Dead trees decaying in the forest ecosystem (called also CWD – coarse woody debris) fulfil a variety of beneficial functions like promoting the diversity of mycorrhizal fungi or enrichment of soil by supplying nitrogen and other nutrients. In specific conditions, decaying trees may become micro-sites for seed germination. We investigated some chemical properties of the samples collected from twelve CWD profiles (derived from decaying Norway spruce and silver fir trees) with particular attention paid to aluminium and other exchange cations. While investigating the mechanism controlling pH in the examined CWD samples, we tested the Henderson-Hasselbalch equation. Our results confirmed that to arrive at a full explanation of the mechanism, the H-H model has to be modified. A successful modification was done by employing the theory claiming that Al behaves like a base cation in acid soils. The role of aluminium in the ion exchange properties of CWD samples is limited, mostly due to the lack of its mineral sources, and thus its toxic impact is not expected.