Coarse root growth of Veronese poplar trees varies with position on an erodible slope in New Zealand

Abstract

Poplars are commonly planted on moist, unstable pastoral hill country to prevent or reduce soil erosion, thereby maintaining hillslope integrity and pasture production. Mechanical reinforcement by poplar root systems aids slope stabilisation, particularly when the roots are anchored into the fragipan or underlying rock. Total root length, mass and distribution of coarse roots (C2 mmdiameter) were determined for three Populus deltoides 9 nigra ‘Veronese’ trees in their 12th growing season after being planted as 3 m poles at upper slope (TU), mid-slope (TM) and lower slope (TL) positions on an erodible hillslope near Palmerston North in the southern North Island. Most of the roots were distributed in the top 40 cmof soil. Depth of penetration of vertical roots was dependent on slope position and limited by the available depth of the soil above a fragipan (0.35 m at the upper slope to 1.4 m at the lower slope). Roots penetrated the fragipan at the upper slope position where the soil depth was shallowest,and at the mid-slope, but not the lower slope position. Total coarse root length was 287.9 m for TU, 1,131.3 m for TM and 1,611.3 m for TL, and total coarse root dry mass (excluding root crown) was 8.15 kg for TU, 38.77 kg for TM and 81.35 kg for TL