Regeneration of mixed deciduous forest in a Dutch forest-heathland, following a reduction of ungulate densities

The conversion of single-species coniferous forest stands into mixed stands by promoting the natural regeneration of indigenous broadleaved tree species was studied in a forest-heathland on the Veluwe, in the central part of the Netherlands. Red deer (Cervus elaphus), roe deer (Capreolus capreolus) and wild boar (Sus scrofa) had a large impact on regeneration dynamics, as was established by comparing 20 pairs of fenced and unfenced plots (40 m x 40 m) during a 10-year period. A fivefold reduction of total herbivore biomass to 500 kg per kmr, resulted in a strong increase of shrub and tree sapling numbers in all vegetation types. However, height growth of the most palatable broadleaved tree species was still strongly impeded. Under the present-day grazing pressure, Scots pine (Pinus sylvestris) and beech (Fagus sylvatica) will become the dominant canopy species in the forests in the near future. It is argued that the most browse-sensitive woody species such as pedunculate and sessile oak (Quercus robur and Q. petraea) will successfully regenerate, only if temporal and spatial variation in browsing pressure is allowed to occur