Abstract
Poplar plantations harbor large potential as a renewable source of biomass for bioenergy and other industrial applications. The overall aim of this study is to analyze growth, phenology, stem form, and branching characteristics of 32 poplar clones grown in a trial in southern Sweden for their suitability to be grown as industrial feedstock. In a linear mixed model, performed for diameter at breast height and stem volume, the precision was improved by the use of two competition indices. The significance of phenology and quality characteristics for growth performance and ranking of poplar clones was evaluated through genotypic correlations, and multivariate hierarchical cluster analysis used to group the material. All traits showed moderate to high broad sense heritability. In general, higher stem volume was positively correlated with later leaf senescence, and uncorrelated with spring phenology. Selection efficiency for stem diameter and height was greatly improved between age 3 and 6 years allowing a better precision in selecting a subset of clones to be further tested in production plots and pilot plantations. Two commercial Populus maximowiczii Henry × trichocarpa Torr. & Gray cultivars performed best, while some intraspecific hybrids of P. trichocarpa are considered useful to genetically diversify commercial plantations in Southern Sweden (Belgian clones) or establish plantations in north-central parts of Sweden (Swedish clones). The cluster analysis emphasized growth traits and the grouping of the clones corresponded to their origin (or parentage). The results will facilitate decisions on the use of studied material in breeding, further testing and commercial deployment of poplar plantations in Sweden.
Highlights
Transformation towards sustainable land and material use benefits from an increased availability of fossil-free and regionally produced raw materials such as woody biomass
Blocks I and II were located on the northern slope, whilst blocks III and IV were placed at the bottom of the slope where ground water table was occasionally high, decreasing the tree survival in a part of block III
The two reference clones (REF) established their dominance during the period between age 3 and 6 years reaching at age 12 a mean diameter of 260 mm and a height above 20 m (Fig. 1)
Summary
Transformation towards sustainable land and material use benefits from an increased availability of fossil-free and regionally produced raw materials such as woody biomass. Breeding and selection of Populus in Sweden was first focused on hybrid aspen, whereas poplars have been only occasionally tested [12]. Originally introduced mainly from collections in the Netherlands and Germany, was later expanded with Belgian material consisting of P. trichocarpa and its hybrids with P. deltoides Bartr. In 1990s, a short poplar breeding program was started as a result of a growing insight into the importance of adaptation of material for Swedish climate conditions. A relatively small portion of the resulting progeny population was saved and is presently under field evaluation across the whole Baltic Region. Six clones from this program were included in the trial presented here
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