Long-Term Effects of Biochar Addition on Diameter Growth in Young Established Boreal Scots Pine Stands

Abstract

Wood biochar amendment can be used to improve soil properties, support tree growth, and increase soil carbon stocks. The long-term (> 5 years) effects of different biochar types and doses on established stand growth are unknown, as most studies are short-term (≤ 5 years) pot or field trials with small seedlings. We applied 0, 5, and 10 Mg ha⁻¹ wood biochar pyrolyzed at 500°C and 650°C in young established boreal Scots pine (Pinus sylvestris L.) stands in Finland and studied tree growth response during the first 10 years after amendment. Biochar did not affect the 10-year cumulative growth, but annual growth response analysis indicated that biochar application tends to increase growth at least in the short-term. Growth response increased with biochar dose, but not consistently with pyrolysis temperature. The 10 Mg ha⁻¹ dose of biochar pyrolyzed at 650°C increased the annual diameter growth of dominant trees by 0.25 mm (7.2% higher than control). Large-scale use of biochar to enhance forest growth in practical forestry may not be economically feasible because of its high cost, but biochar application remains a possible strategy for increasing long-term soil carbon stocks. However, more long-term field studies from boreal forests are still needed to confirm these perceptions about growth response duration after biochar application.