Stem selection reduces the resprouting vigor of box-tree (Buxus sempervirens L.) understory in sub-Mediterranean pine forest

Abstract

Understory cover may constraint tree regeneration, impair livestock grazing and increase wildfire hazard. While prescribed burning and thinning are potential options for managing understory, resprouting vigor of large shrubs and small trees negatively affects their cost–benefit ratio. Selection of the largest stem and cleaning the rest of the stools can be an alternative option, if the stem left competes with resprouts for belowground resources. Alternatively, resources stored in the reserved stem may promote the growth of resprouts. Although few studies documented the effects of stem selection on resprouting vigor, no information is available for understory species. This study assessed the effect of stem selection (SS) in comparison to cleaning (CC) on resprouting vigor of box-tree. Both options were randomly applied to individuals growing in the understory of black pine forest in four localities. The resprout number resprouts (Rn) and the maximum resprout length (Lmax) were modeled against treatment, stand canopy cover, and pre-treatment stool basal area. Light availability at the individual level was assessed in a subset (n = 38) growing in two localities. Rn and Lmax were lower in SS than in CC. SS apparently inhibited bud initiation and prompted the reserved stem to compete for belowground resources with new resprouts. Resprouting was negatively related to the stand canopy cover. This effect of light availability was corroborated when measured at the individual level. As a conclusion, the implementation of SS in sub-Mediterranean forests with understory dominated by box-tree is a better management alternative than CC for fuel and forest management purposes.