Large old trees are the dominant primary producers of native pine forest, but their influence on spatial patterns of soil properties and potential feedback to tree regeneration in their neighbourhood is poorly understood. We measured stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in soil and litter taken from three zones of influence (inner, middle and outer zone) around the trunk of freestanding old Scots pine (Pinus sylvestris L.) trees, to determine the trees' influence on below‐ground properties. We also measured δ¹⁵N and δ¹³C in wood cores extracted from the old trees and from regenerating trees growing within their three zones of influence. We found a significant and positive gradient in soil δ¹⁵N from the inner zone, nearest to the tree centre, to the outer zone beyond the tree crown. This was probably caused by the higher input of ¹⁵N‐depleted litter below the tree crown. In contrast, the soil δ¹³C did not change along the gradient of tree influence. Distance‐related trends, although weak, were visible in the wood δ¹⁵N and δ¹³C of regenerating trees. Moreover, the wood δ¹⁵N of small trees showed a weak negative relationship with soil N content in the relevant zone of influence. Our results indicate that large old trees control below‐ground conditions in their immediate surroundings, and that stable isotopes might act as markers for the spatial and temporal extent of these below‐ground effects.