Spruce Lichen Woodland Research Articles

Natural seeding as an alternative to planting in black spruce-lichen woodlands

Regeneration failures in the closed-crown boreal forest, which lead to the creation of open lichen woodlands, are expected to increase with climate change due to a rise in burn rates. Past studies have shown that it was possible to restore the productivity of those stands through planting. Since most lichen woodland stands are remotely located, afforestation through planting can be prohibitive. Therefore, the objective of this research was to measure the afforestation efficiency of lichen woodlands through scarification and natural seeding after clear-cutting. Our results showed that clear-cutting, when combined with scarification, promoted seedling establishment more strongly than clear-cutting alone. Scarification was also necessary for creating suitable microsites for germination, which were essentially bare mineral soil and decomposed organic matter. Last, seedling growth was higher in lichen woodlands when logging and scarification were combined, but lower than their counterpart feather moss stands. We conclude that afforestation of lichen woodlands in the closed-crown boreal forest is possible through natural seeding following scarification and could be a cost-effective option compared to planting.

Comparing soil profiles of adjacent forest stands with contrasting tree densities: lichen woodlands vs. black spruce–feathermoss stands in the continuous boreal forest

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.

Landscape-gradient assessment of thermokarst lake hydrology using water isotope tracers

Thermokarst lakes are widespread in arctic and subarctic regions. In subarctic Québec (Nunavik), they have grown in number and size since the mid-20th century. Recent studies have identified that these lakes are important sources of greenhouse gases. This is mainly due to the supply of catchment-derived dissolved organic carbon that generates anoxic conditions leading to methane production. To assess the potential role of climate-driven changes in hydrological processes to influence greenhouse-gas emissions, we utilized water isotope tracers to characterize the water balance of thermokarst lakes in Nunavik during three consecutive mid- to late summer sampling campaigns (2012–2014). Lake distribution stretches from shrub-tundra overlying discontinuous permafrost in the north to spruce-lichen woodland with sporadic permafrost in the south. Calculation of lake-specific input water isotope compositions (δI) and lake-specific evaporation-to-inflow (E/I) ratios based on an isotope-mass balance model reveal a narrow hydrological gradient regardless of diversity in regional landscape characteristics. Nearly all lakes sampled were predominantly fed by rainfall and/or permafrost meltwater, which suppressed the effects of evaporative loss. Only a few lakes in one of the southern sampling locations, which overly highly degraded sporadic permafrost terrain, appear to be susceptible to evaporative lake-level drawdown. We attribute this lake hydrological resiliency to the strong maritime climate in coastal regions of Nunavik. Predicted climate-driven increases in precipitation and permafrost degradation will likely contribute to persistence and expansion of thermokarst lakes throughout the region. If coupled with an increase in terrestrial carbon inputs to thermokarst lakes from surface runoff, conditions favorable for mineralization and emission of methane, these water bodies may become even more important sources of greenhouse gases.

Can partial‐cut harvesting be used to manage terrestrial lichen habitat? A review of recent evidence

Recent research suggests that partial-cut harvesting techniques can be used to alter successional trajectories in pine- and spruce-lichen woodlands, allowing forest managers to extend the period of reindeer lichen growth in mid- to late seral boreal forest stands. In Quebec, a fully replicated partial-cutting trial found that terrestrial lichen abundance remained at least as high in the partial cut as in the clearcuts or unlogged stands, and that the partial cut appeared to be on a trajectory to have even more terrestrial lichen due to sustained higher growth rates. In Alberta, a retrospective study found higher terrestrial lichen abundance in an early horse-logged partial cut than in undisturbed adjacent old forests or in clearcuts. Follow-up studies of partial-cut harvesting trials in British Columbia found that group selection plots 10 years after harvesting had lichen cover equivalent to that of undisturbed forest. In contrast, studies on lichen woodlands that have been defoliated by mountain pine beetle showed a major decline in reindeer lichen cover and a corresponding increase in vascular plant cover, similar to the results of previous studies on clear-cut logging impacts. Taken together these studies provide qualified support for the hypothesis that partial-cut harvesting can be used to enhance, or at least maintain, terrestrial lichen mats used as forage by caribou.

