Reproductive collapse in European beech results from declining pollination efficiency in large trees

Climate warming increases tree mortality which will require sufficient reproduction to ensure population viability. However, the response of tree reproduction to climate change remains poorly understood. Warming can reduce synchrony and interannual variability of seed production (“masting breakdown”) which can increase seed predation and decrease pollination efficiency in trees. Here, using 40 years of observations of individual seed production in European beech (Fagus sylvatica), we showed that masting breakdown results in declining viable seed production over time, in contrast to the positive trend apparent in raw seed count data. Furthermore, tree size modulates the consequences of masting breakdown on viable seed production. While seed predation increased over time mainly in small trees, pollination efficiency disproportionately decreased in larger individuals. Consequently, fecundity declined over time across all size classes, but the overall effect was greatest in large trees. Our study showed that a fundamental biological relationship—correlation between tree size and viable seed production—has been reversed as the climate has warmed. That reversal has diverse consequences for forest dynamics; including for stand- and biogeographical-level dynamics of forest regeneration. The tree size effects suggest management options to increase forest resilience under changing climates.     

Investigating the relationship between climate,stand age,and temporal trends in masting behavior of European forest trees

Masting—temporally variable seed production with high spatial synchrony—is a pervasive strategy in wind‐pollinated trees that is hypothesized to be vulnerable to climate change due to its correlation with variability in abiotic conditions. Recent work suggests that aging may also have strong effects on seed production patterns of trees, but this potential confounding factor has not been considered in previous times series analysis of climate change effects. Using a 54 year dataset for seven dominant species in 17 forests across Poland, we used the proportion of seed‐producing trees (PST) to contrast the predictions of the climate change and aging hypotheses in Abies alba, Fagus sylvatica, Larix decidua, Picea abies, Pinus sylvestris, Quercus petraea, and Quercus robur. Our results show that in all species, PST increased over time and that this change correlated most strongly with stand age, while the standardized precipitation–evapotranspiration index, a measure of drought, contributed to temporal trends in PST of F. sylvatica and Q. robur. Temporal variability of PST also increased over time in all species except P. sylvestris, while trends in temporal autocorrelation and among‐stand synchrony reflect species‐specific masting strategies. Our results suggest a pivotal role of plant ontogeny in driving not only the extent but also variability and synchrony of reproduction in temperate forest trees. In a time of increasing forest regrowth in Europe, we therefore call for increased attention to demographic effects such as aging on plant reproductive behavior, particularly in studies examining global change effects using long‐term time series data.     

Evolutionary ecology of mast-seeding in temperate and tropical oaks (Quercus spp.)

Mast-seeding is the synchronous production of large seed crops within a population or community of species every two or more years. This paper addresses three non-mutually exclusive hypotheses explaining the evolution of mast-seeding in temperate tree species, especially the genus Quercus: (1) mast-seeding is a consequence of mast-flowering which evolves to increased pollination efficiency in mast-flowering years; (2) mast-seeding has evolved as an anti-predator adaptation by which large seed crops during mast years satiate the seed predators and allow survival of some of the seeds; (3) selection on seed size by habitat can indirectly affect the evolution of masting if trees with large seeds require more time to accumulate reserves to mature those seeds. I find support for the pollination hypothesis in several wind-pollinated temperate tree species but not oaks. However, oaks show evidence favoring the predation and seed size hypotheses. I then develop a model to illustrate the relationships among the three hypotheses in their effects on the evolution of masting. Finally, using data from herbaria and Floras, the influence of selection via flowering, fruiting, and seed size in the evolution of masting in tropical oaks is discussed. I conclude that the need for a supra-annual cue to synchronize flowering and fruiting as well as the larger seed size found in many tropical oak species should contribute to the evolution of masting to a greater extent than seen among temperate oaks.     

