Silvicultural methods of oak regeneration with special respect to shade tolerant mixed species

Abstract

An overview is presented of the silviculture of pedunculate oak ( Quercus robur L.) and sessile oak ( Q. petraea Liebl.) in Germany. This presentation is confined to less dry to moist and stagnic gleysol sites, where the intention is to produce primary timbers in long rotation periods. Incorporation of a shade tolerant species as an admixture species is indispensable to the suppression of epicormic branches. The most frequent and recommended admixture species for this purpose is beech ( Fagus sylvatica L.). Because beech is competitively stronger than the oaks on these sites, silvicultural measures must be taken to keep it in check. According to the classic silviculture which has taken shape in the Spessart and Pfälzer forests, the desired goal of a two-storeyed stand with oak in the overstorey and beech in the understorey is achieved by means of heavy seeding beneath an open and rapidly cleared canopy. Because this procedure resembles clear cutting and entails its recognized disadvantages, trials have recently been undertaken to regenerate oaks in a silviculture with permanent canopy cover. Trials with young oaks show that they still achieve satisfactory growth at 15–20% of full light. Accordingly, successful regeneration is possible in beech stands under an open canopy or in gaps, and under an approximately closed canopy cover in pine stands due to their more penetrable crowns. The problematic aspect of this, especially in beech stands, is that young beeches become competitively stronger than oaks as canopy cover increases. This requires great effort in restraining the beech during cleanings and thinnings. Furthermore, browsing by wild animals must be minimized as it exclusively affects oak. As a result, however, there will be significantly fewer oaks and more beeches in the dominant layer than when using classic methods.