Regeneration of Mediterranean Pinus sylvestris under two alternative shelterwood systems within a multiscale framework

The inability to obtain sufficient numbers of naturally regenerated trees following partial harvests of some Mediterranean Basin managed forests has prompted the need to critically assess common silvicultural practices. In this study, we examined Scots pine (Pinus sylvestris L.) regeneration patterns under two shelterwood systems using a multiscale framework. The uniform shelterwood (US) system includes heavier and less frequent timber extractions than the group shelterwood (GS) system. Removal of competing vegetation to expose mineral soil (soil preparation) is sometimes used for US but is not commonly needed in GS. A generalized linear model was used to predict regeneration density for each shelterwood system using environmental variables at microsite-and forest-level scales, medium-scale overstory tree characteristics, and spatial metrics that represent a range of spatial scales. Although US had a higher mean regeneration density, GS had a wider range of regeneration ages. The results derived from this study suggest that ground-level disturbance to break up the herb or organic layer may be required for regeneration establishment. This may occur during repeated partial harvests; otherwise, soil preparation may be required. Overall, this multiscale framework approach resulted in improved predictions and a better understanding of regeneration processes.