SEARCH

SEARCH BY CITATION

Keywords:

  • Abies balsamea;
  • Acer saccharum;
  • Betula alleghaniensis;
  • climate;
  • crop efficiency;
  • mast flowering;
  • mast seeding;
  • potential seed crop;
  • viable seed crop

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References

1 Several hypotheses have been put forward to explain the phenomenon of masting or mast seeding, i.e. the supra-annual, periodic production of a large number of seeds in long-lived plants. Some of these hypotheses deal with the proximate causes of masting (e.g. the climate hypothesis) but others are concerned mostly with ultimate, evolutionary explanations (e.g. the pollination efficiency hypothesis).

2 The seed production of three tree species, Abies balsamea, Acer saccharum and Betula alleghaniensis, was followed over a 7-year period in an old-growth, cold temperate forest of north-eastern North America. The main objectives were to determine the extent of interannual variations in seed production, to investigate the relationship between viable and potential seed crop and crop efficiency, and to explore the effects of climate on seed production.

3 Potential and viable seed production varied significantly among years for all three species. However, the timing of dispersal remained the same regardless of the level of seed production.

4 Seed rain was spatially less heterogeneous in years of high seed production, suggesting that most trees were reproducing in such years.

5 Over the 7-year period, there was a significant concordance among species in their viable seed crop and crop efficiency, but not in their potential seed crop. Crop efficiency was positively correlated to potential seed crop for Abies and Betula, but not for Acer.

6 High seed production was related to warm, dry conditions in the spring of the previous year (i.e. at reproductive bud initiation) but to a moist summer in the year of seed maturation.

7 Masting in these three species thus appears to be controlled by several factors, including climate and pollination efficiency.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References

Mast seeding or masting is the supra-annual, periodic, synchronous production of large numbers of seeds by individuals in populations of long-lived plants (Silvertown 1980; Kelly 1994). This implies that years of high seed production are separated by years of no or low seed output. Because reproductive opportunities are lost in intermast years, mast seeding has fitness consequences for the individuals (Waller 1979). Both proximate and ultimate, i.e. evolutionary, explanations have been proposed for this phenomenon.

Interannual variations in seed production may be the consequence of interannual fluctuations in climate (a proximate cause), but in this case the periodicity that is characteristic of masting will rarely be observed (Lindquist 1931; Matthews 1963; van Vredenburch & la Bastide 1969; Norton & Kelly 1988). In fact, the climate hypothesis is often put forward as the null hypothesis to explain interannual variations in seed production (Sork 1993).

Masting may also be related to physiological and/or morphological constraints within the plant, for instance if massive bouts of reproduction significantly reduce the reserves of carbohydrates, nutrients and/or buds for a specific number of years, which may vary between species (Davis 1957; Gardner 1977; Allen & Platt 1990; Sork et al. 1993). Such constraints may generate periodicity in seed production, but individuals and populations will not necessarily be synchronous.

Pollination efficiency may have favoured the evolution of masting, particularly in wind-pollinated species (Nilsson & Wästljung 1987). According to the pollination efficiency hypothesis, mast years are years of massive flowering, pollen production and fertilization (Sork 1993). In species for which a significant part of the investment in reproduction occurs at flowering, as in Betula and Abies, such synchronized massive reproduction assures efficient fertilization. Although this hypothesis predicts that individuals and populations will be synchronous, and that seed production will fluctuate, periodicity does not necessarily follow.

Mast seeding might also have evolved as a result of predator pressures (Janzen 1971; Silvertown 1980), as a larger proportion of the seed crop would escape from predation in years of high seed production because of predator satiation. Although both periodicity in seed production and synchronism among individuals and populations may be explained by this hypothesis, masting may in fact be the result of a combination of several of proximate and ultimate factors (Owens & Blake 1985; Nilsson & Wästljung 1987; Lalonde & Roitberg 1992; Donaldson 1993; Sork 1993; Sork et al. 1993; Kelly 1994; Mencuccini et al. 1995).

In the present study, traps were used to follow the production and dispersal of reproductive structures (abscised flowers, and seeds or fruits, whether aborted or fully developed) of three sympatric tree species, Abies balsamea (L.) Mill., Acer saccharum Marsh. and Betula alleghaniensis Britt., over a 7-year period. The objectives were to determine the extent of interannual variations in seed production, to investigate the relationship between viable and potential seed crop and crop efficiency, to ascertain if variations in seed production influenced the timing of dispersal, and to explore the effects of climate on seed production.

