Seedling Bank Research Articles

Ground Layer Competition and Herbivory Effects on Cherrybark Oak (Quercus pagoda Raf.) Regeneration in Experimental Canopy Gaps

COLLINS, BEVERLY (Savannah River Ecology Laboratory, Aiken, SC 29802). Ground layer competition and herbivory effects on cherrybark oak (Quercus pagoda Raf.) regeneration in experimental canopy gaps. J. Torrey Bot. Soc. 130:147-157. 2003. -Windthrows and small-scale forest harvests generate environmental heterogeneity and dense regrowth. In such sites, interactions among environmental factors, competition with ground layer vegetation, and herbivores attracted to the disturbed area all potentially influence recruitment and early establishment of canopy tree species. I examined the interactive effects of overstory gap size, canopy openness, herb layer competition, and mammalian (deer, swamp rabbits) herbivory on emergence and seedling bank formation of cherrybark oak, Quercus pagoda Raf., in experimental gaps created by mechanized logging in a bottomland hardwood forest. Acorns were planted in exclosures (deer, swamp rabbits, deer + swamp rabbits, neither) in the center of three gaps of each of six gap sizes (7, 10, 14, 20, 29, 40 m radius) and outside the exclosures in center, edge, and forest positions. Mortality was greatest during recruitment (within the first season), and was due primarily to damage to acorns by seed predators and shade effects on seedling establishment. After three seasons, seedlings from damaged acorns in the exclosure plots were shorter than those from undamaged acorns; however, these seedlings had higher relative growth rate, which suggests that acorn damage effects decline over time. Herb layer competition and shade due to position within a gap or gap size were associated with reduced survival or height of seedlings, both in the exclosures and in center, edge, and forest positions. Deer or rabbit herbivory had no measurable effect on seedling survival or growth over the first three seasons. Natural or created canopy gaps ' 14 m radius can be foci for Q. pagoda regeneration if acorns are protected from predators; however, the dense vegetation in regenerating gaps could limit seedling height growth and multiple openings may be necessary for ascent out of the seedling bank.

Establishment and dynamics of the balsam fir seedling bank in old forests of northeastern Quebec

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 (<50 cm tall) present in the quadrats were located, harvested whole (root and shoot), and described (age, height, presence of adventitious roots, etc). Fir seedlings were strongly associated with woody mounds covered with thin mats of mixed mosses and Pleurozium shreberi (Bird.) Mitt. but negatively associated with flat topography particularly dominated by Hylocomium splendens (Hedw.) B.S.G. The presence of adventitious root is related to seedling age more than substrate type or topography. The age structure is in agreement with seed production and disturbance regime.

Chronologie de la croissance chez des semis de sapin baumier (Abies balsamea (L.) Mill.) après une coupe à blanc avec protection de la régénération

The method of harvesting with protection of the advanced regeneration consists of a complete removal of the main canopy to release a seedling bank established under the overstory shade. After harvesting, seedlings acclimated to understory conditions could suffer from moisture stress, especially the small, juvenile seedlings (less than six years). The objective of the study is to determine the capacity of understory-acclimated balsam fir seedlings to respond positively and immediately to release. The response to release was studied in two seedling populations belonging to two distinct climatic regions of Quebec, the Western and the Eastern sections of the balsam fir-white birch ecological domain. Results show that the response patterns were similar in both populations. Response to release occurred in two steps. One year after harvesting, basal ring width was on the average five times larger than prior to harvesting (p > 0.001). Height growth only became significantly higher the second year after release (p < 0.001). On average, juveniles showed higher height growth rates (height growth/height) than older seedlings. This rate was negatively correlated to seedling height at harvesting (r = -0,68, p < 0.001). Our study clearly shows that balsam fir seedlings can respond immediately and positively to large openings. The strong response of juvenile seedlings to release indicates that these can contribute significantly to the future stand. The geographic and climatic differences between the two stands under study suggest that these observations apply to a wide range of balsam fir stands. Key words: advance growth, balsam fir, release

