Abstract
In New Zealand 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. Root mass and distribution were determined for three Populus deltoides × nigra ‘Veronese’ trees aged 5, 7 and 9.5 year planted as 3 m poles at 8 m × 8 m spacing on a hillslope near Palmerston North in the southern North Island. Most of the structural roots (≥2 mm diameter) were distributed in the top 40 cm of soil. Vertical roots penetrated to about 1.0 m, being the depth of the soil above a fragipan. Total structural root dry masses (excluding root crown) were 0.57, 7.8 and 17.90 kg for the trees aged 5, 7 and 9.5 year, respectively. Total structural root length was 79.4 m for the 5 year tree and 663.5 m for the 9.5 year tree. Surrounding trees were estimated to increase root mass density to 3 times and root length density to 4–5 times the contribution of the single tree at 9.5 year. The study indicated that root development of wide-spaced poplar trees on hillslopes was minimal in the first 5 years but then increased rapidly. These results suggest that poplar trees established from poles may take at least 5 years to develop a structural root network that will effectively bind soil.
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Acknowledgements
Thanks to several visiting scientists and students involved in the excavations and measurements. Alistair Hall provided the analytical solution for measuring the contribution of surrounding trees to the root density in the space surrounding a single tree. Excavation of the tree aged 9.5 year and this paper were funded by the Soils and Land Use Research Initiative, FRST programme C02X0405.
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McIvor, I.R., Douglas, G.B., Hurst, S.E. et al. Structural root growth of young Veronese poplars on erodible slopes in the southern North Island, New Zealand. Agroforest Syst 72, 75–86 (2008). https://doi.org/10.1007/s10457-007-9090-5
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DOI: https://doi.org/10.1007/s10457-007-9090-5