The study species

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References

Abies balsamea, Acer saccharum and Betula alleghaniensis are typical components of the sugar maple-yellow birch forests of north-eastern North America (Grandtner 1966).

Abies balsamea (hereafter called Abies) tree longevity rarely exceeds 125 years (Loehle 1988). Trees reach sexual maturity when they are 20–30 years old (Bakuzis & Hansen 1965). Both male and female cones are produced on the same individual, and wind pollination occurs from May to early June (Frank 1990). Seeds mature during the summer months and are disseminated by the wind, mostly in the autumn. Abies trees produce seeds at approximately 2-year intervals (Ghent 1958; Schopmeyer 1974), but during any given year a great number of seeds may be empty because of inadequate pollination. Seed production has been shown to increase with tree age and hierarchical position within the canopy (Morris 1951).

Tree longevity for Acer saccharum (hereafter called Acer) is approximately 250–300 years, but some trees may attain 400 years of age (Loehle 1988). Under natural conditions, individuals of the species reach reproductive maturity when they are 30–60 years old (Schopmeyer 1974). The flowering period starts in late April and extends into May. Flowers are in small fascicles and functionally either male or female (Godman et al. 1990); pollination is accomplished mainly by insects, but wind pollination also occurs (Gabriel & Garrett 1984). Seeds mature during the summer and fruits are disseminated by the wind from early autumn through early winter. Acer is known to produce an abundant seed crop irregularly, every 3–7 years (Curtis 1959; Schopmeyer 1974; Grisez 1975). The dispersal unit is a samara (usually containing a single embryo), but often two samaras from one flower remain attached to one another during dispersal. Usually only one of the two samaras from a flower contains a fully developed embryo. Seeds germinate early in the spring, often before complete snow melt (Tubbs 1965).

Individuals of Betula alleghaniensis (hereafter called Betula) may live for over 300 years, but tree longevity more typically is approximately 150 years (Erdmann 1990). Betula trees bear both male and female catkins, and flowering occurs from April to May. Pollination is effected by wind. Embryos develop from May to September, and fruits (samaras) are disseminated from late summer through the following spring. The small samaras are wind-disseminated and usually contain a single fully developed embryo. Trees may start producing seeds at approximately 40 years of age and abundant seed production occurs every 2 or 3 years (Schopmeyer 1974; Erdmann 1990).

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References

Study site and sampling design

The study area was at the north-eastern limit of the Laurentian Section of the Great Lakes–St Lawrence region of Canada (Rowe 1972), a region characterized by forests of Acer saccharum and Betula alleghaniensis, in association with Picea rubens Sarg., Abies balsamea, Acer rubrum L. and Betula papyrifera Marsh. The stand selected for the study was located within the boundaries of the Tantaré Ecological Reserve (47°04′ N, 71°32′ W, 380 m a.s.l.), approximately 30 km north of Quebec City (Canada). The Tantaré Ecological Reserve comprises 1300 ha of old-growth deciduous and mixed forests. The stand studied occupied the mid-section of a 20° slope on the shore of Lake Tantaré. At a nearby weather station (Québec A, 46°48′ N, 71°23′ W, 73 m a.s.l.), mean annual temperature is 4.1 °C and annual precipitation totals 1170 mm, of which 340 mm falls as snow (Atmospheric Environment Service 1981). The frost-free season averages 137 days (Atmospheric Environment Service 1982). Payette et al. (1990) have described the disturbance regime of this old-growth forest: most gaps are < 200 m2 and result from the fall of one or a few trees, or from self-pruning (particularly in Betula). Gap dynamics contribute to maintaining the uneven age distribution of the major tree species populations on the site.

Sampling for the period 1988–91 was carried out in a 50 × 30-m area subdivided into 60 5 × 5-m quadrats in an homogeneous section of the stand (Houle & Payette 1990, 1991). Thirty of these quadrats, in a checkerboard pattern within the larger area, were sampled. For the period 1991–95, sampling was carried out in a different layout established approximately 50 m from the previous one. There, three 120-m long transects starting from, and perpendicular to, the shore of Lake Tantaré were positioned 15 m apart (Houle 1995, 1998). Quadrats, 5 × 5 m, were marked every 10 m along these transects. For the present analysis, only data from the upper section of the transects (upper 80 m) were considered because they correspond to the position of the first layout along the 20° slope.