Dynamics of an old-growth, fire-initiated, subalpine forest in southern interior British Columbia: tree size, age, and spatial structure

We used dendrochronological analysis of over 2000 trees in four 50 × 50 m plots to reconstruct the history and dynamics of a 330-year-old, fire-initiated spruce-fir forest. All lodgepole pine (Pinus contorta Dougl. ex Loud.), half of the canopy Engelmann spruce (Picea engelmannii Parry ex Engelm.), but less than 10% of the canopy subalpine fir (Abies lasiocarpa (Hook.) Nutt.) dated from the first 50 years of stand development. Tree-ring patterns of individual surviving trees showed no evidence of disturbance during the first 200 years after stand initiation; subsequently, episodes of disturbance are indicated by periods of release in understory fir. Although many fir owe their canopy position to release after disturbance, few canopy fir in the current stand established in response to either the stand-initiating event or subsequent partial disturbances. A seedling bank of long-lived fir appears critical to the dynamics of this forest. In contrast, establishment of almost all canopy spruce can be related to disturbance. This stand, although fire initiated, was structured primarily by a combination of partial disturbances and autogenic processes. We suspect that most old, fire-initiated stands in many forest regions are similarly structured and emphasize that the contribution of partial disturbances and autogenic processes should be fully assessed when examining their dynamics or managing such forests.

NITROGEN AVAILABILITY INFLUENCES REGENERATION OF TEMPERATE TREE SPECIES IN THE UNDERSTORY SEEDLING BANK

While we have a good mechanistic understanding of effects of light availability on tree seedling regeneration in forests, we know little of the processes controlling seedling responses to changes in nutrient availability in the understory (low light). To examine how nitrogen availability may influence patterns of seedling regeneration in mixed temperate forests in eastern North America, we investigated nitrogen impacts on the dynamics of both coniferous and broad-leaved tree species in the understory. In addition, we compared these regeneration responses across coniferous (eastern hemlock) and broad-leaved (red oak) stand types. We applied nitrogen (0, 2.5, or 7.5 g·m−2·yr−1) to replicated understory plots in three hemlock and three red oak dominated stands, and examined seedling survival and growth for three coniferous and three broad-leaved species over two years. Nitrogen addition influenced different demographic stages in contrasting ways, leading to a complex series of seedling responses to increased nitrogen availability in the understory. Hemlock was the only species to show a positive survival response to nitrogen addition, and these effects only became apparent after the first growing season. In contrast, a suite of midsuccessional species (red maple, white pine, and red spruce) underwent nitrogen-induced declines in survival, particularly at early stages of regeneration. Both successional position and species' habitat preferences emerged as better determinants of species' responses to nitrogen deposition in the understory than did leaf habit (coniferous vs. broad-leaved). Effects were often, but not always, more marked in hemlock stands (characterized by very low light availability), suggesting nitrogen-induced declines in seedling abundance were likely due to an imbalance between above- and belowground resources. In the present study, we have clearly demonstrated that nitrogen availability can be an important determinant of understory seedling bank dynamics in mixed temperate forests in eastern North America. Nitrogen-induced changes in seedling performance in the understory will ultimately influence the spatial and temporal patterns of regeneration of these mixed forests.

