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The resilience of closed-crown coniferous stands within the boreal forest of North America is highly dependent on successful re-establishment of tree species following fire. A shift from closedcrown forest to open lichen woodland is possible following poor natural regeneration during the initial establishment phase, followed by the development of extensive lichen cover, which may hinder ongoing recruitment. We examined the development of the crustose lichen Trapeliopsis granulosa (Hoffm.) 18 to 21 years following fire within six sites in the boreal forest of northwestern Quebec, and explored its potential to affect ongoing recruitment during early successional stages of stand development. Germination and survivorship trials were conducted within the laboratory to determine the establishment rate of Pinus banksiana Lamb. (jack pine) on T. granulosa, mineral soil, and burnt duff under two separate watering frequencies (observed and drought). Survival and establishment rates of jack pine were highest on burnt duff, and poor on both T. granulosa and mineral soil. Under the drought treatment, no seedlings survived on any substrates. In the field, T. granulosa cover had a positive relationship with mineral soil cover, and negative relationships with duff cover, ericaceous shrub cover, organic layer depth, other lichen cover, and Sphagnum moss cover. No discernable relationship was found between T. granulosa and tree density, rock cover, dead wood cover or other moss cover. The development of extensive T. granulosa cover in fire-initiated stands can impede ongoing recruitment of conifer species due to its poor seedbed quality, thereby maintaining open forests.

We studied mature and adjacent open lichen–spruce woodlands (LWs) and closed-canopy spruce–feathermoss stands (FMs) growing under similar edaphic conditions in the continuous boreal forest zone in Quebec (Canada). A total of six pairs of stands were investigated by profile sampling. Stem density, basal area, and biomass were about four times greater in FMs than in LWs on an area basis. In the humus layer, total stocks of C and N and of exchangeable K, Ca, Mg, Al, and Na were 1.4–2.3 times larger in FM than in LW soils. The first 30 cm and the first metre of mineral soils in LWs and FMs displayed similar available nutrient pools except for total C stocks, which were more than twice as large in FM as in LW soils in these soil layers. For the whole profile, total stocks of C and N and stocks of exchangeable Ca and Mg were 1.3–2.6 times larger in FM than in LW soils. These results highlight the low intrinsic fertility of LW soils, primarily due to the humus layer, but also the importance of the biological control of C, N, and mineral nutrients in these boreal soils. Nous avons étudié des pessières à lichens (LW) ouvertes et des pessières à mousses (FM) fermées adjacentes et croissant dans des conditions édaphiques semblables en forêt boréale au Québec (Canada). Les profils de sol de 6 paires de peuplements ont été échantillonnés. Sur une base surfacique, la densité des tiges, la surface terrière et la biomasse dans les FM étaient environ 4 fois celles des LW. Dans l’humus des FM, les stocks de C et de N totaux et ceux de K, Ca, Mg, Al et Na échangeables étaient de 1.4 à 2.3 fois ceux des LW. Dans les 30 premiers centimètres et le premier mètre de sol minéral des deux types de peuplements, les réserves nutritives étaient similaires, sauf le stock de C total dans les FM qui était plus du double de celui des LW. Dans le profil de sol entier des FM, les stocks de C et de N totaux et ceux de Ca et Mg échangeables étaient de 1.3 à 2.6 fois ceux des LW. Ces résultats démontren

The afforestation of widely distributed boreal open woodlands such as lichen woodlands (LWs) could provide both a restoration of the closed-crown forest structure in the boreal forest and a mitigation measure against global warming. By comparing natural, mature stands of LW with their dense counterparts — black-spruce–feathermoss stands as a plantation surrogate — this study aims to validate the long-term LW growth support capacity for a high tree density and their carbon sequestration potential after afforestation. Our results reveal that the site potential of LWs can be either lower or equivalent to that of dense stands. This finding contradicts the paradigm of systematic lower tree growth in LWs. The site potential of LWs can be assessed by dominant tree volume at 50 years. This study also shows that the CBM-CFS3 model can simulate the conservative net carbon balance of afforested LW, and, as such, can help reduce uncertainties regarding the long-term net carbon drawdown of afforested LWs.

Open lichen woodlands (LWs) are degraded stands that lack the ability to regenerate naturally due to a succession of natural and/or anthropogenic disturbances. As they represent both interesting forest restoration and carbon sequestration opportunities, we tested disc scarification and planting of two sizes of containerized black spruce (Picea mariana Mill. (BSP)) seedlings for their afforestation. We compared treatment of unproductive LWs to reforestation of harvested, closed-crown black spruce-feathermoss (BSFM) stands. After one year, seedling survival and nutritional status were equivalent among stand types but despite higher root elongation index (REI), planted seedlings in LWs had lower relative growth rate, smaller total biomass and stem diameter than those in BSFM stands. Soil fertility variables, soil temperature, nor seedling water potential, helped at explaining this early growth response. Disc scarification significantly improved seedling first-year survival, biomass and foliar nutrient concentrations of P, Ca, and Mg. Smaller planting stock showed higher REI, higher shoot water potential, and higher foliar nutrient concentration of all but one of the measured nutrients (N, P, K and Mg). Hence, preliminary results suggest that planting of smaller containerized black spruce stock, combined with disc scarification, shows potential for afforestation of unproductive LWs. The impact of the lichen mat and other potential growth limiting factors on afforestation of these sites requires further investigation.

Black spruce-lichen woodlands are low tree density stands within the closed crown, North American boreal forest that represent a diverging post-fire type of black spruce forest. As natural densification of lichen woodlands has never been observed, afforestation remains the only way of shifting these stands to closed canopy stands. The objective of the study was to evaluate site preparation effects on growth and water relations of black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) seedlings in black spruce-lichen woodlands (LW), compared to managed black spruce-feathermoss stands (BSFM). Site preparation treatments in LW were no preparation (LWno), patch scarification (LWps), and disk scarification (LWds). The operationally managed BSFM stands stood for the control. Results from the third growing season indicate that soil water availability in intact or lightly prepared patch scarified LW is a limiting variable for seedling growth for both black spruce and jack pine seedlings. However, once LW are prepared with disk scarification, this planting check factor is significantly reduced, to the point of being equal to BSFM in terms of water availability and seedling water relations. The significant seedling growth difference, in favor of BSFM, might be a consequence of the lower level of pre-plantation disturbance in LW, compared to BSFM. Our results also suggest that jack pine, through higher water stress tolerance, could constitute a wise silvicultural choice over black spruce, especially with LW established on coarse drought-prone material.