If the area is large enough, species richness can be achieved by a horizontal change of species mixture over the area. Here sub-groups with or without distinct layers can be recommended as part of a larger pattern. Moreover, a large enough size also makes it possible to increase the complexity even more by including glades and denser thickets. When used in the park tradition, it has been important to keep the different layers apart in a strict manner, using shrub species for the shrub layer, whilst in the conservation and forestry traditions the different layers are often more difficult to separate from each other, and the shrub layer normally consists of young tree species which have future roles in the layers above. Very similar systems and design principles are used within the ‘garden woodland’ as a widely spread design concept. Here exotic species are widely used, and the shrub layer and the perennials in the field layer are given prominence. A rule ‘of the wandering sunlight’ is often referred to here: the upper canopy is designed to be open so that rays of sunlight illuminate the woodland floor throughout the day.
Key character species
Upper tree layer: ash, oak and aspen. Lower tree layer (middle layer): lime, rowan, whitebeam, hornbeam, beech, wild cherry, bird cherry, maple and hazel. Higher and lower shrub layers: hazel, hawthorn, bird cherry, young individuals of shadow-tolerant tree species, Cornus, Viburnum and Ribes species.
The edges can be very varied.
Establishment methods—trees and shrubs
An ambitious weeding in the first two to three years always creates a fast start, especially for the slow starters. However, strong competition from the herbaceous layer can support diversity and differentiation in the various layers.
Establishment methods—the field layer
Direct seeding in combination with strategic planting in groups. The soil conditions and the type of litter that is created is critical for the choice of species.