The seed rain (which includes carpels and aborted fruits along with aborted, empty and filled seeds, whether viable or not) was sampled with traps consisting of a 15-cm diameter × 20-cm deep metal cylinder within which a fibreglass net (1 mm mesh size) had been draped to form a 15-cm deep pouch. The seed trap was attached to a stick approximately 50 cm above the ground. Five seed traps were located (one at each corner and one at the centre) in each 5 × 5-m quadrat. There were thus 150 (total sampling surface 2.65 m2) and 120 (total sampling surface 2.12 m2) seed traps for the first and the second layout, respectively. Traps were emptied every week from May to November. Reproductive structures (carpels, flowers, seeds or fruits) were sorted by species and counted, and mature structures were tested for embryo viability in controlled-environment cabinets. Seeds of Abies and samaras of Acer (but not those of Betula) were stratified at 5 °C for 2 months in darkness prior to the germination trials. Tests were carried out separately for each sampling period. Germination conditions were 30 °C (day)/20 °C (night) for Abies and Betula, and constant 5 °C for Acer, with an 8-hr photoperiod (Schopmeyer 1974).

When an adequate number of seeds or fruits was available from a given sampling episode, five germination trials of 50 seeds each per species were performed. When the number of seeds or fruits sampled for a given episode was < 250, as many trials of 50 seeds each were done as possible. When the number of seeds or fruits available was < 50, all seeds were used for the trial. Seeds or fruits were placed on two filter papers wetted with an aqueous solution (300 mg l−1) of a fungicide (Captan 10%, Benomyl 2% Cil, Longueuil, Québec), in 15-cm (Abies and Betula) or 25-cm (Acer) diameter Petri dishes. Seeds were allowed to germinate for a period of 42 days and germination counts were done weekly. At the end of the period, those seeds that had not germinated were opened (taken out of the fruit coat and/or the testa); when an embryo was present, it was excised and tested for viability with a 1% aqueous solution of tetrazolium chloride. Only completely coloured embryos were counted as viable. Final viability results were based on totals from both germination and staining trials.

Statistical analyses

Three variables, potential seed crop, viable seed crop and crop efficiency, were analysed for each species. Potential seed crop represents the density of structures (carpels in Acer and flowerets in Betula) capable of developing into a fruit, or the density of seeds produced and dispersed (in Abies). Viable seed crop is defined as the density of fruits (Acer or Betula) or seeds (Abies) with a viable embryo. Crop efficiency is the ratio of viable seeds to potential seeds for each species. Crop efficiency is an estimate of pollination, fertilization and seed maturation success. The coefficient of variation (CV for the 7-year period) was calculated for the potential and viable seed crop of each species to estimate interannual variability in seed production or intensity of masting (Silvertown 1980).

For each species, crop efficiency was correlated to potential seed crop for the 7-year period. Kendall’s coefficients of concordance (W) were calculated to estimate the degree of synchrony among species in potential and viable seed crop and in crop efficiency (Sokal & Rohlf 1995). W behaves like a standard correlation coefficient (i.e. it varies from –1 to +1) but it analyses the relationship among more than two variables (e.g. among the three tree species in the present study). To estimate the degree of similarity among years in the timing of seed dispersal for a given species, Kendall’s coefficient of concordance, W, was calculated using the weekly seed crop data over the 7-year period.

To identify potentially important weather variables for the seed production of the three species, correlation coefficients between mean monthly temperature, monthly precipitation and seed production were estimated. However, no significance tests were possible because of the short chronology involved and the large number of weather variables used. Meteorological data were obtained from the Québec A station (see above), from the time of reproductive bud initiation (May–July of the previous year; Matthews 1963; Owens & Blake 1985) to the time of seed maturation (August of the year of seed dispersal).

As a means of estimating the degree of synchrony in seed production among trees of a given species, the CV was calculated over the 150 (or 120) seed traps for each of the 7 years. It was postulated that seed crop would be spatially more variable in years of low synchrony among trees (or in years when only a few trees reproduced), thus leading to a higher CV (Allen & Platt 1990; Mencuccini et al. 1995). For each species, spatial CVs were correlated to seed crop, over the 7-year period, to test for increased synchrony among trees in mast years. For all of the above correlation analyses, the Pearson’s coefficient of correlation was used.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References

The potential seed crop was quite variable among years for all three species studied (Table 1), varying from 300-fold in Abies to 25-fold in Acer. Maximum and minimum years were somewhat different for the three species. Interannual variations in viable seed crop were also important and often followed over time a pattern similar to that of the potential seed crop. CV values were always higher for the viable than for the potential seed crop. Only a very small percentage (< 0.1%) of the seeds of the three species showed any sign of predispersal predation over the 7-year study.