Lichen-Spruce Woodland Early Indicators of Ecological Resilience Following Silvicultural Disturbances in Québec’s Closed-Crown Forest Zone

Lichen woodlands (LW) located in the closed-crown boreal forest are not a successional stage moving towards a closed black spruce feathermoss stand (FM), but an alternative stable state, due to their previous forest history, and the occurrence of LWs located nearby closed-crown FM stands. Therefore, afforestation in those LWs through site preparation and plantation could shift back LW into FM stands. We implemented an experimental design with different combinations of silvicultural treatments in both site types (LW, FM). We monitored the evolution of plant diversity and the physiology of three bio-indicators (Picea mariana, Kalmia angustifolia, Rhododendron groenlandicum) in different microsites created by the silvicultural treatments. The return to the initial composition was noticed only two years after treatments, especially in the LW stands, thus indicating a higher level of early ecosystem resilience in LWs compared to FM stands. Mean species cover, especially in the FM stands, decreased the most in the skid trails created by logging, probably due to a lack of acclimation of bryophytes to open stand conditions. Conversely, ericaceous shrubs and lichens found in the LWs were already acclimated to open stand conditions, which give to LWs a restructuring advantage compared to FM plant communities after silvicultural treatments. Overall, FM and LW short-term resilience was similar, indicating equally efficient ecosystem reorganization in both stands. The comparable early resilience in managed LW and FM stands, in terms of plant biodiversity, contradicts the presumed fragility of LW stands, especially in this case where LWs are assumed to be an alternative stable state created by compound disturbances. Silvicultural treatments maintained the functional group diversity in LWs, a key element for ecosystem resilience. Therefore, this study support the idea that plantation following site preparation in LWs could be a valuable management strategy to reach several objectives, such as increasing forest carbon sinks.

Afforestation of Black Spruce Lichen Woodlands by Natural Seeding

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 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 scarification was performed amid scattered seed trees in six study sites located in the central area of boreal Quebec's spruce-moss bioclimatic domain. Newly established black spruce seedlings were significantly more abundant (ca. 81%; χ2 = 28.72, P < 0.001) in the furrows of scarified plots even though the 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 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.

Is the closed‐crown boreal forest resilient after successive stand disturbances? A quantitative demonstration from a case study

AbstractQuestionRecent studies revealed by indirect evidence that lichen–spruce woodlands in the closed‐crown boreal forest are an alternative stable state of black spruce–feathermoss stands. This paper aims to demonstrate and quantify black spruce forest cover regression following successive wildfire events in the closed‐crown forest zone during the 20th century. A case study in north‐eastern North American closed‐crown forest zone is presented.LocationThe study area is at the centre of the closed‐crown boreal forest zone of eastern Canada (49°59′ N, 71°59′ W).MethodsA burned area of 25 ha was selected in which three tree cohorts were visible. The first cohort contains partly buried trunks and stumps of a stand destroyed by a forest fire in 1920, the second contains standing dead trees from a 1995 forest fire and the third contains seedlings established after the 1995 fire. Fires were dated by scar analyses of living trees at the edge of the site. An array of sample plots was established in autumn 1997 to evaluate each cohort in terms of stocking and tree density.ResultsBlack spruce stocking decreased significantly between cohorts, from 43.5% in Cohort 1 (all coniferous trees) to 25.6% in Cohort 2 and 11.5% in Cohort 3 (2011). Jack pine showed an inverse tendency, from 0% in Cohort 1 (not determined) to 0% in Cohort 2 and 3.8% in Cohort 3. Black spruce stems per hectare also dropped significantly from a minimum of 1322 in Cohort 1 to 1088 in Cohort 2 and 976 in Cohort 3.ConclusionsThis study is the first quantitative demonstration that lichen–spruce woodlands in the closed‐crown boreal forest zone are an alternative stable state of black spruce–feathermoss stands. Stocking levels and densities markedly declined after each of the two fires (1920 and 1995) that both occurred after spruce budworm outbreaks (1910 and 1980) and are most likely responsible for the shift from a closed‐crown to an open woodland.

