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Balsam fir (Abies balsames (L.) Mill.) seeds dispersed in autumn–winter can be covered by many layers of broadleaves when they germinate under deciduous trees during the following growing season. Our goal was to test the effect of seed density, broadleaf litter thickness, and substrate type on emergence, morphology, and dry mass allocation of balsam fir. The greenhouse experiment included three seeding densities, four litter thicknesses covering the seeds, and two substrate types. The broadleaf mixture was composed of white birch (Betula payrifera Marsh.), trembling aspen (Populus tremuloides Michx.), and pin cherry (Prunus pensylvanica L.f.) collected on the forest floor of a 30-year-old postfire stand. Seed density had no effect on emergence from under broadleaf litter. Emergence was lower on the litter substrate than on potting soil. Seedling emergence and vigor declined as broadleaf thickness increased. Depending on substrate type, emergence was reduced by 20% (leaf litter substrate) to 28% (potting soil) when seeds were covered by 1.4–2.0 cm of broadleaves. An overtopping layer of 2.5–3.0 cm reduced emergence by 57%. Balsam firs emerging from under broadleaf litter allocated more dry mass to longer and thinner hypocotyls at the expense of cotyledon and root growth, albeit seeded on potting soil. This study identifies biomechanical constraints that severely reduce early seedling vigour suggesting that in situ survival under broadleaf litter is very low.

This study examines the variability of the potential aging error for saplings (height ≤1.5 m) of black spruce (Picea mariana (Mill.) B.S.P.) in mature fire-dominated stands (n = 14 stands) of the northern boreal forest of northwestern Quebec. Age underestimation was determined by counting the number of underground bud scars of saplings. The magnitude and variability of age underestimation was compared within and among stands. The relationship between corrected ages (the sum of age underestimation and the number of growth rings at ground level) and ground-level ages was strongly linear and was therefore described with simple linear regression models. To evaluate landscape-level variability in this relationship, the regressions were compared among stands using mixed models. Despite high variability in age underestimation at the stand level, the relationship between corrected and ground-level age was highly significant (p

This study examines balsam fir (Abies balsamea (L.) Mill.) recruitment in old fir stands. Studying the regeneration of these stands is essential to understand the regeneration dynamic of the species in the absence of stand-destroying disturbances. The objectives were (1) to obtain substrate–seedling associations for different age-classes and according to the presence or absence of adventitious roots; (2) to evaluate the contribution of the seed rain to seedling recruitment; (3) to re-examine age structures using the most appropriate method that minimizes estimation errors due to the presence of adventitious roots. A total of 90 quadrats (1 m2) were established along transects. In each quadrat, subtrates were characterized (type and topography) and their area was estimated. All balsam fir seedlings (

Numerous researchers have suggested a causal relationship between low leaf biomass in suppressed trees and the lack of radial growth at the base of the trunk. The objective of this study was to verify this relationship with suppressed balsam fir (Abies balsamea (L.) Mill.) saplings found growing in an old-growth fir stand. A total of 29 saplings varying in height from 67 to 183 cm were uprooted. All saplings had adventitious roots. All terminal bud scars (TBS) found between the apex of the terminal leader and the trunk base (first adventitious root) as well as those found below ground were localized, and rings were counted between TBS along the aboveground trunk. Various morphological traits and the ratio of photosynthetic tissue dry mass (P, needles) to non-photosynthetic tissue dry mass (nP, aboveground stem) were used as an indicator of tree vigour. Between 3 and 33 rings counted along the aboveground trunk were missing at the trunk base. The number of missing rings at the base of the trunk was correlated with total height (r = 0.41), height growth (r = –0.51), radial growth (r = –0.44), the P/nP ratio (r = –0.73), and the proportion of live crown (r = –0.62). Moreover, from 2 to 35 additional rings, missing at the trunk base, were found in the belowground section of trunk and these missing rings were associated with the adventitious roots phenomenon. In conclusion, suppressed firs had missing rings at the base of the trunk. When all of the missing rings were added to the number of rings counted at the base of the trunk, age estimates provided a different temporal pattern of recruitment compared with that obtained by solely counting rings at the base of the trunk. Stem analysis on the entire trunk is the best aging method for suppressed balsam fir saplings.

