Forest development phases (FDPs) represent patches that are in different stages of the forest life cycle as conceived in the shifting mosaic concept. FDPs are a widely used framework to describe forest stand structure and dynamics. Natural forests are characterized by small patch sizes, a full set of FDPs and a large vertical heterogeneity which is considered crucial for their biodiversity. Forest management approaches that promote such characteristics of high naturalness are increasingly recommended for biodiversity conservation. Here we investigate the effect of a 10-year naturalness-promoting management regime on forest stand structure, expressed through different patterns in FDP structure and composition.

We studied 22 beech forest stands in north-eastern Germany that are managed in two different ways (naturalness-promoting management and other management) or that have been unmanaged for varying periods of time (recently, 20–35 years and long-term, 65 to more than 100 years). FDPs were investigated in 2012/13 across the total area of the study sites (714 ha). The FDP assignment is based on a dichotomic decision tree with variables such as diameter at breast height, canopy cover, deadwood amount, regeneration cover and tree height. We analyzed FDP patch size, aggregation and mean minimum distance between patches of the same FDP and structural evenness of FDP proportions.

For stands with naturalness-promoting management we found that: (1) there are different FDP proportions, FDP patch sizes and distances between patches of the same FDP compared to the other three management types; (2) there are significant differences in comparison to long-term unmanaged stands in terms of the aggregation indices of the initial phase, optimum phases and the disintegration phase; (3) these stands have the highest aggregation of the regeneration phase, which differs significantly from the other management types; and (4) they contain a similar FDP distribution to that in natural beech forests.

In conclusion, naturalness-promoting management supports small-scale patch heterogeneity and maintains forest structure and life cycle that are closer to natural and unmanaged stands compared to other management types.