Planting spacing affects canopy structure, biomass production and stem roundness in poplar plantations

ABSTRACT

To improve the productivity and wood quality of poplar plantations, effects of four planting spacing on canopy characteristics, biomass production and stem roundness in poplar plantations were evaluated over 8 years. Planting spacing influenced canopy characteristics of the plantations, and further affected the understory vegetation and plantation productivity. Understory vegetation biomass and Shannon-Wiener index were negatively correlated with leaf area index, but both diversity indexes and aboveground biomass of understory vegetation were higher in stands with a wider spacing. Tree diameter growth increased with increasing planting spacing, while the increment in plantations of square configurations (5 × 5 m and 6 × 6 m) was higher than those with rectangular configurations (3 × 8 m, 4.5 × 8 m). The highest poplar biomass production was achieved in the plantation with 5 × 5 m spacing at age 8. Moreover, poplar trees showed a tendency with better stem roundness in a square configuration. The results suggest that planting spacing not only affect canopy characteristics, understory vegetation and tree growth but also wood quality, and square configurations (5 × 5 m and 6 × 6 m) could be a better option for poplar plywood timber production at similar sites.

KEYWORDS:

• Poplar clone
• planting density
• leaf area index
• tree growth
• stem roundness
• understory vegetation biomass
• Shannon-Wiener index

Disclosure statement

No potential conflict of interest was reported by the authors.

Acknowledgements

This work was supported by The National Key Research and Development Program of China (Grant No. 2016YFD0600402), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (Grant No. PAPD). The authors would like to thank Luozhong Tang, Ye Li, Gang Sun, Yafei Yan, Fan Zhang and Xingjian Dun from Nanjing Forestry University for their contribution and assistance. We are also grateful to Professor Scott X. Chang from University of Alberta for his valuable comments and English corrections on the manuscript.

Additional information

Funding

This work was supported by The National Key Research and Development Program of China [grant number 2016YFD0600402], and the Priority Academic Program Development of Jiangsu Higher Education Institutions [grant number PAPD].