Dynamics of Coarse Root Production in a Young Plantation of Picea sitchensis

Abstract

The intact root systems of seven Sitka spruce trees were excavated by hand in a plantation 16-years-old. All roots in excess of 0.5 cm diameter were retained for study. Roots were separated into differing diameter size classes and their biomass determined. Annual increments of root biomass were assessed by sequential removal of annual rings from root sections in differing diameter classes. On average thin roots made the largest contribution to root biomass and had larger radial gowth rates than thick roots. However rapid rates of growth were not sustained at distances in excess of 1 m from parent trees. Within 1 m of trees, roots branched frequently and tapered more rapidly than elsewhere with mean root diameters decreasing from about 6 cm at stumps to about 1 cm at a distance of 0.8 m. Biomass of roots with diameters larger than 0.5 cm exceeded 5 kg tree ⁻¹ and total root biomass (inclusive of finer roots (Ford & Deans, 1977)) was about 6.58 kg tree ⁻¹ , (which exceeds 25000 kg ha ⁻¹ with 3800 trees ha ⁻¹ ). Annual production of roots in excess of 0.5 cm diameter was 0.83 kg tree ⁻¹ while total annual root production exceeded 2.2 kg tree ⁻¹ , approximately 34 per cent of total root biomass. Maximum current annual increment of roots occurred 14 years after plantation establishment.