The unstable fate of seedlings of the small-seeded pioneer tree species, Betula maximowicziana

The dynamics of the seedling population of the pioneer tree, Betula maximowicziana, were studied for 6 years under various site conditions, with special reference to mortality and mortality factors, in order to better understand their seedling bank formation process. We found that current year seedlings suffered high annual mortality of more than 80%, but that mortality fell with age. Canopy covers and cohorts maintained strong influences on seedling mortality during the first 3 years after emergence. The open site with disturbed soil surface was best suited for 3-year seedling survival. Since the seedlings of B. maximowicziana emerged regardless of canopy covers, high seedling mortality was thought to be the main factor that interrupted their regeneration under a canopy. The occurrence of various hazards together caused high seedling mortality. The major mortality factors, regardless of site conditions, were drought, cold hazard and debilitation, though occurrence of the three factors varied, dependent upon the climate of that particular year. Annual mortality and the occurrence of each mortality factor at a fine scale of 0.2 m 2 quadrate each showed certain spatio-temporal variations within the same site condition. The extremely high mortality of B. maximowicziana seedlings should be attributed to their inherently small, initial size. The poor root system of the small seedlings may be responsible for their low resistance to various hazards, such as drought and frost heaving.

Seed rain of fleshy-fruited species in tropical pastures in Los Tuxtlas, Mexico

In abandoned pastures where the seed bank of forest species has been depleted and a seedling bank does not exist, dispersal events are the only source of forest seeds for natural regeneration (Gómez-Pompa & Vázquez-Yanes 1981). Lack of dispersal has been reported as an important limitation for rain-forest regeneration in pastures (Hardwick et al. 1997 in Thailand; Holl 1999 in Costa Rica; Nepstad et al. 1990 in Brazil) or colonization of fallow land (Kollmann 1995). A high percentage of tropical plant species have fleshy fruits that are dispersed by birds and flying and terrestrial mammals (Howe & Smallwood 1982, Snow 1981). In this study we report the spatial distribution of fleshy-fruited species dispersed to tropical pastures at different distances from the vegetation border in 12 tropical pastures as a measure of the instant regenerative potential of these sites.

The effects of Sasa and canopy gap formation on tree regeneration in an old beech forest

Abstract. We examined the response of tree seedling emergence and survival to the dieback of Sasa and canopy gap formation in an old‐growth forest near Lake Towada, northern Japan. Synchronous death of Sasa occurred in 1995. We established four types of sampling sites differing in forest canopy conditions (Closed or Gap) and Sasa status (Dead or Live). Gap‐Dead sites had the highest light levels and the greatest fluctuation in soil temperatures. The death of Sasa alone facilitated the emergence (Acer japonicum, Fagus crenata, Fraxinus lanuginosa, and Tilia japonica) and survival (Acanthopanax sciadophylloides, F. crenata, F. lanuginosa, Kalopanax pictus, and Sorbus commixta) of species with a seedling bank strategy. Cercidiphyllum japonicum grew at all sites at a higher density than other species, but survived well only in Gap‐Dead sites. This behaviour was associated with a seed rain strategy. The additive effects of Sasa death and canopy gap formation promoted seedling emergence of pioneer tree species (Betula maximowicziana, Lindera umbellata, and Magnolia obovata), probably through break of dormancy by the large temperature fluctuation. In addition, the scarcity of advance regeneration in canopy gaps due to Sasa cover facilitates the regeneration of pioneer species. The dominance and dieback cycle of Sasa contributes to species diversity in this forest.

Seedling bank dynamics of Fagus grandifolia var. mexicana before and after a mast year in a Mexican cloud forest

Abstract. Fagus grandifolia var. mexicana seedling dynamics were studied in a relict forest inside the crater of a volcano where it is the only canopy tree species. The objectives of the study were (1) to determine changes in seedling density before and after a mast year, as well as to monitor seedling recruitment, mortality and growth rate in relation to the micro‐environment, and (2) to discuss the impact of masting on seedling dynamics of the population. Before masting, seedling density was 8.8 seedlings m–2, afterwards seedling density peaked at 51.5 seedlings m–2, then decreased by 50% in 3 months and by 85% after 8 months, down to levels of before the mast year (9.9 seedlings m–2) after 16 months. Seedlings in the forest floor before the mast‐seeding event showed a low relative growth rate – 0.14 mm mm–1 mo–1 against 1.27 mm mm–1 mo–1 for seedlings that emerged immediately after masting. Seed germination was high (83%) and rapid (L50= 7 days) following masting. Seedling growth was positively correlated with soil water content but not with temperatures and relative humidity. Data suggested that seed production in mast years is important in maintaining the seedling bank, and thus the viability of relict Fagus populations.

