Data from: Natural tree colonisation of organo-mineral soils does not provide a net carbon capture benefit at decadal timescales

Tree cover is often increased with the aim of increasing ecosystem carbon
sequestration and mitigating climate change. However, when planting trees
in ecosystems with carbon-rich soils, soil disturbance during ground
preparation can cause soil carbon losses not counteracted by tree carbon
gains at the decadal timescales relevant to climate change mitigation.
Tree establishment via natural colonisation, which does not involve soil
disturbance, might prevent these soil carbon losses, but this is
unknown. We measured soil, ground vegetation, and tree carbon
stocks and tree inputs along an 8 metre transect from single, native,
25-year-old naturally colonised trees (Pinus sylvestris or Betula spp.)
onto Calluna vulgaris-dominated moorland, at sites with carbon-rich
organo-mineral soils in the Cairngorms, UK.  Along the transect
away from the tree, organic soil carbon stocks increased from 4.0 kg C m-2
at 0.5 metres, to 6.0 kg C m-2 at 8 metres. Meanwhile, carbon stocks in
the top 10 cm of the mineral soil horizon, 3.6 kg C m-2, did not vary.
Ground vegetation carbon stocks increased only slightly, from 1.0 kg C m-2
at 0.5 metres, to 1.3 kg C m-2 at 8 metres. Mean carbon stock per tree was
32.4 kg, so overall, sparse natural colonisation resulted in no net
ecosystem carbon gain. Policy implications: Sparse natural colonisation of
carbon-rich soils by low biomass trees might not result in net ecosystem
carbon gains at decadal timescales, and instead lead to unforeseen soil
carbon losses. Soil carbon changes should be taken into account when
quantifying the climate change mitigation potential of natural
colonisation.