Ripley's K-function was used to investigate the changes in spatial pattern among trees in a semi-natural mixed deciduous forest in Denmark over 50 years, from 1948 to 2001. Trees larger than 10 cm diameter in breast height (dbh) were mapped at 10-year intervals in 16 blocks within two former compartments. At the start of the observation, trees were found to be regularly distributed at distances less than 10 m. This pattern changed with time in different ways, depending on tree density at the beginning of the recording. Tree density has a greater influence on the number of recruits than on the number of dead trees. New recruits were significantly aggregated and positively correlated with dead trees, which suggests that regeneration occurred in canopy gaps. Compartments with many new recruits therefore showed a change in pattern towards more random distribution or even towards aggregation. In blocks with high basal area and few recruits, the pattern changed only slightly. Past management was found to be important in generating the patterns of tree distribution.