Amira Fetouab, Nicole J. Fenton, Nelson Thiffault, Martin Barrette. (2024). Planting density and mechanical site preparation effects on understory composition, functional diversity and planted black spruce growth in boreal forests. Silva Fennica vol. 58 no. 2 article id 23029. https://doi.org/10.14214/sf.23029

Keywords: silviculture; paludification; reforestation; plantation establishment; community ecology; functional ecology

Highlights: Mechanical site preparation and planting density interacted to influence understory diversity and composition in plowed plots; Careful logging alone resulted in higher density of naturally established conifers; Planting density and site preparation alone had no effect on tree height and diameter; Findings provide insights for managing paludified forests and enhancing forest ecosystem functions.

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Mechanical site preparation (MSP) is used prior to planting to control competing vegetation and enhance soil conditions, particularly in areas prone to paludification. Tree planting density can be adapted to the management context and objectives, as it influences yield and wood quality. However, the combined effects of MSP and planting density on understory vegetation composition, functional traits, and diversity remain uncertain. We thus conducted a study in the Clay Belt region of northwestern Quebec, Canada. After careful logging, the study area was divided into nine sites, each receiving one of three treatments: plowing, disc trenching, or no preparation. Sites were further divided into two, with black spruce (Picea mariana [Mill.] Britton, Sterns & Poggenb.) seedlings planted at either a low planting density of 1100 seedlings ha^-1 or a high planting density of 2500 seedlings ha^-1. After nine years, we assessed understory composition, diversity, key functional traits, sapling density and growth of planted trees. Careful logging alone led to a higher density of naturally established conifers compared to plowing or disc trenching. The interaction between planting density and MSP significantly influenced understory diversity and composition in plowed plots. Understory composition was affected by the soil C/N ratio, coniferous species, and deciduous species density. The growth of black spruce was notably enhanced with higher planting density in the plow treatment only. Neither planting density nor MSP alone affected tree height and diameter. Our results suggest that combining plowing with high-density planting can enhance stand growth and improve forest productivity. These findings guide future research on paludified forests.

Fetouab, Institute for Forest Research and Centre for Forest Research, Université du Québec en Abitibi-Témiscamingue, 445 boul. de l’Université, Rouyn-Noranda, QC J9X 5E4, Canada E-mail: amira.fetouab@uqat.ca
Fenton, Institute for Forest Research and Centre for Forest Research, Université du Québec en Abitibi-Témiscamingue, 445 boul. de l’Université, Rouyn-Noranda, QC J9X 5E4, Canada https://orcid.org/0000-0002-3782-2361 E-mail: nicole.fenton@uqat.ca
Thiffault, Institute for Forest Research and Centre for Forest Research, Université du Québec en Abitibi-Témiscamingue, 445 boul. de l’Université, Rouyn-Noranda, QC J9X 5E4, Canada; Canadian Wood Fibre Centre, Natural Resources Canada, 1055 du P.E.P.S, P.O. Box 10380, Sainte-Foy Stn, Québec, QC G1V 4C7, Canada https://orcid.org/0000-0003-2017-6890 E-mail: nelson.thiffault@canada.ca
Barrette, Institute for Forest Research and Centre for Forest Research, Université du Québec en Abitibi-Témiscamingue, 445 boul. de l’Université, Rouyn-Noranda, QC J9X 5E4, Canada; Direction de la recherche forestière, Ministère des Ressources naturelles et des Forêts, 2700 rue Einstein, Québec, QC G1P 3W8, Canada https://orcid.org/0000-0001-5937-382X E-mail: martin.barrette@mffp.gouv.qc.ca

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