Effects of initial planting density on stand growth of four Populus sect. Aigeiros clones in the Jianghan plain

To explore the suitable planting density of the main varieties of Populus sect. Aigeiros in the Jianghan plain, establish a more scientific and suitable technical system for poplar afforestation in the Jianghan plain, and to provide technical support and theoretical support for efficient stand cultivation.

4 main Section Aigeiros were selected in the Jianghan plain and planted in spring in 2017. Three replicates were set up in the experiment. In each replicate, five initial planting density zones (6 m×2 m, 6 m×3 m, 6 m×4 m, 6 m×5 m, and 6 m×6 m) were designed. Different varieties were randomly arranged in the same density zone using a random block design. There were 12 plants per density, per variety, and per plot. From 2017 to 2024, the tree height and DBH were investigated after each leaf fall for eight consecutive years. Then, the changes in growth of different varieties at different densities over the years were analyzed, and multiple comparisons and analysis of variance were conducted.

Under the same density, the DBH, tree height, volume per plant, and volume per unit area of P. deltoides ‘Huashi 2’ were all optimal, while P. deltoides ‘2025’ was the worst. Compared with other species, P. deltoides ‘Danhong’ was suitable for cultivation of large-diameter wood at small density, while P. deltoides ‘Huashi 2’ was more suitable for maximizing the benefits of the accumulated volume at medium density. There were extremely significant differences in DBH, tree height, volume per plant, and volume per unit area among different densities and varieties in the 8th year after planting.

With the growth of tree age, the DBH and volume per plant of the four black poplar cultivars decreased with the increase of density, and the growth rate slowed down after 6 years. The differences in tree height growth under different initial planting densities were small, but the growth also slowed down after 6 years. At the density of 6 m×2 m, P. deltoides ‘Huashi 2’, P. deltoides ‘Danhong’ and Populus×euramericana ‘Chulin 2’ could obtain the maximum volume per unit area, while P. deltoides ‘2025’ could obtain the maximum volume per unit area at the density of 6 m×6 m. P. deltoides ‘Huashi 2’ and P. deltoides ‘Danhong’are more suitable for cultivation in the Jianghan Plain. They feature rapid growth, and can be cultivated as short-rotation stands for medium-and small-diameter timber, while also possessing great potential for targeted cultivation of large-diameter timber. The interaction effect between varieties and density began to emerge after 3 years. The interaction effect between cultivars and density began to emerge after 3 years, with growth indicators differing among the 4 poplar stands, but these differences weakened or disappeared as stand age increased.