Factors influencing presence-absence of oak (Quercus spp.) seedlings after conservation-oriented partial cutting of high forests in Sweden

We studied occurrence of oak seedlings (Quercus robur L. and Q. petraea Liebl.) in 11 semi-natural oak-rich temperate forests in south Sweden after partial cutting (mean harvest; 26% of basal area). Earlier studies show that canopy openness is positively correlated with oak seedling performance. We used 20 pairs of subplots in each forest, with and without oak seedlings and matched with respect to canopy openness, to analyse other factors associated with seedling establishment and growth. The height of the ground layer (herbs and woody plants) had negative influence, i.e. higher height was associated with reduced probability of seedling occurrence. Higher soil water content had positive influence on seedling occurrence. Protection of seedlings by e.g. Rubus spp., twigs or dead wood was associated with lower seedling occurrence, but seedlings that did establish there tended to be taller. Type of ground vegetation and species composition did not differ between subplots with and without oak seedling. Thus, after conservation-oriented partial cutting of closed canopy high forests, increasing height of the ground vegetation disfavours oak seedlings (independent of canopy openness). High soil moisture favours oak seedlings, as does protected microsites for seedlings that can maintain high growth rate among their competitors.