Aridity drives spatiotemporal patterns of masting across the latitudinal range of a dryland conifer

Masting, or the synchronous and irregular production of seed crops, is controlled by environmental conditions and resource budgets. Increasing temperatures and shifting precipitation regimes may alter the frequency and magnitude of masting, especially in species that experience chronic resource stress. Yet the effects of a changing climate on seed production are unlikely to be uniform across populations, particularly those that span broad abiotic gradients. In this study, we assessed the spatiotemporal patterns of masting across the latitudinal distribution of a widely distributed dryland conifer species, piñon pine Pinus edulis. We quantified seed cone production from 2004 to 2017 using cone abscission scars in 187 trees from 28 sites along an 1100 km latitudinal gradient to investigate the spatiotemporal drivers of seed cone production and synchrony across populations. Populations from chronically hot and dry areas (greater climatic water deficits and less monsoonal precipitation) tended to have greater interannual variability in seed cone production and smaller crop sizes. Mast years generally followed years with low vapor pressure deficits and high precipitation during key periods of the reproductive process, but the strength of these relationships varied across the region. Populations that received greater monsoonal precipitation were less sensitive to late summer vapor pressure deficits during seed cone initiation yet more sensitive to spring vapor pressure deficits during pollination. Spatially correlated patterns of vapor pressure deficit better predicted synchrony in seed cone production than geographic distance, and these patterns were conserved at distances up to 500 km. These results demonstrate that aridity drives spatiotemporal variability in seed cone production. As a result, projected increases in aridity are likely to decrease the frequency and magnitude of masting in these dry forests and woodlands. Declines in seed production may compound climatic limitations to recruitment and impede tree regeneration, with cascading effects for numerous wildlife species.     

Mechanisms driving interspecific variation in regional synchrony of trees reproduction

Seed production in many plants is characterized by large interannual variation, which is synchronized at subcontinental scales in some species but local in others. The reproductive synchrony affects animal migrations, trophic responses to resource pulses and the planning of management and conservation. Spatial synchrony of reproduction is typically attributed to the Moran effect, but this alone is unable to explain interspecific differences in synchrony. We show that interspecific differences in the conservation of seed production-weather relationships combine with the Moran effect to explain variation in reproductive synchrony. Conservative timing of weather cues that trigger masting allows populations to be synchronized at distances >1000 km. Conversely, if populations respond to variable weather signals, synchrony cannot be achieved. Our study shows that species vary in the extent to which their weather cueing is spatiotemporally conserved, with important consequences, including an interspecific variation of masting vulnerability to climate change.     

Of mast and mean: differential‐temperature cue makes mast seeding insensitive to climate change

Mast‐seeding plants often produce high seed crops the year after a warm spring or summer, but the warm‐temperature model has inconsistent predictive ability. Here, we show for 26 long‐term data sets from five plant families that the temperature difference between the two previous summers (ΔT) better predicts seed crops. This discovery explains how masting species tailor their flowering patterns to sites across altitudinal temperature gradients; predicts that masting will be unaffected by increasing mean temperatures under climate change; improves prediction of impacts on seed consumers; demonstrates that strongly masting species are hypersensitive to climate; explains the rarity of consecutive high‐seed years without invoking resource constraints; and generates hypotheses about physiological mechanisms in plants and insect seed predators. For plants, ΔT has many attributes of an ideal cue. This temperature‐difference model clarifies our understanding of mast seeding under environmental change, and could also be applied to other cues, such as rainfall.     

The evolutionary ecology of mast seeding

The past seven years have seen a revolution in understanding the causes of mast seeding In perennial plants. Before 1987, the two main theories were resource matching (i.e. plants vary their reproductive output to match variable resources) and predator satiation (i.e. losses to predators are reduced by varying the seed crop). Today, resource matching is restricted to a proximate role, and predator satiation is only one of many theories for the ultimate advantage of masting. Wind pollination, prediction of favourable years for seedling establishment, animal pollination, animal dispersal of fruits, high accessory costs of reproduction and large seed size have all been advanced as possible causes of masting. Of these, wind pollination, predator satiation and environmental prediction are important in a number of species, but the other theories have less support. In future, Important advances seem likely from quantifying synchrony within a population, and examining species with very constant reproduction between years.     