The effects of Sasa and canopy gap formation on tree regeneration in an old beech forest

Abstract We examined the response of tree seedling emergence and survival to the dieback of Sasa and canopy gap formation in an old-growth forest near Lake Towada, northern Japan. Synchronous death of Sasa occurred in 1995. We established four types of sampling sites differing in forest canopy conditions (Closed or Gap) and Sasa status (Dead or Live). Gap-Dead sites had the highest light levels and the greatest fluctuation in soil temperatures. The death of Sasa alone facilitated the emergence (Acer japonicum, Fagus crenata, Fraxinus lanuginosa, and Tilia japonica) and survival (Acanthopanax sciadophylloides, F. crenata, F. lanuginosa, Kalopanax pictus, and Sorbus commixta) of species with a seedling bank strategy. Cercidiphyllum japonicum grew at all sites at a higher density than other species, but survived well only in Gap-Dead sites. This behaviour was associated with a seed rain strategy. The additive effects of Sasa death and canopy gap formation promoted seedling emergence of pioneer tree species (...

Microenvironmental heterogeneity and Quercus michauxii regeneration in experimental gaps

Canopy gaps are foci for forest regeneration; the gap environment promotes establishment and tree growth into the canopy. In bottomland hardwood forests, microtopography and light are modified simultaneously in natural gaps. Their combined effects may influence seedling establishment and growth. Desirable red and white oaks are often regenerated in bottomland hardwood forests through group selection cutting that mimics the gap environment. We tested effects of canopy openness and microtopography on regeneration of a moderately shade-intolerant oak, Quercus michauxii, in experimental canopy gaps in a bottomland hardwood forest on the Atlantic Coastal Plain. Gap sizes were centered on the median opening size of natural gaps in an old-growth bottomland hardwood forest. Acorns were planted at 100 random level locations in and around each of two replicate 7, 10, 14, 20, 29, and 40 m radius gaps in early spring. Acorns were also planted on pit and mound microtopography complexes created in the center, at the edge, and under intact canopy surrounding two 29 m and three 40 m radius gaps. Over all gaps, 21–37% of the randomly located acorns emerged and survived one summer; 8–26% survived two summers. Survival was influenced more by seedling size than by gap size or distance from gap center. Seedlings on level locations that survived two seasons were taller in the first year, had greater maximum leaf area, and tended to be farther from the center of large gaps than seedlings that died after 1 year. Height of second-year seedlings was related more to first-year plant size than to distance from gap center or gap size. Seedling emergence from acorns planted on microtopography complexes was greater on mounds than in pits at gap center and beneath intact canopy; no seedlings emerged in pits in the gap center. Once established, seedling survival and growth on the microtopography complexes was higher at the gap center. Management of bottomland hardwoods for Q. michauxii regeneration from acorns may be most successful if practices that create conditions favorable for formation of a seedling bank, i.e. raised topography beneath a thin canopy, are followed by light harvests that promote seedling growth and ascent into open canopy.

Notes on Beech (Fagus crenata Blume) Seed and Seedling Mortality Due to Rodent Herbivory in a Northernmost Beech Forest, Utasai, Hokkaido

