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Open AccessArticle

Planting Density and Site Effects on Stem Dimensions, Stand Productivity, Biomass Partitioning, Carbon Stocks and Soil Nutrient Supply in Hybrid Poplar Plantations

1
Fiducie de Recherche sur la Forêt des Cantons-de-l’Est/Eastern Townships Forest Research Trust, 1 rue Principale, Saint-Benoît-du-Lac, QC J0B 2M0, Canada
2
Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada
*
Author to whom correspondence should be addressed.
Forests 2018, 9(6), 293; https://doi.org/10.3390/f9060293
Received: 17 April 2018 / Revised: 15 May 2018 / Accepted: 22 May 2018 / Published: 25 May 2018
In this study, planting density and site effects on hybrid poplar productivity and stem dimensions were evaluated on the mid-term and longer term (8 and 14 years) in southern Québec (Canada). We also evaluated the effects of planting density and site on biomass accumulation and carbon stocks in different plantation compartments, on biomass partitioning at the stand-level, on soil carbon stocks and on soil nutrient supply rate after 14 years. The experimental design consisted of three replicate poplar stands located along a site fertility gradient. Each stand contained six planting densities (ranging from 494 to 1975 trees/ha) and a single genotype (Populus canadensis × P. maximowiczii hybrid). Planting density had a large effect on stem dimensions, but a minor effect on stand volume, aboveground woody biomass production, and aboveground biomass carbon stocks. Site selection and tree survival were more important factors affecting these variables. At all sites, and independent of planting density, mean annual volume increments were also higher after 14 vs. 8 years. On fertile sites, strong correlations between area per tree at planting and biomass partitioning, carbon allocation belowground, soil nutrient supply rate and soil carbon stocks were observed. Aboveground, higher competition for light with increasing planting density resulted in an increase in the stem to branch ratio. Belowground, higher competition for soil resources with increasing planting density reduced soil macronutrient availability (except for potassium), which likely stimulated carbon allocation belowground and carbon accumulation in the soil. Over the longer-term, higher density plantations of poplars could provide greater benefits in terms of carbon storage belowground (soil and roots). View Full-Text
Keywords: spacing trial; stocking level; carbon sequestration; allocation; ecosystem services; abandoned farmland; Populus canadensis × Populus maximowiczii; southern Québec (Eastern Canada); short-rotation woody crops; intraspecific competition spacing trial; stocking level; carbon sequestration; allocation; ecosystem services; abandoned farmland; Populus canadensis × Populus maximowiczii; southern Québec (Eastern Canada); short-rotation woody crops; intraspecific competition
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Truax, B.; Fortier, J.; Gagnon, D.; Lambert, F. Planting Density and Site Effects on Stem Dimensions, Stand Productivity, Biomass Partitioning, Carbon Stocks and Soil Nutrient Supply in Hybrid Poplar Plantations. Forests 2018, 9, 293.

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