Dendroecological analysis of black spruce in lichen—spruce woodlands of the closed-crown forest zone in eastern Canada

Lichen—spruce woodlands occur in the closed-crown forest zone as a divergent type of the spruce-moss forest because of regeneration failure caused by compounded disturbances (fire, insect outbreaks, and logging). From the southern limit of distribution of lichen woodlands (47° 30′ N) to the northern limit of the closed-crown forest zone (52° 40′ N), 53 lichen woodlands were sampled for a detailed dendroecological analysis. Radial, height, and volumetric growth of black spruce (Picea mariana) trees among the woodlands varied significantly according to stand age. Growth rates were similar for all even-aged spruce trees, whereas growth rates of trees < 100 y old were significantly greater than those of trees > 100 y old. No significant differences were found in growth rates of spruces distributed along the latitudinal gradient. Spruce trees were generally small in all the woodlands studied, with only a few trees taller than 12 m. Although spruce budworm may have affected all stands, the timing and intensity of the infestations were not necessarily synchronous among the studied stands. Partial least square response (PLS) functions were calculated to evaluate the impact of climate on tree-rings with latitude. Along the 600-km transect, PLS response functions indicated that growth was strongly influenced by current and previous year climatic conditions, particularly precipitation.

Boreal lichen woodlands: A possible negative feedback to climate change in eastern North America

Because of successive forest fires, closed-canopy black spruce forests are susceptible to a shift towards open lichen–spruce woodlands in parts of the boreal forest of eastern North America. The shift from dark black spruce canopies to pale lichen ground cover offers a dramatic contrast in reflectance that may compensate for the CO 2 emissions from forest fires in terms of radiative forcing. We have therefore looked at the climate change feedback that would result from the generation of lichen woodlands through changes in albedo and in stored carbon. Using albedo estimates based on MODIS imagery and incoming solar radiation for the period between 2000 and 2008 along with forest biomass estimates for eastern Canada, we have estimated that net radiative forcing for the conversion from closed-canopy coniferous forests to open lichen woodlands would be about −0.12 nW m −2 ha −1, and would therefore generate a cooling effect in the atmosphere. Based on current estimates of area in open lichen woodlands within the closed-canopy black spruce–moss forests of eastern Canada, we estimate that a current net forcing of −0.094 mW m −2 has already arisen from such conversions. As projections of future climate have been linked to increased probability of forest fires, the generation of open lichen woodlands provides a possible negative feedback to climate change. Results also suggest that carbon sequestration through the afforestation of boreal lichen woodlands may not provide a climate change mitigation benefit.

Origin of the lichen–spruce woodland in the closed‐crown forest zone of eastern Canada

ABSTRACTAim We investigate the timing and factors responsible for the transformation of closed‐crown forests into lichen–spruce woodlands.Location The study area extends between 70° and 72° W in the closed‐crown forest zone from its southern limit near 47°30′ N to its northern limit at the contact with the lichen–spruce woodland zone around 52°10′ N. A total of 24 lichen–spruce woodlands were selected.Methods Radiocarbon dating of charcoals at mineral soil contact and within the organic horizons allowed the principal factors causing the degradation of the closed‐crown forest to be identified, i.e. light fires, successive fires and the occurrence of a spruce budworm epidemic followed by a fire.Results Charcoals dated in the organic horizon were less than 200 years old, suggesting a recent transformation of the closed‐crown forest following surface fires. Before their transformation into lichen–spruce woodlands, stands were occupied by old, dense forests that originated from fires dating back to 1000 yr bp. The radiocarbon dating of charcoals in the organic horizon indicated that several stands burned twice in less than 50 years, while others burned shortly after a spruce budworm epidemic. Light fires are frequent within the lichen–spruce woodlands according to multiple charcoal layers found within the organic matter horizon.Main conclusions While closed‐crown forests are predicted to expand under climate warming, compound disturbances diminish the natural regeneration of the closed‐crown forests in the south and favour the expansion of lichen–spruce woodlands. As black spruce germinates on mineral soils, surface fires accentuate the expansion of the lichen–spruce woodlands southward. Under global warming, warmer springs will lead to earlier low‐intensity fires that do not remove as much organic matter, and hence prevent conditions suitable for black spruce regeneration. Also, spruce budworm reduces seed production for a certain time. The occurrence of fire during this period is critical for regeneration of black spruce.

