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.

Toona ciliata is an important local species in Hubei province, but it has not been naturally distributed and artificially cultivated in the Jianghan plain. In order to select superior families of T. ciliata which are suitable for the Jianghan plain area, and to provide valuable timber tree species afforestation resources for this area.

A comparative afforestation experiment was carried out in Shishou city, which was located in the Jianghan plain, using a randomized block design for 17 T. ciliata superior half-sib families from Enshi area in Hubei province to compare the 2-year seedling stage and 2-year young forest stage, and to carry out the early selection of superior families by analyzing and comparing the characteristics of DBH (the ground diameter was measured in the first year), tree height and volume of different families for 4 consecutive years.

There were significant differences in DBH(ground diameter) and tree height traits among different families at all ages. All DBH and tree height traits in the following 3 years were significantly correlated with each other from the second year of seedling stage. The family heritability of DBH, tree height and volume traits exceeded 0.85 from 2020 to 2022. According to the genetic gain of different traits of different families, mainly by volume gain, 3 families with excellent early performance were selected from 17 families, namely E13, E15 and E06 families, with the selection intensity 17.65%.

3 families with excellent early performance were selected from 17 T. ciliata superior half-sib families, whose volume genetic gain exceeded 20% of the population average, with high selection intensity and obvious early growth advantage. The average annual DBH was 2.09 cm and annual tree height was 1.78 m. These families will become important germplasm resources for breeding of improved varieties of T. ciliata in Jianghan plain, Hubei province.