Insect pollinators improve seed production in globe artichoke (Cynara cardunculus var. scolymus)

The role of many insect species in crop pollination has been widely studied. The use of entomophilous pollination, commonly adopted for other crops, may be of key importance in order to improve seed yields in seed-propagated globe artichoke (Cynara cardunculus var. scolymus) cultivars. In this regard, in a 2-year field experiment, the role of two honeybees (Apis mellifera ligustica and A. mellifera siciliana) and one bumblebee (Bombus terrestris) was evaluated on the seed production of two globe artichoke cultivars in caged-protected environments. Overall, the number and weight of seeds plant⁻¹ and head⁻¹, 1,000 seed weight and fruit setting were higher in caged plants with imposed pollination than open field plants. The pollination efficiency was both insect and cultivar dependent. Both honeybee species performed better on the Mediterranean cultivar ‘Violetto di Sicilia’, while the bumblebee performed better on the Brazilian cultivar ‘NP4’. These results could be very useful to modernise the agronomic management of globe artichoke and reduce the costs of cultivation. In addition, such knowledge can be used to improve the seed production in globe artichoke seed-propagated cultivars and cardoon. This will benefit the bioenergy, nutraceutical, cosmetic and ornamental applications.     

Seed survival on experimental dishes in a central European old‐growth mixed‐species forest – effects of predator guilds,tree masting and small mammal population dynamics

Predation of tree seeds can be a major factor structuring plant communities. We present a three year study on tree seed survival on experimental dishes in an old‐growth forest in central Europe in Austria. We addressed species specific, spatial and temporal aspects of post‐dispersal seed predation. Seeds of Norway spruce Picea abies, European beech Fagus sylvatica, and silver fir Abies alba were exposed on dishes in different types of exclosures which allowed access only to specific guilds of seed predators. Removal experiments were carried out in two old‐growth forests and a managed forest (macro‐sites), including micro‐sites with and without cover of ground vegetation. We conducted the experiment in three consecutive years with a mast year of beech and spruce before the first year of the study. The seed removal experiments were combined with live trapping of small mammals being potential seed predators. Our experiments showed a distinctly different impact of different predator guilds on seed survival on the dishes with highest removal rates of seeds from dishes accessible for small mammals. We observed differing preferences of small mammals for the different tree species. Seed survival in different macro‐ and micro‐habitats were highly variable with lower seed survival in old growth forests. In contrast to our assumption, and in contrast to the satiation hypothesis which assumes higher seed survival in and directly after mast years, seed survival was lower in the year following the mast year of beech when a population peak of small mammals occurred and higher in intermast periods when subsequently small mammal population crashed. This suggests a higher importance of sporadic masting shortly after mast years in intermast periods for establishment of forest trees provided that pollination efficiency is high enough in such years. Combined with the high seed mortality observed after the mast year, this corroborates the important role of seed predation for forest dynamics. An altered synchrony or asynchrony of masting of different tree species and changed masting frequencies through climate change may thus lead to strong and non‐linear effects on forest dynamics.     

Climate-driven synchrony in seed production of masting deciduous and conifer tree species

