species or soils. In addition, there seems to have been a change compared to samples taken in 1990, but this still needs to be examined in more detail (comparison of methods, for example).