Table 1.  Potential and viable seed crop (units m–2; mean ± 1 SE) and crop efficiency [(viable seed crop/potential seed crop) × 100] of Abies balsamea, Acer saccharum and Betula alleghaniensis for the period 1988–94 at the Tantaré Ecological Reserve, Québec, Canada. Coefficients of variation (CV) over the 1988–94 period for potential and viable seed crop and for crop efficiency
 Species
 Abies balsameaAcer saccharumBetula alleghaniensis
1988
Potential seed crop 92.1 ± 7.0120.4 ± 9.628 129.8 ± 414.8
Viable seed crop 28.7 ± 2.2 22.4 ± 2.218 251.8 ± 228.6
Crop efficiency (%)31.218.664.9
1989
Potential seed crop 4.5 ± 1.7165.3 ± 16.5 2897.2 ± 203.2
Viable seed crop 0.4 ± 0.4 8.0 ± 0.8 661.1 ± 48.6
Crop efficiency (%)8.94.822.8
1990
Potential seed crop 12.8 ± 2.3193.9 ± 14.2 4382.0 ± 138.6
Viable seed crop 0.8 ± 0.2 30.7 ± 2.3 806.0 ± 25.9
Crop efficiency (%)6.315.818.4
1991
Potential seed crop 0.9 ± 0.7 8.0 ± 2.4 2800.3 ± 117.4
Viable seed crop 0.2 ± 0.2 0.5 ± 0.3 330.2 ± 14.8
Crop efficiency (%)22.26.311.8
1992
Potential seed crop238.2 ± 21.6107.1 ± 13.725 884.6 ± 796.0
Viable seed crop 91.2 ± 7.2 36.6 ± 4.0 8532.3 ± 230.3
Crop efficiency (%)38.334.233.0
1993
Potential seed crop 13.2 ± 3.0 8.0 ± 3.5 737.7 ± 74.4
Viable seed crop 0.3 ± 0.10 72.8 ± 4.4
Crop efficiency (%)2.309.9
1994
Potential seed crop292.4 ± 98.9 93.4 ± 10.418 795.9 ± 628.3
Viable seed crop 96.5 ± 54.4 16.7 ± 1.9 9518.3 ± 305.9
Crop efficiency (%)33.017.950.6
CV
Potential seed crop131.071.799.7
Viable seed crop141.587.6127.4
Crop efficiency (%)71.382.268.6

Crop efficiency was quite variable among years for all three species (Table 1). Efficiency was positively correlated to potential seed crop for all three species (Fig. 1), but significantly so only for Abies and Betula.

image

Figure 1. Crop efficiency (viable seed crop/potential seed crop) as a function of potential seed crop for Abies balsamea, Acer saccharum and Betula alleghaniensis. The r-value represents the coefficient of correlation (*significant at P≤ 0.05; ns, not significant).

Download figure to PowerPoint

Kendall’s coefficient of concordance (W) indicated that the species were well synchronized over the 7-year period in their viable seed crop and crop efficiency, but less so in their potential seed crop: potential seed crop W = 0.565 (P = 0.1178); viable seed crop W = 0.841 (P = 0.0192); crop efficiency W = 0.865 (P = 0.0162).

Spatial variability in seed crop abundance (as estimated by the among-seed trap CV) was consistently lower in years of abundant seed production (for both potential and viable seed crop) for all three species. However, Pearson’s coefficient of correlation (r) between CV and seed crop abundance was rarely significant (Fig. 2).

image

Figure 2. Spatial coefficient of variation as a function of potential and viable seed crop for Abies balsamea, Acer saccharum and Betula alleghaniensis. Significance levels as in Fig. 1.

Download figure to PowerPoint

The timing of seed dispersal was significantly concordant among years for each of the three species studied (Fig. 3). Values of Kendall’s coefficient of concordance, W, were 0.342, 0.347 and 0.435 (potential seed crop) and 0.317, 0.526 and 0.519 (viable seed crop) for Abies, Acer and Betula, respectively (all values are significant at P≤ 0.001).

image

Figure 3. Weekly seed rain of Abies balsamea, Acer saccharum and Betula alleghaniensis for the period 1988–94, showing potential (line) and viable (shaded portion) seeds (units m–2). Units dispersed during the winter months (November–April) are represented in the separate peak on the right-hand side.

