Structural root morphology and biomass of three age-classes of Pinus radiata.

Abstract

The root systems of 13 Pinus radiata D. Don. trees from three age-classes in Mangatu Forest were hydraulically excavated. Each system was drawn in plan and elevation, then dissected and sorted into six diameter-classes for weight and length measurements to obtain information on changes in root biomass and root extension with time. Lateral roots had a maximum length of 4.7,6.4, and 10.4 m at ages 8,16, and 25 years respectively. Vertical roots grew to depths of 2.1, 2.6, and 3.1 m for the three age-classes respectively. At 8 years the root bole contained 40 % of the total root weight. This increased to approximately 50 % after 16 years. Stand biomass of roots was 9, 67, and 151 tonnes/ha at a stocking rate of 253 stems/ha for the three age-classes respectively. Total root weight (kg) was regressed on diameter at breast height (cm) to give the relationship: loge(total root weight) = 2.24 loge(dbh)- 2.68 (r2 = 0.99), which can be used to estimate the below-ground biomass from dbh.