Amounts of logging residues affect planting microsites: A manipulative study across northern forest ecosystems

• We assessed how loads of logging residues altered the microenvironment of seedlings.
• Soil temperatures decreased with increasing forest logging residue load.
• Reduction of competing vegetation cover by logging residues was site-dependent.
• Logging residues had no effect on soil available nutrients.
• Seedlings showed little growth response to different loads of logging residues.

We quantified the effects of different loads of forest logging residues on the microenvironment (soil temperature, soil volumetric water content, competing vegetation cover, and available nutrients) of planted hybrid poplars one year after planting, and assessed the corresponding seedling growth until the third growing season. In four experimental plantations across Quebec (Canada), we used a factorial design of four residue loads that were applied at the tree-level over three planted species: hybrid poplars (Populus spp.), black spruce (Picea mariana (Mill.) BSP), and either jack pine (Pinus banksiana Lamb.) or white spruce (Picea glauca (Moench) Voss), depending upon the site. Logging residues linearly decreased competing vegetation cover on two of four sites and reduced fluctuations in soil temperature on all sites. Logging residues also decreased summer soil temperatures at all sites through a negative quadratic effect. On one site, the frequency of freeze–thaw cycles increased under logging residues, while logging residues increased soil water content on another site, for certain measurement events. Logging residues did not affect available nutrients. Seedlings showed no consistent growth response to logging residues for three years after planting, except for a beneficial effect of logging residues on hybrid poplar growth on one site. Because logging residues affected seedling microclimate and competing vegetation, their maintenance and on-site spatial arrangement on site could be used to manipulate the growing conditions for planted trees.