Influence of early thinning in broadleaved stands on development of remaining stems

Precommercial thinning studies were performed in eight hardwood stands in southern Sweden. Birch (Betula pendula Roth and B. pubescens Ehrh.) was the dominating tree species, but aspen (Populus tremula L.), black alder [Alnus glutinosa ( L.) Gaertn.] and lime (Tilia cordata Mill.) were also present. Main stems were selected before thinning. Three treatments were applied in each stand: ( 1) no thinning ( control), ( 2) standard thinning, and ( 3) strong thinning, i.e. leaving about two-thirds of the stem number of treatment 2. Each treatment was replicated three times on all sites. The development of the main stems were recorded during the five consecutive years. Breast height diameter and green crown size ( length and width) developed significantly more slowly in the control treatment than in the thinned ones, whereas tree height development was little affected by treatment. Simulation of 10 years' future growth from the time of the end of the study indicated that future diameter growth will be lower in initially non-thinned stands than in immediately thinned ones. The study results stress the importance for future growth of proper early silviculture in young broadleaved stands (i.e. early and high intensity thinning), a topic that has not been fully evaluated before.