Root Plasticity as Influenced by Planting Material and Planting Density in Teak Using Logarithmic Spiral Trenching in Kerala, India

Teak (Tectona grandis L.f.), a premier tropical timber species, is widely adopted in agroforestry systems, though its shallow, spreading root system raises concerns over competition with intercrops. Traditionally established through stump planting teak typically develops horizontally oriented, fibrous roots with limited vertical development. Alternatively, root trainer seedlings are hypothesized to promote deeper, more compact root systems, potentially mitigating belowground competition. This study investigates the root distribution of five-year-old teak plantations established through stump and root trainer methods at 3 × 3 m spacing in Karakkad, Kalady Range, Malayattoor Forest Division, Kerala, using the logarithmic spiral trenching method. Additionally, it evaluates the effect of tree spacing (2 × 2 m vs. 3 × 3 m) on the root distribution of root trainer-raised teak. Root intensity (roots m⁻²) was quantified at various lateral distances from the teak plants and soil depths up to 50 cm. Root trainer-grown trees consistently showed higher root intensities (3205 roots m⁻²) than stump-grown trees (2750 roots m⁻²) at 0.35 m lateral distance, while the corresponding root intensities were 1355 and 900 roots m⁻² at 2.35 m lateral distance from the tree base, for root trainer and stump-grown trees, respectively. Root trainer seedlings also exhibited higher root presence at deeper soil layers. Tree spacing significantly influenced the rooting behavior with the closely spaced (2 x 2 m) stand showing root intensity confining to the proximal distance to the tree while the widely spaced (3 x 3 m) stand showed better root spread with respect to vertical and lateral distribution. The findings demonstrate the superior vertical rooting of root trainer-raised teak, reducing crop competition and improving resource uptake making it well-suited for agroforestry. The spacing-induced root plasticity highlights the importance of tree density in shaping root distribution patterns and optimizing belowground resource utilization in a plantation as well as agroforestry systems.