We examined the effect on soil organic carbon (SOC) 14 years after planting trees on a pasture.

SOC in the top 10 cm of soil was lower in the woodland than the grazed pasture.

This loss was equivalent to 37% of the carbon stored in the woodland trees.

Silvopastoral agroforestry stored more carbon than equivalent areas of separate woodland and pasture.

We sampled intensively but failed to maintain sufficient power at all depths.

This highlights the importance of power analyses when studying soil carbon.