We investigated the mortality of post-dispersal seeds and current-year seedlings of a beech species (Fagus crenata Blume) at the northernmost extent of its geographical range at Utasai (Kuromatsunai), Hokkaido, Japan. Introduced seeds that were protected from rodent predation by wire cages had a higher survival rate from winter to the following spring (mean ± SD: 84 ± 16.7%,n = 10) than controls without cages (mean ± SD: 12 ± 17.9%,n = 10). Unprotected transplanted current-year seedlings with almost fully opened primary leaves never survived more than three days (0%,n = 30), while more than 80% (n = 30) of seedlings within cages survived to the end of the growing season. These results indicate that rodent herbivory is a major mortality factor that strongly prevents the establishment of beech seedlings. In a natural population, we observed that 90% of seedlings (n = 197) disappeared within 10 days after their emergence and rodent herbivory caused this heavy mortality. A herbivorous rodent, the gray-backed vole, Clethrionomys rufocanus bedfordiae, was remarkably abundant in late June (101.5 voles/ha), suggesting that this species strongly affects the formation of the seedling bank. The presence of C. rufocanus bedfordiae may be one of the reasons for the scarcity of beech seedlings and saplings and the rarity of recruitment in this northernmost beech forest.

Response of Native and Exotic Maple Seedling Banks to Removal of the Exotic, Invasive Norway Maple (Acer platanoides)

WEBB, S. L., T H. PENDERGAST IV, AND M. E. DWYER (Drew University, Biology Department, Madison, NJ 07940.) Response of native and invasive maple seedling banks to removal of the exotic, invasive Norway maple (Acer platanoides). J. Torrey Bot. Soc. 128:000-000. 2001.-Acer platanoides is an exotic, invasive tree in eastern deciduous forests of North America where past research shows it to thrive in the forest interior and to suppress understory diversity. To test the efficacy of restoration strategies and to probe dynamics of this tree's seedling bank, trees and seedlings of Acer platanoides were removed in 1997 from a mixed maple forest carpeted by an even mix of exotic Acer platanoides and native Acer saccharum seedlings. The treatments were removal of trees (height > 1.5 m) and removal of small seedlings (height < 1.5 m), using a crossed design with a total of 80 permanent plots, all sampled before removals and two years later. After two years, removal of Acer platanoides trees had caused an increase in native Acer saccharum seedling densities over those in control areas and had caused a decrease of new Acer platanoides recruitment. Conversely, removal of Acer platanoides seedlings initiated far more new Acer platanoides than Acer saccharum seedlings. The Acer platanoides seedling bank was partially, but not fully, replenished two years after its removal. Although removal of canopy trees appears effective as a restoration tool, other exotic species (especially Lonicera japonica, Alliaria petiolata, and Robinia pseudoacacia) proliferated where tree removals opened the canopy. Restoring the pre-invasion community will thus require future intervention.

Dynamics of seedling banks in beech forest: results of a 10-year study on germination, growth and survival

The dynamics of a seedling bank was studied in four plots located in the Krynica Experimental Forest, southern Poland. Each sample plot was divided into eight sectors, in which germinants and seedlings were mapped, measured, and labelled; their survival was checked twice a year between 1989 and 1996. Maps of relative light intensities on the forest floor in sample plots were produced on the basis of measurements conducted in June and August 1991. During the entire period of study, European beech ( Fagus sylvatica L.) made up over 96% of germinants and seedlings. Numbers of beech germinants varied strongly (from 0 to 1178) among plots and years. Each year of abundant germination was followed by one or two years of scarce germination, and there was an increasing trend in the number of germinants in three plots between 1989 and 1996. Seedling emergence was almost independent of relative light intensity and first-season survival was positively, but weakly correlated with it. Long-term survival of seedlings was low and strongly related to relative illumination. Results of analyses of spatial patterns in seedlings suggested that some microsites were more conducive than others to germination and early survival of seedlings. Survival among taller germinants was greater than among shorter ones. A true seedling bank was observed only in two plots, where relative light intensities were 9 and 15% of full sunlight. In a plot with relative light intensity of 4%, the seedling bank was unstable and in the least illuminated plot (<3% of full sunlight) no seedling bank was formed. Results indicate that, even in a strongly shade-tolerant species like beech, formation of a seedling bank requires the occurrence of canopy openings in the close proximity.

