The paper presents changes in the structure of a Fraxino-Alnetum stand in a permanent study plot established in 1979 in the Ochojec Nature Reserve in Katowice. During the research period (1979–2019), 17 tree and shrub species were found on the plot. The dominant species of the stand is black alder. Pedunculate oak and rowan dominated among saplings. The volume of timber increased from 247.99 to 527.36 m³/ha during the study period. The share of standing dead trees in the stand was small: 5 trees in 1987 (0.90% N/ha and 0.02% V/ha of living trees) and 51 trees in 2019 (11.80%, 0.84%). Oak and rowan dominated in quantity, and black alder in volume. Lying dead trees form the coarse woody debris. In 2004, 147 trees (which were measured as standing in 1987) with a total volume of 15.86 m³/ha were lying on the forest floor. In 2019, another 174 trees (measured as standing in 2004) with a total volume of 24.82 m³/ha were on the forest floor. In this category as well, oak and rowan dominated in quantity, and black alder in volume.