Response of growth and branch development of Betula alnoides young plantation to light environment

Objective  A canopy shading experiment was conducted by simulating the light environments of plantations with a series of planting densities, to explore the effects of light environments on tree growth and branch development, and provide a theoretical guidance for the efficient cultivation of large-sized and high quality timber of Betula alnoides through reasonable arrangement of planting density.

Method  On the basis of a series of afforestation density tests, three shading treatments (40%–45%, 55%–60% and 80%–90% shade rate) with 2/3 of the lower crown shaded and one control (CK) of no shade were set in plots with planting density of 4 m×4 m from a 5-year-old planting density trail of B. alnoides in early October following the local phenology of this species. The dominant tree and the subdominant tree were selected as experiment objects. The tree growth and branch development of all treated individuals were investigated every three or six months.

Result  The increments of tree height and diameter at breast height (DBH) in each interval and the whole experimental period did not differ significantly among shading treatments (P≥0.05). DBH increment was the highest from January to April, and exceeded 0.73 cm in each treatment. However, branch development in each interval and the whole experimental period was significantly affected by shading (P<0.05), excepting branch length growth from April to July in 2018. Both the increments of branch diameter and length decreased significantly with the increase of shading rate, and the increasing trend was more significant in fast-growing season (from January to April), in which the increments of branch diameter and length of CK was 1.74 and 1.78 times higher than those of 80%–90% shade rate treatment, and reached 1.197 mm and 0.135 m, respectively. Moreover, the natural pruning rate ofB. alnoides young plantations also showed an obvious increasing trend with the increase of shading rate, and the natural pruning was focused from April to July with pruning rate increment over 47%.

Conclusion  The low light environment caused by appropriate high planting density almost has no significant effect on the individual growth of B. alnoides, while it can efficiently control branch development and promote natural pruning. The planting with an appropriate high density would be beneficial for large-sized and high quality timber cultivation of B. alnoides in practice.