Canadian Forest Service Publications

Comparing growth and fine root distribution in monocultures and mixed plantations of hybrid poplar and spruce. 2013. Benomar, L.; DesRochers, A.; Larocque, G.R. J. For. Res. 24:247-254.

Year: 2013

Issued by: Laurentian Forestry Centre

Catalog ID: 34767

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1007/s11676-013-0348-7

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Disease prevention, biodiversity, productivity improvement and ecological considerations are all factors that contribute to increasing interest in mixed plantations. The objective of this study was to evaluate early growth and productivity of two hybrid poplar clones, P. balsamifera x trichocarpa (PBT) and P. maximowiczii x balsamifera (PMB), one improved family of Norway spruce (Picea glauca (PA)) and one improved family of white spruce (Picea abies (PG)) growing under different spacings in monocultures and mixed plots. The plantations were established in 2003 in Abitibi-Témiscamingue, Quebec, Canada, in a split plot design with spacing as the whole plot factor (1 × 1 m, 3 × 3 m and 5 × 5 m) and mixture treatments as subplot factor (pure: PBT, PMB, PA and PG, and 1:1 mixture PBT:PA, PBT:PG, PMB:PA and PMB:PG). Results showed a beneficial effect of the hybrid poplar-spruce mixture on diameter growth for hybrid poplar clones, but not for the 5 × 5 m spacing because of the relatively young age of the plantations. Diameter growth of the spruces decreased in mixed plantings in the 1 × 1 m, while their height growth increased, resulting in similar aboveground biomass per tree across treatments. Because of the large size differences between spruces and poplars, aboveground biomass in the mixed plantings was generally less than that in pure poplar plots. Leaf nitrogen concentration for the two spruce families and hybrid poplar clone PMB was greater in mixed plots than in monocultures, while leaf nitrogen concentration of clone PBT was similar among mixture treatments. Because of its faster growth rate and greater soil resources demands, clone PMB was the only one showing an increase in leaf N with increased spacing between trees. Fine roots density was greater for both hybrid poplars than spruces. The vertical distribution of fine roots was insensitive to mixture treatment.

Plain Language Summary

Planting hybrid poplars is one of the options often considered for rapid production of biomass. However, forest managers also have the option of establishing mixed stands, namely those comprised of at least two species.

Researchers studied the effect of this combination on growth (height and diameter) and on the number of fine roots in two hybrid poplar clones that were planted with genetically improved white and Norway spruce trees. The effect of different spacings between trees was also studied.

The results of these tests carried out in Abitibi showed that diameter growth in hybrid poplars was greater in the presence of competition in mixed stands, while growth in height was higher in one of the two hybrid poplar clones tested.

The hybrid poplars in mixed stands developed a larger number of fine roots. These roots are involved in water and nutrient uptake from the soil. They also serve as an indicator of a tree's ability to adapt to variable site conditions.

Mixed stands are more costly to establish than pure stands. However, the results of this study show that mixed stands have a greater potential for biomass production.