Estimating the net carbon balance of boreal open woodland afforestation: A case-study in Québec’s closed-crown boreal forest

Black spruce ( Picea mariana (Mill.) B.S.P.) is the dominant tree species in the Canadian province of Québec’s boreal ecosystem, particularly in the black spruce-feathermoss (BSFM) domain (between the 49th and the 52nd parallels). While black spruce is generally well adapted to regenerate after wildfires, regeneration failure can sometimes occur, resulting in the irreversible conversion of closed-crown BSFM to open black spruce-lichen woodlands (OW). With OWs representing approximately 7% (1.6 M ha) of Québec’s BSFM domain, the afforestation of OWs carries significant theoretical potential for carbon (C) sequestration, which has not yet been evaluated. The main objectives of the study were then: (i) to estimate the theoretical C balance of OW afforestation within the closed-crown BSFM domain in Québec’s boreal forest; (ii) to calculate, using the life cycle analysis (LCA) method, all the GHG emissions related to black spruce OW afforestation in the closed-crown BSFM domain of Québec. The CO2FIX v. 3.1 model was used to calculate the biological C balance between the baseline (natural OW of site index 9 at age 50) and afforestation (black spruce plantation of site index 6 at age 25) scenarios, using the best estimates available for all five recommended C compartments (aboveground biomass, belowground biomass, litter, deadwood, and soil). The simulation revealed a biological C balance of 77.0 t C ha −1, 70 years following afforestation, for an average net sequestration rate of 1.1 t C ha −1 year −1. Biological C balance only turns positive after 27 years. When integrating the uncertainties related to both the plantation growth yield and the wildfire disturbance, the average sequestration rate varies between 0.2 and 1.9 t C ha −1 year −1. GHG emissions are 1.3 t CO 2 equiv. ha −1 for all afforestation-related operations, which is less than 0.5% of the biological C balance after 70 years. Thus, GHG emissions do not significantly affect the net C balance of the afforestation project simulated. Several recommendations are made, mostly centered on the factors influencing the growth rate of carbon stocks and the impact of natural disturbances, to minimize the range of uncertainties associated to the sequestration potential and maximize the mitigation benefits of an OW afforestation project.

Ground-Nesting Ant Assemblages and Their Relationships to Habitat Factors Along a Chronosequence of Postfire-Regenerated Lichen–Spruce Woodland

Abstract Ground-nest densities and nesting habits of 13 ant species were quantified in five postfire age classes (1, 9, 23, 47, and 79 yr old) in the lichen–spruce woodland of Quebec, Canada. There were no significant differences in ant nest densities between age-classes (average of 163 nests/ha), but there were significant differences in ant community structure. Ant communities were dominated by Formica podzolica, F. aserva, F. hewetti, and Myrmica detritinodis, which accounted for 77% of occupied nests. Some species (e.g., F. podzolica) were specialists in their nesting habits, whereas others (e.g., F. aserva) were generalists and built their nest in a variety of substrates. Nest densities of F. aserva correlated with several habitat factors, but these correlations could have been spurious because they were not related to this species’ nesting habits. However, significant positive correlations found between Camponotus herculeanus and Leptothorax canadensis and coarse woody debris (CWD) may be biological...

Ground-Nesting Ant Assemblages and Their Relationships to Habitat Factors Along a Chronosequence of Postfire-Regenerated Lichen–Spruce Woodland

Ground-Nesting Ant Assemblages and Their Relationships to Habitat Factors Along a Chronosequence of Postfire-Regenerated Lichen–Spruce Woodland

Growth response and water relations of 3-year-old planted black spruce and jack pine seedlings in site prepared lichen woodlands

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.

