Long-term effects on growth and yield of corridor thinning in young Pinus sylvestris stands

Corridor thinning can be an efficient method for extracting biomass from young stands, but its effects on subsequent productivity are uncertain. Therefore, its long-term effects were studied, using data obtained from two pre-commercial thinning (PCT) experiments (over 28 years) and nine thinning experiments (over 22 years). In the PCT experiments, thinning with total corridor areas of 0 (control), 57, 65, 73, 79 and 82% were compared to selective PCT leaving 1000 and 1400 stems/ha. In the thinning experiments corridor thinning (50% corridor area) and selective thinning from below (50% of basal area) were compared. No significant differences in diameter at breast height (DBH) were found between the corridor PCT and control treatments, but the control resulted in approximately 28-83% higher standing volumes/ha than the PCT treatments. Corridor PCT and thinning treatments resulted in higher stand stem density and lower mean DBH than selective treatments. No significant differences in volume growth, standing volume, mortality volume or height growth were detected between selective and corridor thinning or between most of the PCT treatments. The findings indicate that relatively large amounts of biomass could be extracted schematically, by early thinning instead of PCT, in young Scots pine stands without significant future yield losses.