Patterns and levels of gene flow in Rhododendron metternichii var. hondoense revealed by microsatellite analysis.

Parentage analysis was conducted to elucidate the patterns and levels of gene flow in Rhododendron metternichii Sieb. et Zucc. var. hondoense Nakai in a 150 x 70 m quadrant in Hiroshima Prefecture, western Japan. The population of R. metternichii occurred as three subpopulations at the study site. Seventy seedlings were randomly collected from each of three 10 x 10 m plots (S1, S2, and S3) on the forest floor of each subpopulation (A1, A2, and A3). Almost all parents (93.8%) of the 70 seedlings were unambiguously identified by using 12 pairs of microsatellite markers. Within the quadrant, adult trees less than 5 m from the centre of the seedling bank (plots S1, S2, and S3) produced large numbers of seedlings. The effects of tree height and distance from the seedling bank on the relative fertilities of adult trees were highly variable among subpopulations because of the differences in population structure near the seedling bank: neither distance nor tree height had any significant effect in subpopulation A1; distance from the seedling bank had a significant effect in subpopulation A2; and tree height had a significant effect in subpopulation A3. Although gene flow within each subpopulation was highly restricted to less than 25 m and gene flow among the three subpopulations was extremely small (0-2%), long-distance gene flow from outside the quadrant reached 50%. This long-distance gene flow may be caused by a combination of topographical and vegetational heterogeneity, differences in flowering phenology, and genetic substructuring within subpopulations.

Seedling bank dynamics in managed holm oak (Quercus ilex) forests

The present study reports spatiotemporal variations in seedling bank dynamics during a 5-year period in thinned and unthin- ned holm oak (Quercus ilex) plots in the Montseny Massif (NE Spain). Large spatial and temporal variations in seedling density have been found in the three plots studied, while the spatial pattern has shown low temporal fluctuations. However, differences in recruitment and survival among thinned and unthinned plots were small, but both variables had large between-year variability. The monitoring of seedling growth over time demonstrated that holm oak seedlings hardly grew in height after five years. According to these results, holm oak seedlings persisted through time in the understory and remained suppressed while in the shade, but did not show any release after thinning. Thus, the seedling bank only represents a reserve of small individuals that do not have any evident role in holm oak forest dyna - mics under the present disturbance/management regime. holm oak / seedling / recruitment / growth / survival

A relict population of Fagus grandifolia var. mexicana at the Acatlan Volcano, Mexico: structure, litterfall, phenology and dendroecology

Aim Fagus grandifolia var. mexicana (Martinez) Little has an extraordinarily restricted distribution in the Mexican montane cloud forests. Isolated Fagus (beech) populations have been recorded in less than 10 small areas (2–40 ha) in the eastern Sierra Madre at altitudes from 1400 to 2000 m. The objectives were to determine tree and seedling age, forest structure, phenology, litterfall patterns and the relationship between mast and climatic variables. Location We report on three Fagus stands at the Acatlan Volcano, Veracruz, Mexico. Methods Changes in forest cover were determined using aerial photographs. Within each stand, basal area, density and tree species composition were determined in a 0.1-ha band transect. Additionally, litterfall production was quantified and phenophases were recorded monthly over a 3-year period, and 60 tree cores were collected to determine age distribution and tree-ring growth. Results The forest was atypical in several respects. Fagus was the only dominant tree species in the crater stand, although in the rim and at the top of the volcano it was codominant with other tree species. Juveniles occurred only on the rim, but there was a seedling bank in the crater. Although forest cover in the area increased between 1968 and 1993, the Fagus stands did not change in size. Leaf production peaked in March and April, and leaf fall occurred from October through February. Litterfall production was the highest in November. During mast years, flowering started in February and between mast events there were no flowers or fruits. Minimum temperatures were highly correlated with Fagus litterfall and leaf fall. Seedlings ranged in age from 2 to 18 years and were 13–60 cm tall. Tree cores ranged from 76 to 120 years, but trees were older than the core samples. Main conclusions Although beech is considered a gap regeneration species that reaches the canopy after alternating periods of release and suppression, the trees in the crater were released when less than 1.5 m tall and have suffered few periods of suppression since. The results indicate that the crater stand was established after a severe disturbance destroyed the existing forest. We conclude that the relict beech population should be able to maintain itself, if not severely disturbed by humans or by climatic changes related to global warming.

