Canadian Forest Service Publications

Ground layer composition affects tree fine root biomass and soil nutrient availability in jack pine and black spruce forests under extreme drainage conditions. 2017. Pacé, M.; Fenton, J.N.; Paré, D.; Bergeron, Y. Can. J. For. Res. 47: 433-444.

Year: 2017

Issued by: Laurentian Forestry Centre

Catalog ID: 37899

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1139/cjfr-2016-0352

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In the boreal forest, long-lasting canopy gaps are associated with lichens on dry sites and with Sphagnum spp. on wet sites. We hypothesize that ground-layer composition plays a role in maintaining gaps through its effects on fine root biomass (diameter ≤ 2 mm) and soil nutrient availability. Along gradients of canopy openness in both jack pine (Pinus banksiana Lamb.) – lichen and black spruce (Picea mariana (Mill.) B.S.P.) – moss forests, the relationships between canopy closure, ground-layer composition, tree fine root biomass, and soil nutrients were analyzed and decomposed using path analysis. The effects of lichen and Sphagnum spp. removal on tree fine root biomass and soil nutrients were tested in situ. Although variations in pine fine root biomass were mainly explained by stand aboveground biomass, lichen removal locally increased fine root biomass by more than 50%, resin extractable soil potassium by 580%, and base cations by 180%. While Sphagnum cover was identified as a key driver of stand aboveground biomass reduction in paludified forest sites, its removal had no short-term effects on spruce fine root biomass and soil nutrients. Our results suggest that lichens, more than Sphagnum spp., affect tree growth via direct effects on soil nutrients. These two different patterns call for different silvicultural solutions to maintain productive stands.

Plain Language Summary

Based on field work, the researchers have concluded that lichens, unlike sphagnum, affect tree growth through their direct effects on soil nutrients. In the boreal forest, the presence of canopy gaps in low-productivity stands is associated with a lichen cover in dry sites populated with jack pine, and with sphagnum in humid sites where black spruce grows. This study suggests that the composition of the vegetation covering the soil contributes to maintaining these canopy gaps.

This is an additional element that must be taken into account in planning forest interventions in order to maintain the productivity of sites, especially by promoting rapid regeneration in humid sites prone to paludification (bog formation) and in dry sites prone to become tracts of lichen.