Download figure to PowerPoint

High temperatures together with low precipitation during the previous summer were correlated with high seed production for all three species (Fig. 4). These conditions are indicative of drought at the time of reproductive bud initiation. However, seed crop was negatively correlated with high temperatures in either early spring or August in the year of seed maturation, and with low rainfall in July–August of that year. These relationships were similar for both the potential and the viable seed crop (Fig. 4).

image

Figure 4. Correlation coefficients between mean monthly temperature or total monthly precipitation and potential (black bars) or viable (white bars) seed crop, for Abies balsamea, Acer saccharum and Betula alleghaniensis. The weather data used for the analyses cover the period from the time of reproductive bud initiation and differentiation (May–1) to the time of seed maturation (August).

Download figure to PowerPoint

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References

Both potential and viable seed production varied markedly among years for all three species, although interannual variability was higher for the viable, than for the potential, seed crop. Of the three species studied, Abies had the highest, and Acer the lowest, intensity of masting (sensuSilvertown 1980). However, the CV values were not exceptionally high (between 72% and 142%); indeed, Kelly (1994) reported modal CV values of 80–120% for a sample of 42 polycarpic plants. However, CV values are not sufficient to identify masting species, as a strict masting species that produces similar quantities of seeds every other year and no seeds at all in intervening years would have a CV value of 100%. Periodicity in seed crop and among-individual synchrony must also be demonstrated (Kelly 1994).

Because of the restricted length of the chronology (7 years), it was not possible to test critically for periodicity in seed production. Consequently, this criterion of masting could not be verified for the species studied here.

In masting species, few trees in a population flower and/or seed in intermast years, and this creates a seed rain that is spatially very heterogeneous (Goodrum et al. 1971; Sork et al. 1993). During mast years, most trees produce flowers and seeds and this should generate a less spatially variable seed rain. Thus, the year by year pattern of seed crop spatial variability may reflect, to some extent, within-population synchrony. The negative relationship reported here between spatial CVs and seed crop abundance does indeed suggest higher among-tree synchrony during mast years.

Pollination efficiency

Crop efficiency varied significantly among years and it was positively correlated with potential seed crop. This result is consistent with the pollination efficiency hypothesis of masting (Sork 1993). Reduced crop efficiency in years of low potential seed crop (Bjorkbom et al. 1965; Alexander 1986; Norton & Kelly 1988; Allen & Platt 1990; Burrows & Allen 1991; Sork et al. 1993; Mencuccini et al. 1995) may be related to the lower proportion of trees that reproduce (Goodrum et al. 1971; Nilsson & Wästljung 1987; Herrera et al. 1994; Tapper 1996), the more diffuse pollen rain (Hyde 1951; Smith et al. 1988), and the higher level of self-pollination and associated low level of fertilization or embryo development (Matthews 1963; Stephenson 1981; Smith et al. 1988; Lalonde & Roitberg 1992; Owens 1995). In mast years, most of the trees in the population reproduce: the pollen rain is then more abundant and genetically more diverse, and the level of cross-pollination is higher. Such a scenario may be more appropriate for wind- than for insect-pollinated species (Smith et al. 1990; Kelly 1994), and the relationship between potential seed crop and crop efficiency, although positive for all three species studied here, was indeed significant for the wind-pollinated Abies and Betula, but not for the typically insect-pollinated Acer. As a consequence of the relationship between potential seed crop and crop efficiency, years of high potential seed crop were also years of high viable seed crop for Abies and Betula (for similar results on Quercus, see Sork et al. 1993; Sork et al. 1993) but not necessarily for Acer.

Despite large interannual fluctuations in seed production, the timing of seed dispersal was consistent across years for each of the species studied. Most viable seeds of Abies and Acer were dispersed from September to November, but a significant proportion of the viable seeds of Betula was disseminated during the winter months (Houle & Payette 1990, 1991). In Acer, a significant number of carpels was shed soon after anthesis (Boucher & Sork 1979 for Carya glabra;Tanouchi et al. 1994 for Quercus spp.; Garrett & Graber 1995 for Acer saccharum). The proportion of the potential seed crop represented by these shed structures was higher in years of low viable seed production (Sork et al. 1993), perhaps as a result of failure of fertilization (Stephenson 1981; Sork et al. 1993). Such a phenomenon appears to be frequent in species for which more of the investment in accessory structures occurs after fertilization has taken place, as in Acer. Resources thus saved (by not investing in what would be empty fruits) may be invested in current and/or future growth and reproduction. For species such as Abies and Betula, where a significant part of the investment in the accessory structures takes place prior to pollination and fertilization, female cones or catkins are rarely shed unless they contain very few or no viable seeds (Bakuzis & Hansen 1965; Owens & Blake 1985).

