Abstract
Poplar is raw material for various panel, paper and fiber products. The 12 sample trees of clone Nanlin-895 from four spacings were destructively harvested after thirteen growing seasons to assess the influence of spacing on radial growth and wood properties. Spacing significantly affected tree-ring width and wood basic density (p < 0.05) but not fiber traits. The highest diameter and wood basic density at breast height (1.3 m) was in 6 m × 6 m and 3 m × 8 m spacings, respectively. However, no significant differences in tree-ring width, wood basic density and fiber traits were observed among the four sampling directions in discs taken at 1.3 m for each spacing. Growth rings from the pith and tree heights had significant effects on wood basic density and fiber anatomical characteristics, highlighting obvious temporal-spatial variations. Pearson correlation analysis showed a significantly negative relationship of tree-ring width to wood basic density, fiber length and fiber width, but a significantly positive relationship to hemicellulose. There was no relationship with cellulose and lignin contents. Based on a comprehensive assessment by the TOPSIS method, the 6 m × 6 m spacing is recommended for producing wood fiber at similar sites in the future.
Highlights
Declining availability of wood supplies and increasing demand have prompted a renewed interest in short rotation woody crops (SRWC) around the world (Zhang et al 2012; Wang et al 2016a, b)
The arithmetic mean over 13 years of tree-ring width (TRW) in the four spacings showed a similar order with stemwood diameters, whereas significant differences in TRW were only observed among the four planting spacings after six growing seasons (p < 0.05, Fig. 1b)
With regards to the effects of sampling directions on TRW and wood properties, the results show no significant differences among the four sampling directions at 1.3 m for each spacing, except for a few growth rings of fiber anatomical characteristics (Tables S1–S4 and Fig. 2a–d)
Summary
Declining availability of wood supplies and increasing demand have prompted a renewed interest in short rotation woody crops (SRWC) around the world (Zhang et al 2012; Wang et al 2016a, b). More short-term waterlogged areas are projected (IPCC 2014), which would lead to unfavorable conditions for tree growth. One option to minimize the effects of waterlogging stress on tree growth and yield is to select species/genotypes capable of tolerating waterlogging. As the best SRWC species, the total area of poplar plantations has reached 8.54 million ha in China (IPC 2016; Tun et al 2018), while poplar wood is mainly used as raw materials for various panel, paper and fiber products. The chemical composition, anatomy, and morphology of raw materials influence paper and fiber products and determine its quality and appropriate end-use (Neiva et al 2015). Some results indicate that fiber morphology is an important feature of papermaking,
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