Aims Understanding fluctuations in plant reproductive investment can constitute a key challenge in ecology, conservation and management. Masting events of trees (i.e. the intermittent and synchronous production of abundant seeding material) is an extreme example of such fluctuations. Our objective was to establish the degree of spatial and temporal synchrony in common four masting tree species in boreal Finland and account for potential causal drivers of these patterns.Methods We investigated the spatial intraspecific and temporal interspecific fluctuations in annual seed production of four tree species in Finland, silver birch Betula pendula Roth, downy birch Betula pubescens Ehrh., Norway spruce Picea abies (L.) H.Karst. and rowanberry Sorbus aucuparia L. We also tested to see whether variations in seed production were linked to annual weather conditions. Seeding abundance data were derived from tens of stands per species across large spatial scales within Finland during 1979 to 2014 (for rowanberries only 1986 to 2014).Important findings All species showed spatial synchrony in seed production at scales up to 1000 km. Annual estimates of seed production were strongly correlated between species. Spring and summer temperatures explained most variation in crop sizes of tree species with 0-to 2-year time lags, whereas rainfall had relatively little influence. Warm weather during flowering (May temperature) in the flowering year (Year t) and 2 years before (t ?2) were correlated with seed production. However, high May temperatures during the previous year (t^-1) adversely affected seed production. Summer temperatures in Year t^-1 was positively correlated with seed production, likely because this parameter enhances the development of flower primordials, but the effect was negative with a time lag of 2 years. The negative feedback in temperature coefficients is also likely due to patterns of resource allocation, as abundant flowering and seed production in these species is thought to reduce the subsequent initiation of potential new flower buds. Since the most important weather variables also showed spatial correlation up to 1000 km, weather parameters likely explain much of the spatial and temporal synchrony in seed production of these four studied tree species.     

Seed dispersal and seedling recruitment of trees at different successional stages in a temperate forest in northeastern China

Aims Spatial distribution of adult trees in a forest community is determined by patterns of both seed dispersal and seedling recruitment. The objectives of our study were to understand the processes of seed dispersal and seedling recruitment of dominant tree species in a temperate forest of northeastern China and to identify the factors constraining seed dispersal and seedling establishment at different stages of forest succession.Methods During three summer and autumn sessions between 2006 and 2008, altogether 113080 seeds from 22 different tree species were collected in three large field plots representing different forest types in the Changbai Mountain region of northeastern China. The spatial distribution of seed abundance was analyzed using a Syrjala test. Regeneration success of nine major tree species was assessed using variables defining 'limitations' in 'seeds' and 'seedling establishment'.Important findings We found that seed production fluctuated between years and varied greatly with forest types. Four tree species, Acer spp., Fraxinus mandshurica, Tilia amurensis and Betula spp., had the greatest seed production and the widest range of seed dispersal, whereas Quercus mongolica showed the most sustained seed production pattern. The spatial patterns of seed abundance differed significantly among forest types and years. The tree species investigated in this study differed in the degree of seed limitation, as well as in limitation of seedling establishment. There were both negative and positive correlations between seed density and seedling density, depending on site and parental tree density. Seeds of 16 tree species were found in the Populus davidiana–Betula platyphylla forest (PBF) plot, 11 in the conifer and broad-leaved mixed forest (CBF) plot but only 8 in the broad-leaved-Korean pine mixed forest (BKF) plot. The number of seed-contributing species was not only greater in the secondary forests (CBF and PBF plots) than in the primary forest (BKF plot) but was also more variable during the 3 years of assessment. Results from the correlations between seed density and seedling occurrence and that between parental tree density or seed weight and dispersal limitation confirm our intuitive expectations, i.e. heavy seeds had greater dispersal limitation but higher establishment success than light seeds.     

Breeding system and pollen limitation in the masting tree Sorbus aucuparia L. (Rosaceae) in the NW Iberian Peninsula

Mast seeding or masting is the supra-annual periodic production of a large number of seeds by long-lived plants. It has been suggested that this may be a strategy to increase pollination efficiency. Sorbus aucuparia is a masting tree typically showing rather low fruit set, though with some variation among years and populations, together with marked among-year variation in flower and fruit production. Here we report a study of the reproductive biology and insect-visitor spectrum of S. aucuparia in the NW Iberian Peninsula. Results obtained over a 4-year period indicate marked self-incompatibility, so that fruit set is strongly dependent on pollinator service. Nevertheless, fruit and seed set were not limited by pollen supply in any of the years of study, since fruit and seed set after manual cross-pollination were no higher than after natural pollination. Inflorescences were visited by diverse insect species. There was no significant correlation between fruit set and insect visit frequency. Taken together, these findings indicate that the rather low fruit and seed sets observed in this species, and the spatiotemporal variation in these parameters, must be attributed to other factors, such as abiotic resource availability. We conclude that masting in S. aucuparia is probably not a strategy for increasing pollination efficiency.     