Climatic constraints

Climate had an overall similar effect on seed production in the three species. Dry conditions at the time of reproductive bud initiation appeared to favour seed production, as has been found for several other tree species (Lindquist 1931; Matthews 1963; Owens & Blake 1985; Hilton & Packham 1997). Concordance (i.e. synchrony) among species was significant for viable seed production and crop efficiency, but not for potential seed production. These results suggest that climate may have a more consistent effect among species on pollination, fertilization and/or seed maturation than on reproductive bud initiation. Although several previous studies have found a positive relationship between spring temperature and seed production, high temperatures in April were here related to low seed production in that year (potential and viable seed crop) for all three species. It is suggested that night frosts that are still frequent in late spring in the study area may damage the emerging reproductive structures in years when otherwise unusually warm temperatures induce early bud break. Such unusual climatic events may thus significantly reduce the viable seed crop (Lindquist 1931; Goodrum et al. 1971; Gardner 1977; Erdmann 1990; Owens et al. 1991).

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References

Pollination efficiency is higher in years of high potential seed production for the two wind-pollinated species studied, i.e. Abies and Betula, but not for the typically insect-pollinated Acer. In years of low crop efficiency, a large proportion of the non-viable reproductive structures are shed in Acer, which invests in the accessory structures mostly after anthesis, but not in the cone/catkin-producing Abies and Betula. However, climate has similar effects on reproduction in all three species and may explain the among-species concordance in reproductive chronology. Several factors thus seem to interact to create variations in the seed production of these species on the study site. Climate is a proximate constraint for reproduction in all species, and pollination efficiency may be an ultimate cause in Abies and Betula. Tree reserves may impose further restriction on reproduction for all three species, as there were never two successive years of high viable seed production, even when there were two successive years of large potential seed crop (e.g. for Acer). Pre-dispersal predation was not important and can be discounted as an ultimate explanation for the observed interannual variations in reproduction.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References