Evolutionary and ecological aspects of recalcitrant seed biology

AbstractThere is a substantial literature on the basic physiology and response to desiccation of recalcitrant seeds, but little is known about their ecology and even less of their evolutionary status. It is difficult to assess the response of early land plants to dehydration, but it is likely that desiccation tolerance in vegetative tissue arose concomitantly with the invasion of the land. Similarly, from the fossil record it is not possible to assess the desiccation response of early seeds, and furthermore, it is difficult to see phylogenetic relationships among species producing recalcitrant seeds. A consideration of the available evidence, however, suggests that the first seeds were desiccation-sensitive, but tolerance evolved early and probably a number of times, independently. The desiccation sensitivity and short life span (generally shorter than the interval between flowering) of recalcitrant seeds have implications in terms of regeneration ecology. A long-term soil seed bank as such does not exist; rather the seeds germinate and form a seedling bank. However, there is a wide range in post-shedding physiology among recalcitrant seed species, and although species producing recalcitrant seeds are common in the humid tropics, they do occur in habitats with more marked seasonal variation. Here regeneration strategies may be more specialized.

Some thoughts on the evolution and ecology of recalcitrant seeds

AbstractThere are substantial scientific reports on the basic physiology and desiccation sensitivity of recalcitrant seeds, but ecological and evolutionary aspects of their biology have received scant attention. Recalcitrant seeds are shed hydrated, are desiccation sensitive and have a short lifespan. In vegetative tissue, desiccation sensitivity is probably the ancestral state, but tolerance is thought to have evolved early and a number of times independently. It is difficult to see evolutionary relationships among species producing recalcitrant seeds. However, it is suggested that early evolved seeds were desiccation sensitive and that desiccation tolerance is a derived characteristic. Desiccation sensitivity and short lifespan of recalcitrant seeds places constraints on the range of environmental conditions in which reproductive success can occur. Species producing recalcitrant seeds are common in humid tropical forests, where the seeds of climax species germinate and form a seedling bank, rather than contributing to the soil seed bank. However, there is a wide range in post‐shedding physiology among recalcitrant seed species, and recalcitrant seeds do occur in habitats with seasonal climates. Here, regeneration strategies may be more specialized.

Succession après épidémie de la tordeuse des bourgeons de l'épinette (Choristoneura fumiferana) dans des sapinières boréales pluviales de seconde venue

Following spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks, Baskerville's model (G.L. Baskerville. 1975. Spruce budworm: super silviculturalist. For. Chron. 51: 138-140), referred to as the cyclic model, is generally accepted as one of the best established regeneration models in wet boreal fir stands typical of northeastern America. According to that model, old virgin fir stands killed by the insect are replaced by other fir stands. In this study, we wanted to check if the cyclic model would work with wet boreal fir stands originating from harvest and having reached the felling age (50-60 years old) observed in Quebec. The study set up after the last budworm outbreak (1974-1987) shows that, although coniferous regeneration is abundant, the seedling bank is obviously immature: young and small seedlings, empty microsites. In most cases, the regeneration is codominated or dominated by deciduous species, which may bring about the development of a deciduous stand. Thus, the cyclic model does not seem suited to describe dynamics of second-growth boreal fir stands when it is kept in a premature state (&lt;50-60 years old). These stands may not be as resilient as virgin ones, which are characterized by ecological rotations longer than 90 years.[Translated by the Journal]