Reduction of black spruce seed bank by spruce budworm infestation compromises postfire stand regeneration

In the southern boreal forest of eastern Canada, black spruce (Picea mariana (Mill.) BSP) is subjected to both defoliating insect and fire disturbances. As black spruce depends on its aerial seed bank for postfire regeneration, reduction of cone crop during a spruce budworm (Choristoneura fumiferana (Clem.)) outbreak opens a vulnerability window during which stand regeneration could be hindered in the event of a fire. To assess the long-term effect of spruce budworm outbreak on black spruce reproductive potential, cone production and viable seed bank were estimated using cone crop surveys and germination trials in black spruce – lichen woodland stands that sustained different levels of defoliation during the 1980s. Black spruce cone crop was significantly related to the defoliation history of the stands (R2 = 0.89), but not to stand age, basal area, or tree density. Black spruce stands damaged by severe defoliation showed a smaller number of cones, a higher incidence of insect-damaged cones, and a viable seed bank 3 to 17 times smaller than a lightly defoliated stand. The vulnerability window for black spruce regeneration following a spruce budworm outbreak may be as long as 20 years in the study area because black spruce seed bank in heavily defoliated stands has not yet replenished. Our work supports conclusions from stand reconstruction studies that suggest closed-crown spruce–moss stands convert to open lichen woodlands as a result of weak postfire regeneration caused by successive insect and fire disturbances.

THE CREATION OF ALTERNATIVE STABLE STATES IN THE SOUTHERN BOREAL FOREST, QUÉBEC, CANADA

The southernmost spruce–lichen woodlands in the Parc des Grands‐Jardins, Québec, Canada, are situated 500 km south of their usual range in the northern lichen woodland zone. Their co‐occurrence within a spruce–moss forest matrix suggests the existence of alternative stable states. We investigate the possibility of these spruce–lichen woodlands as an alternative stable state along with the factors contributing to their origin and spatiotemporal distribution. Analysis of plant macrofossils, charcoal, head capsules of defoliating insects, and pollen were used along with vegetation surveys to reconstruct the past and present disturbance dynamics along an east–west transect, corresponding to a precipitation and fire frequency gradient. At each site, spruce budworm head capsules were found preceding the charcoal layer delineating the shift to spruce–lichen woodland, demonstrating the compound disturbance (insect–fire) origin of the lichen woodlands. Moss forests previously occupied all lichen woodland sites, with the oldest record starting ca. 8300–9400 yr BP. A change to a higher fire frequency around 2500 yr BP was evident in the lichen woodland zone of the park. A lower fire frequency west of the lichen woodland zone likely is a result of orographic precipitation. While the spruce budworm affects the entire region, lichen woodlands are found exclusively within an increased fire frequency zone. Thus, it is the superimposition of these two disturbance factors that is responsible both for their creation and spatial distribution. Lichen woodland inception dates range between 580 and 1440 yr BP, demonstrating that these lichen woodlands have maintained their open structure with time and have not transformed into closed forests. Their persistence, along with their previous moss forest histories and current occurrence adjacent to closed moss forests, indicate that they are an alternative stable state to the spruce–moss forests and not a successional stage. In contrast to other examples of reported alternative stable states, this one is a result of natural disturbances inherent to the system and not anthropogenic impacts.

Contrasted Growth of Black Spruce (Picea mariana) Forest Trees at Treeline Associated with Climate Change over the Last 400 Years

Several environmental indicators show that climate changed dramatically at the turn of the 19th century, with global warming throughout the 20th century. Among the most used proxies to evaluate long-term changes in climate are trees located at their northern range limit. Several studies have shown enhanced tree regeneration at treeline caused by recent warming, but no data are available on height growth performance of forest trees at treeline before and during the 20th century warmth. In this study, we examined the long-term growth performance of black spruce (Picea mariana [Mill.] B.S.P.) trees located in a lichen-spruce woodland, near the arctic treeline in eastern Canada. The study woodland is an old-growth stand that has escaped fire approximately during the past two millennia. We performed stem analysis on normally developed trees which grew in the woodland over the last centuries. The sampled trees are ramets from long-lived, self-regenerating black spruce clones that are forming small tree islands within the woodland. The co-occurrence of living and dead tree stems inside clones gives the opportunity to evaluate the growth performance of the same genets through time. Height and radial growth of 60 tree stems from 15 old-growth clones were evaluated for a period spanning the last 400 yr. Sampling included the two tallest living stems and the two tallest dead stems of randomly selected clones. No differences in height and radial growth were found among the 30 living stems nor among the 30 dead stems within clones. Living stems were 2 m taller and radial growth was 1.6 times greater than dead stems. Vertical development of stems was divided into two parts according to position of snow cover. Growth of dead and living stems was similar below the snowpack line. However, significant differences were found for growth above snowpack for the two types of stems. Growth above snow cover for all dead stems occurred between the 17th and 19th centuries. In contrast, growth of living stems above snow cover started during the late 19th century. Our data indicate that stems of the same genotype responded directly to climate change, in conjunction with climatic conditions prevailing at the time when they were protruding above the snowpack. Compared to extant trees, significantly smaller trees grew in the woodland during the Little Ice Age. Potential causal factors of differential growth performance through time are discussed.