In many Canadian boreal forests, balsam fir (Abies balsamea (L.) Mill.) seedlings established under closed canopy generally develop adventitious roots. Adventitious roots induce the formation of a reverse taper, i.e., a reduction of the diameter and of the number of growth rings towards the true collar (hypocotyl region). Consequently, ring count at any level of the trunk underestimates the true age of firs, and we recommend a reassessment of balsam fir dynamics inferred from studies based on ages estimated by ring count. Recently, Kneeshaw and Claveau (D.D. Kneeshaw and Y. Claveau. 2001. Can. J. For. Res. 31: 1292-1295) presented data from a subsample of fir seedlings to demonstrate that ring count is an accurate aging technique for most fir regeneration. A careful examination of the methodology, data, and samples presented suggests that true collars were not precisely located. We also present data collected on seedlings sampled in the same study area as Kneeshaw and Claveau. Most of the seedlings (57 of 60 seedlings

The effects of recurrent spruce budworm (Choristoneura fumiferana(Clem.)) outbreaks on balsam fir (Abies balsamea (L.) Mill.) mortality have been extensively studied in Canada. Most studies report substantial seedling recruit - ment of balsam fir during outbreaks when reproductive trees are dying. According to previous research, this contradic - tion could be due to inaccuracies in the conventional aging method. Counting the maximum number of growth rings found at the tree base would significantly underestimate tree age. Counting terminal bud scars found on the entire trunk, including buried stem, would give a more accurate tree age. In this study, we compare recruitment dynamics ob- tained for aging seedlings in two balsam fir populations (about 500 km apart) using (i) the conventional method and (ii) bud scar counts. For both populations, the conventional method shows substantial recruitment during adult mortal- ity, while the second aging technique reveals reduced recruitment during the epidemic phase of the spruce budworm outbreak. Resume : Les effets des epidemies de la tordeuse des bourgeons de l'epinette (Choristoneura fumiferana(Clem.)) sur la mortalite des sapinieres boreales (Abies balsamea (L.) Mill.) ont ete largement documentes au Canada. La plupart des etudes rapportent un important recrutement de semis de sapin durant une epidemie alors que meurent les sapins matures. Selon la recherche auparavant, cette contradiction serait due a l'inexactitude de la methode conventionnelle- ment utilisee pour estimer l'âge des semis. Le decompte du nombre maximal de cernes de croissance a la base du tronc sous-estimerait de facon importante l'âge reel des semis. Le compte des cicatrices d'ecailles du bourgeon termi - nal sur tout le tronc, incluant la partie enfouie de la tige, serait une methode plus appropriee. La presente etude com - pare la dynamique du recrutement de deux populations de semis de sapin baumier lorsque l'âge est estime (i) par la methode conventionnelle et (ii) par le compte des cicatrices d'ecailles du bourgeon terminal sur tout le tronc. Environ 500 km separaient les deux populations. Dans les deux cas, la methode conventionnelle revele des structures d'âge dis- cordantes avec la mortalite des adultes. Par contre, les structures d'âge obtenues avec l'autre methode indiquent une re - duction du recrutement des semis durant la periode epidemique. Rapid communication / Communication rapide 376

The age structure of balsam fir (Abies balsamea (L.) Mill.) regeneration is frequently used to investigate boreal forest dynamics of North America. Tree ages are usually estimated by counting annual growth rings at the shoot-root interface located above or close to the root system. Inaccurately locating the shoot-root interface could lead to imprecise age determination. In this study, balsam fir seedlings (

The age structure of balsam fir (Abies balsamea (L.) Mill.) regeneration is frequently used to investigate boreal forest dynamics of North America. Tree ages are usually estimated by counting annual growth rings at the shoot-root interface located above or close to the root system. Inaccurately locating the shoot-root interface could lead to imprecise age determination. In this study, balsam fir seedlings (

This study presents a new, simple, and efficient method for estimating microsite light availability in the understory of a forest. The percentage of above-canopy photosynthetic photon flux density (%PPFD) transmitted above 16 microsites in the understory of a mixed conifer–broadleaf forest was measured every minute between 07:00 and 19:00 for both a completely overcast and a cloudless day. Instantaneous measures of %PPFD were also taken at different times on 3 overcast days. The instantaneous measures of %PPFD were strongly and directly related (P < 0.001) among themselves and with mean daily %PPFD values. These results demonstrate the usefulness of using an instantaneous measure of %PPFD taken under overcast sky conditions for estimating the mean daily %PPFD at any microsite under a forest canopy.