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• The performance of various conifer species in boreal lichen woodlands is unknown. • Four conifer species were planted at two sites with contrasting fertility. • Survival rate 5 years after planting was high for all species at both sites. • Soil quality had a large impact on growth but not on aboveground biomass traits. • Jack pine had a better performance and benefited more from increased soil quality. Lichen woodlands (LWs) are persistent unproductive areas of the Canadian boreal forests whose afforestation may potentially remove significant amounts of anthropogenic C from the atmosphere. The choice of species to be planted is nevertheless uncertain given the particular pedoclimatic conditions prevailing in this habitat as well as the rapidly changing climate at northern latitudes. In this study, we assessed the survival and the growth rates of four boreal coniferous species in two LWs with contrasting soil fertility. Five years after afforestation, survival rate was high for all species at both sites, ranging from 60 to 100 %. Tree height and diameter at stump height (DSH) were up to 60 % and 97 % higher at the LW with higher soil fertility, respectively. The height of jack pine (Pinus banksiana Lamb.; JP) trees was on average 15 %, 56 % and 68 % higher than that of tamarack (Larix laricina [DuRoi] K. Koch; TK), black spruce (Picea mariana [Mill.] BSP; BS) and white spruce (Picea glauca [Moench] Voss; WS), respectively. There was a significant species × soil fertility interaction, reflecting a much higher growth difference between the two sites for JP than for the other species. Annual apical growth increased from one year to the other in JP, suggesting its ability to expand its root system and to acquire resources from the mineral soil rapidly after planting. The much larger photosynthetic biomass at the more fertile site was driven by a higher number of needles produced annually rather than by a higher mass of individual needles, which did not vary between sites. The photosynthetic biomass / woody biomass ratio was not significantly impacted by soil fertility. Overall, these results suggest that JP and TK may be good candidates for the afforestation of boreal LWs and that site selection is of crucial importance to optimize plantation productivity in the mid-term. Further studies must be conducted to assess the survival and the C sequestration potential of these species in the long-term. [ABSTRACT FROM AUTHOR]

Black spruce-lichen woodlands (LW) are naturally occurring unproductive low tree density stands within the eastern North American closed-crown boreal forest. Natural reforestation in LWs is impeded by the lichen mat and ericaceous shrubs that inhibit seedling establishment. Disk scarification is a mechanical site preparation method that creates furrows where lichens and shrubs are removed and mineral soil is exposed, which is the preferred seedbed for black spruce KlJ natural regeneration. The objective of this study was to quantify the impact of disk scarification on black spruce establishment in LWs by natural seeding. Disk 13 scarification was performed amid scattered seed trees in six study sites located in the central area of boreal Québec's spruce-moss biodimatic domain. Newly 9 established black spruce seedlings were significantly more abundant (ca. 81%; x2 = 28.72, P < 0.001) in the furrows of scarified plots even though the ·jjfl proportion of disturbed soil was small (ca. 20%). Seedling establishment occurred for at least 3 years following scarification, with a peak in the first year. The El distribution and density of seed trees (112-363 stems ha"1) did not limit natural seedling establishment in this study. Five years after scarification, observed densities and stocking levels of newly established black spruce seedlings were sufficient to expect afforestation without planting in scarified LWs. [ABSTRACT FROM AUTHOR]

• Abandoned agricultural lands (AAL) are potential targets for afforestation plans. • We used CBM-CFS3 to compare C sink of afforested vs. naturally regenerated AAL. • Planted species and natural regeneration (NR) scenario strongly impact the results. • Afforestation may store an additional 41–56 Mg C/ha by 2050 relative to NR. Agricultural land abandonment is a widespread phenomenon that generally results in C accumulation due to natural establishment of woody vegetation. However, whether afforestation of abandoned agricultural lands (AAL) can sequester more C than AAL naturally reverting to woodlands is unclear. In this study, we used the CBM-CFS3 model to compare the additional C sequestration potential of afforested AAL (AR) with a reference scenario where AAL naturally returns to forest (NR). Simulations were performed for stands located in Quebec's boreal zone (Canada) on podzolic soils. The AR scenario corresponded to stands afforested at a density of 2000 trees ha−1 with one of five commonly planted species in the region, namely black spruce (BS), white spruce (WS), eastern white pine (EWP), jack pine (JP) and tamarack (TK). The NR scenario corresponded to stands naturally reverting to natural forests of one of five species naturally occurring in the region, namely BS, WS, balsam fir (BF), trembling aspen (TA) and white birch (WB). The yield tables used for NR were phased out by 5, 10, 15 and 20 years to simulate various dynamics of colonization by woody plants following agricultural abandonment. Net C accumulation in AR stands varies depending on the planted species, from 127 to 255 Mg C ha−1 after 100 years with TK and WS, respectively. Net C accumulation in NR stands after 100 years ranges from 82 to 145 Mg C ha−1 for BS and TA, respectively, but these values are sensitive to both tree density and colonization time following abandonment. In both scenarios, the soil C pool shrinks by 6 to 12 Mg C ha−1 over the first 80–85 years, but the following soil C stock replenishment is faster in AR than in NR stands due to higher litter production (up to 50 Mg C ha−1). The additional C sequestration potential of AAL afforestation, i.e. the difference in net C accumulation between AR and NR stands, is the highest in stands afforested with WS and reaches a peak of 121–175 Mg C ha−1 80–87 years after afforestation depending on the NR scenario. Afterwards, additional C sequestration decreases due to a reduction in plantation growth combined with increasing natural regeneration growth. This modelling approach helps predict AAL additional C sequestration potential and suggests that AAL afforestation yields a more rapid C sequestration than natural regeneration, which could contribute to reaching net-zero emissions by 2050. [ABSTRACT FROM AUTHOR]