Abstract
Low productivity caused by paludification in some parts of the closed black spruce (Picea mariana (Mill.) B.S.P) dominated boreal forest threatens the provision of ecosystem services, including wood fiber production. The accumulation, over time, of organic matter in paludified soils leads to an anaerobic environment that reduces microbial activity, decelerates decomposition of organic matter, and generates nutrient-poor microsites for regeneration. Consequently, it results in significant impacts on site productivity. Considering its ability to disturb the soil, mechanical site preparation (MSP) is viewed as a potential treatment that can help restore productivity of paludified sites following harvesting. We conducted a field experiment to verify if (1) the availability of microsites conducive to reforestation varies with MSP, microtopography (slope and aspect) and initial OLT conditions; (2) the growth of planted seedlings depends on the intensity of mechanical disturbance of the organic layer, type of microsite, planting density, presence of Ericaceae, and the planting position and depth; (3) there are direct and indirect causal relationships between microsites availability after MSP, OLT, microtopography, planting quality and seedlings growth; and (4) if mechanical site preparation and microsite type exposed affect the Ericaceae cover after planting. Our results confirmed that MSP is effective in establishing conditions that permit a productive regeneration cohort on these paludified sites. To ensure successful establishment of plantations on these sites, it is necessary, however, to distinguish between those that are slightly or moderately paludified from those that are highly paludified, as treatment effectiveness of different MSP types depends on organic layer thickness. Our results also show that preference should be given to some microsite types as clay and mixed-substrate microsites for planting to ensure sufficient availability of water and nutrients for seedlings.
Highlights
Forests dominated by black spruce (Picea mariana (Mill.) B.S.P) occupy a large portion of the boreal biome of northeastern Canada, and are an important source of wood for the lumber, and pulp and paper industries [1]
The regression tree analysis (Figure 3) shows that the availability of these microsites varied with the treatment and the post-CLAAG organic layer thickness (OLT) class (≤40 cm vs. >40 cm)
The post-CLAAG OLT node splits into two significantly different terminal nodes: where the OLT was less than 40 cm, the distribution of microsite types varied significantly with the treatment (p ≤ 0.05)
Summary
Forests dominated by black spruce (Picea mariana (Mill.) B.S.P) occupy a large portion of the boreal biome of northeastern Canada, and are an important source of wood for the lumber, and pulp and paper industries [1]. In addition to their economic role, black spruce-dominated forests play key ecological functions, for example as a significant carbon sink [2]; the low productivity caused by paludification in some parts of this ecosystem threatens the provision of ecosystem services [3,4]. On the Clay Belt of northeastern Canada, the long fire interval permits the accumulation of thick organic layers in this region [8,9] and the relatively cold climate and poorly drained soils [10] leads to an anaerobic soil environment that reduces microbial activity and decomposition of organic matter [8,9,11].
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