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Climate change is likely to affect the growth, development and regeneration of the black spruce stands across the boreal forest. Regeneration failures cause gaps in the dense black spruce-feathermoss (SM) mosaic increasing the landscape proportion of open lichen woodland (LW). The aims of the study are to determine whether the contrasting characteristics of SM and LW induce different maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax) and light-saturated maximum photosynthesis (Amax) in black spruce trees across a latitudinal or seasonal gradient. Results show that the Vcmax and Jmax were higher in SM than in LW in western Quebec, at the ecotone of the closed-crown and open forest. Vcmax and Jmax were different between SM and LW mainly because nutrient acquisition seems different between stand types. Latitude affects values of Vcmax and Jmax, but the effect could be explained by soil and vegetation composition between experimental plots rather than by latitude. Physiological capacities do not match Amax values for stand types and latitude. Indeed, Amax rates suggest that black spruce in LWs perform as well as those in SMs at the needle scale because Amax would be limited by CO2 concentration which prevents saturation of Rubisco. Despite the lack of difference between the Amax of SM and LW stands, future increases in CO2 concentration and temperature could induce a gap between their respective photosynthesis rates because of their different physiological capacities. [ABSTRACT FROM AUTHOR]

In the boreal forest, open lichen woodlands have been described as an alternative stable state to closed-crown feather moss forest. In this study, we addressed the role of terricolous lichens in stabilizing open woodlands by hindering tree regeneration and/or growth. Based on field and greenhouse experiments, we compared germination and growth of jack pine (Pinus banksiana) on feather mosses (primarily Pleurozium schreberi) and lichens (primarily Cladonia stellaris), using bare mineral soil as a control. Drivers were investigated by (1) manipulating nutrient supply, (2) simulating shade of a closed canopy on the ground layer with the assumption this would mitigate lichen influence on pine growth, and (3) examining pine root ectomycorrhizal colonization and diversity as indicators of pine ability to take up nutrients. Total growth of 6-month-old greenhouse and 2-3-year-old field seedlings, as well as belowground growth of 2-year-old greenhouse seedlings, was significantly greater in moss than in lichen. Seed germination was not affected by ground cover type. Although field phosphorus and base cation availability was greater in mosses than in lichens, fertilization did not entirely compensate for the negative effects of lichens on pine growth in the greenhouse. Ground layer shading had no impact on pine growth. Lichens were associated with reduced abundance and modified composition of the root ectomycorrhizal community. By suggesting that terricolous lichens constitute a less favorable growth substrate than mosses for pine, our results support the hypothesis that lichens contribute to open woodland stability in the potentially closed-crown feather moss forest. [ABSTRACT FROM AUTHOR]

The subject of conifer regeneration failure after canopy removing disturbance leading to expansion of ericaceous heaths in boreal forests received considerable attention. However, despite seedbed quality being a key factor in tree regeneration, our understanding of the role of lichen and moss dominated seedbeds on tree seedling regeneration after forest fires remains unclear. Objective of this study was to investigate the effect of time since fire and post-fire cryptogamic (lichen and moss) seedbeds with variable organic matter thickness on black spruce regeneration. We conducted black spruce seeding experiment in black spruce – Kalmia forests burned 11, 17 and 37 years ago. In each site we applied three seedbed manipulation treatments (mat-intact, mat-mixed and mat-removed) to test if seedbed manipulation improves spruce regeneration. This experiment was extended to three moss-dominated seedbeds to compare seedbed moisture and temperature effects on spruce regeneration. We also tested potential allelopathic effect of two common lichen and moss species in laboratory bioassay. Seed regeneration was low in all seedbeds. Black spruce germination and seedling growth was lowest in presence of Cladonia cristatella followed by C. stellaris , Polytrichum juniperinnum and Pleurozium schriberi . HPLC analysis of C. cristatella indicated the presence of usnic acid, a common germination inhibiting allelochemical. Moss seedbeds were relatively favourable for spruce regeneration. We conclude that (i) lichen seedbeds inhibit seedling regeneration due to adverse biophysical and chemical (allelopathic) effects, (ii) moss seedbeds facilitate black spruce regeneration by maintaining favourable moisture and temperature, and (iii) seedbed manipulation treatments produce mixed results depending on the dominant cryptogam, organic matter thickness and seedbed moisture and temperature. [ABSTRACT FROM AUTHOR]

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. [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]

Expansion of deciduous shrub species in open subarctic landscapes has been reported at several locations around the circumpolar region. However, few data are available to evaluate the response of shrub species in forested ecosystems. For this study, we conducted a dendrochronological analysis to compare the establishment and growth of Michx. individuals prior to and after an experimental removal of tree cover (1987) in a lichen woodland located at the boreal forest - tundra ecotone. Tree removal was followed by a B. glandulosa recruitment pulse. It is likely that the newly established seedlings benefited more from heavy trampling during tree removal, which destroyed the lichen cover, than from tree removal itself. A strong growth increase after tree removal suggests that the black spruce tree cover suppressed B. glandulosa growth prior to 1987. Moreover, while radial growth for the period prior to tree removal was not a function of the number of growing degree-days during the growing season, the same climatic variable explained 46% of the growth variability in the second period. These results suggest that the presence of a tree cover might limit the response of shrub species to climate change in forested ecosystems. [ABSTRACT FROM AUTHOR]

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