In this period, trees and shrubs reach maturity, and they attain their full height and width. Herbaceous vegetation has evolved into balanced compositions, combining with the tree and shrub canopy. Management will react to the changing situation, here and there species are inserted because the original ones have disappeared, or because a suitable environment for new species has come into being. Some species start decreasing in number, finally to disappear completely if suitable new growing spots are not provided. Others, such as ferns, can thrive at the same spot over a very long period and require little attention. The park manager therefore has to decide again and again what he wishes to retain and what can be let go, whether he wishes to intervene or not, and, if so, how and when exactly. This is one of the fascinating elements of the management of young and older heemparks. Caution, prudence and a feeling for planning in stages are essential. Instead of relying entirely on spontaneous regeneration for ‘propagation’, one can, in a way that is hardly noticeable to the visitor, insert different species into a spontaneous development of the vegetation. When exactly this stage is reached will usually be suggested by one’s ecological intuition. In the course of time, one will keep intervening: patches may be dug over, replanted or re-sown; trees and shrubs pruned and thinned. On wet clay or peat soils, which are rich in nutrients, the woody plantings will already have reached full maturity after 30 years. On such soils they provide the layout with a mature aspect. The park has increased in age, creating new situations.