Growth performance of Cladina stellaris following caribou disturbance in subarctic Quebec

:Cladina stellaris is a dominant lichen species of old-growth lichen-spruce woodlands in subarctic Québec, where the continuous lichen carpet persists for several decades in the absence of disturbance. The lichen carpet is, however, vulnerable to caribou (Rangifer tarandus) disturbance under dry site conditions. Through grazing and trampling, large herds of migratory caribou reduce C. stellaris abundance and modify ground vegetation composition. Here, we have evaluated the age and growth performance of C. stellaris in relation to the recent activity of the George River Caribou Herd (GRCH). We measured the age, length, and growth rate of C. stellaris podetia in and near caribou trails in 15 lichen-spruce woodlands across the summer habitat. The age of lichens, used to evaluate the initial period of lichen recruitment following the decline of the GRCH, indicated that lichen recovery began in the early 1990s in heavily disturbed sites, whereas comparisons between the age structure of border and trail lichens also suggested that the southern part of the calving ground was still heavily used in the early 1990s. Length and growth rate of C. stellaris thallus were closely associated with severity of caribou disturbance, as inferred from the residual ground cover of terrestrial lichens. Growth performance of C. stellaris during the initial stage of lichen recovery varied according to the spatial use of the summer habitat by caribou, with better performance at the edge of the summer and winter habitats and reduced performance in the extensively used calving ground. The analysis of growth performance of C. stellaris provides new insights on lichen-spruce stand recovery associated with caribou disturbance.

The effects of lichens on white spruce seedling establishment and juvenile growth in a spruce-lichen woodland of subarctic Québec

Several studies have proposed that lichens in the spruce-lichen woodlands of the northern section of the Canadian Boreal Region inhibit seed germination and seedling recruitment and even reduce tree growth. In fact, these inhibitory effects of the lichen mat may partly explain the dynamics and spatial structure of the spruce-lichen woodlands. In this study, we followed white spruce seedling establishment on control surfaces and on surfaces on which lichens had been removed in a spruce-lichen woodland in northwest Québec. We also removed lichens around white spruce juveniles of three size classes and monitored their growth over a 5-year period. Lichen-removal increased white spruce seedling establishment but reduced growth, particularly in juveniles > 20 cm in height. These results show that there is a shift from negative to positive in the effects of the lichen mat on white spruce early after the seedling establishment phase.

Accurate dating of spruce budworm infestation using tree growth anomalies

Spruce budworm feeding causes stem and branch deformities that alter the architecture of host trees in a permanent way, easily recognized several years after the defoliation event. Dating of budworm-related growth anomalies using tree rings provides a new means to reconstruct recent infestations of this defoliator. We tested this dendro-architectural method in the southernmost black spruce-lichen woodlands in eastern North America, which were affected by spruce budworm from 1976 to 1985. In these open stands, moribund black spruce trees support high loads of the epiphytic lichen Bryoria arranged in unusual patterns, a phenomenon known as black spruce decline. Because Bryoria was restricted to the dead and deformed parts of the trees, we hypothesized that the lichen only colonized those parts of the trees defoliated by spruce budworm. To test this hypothesis, we dated i) three types of growth anomalies associated with spruce budworm feeding (death of terminal buds, death of axes, and reiteration, i.e., production of new leaders and epicormic shoots) and ii) maximum extent of Bryoria on stem and branches of three spruce trees showing contrasting lichen cover patterns. All trees showed peaks of growth anomalies during periods of known spruce budworm activity. Also, Bryoria was almost exclusively located on internodes that were defoliated by spruce budworm. A model is also proposed to explain the different lichen cover patterns observed. Dating of tree growth anomalies (terminal bud mortality) has better resolution in time and space than tree-ring patterns to determine the first year of insect defoliation.