I would like to thank P. Babeux, J. Bélanger, O. Couture, C. Fortin, I. Gamache, P. Roby, and J. Turcotte for their technical assistance in the field and the laboratory, and J.-M. Gagné, É. Imbert and M. McKenna for their comments on an earlier version of the manuscript. This work was financially supported by the Fonds pour la formation des chercheurs et l’aide à la recherche, the Natural Sciences and Engineering Research Council of Canada, and the Québec Department of Environment.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. The study species
  5. Materials and methods
  6. Results
  7. Discussion
  8. Conclusion
  9. Acknowledgements
  10. References
  • Alexander, R.R. 1986 Engelmann Spruce Seed Production and Dispersal, and Seedling Establishment in the Central Rocky Mountains. General Technical Report RM-134. USDA Forest Service, Fort Collins, CO.
  • Allen, R.B. & Platt, K.H. 1990 Annual seedfall variation in Nothofagus solandri (Fagaceae), Canterbury, New Zealand. Oikos, 57, 199206.
  • Atmospheric Environment Service 1981Canadian Climate Normals. Temperature and Precipitation. 1951–80. Environment Canada, Atmospheric Environment Service, Downsview, Ontario, Canada.
  • Atmospheric Environment Service 1982Canadian Climate Normals. Frost. 1951–80. Environment Canada, Atmospheric Environment Service, Downsview, Ontario, Canada.
  • Bakuzis, E.V. & Hansen, H.L. 1965Balsam Fir. A Monographic Review. The University of Minnesota Press, Minneapolis, MN.
  • Bjorkbom, J.C., Marquis, D.A., Cunningham, F.E. 1965 The Variability of Paper Birch Seed Production, Dispersal, and Germination. Research Paper NE-41. USDA Forest Service, Upper Darby, PA.
  • Boucher, D.H. & Sork, V.L. 1979 Early drop of nuts in response to insect infestation. Oikos, 33, 440443.
  • Burrows, L.E. & Allen, R.B. 1991 Silver beech (Nothofagus menziesii (Hook. f.) Oerst.) seedfall patterns in the Takitimu Range, South Island, New Zealand. New Zealand Journal of Botany, 29, 361365.
  • Curtis, J.T. 1959The Vegetation of Wisconsin. University of Wisconsin press, Madison, WI.
  • Davis, L.D. 1957 Flowering and alternate bearing. Proceedings of the American Society for Horticultural Science, 70, 545556.
  • Donaldson, J.S. 1993 Mast-seeding in the cycad genus Encephalartos: a test of the predator satiation hypothesis. Oecologia, 94, 262271.
  • Erdmann, G.G. 1990 Betula alleghaniensis Britton. Yellow birch. Silvics of North America, Vol. 2. Hardwoods(eds R.M.Burns & B.H.Honkala), pp. 133147. Agricultural Handbook 654. USDA Forest Service, Washington, DC.
  • Frank, R.M. 1990 Abies balsamea (L.) Mill. Balsam fir. Silvics of North America, Vol. 1. Conifers(eds R.M.Burns & B.H.Honkala), pp. 2635. Agricultural Handbook 654. USDA Forest Service, Washington, DC.
  • Gabriel, W.J. & Garrett, P.W. 1984 Pollen vectors in sugar maple (Acer saccharum). Canadian Journal of Botany, 62, 28892890.
  • Gardner, G. 1977 The reproductive capacity of Fraxinus excelsior on the Derbyshire limestone. Journal of Ecology, 65, 107118.
  • Garrett, P.W. & Graber, R.E. 1995 Sugar Maple Seed Production in Northern New Hampshire. Research Paper NE-697. USDA Forest Service, Radnor, PA.
  • Ghent, A.W. 1958 Studies of regeneration in forest stands devastated by the spruce budworm. II. Age, height growth, and related studies of balsam fir seedlings. Forest Science, 4, 135146.
  • Godman, R.M., Yawney, H.W., Tubbs, C.H. 1990 Acer saccharum Marsh. Sugar maple. Silvics of North America, Vol. 2. Hardwoods(eds R.M.Burns & B.H.Honkala), pp. 7891. Agricultural Handbook 654. USDA Forest Service, Washington, DC.
  • Goodrum, P.D., Reid, V.H., Boyd, C.E. 1971 Acorn yields, characteristics, and management criteria of oaks for wildlife. Journal of Wildlife Management, 35, 520532.
  • Grandtner, M.M. 1966La Végétation Forestière Du Québec Méridional. Les Presses de l’Université Laval, Sainte-Foy, Québec, Canada.
  • Grisez. T.J. 1975 Flowering and Seed Production in Seven Hardwood Species. Research Paper NE-315. USDA Forest Service, Upper Darby, PA.
  • Herrera, C.M., Jordano, P., López-Soria, L., Amat, J.A. 1994 Recruitment of a mast-fruiting, bird-dispersed tree: bridging frugivore activity and seedling establishment. Ecological Monographs, 64, 315344.
  • Hilton, G.M. & Packham, J.R. 1997 A sixteen-year record of regional and temporal variation in the fruiting of beech (Fagus sylvatica L.) in England (1980–95). Forestry, 70, 716.
  • Houle, G. 1995 Seed dispersal and seedling recruitment: the missing link (s). Ecoscience, 2, 238244.
  • Houle, G. 1998 Seed dispersal and seedling recruitment of Betula alleghaniensis: spatial inconsistency in time. Ecology, 79, 807818.
