Careful partial harvesting in conservation stands and retention of large oaks favour oak regeneration

In Europe, many semi-open pasture woodlands with oaks (Quercus robur and Q. petraea) have been invaded by other trees. The management alternatives for such stands are often debated. Protection (i.e. no cutting) versus partial harvest to favour oak regeneration was studied in two matched plots in 25 forests in Sweden. A mast year produced on average 45,000 oak seedlings/ha in 2001. On average 26% of the tree basal area, but no large oaks, was harvested in experimental plots in the winter 2002/03. In 2005, seedling densities were on average 3,900 per ha in control plots (protected) and 11,600 in experimental plots (mainly seedlings from 2002 to 2004). Seedling survival and growth rate from 2003 to 2005 were higher in experimental than cutting plots (66% vs 44%; and +2.8 cm vs −0.8 cm, respectively). Survival and growth were positively related to canopy openness; other vegetation, pH, and oak basal area had no or little effect. Seedling height before cutting was also a positive predictor of survival. The plots contained many more intermediate and large oaks than small oak trees. The number of small oak trees (1.3 m tall to 5 cm in diameter at 1.3 m) was positively related to canopy openness, but unrelated to other measured factors. Thus, minor partial cutting increases seedling densities, and adequate light favours seedlings/small trees. When oak regeneration is important for mixed closed canopy stands with high biodiversity values, such partial cutting is useful (e.g. for CO2-neutral biofuel) but needs careful evaluation, including effects on biodiversity.