  • Houle, G. & Payette, S. 1990 Seed dynamics of Betula alleghaniensis in a deciduous forest of north-eastern North America. Journal of Ecology, 78, 677690.
  • Houle, G. & Payette, S. 1991 Seed dynamics of Abies balsamea and Acer saccharum in a deciduous forest of northeastern North America. American Journal of Botany, 78, 895905.
  • Hyde, H.A. 1951 Pollen output and seed production in forest trees. Quarterly Journal of Forestry, 45, 172175.
  • Janzen, D.H. 1971 Seed predation by animals. Annual Review of Ecology and Systematics, 2, 465492.
  • Kelly, D. 1994 The evolutionary ecology of mast seeding. Trends in Ecology and Evolution, 9, 465470.
  • Lalonde, R.G. & Roitberg, B.D. 1992 On the evolution of masting behavior in trees: predation or weather? American Naturalist, 139, 12931304.
  • Lindquist, B. 1931 Den Skandinaviska bogskogens biologi. Svenska SkogsvaÅrdsföreningens Tidskrift, 29, 179532.
  • Loehle, C. 1988 Tree life history strategies: the role of defenses. Canadian Journal of Forest Research, 18, 209222.
  • Matthews, J.D. 1963 Factors affecting the production of seed by forest trees. Forestry Abstracts, 24, i–xiii.
  • Mencuccini, M., Piussi, P., Zanzi Sulli, A. 1995 Thirty years of seed production in a subalpine Norway spruce forest: patterns of temporal and spatial variation. Forest Ecology and Management, 76, 109125.
  • Morris, R.F. 1951 The effects of flowering on the foliage production and growth of balsam fir. Forestry Chronicle, 27, 4057.
  • Nilsson, S.G. & Wästljung, U. 1987 Seed predation and cross-pollination in mast-seeding beech (Fagus sylvatica) patches. Ecology, 68, 260265.
  • Norton, D.A. & Kelly, D. 1988 Mast seeding over 33 years by Dacrydium cupressinum Lamb. (rimu) (Podocarpaceae) in New Zealand: the importance of the economies of scale. Functional Ecology, 2, 399408.
  • Owens, J.N. 1995 Constraints to seed production: temperate and tropical forest trees. Tree Physiology, 15, 477484.
  • Owens, J.N. & Blake, M.D. 1985Forest Tree Seed Production. Information Report PI-X-53. Canadian Forestry Service, Chalk River, Ontario, Canada.
  • Owens, J.N., Colangeli, A.M., Morris, S.J. 1991 Factors affecting seed set in Douglas-fir (Pseudotsuga menziesii). Canadian Journal of Botany, 69, 229238.
  • Payette, S., Filion, L., Delwaide, A. 1990 Disturbance regime of a cold temperate forest as deduced from tree-ring patterns: the Tantaré Ecological Reserve, Quebec. Canadian Journal of Forest Research, 20, 12281241.
  • Rowe, J.S. 1972Les Régions Forestières Du Canada. Publication 1300f. Ministère de l’Environnement, Service canadien des forêts, Ottawa, Ontario, Canada.
  • Schopmeyer, C.S. 1974 Seeds of Woody Plants in the United States. Handbook 450. USDA Forest Service, Washington, DC.
  • Silvertown, J.W. 1980 The evolutionary ecology of mast seeding in trees. Biological Journal of the Linnean Society, 14, 235250.
  • Smith, C.C., Hamrick, J.L., Kramer, C.L. 1988 The effects of stand density on frequency of filled seeds and fecundity in lodgepole pine (Pinus contorta Dougl.). Canadian Journal of Forest Research, 18, 453460.
  • Smith, C.C., Hamrick, J.L., Kramer, C.L. 1990 The advantage of mast years for wind pollination. American Naturalist, 136, 154166.
  • Sokal, R.R. & Rohlf, F.J. 1995Biometry. 3rd edn. Freeman, New York, NY.
  • Sork, V.L. 1993 Evolutionary ecology of mast-seeding in temperate and tropical oaks (Quercus spp.). Vegetatio, 107/108, 133147.
  • Sork, V.L. & Bramble, J. 1993 Prediction of acorn crops in three species of North American oaks: Quercus alba. Q. rubra and Q. velutina. Annales Des Sciences Forestières, 50, 128s136s.[Q1]
  • Sork, V.L., Bramble, J., Sexton, O. 1993 Ecology of mast-fruiting in three species of North American deciduous oaks. Ecology, 74, 528541.
  • Stephenson, A.G. 1981 Flower and fruit abortion: proximate causes and ultimate functions. Annual Review of Ecology and Systematics, 12, 253279.
  • Tanouchi, H., Sato, T., Takeshita, K. 1994 Comparative studies on acorn and seedling dynamics of four Quercus species in an evergreen broad-leaved forest. Journal of Plant Research, 107, 153159.
  • Tapper, P.G. 1996 Long-term patterns of mast fruiting in Fraxinus excelsior. Ecology, 77, 25672572.
  • Tubbs, C.H. 1965Influence of Temperature and Early Spring Conditions on Sugar Maple and Yellow Birch Germination in Upper Michigan. Research Note LS-72. USDA Forest Service, St. Paul, MN.
  • Van Vredenburch, C.L.H. & La Bastide, J.G.A. 1969 The influence of meteorological factors on the cone crop of Douglas-fir in the Netherlands. Silvae Genetica, 18, 182186.
  • Waller, D.M. 1979 Models of mast fruiting in trees. Journal of Theoretical Biology, 80, 223232.

Received 25 March 1998; revision accepted 29 October 1998