Interannual variations in the seed production of Pinus Banksiana at the limit of the species distribution in northern Québec,Canada

Interannual variations in cone and seed production of Pinus banksiana Lamb, were studied at the species northern limit of distribution in Québec (Canada). Cone number per cone-bearing branch, potential number of seeds per cone, number of formed, filled, and viable seeds per cone, and seed viability, germination rate, and mass were determined for two populations of the species, over a 9-year series. There were significant differences among years, but not between populations, in all the variables considered. The populations were well synchronized with each other, suggesting that climatic influence on the variables considered might be significant. Apparent periodicity in reproductive output also suggests the existence of some internal cycle, possibly in relation to tree reserves. Annual viable seed production is the result of a combination of events in the reproductive cycle of an individual (i.e., cone initiation, pollination, fertilization, and embryo maturation), each one specifically affected by climate. There are no apparent trade-offs between seed mass and number of filled seeds per cone over time; moreover, there seems to be a positive relationship between seed mass and number of viable seeds per cone. Climate conditions during fertilization and embryo maturation (both of which occur during the same season) appear to significantly influence the species reproductive output. We present regression models based on meteorological variables to estimate cone and viable seed production, and seed mass.     

川西亚高山暗针叶林不同恢复阶段红桦、 岷江冷杉土壤种子损耗特征

在川西亚高山米亚罗林区海拔3 100—3 600 m阴坡、半阴坡,以立地条件基本一致的箭竹和藓类林型不同恢复阶段(20—40年生的箭竹-阔叶林、藓类-阔叶林,50年生的箭竹-针阔混交林、藓类-针阔混交林、160—200年生的箭竹-暗针叶老龄林、藓类暗针叶老龄林)的群落为研究对象,于种子成熟散落前(8月)采集土壤样品,应用网筛分选法结合体视显微镜挑选种子,实验室发芽试验法和四唑染色法对种子生活力进行测定,分析了土壤内先锋树种红桦(Betula albo-sinensis)和顶极树种岷江冷杉(Abiesfaxoniana)的残余种子总数、组分及其分布格局;采用样方法调查了红桦和岷江冷杉的1年生幼苗密度。结果表明:1)随着森林的恢复,红桦的残余种子总数、外形完整种子数、发育不全种子数、空粒种子数和腐烂种子数呈减少的趋势,而岷江冷杉则相反。箭竹林型不同恢复阶段红桦的残余种子总数、外形完整种子数、发育不全种子数、空粒种子数和腐烂种子数总体上大于藓类林型相应恢复阶段。岷江冷杉的残余种子总数、外形完整种子数、发育不全种子数、空粒种子数、腐烂种子数的最大值均出现在藓类-暗针叶老林龄;2)在阔叶林和针阔混交林阶段,红桦和岷江冷杉的种子组分所占比例最高的分别为腐烂种子和发育不全种子,在暗针叶老龄林阶段,红桦的腐烂种子和空粒种子的比例位居前列,而岷江冷杉的外形完整种子比例最大;3)随着土层深度的增加,红桦和岷江冷杉的外形完整种子数、发育不全种子数、空粒种子数和腐烂种子数均呈减少的趋势。红桦和岷江冷杉不同组分的种子在枯枝落叶层所占地比例在72.85%—94.28%;4)红桦的1年生幼苗密度随着森林的恢复逐渐减小,而岷江冷杉的1年生幼苗密度随着森林的恢复逐渐增大。在8月份,土壤中已经不存在红桦和岷江冷杉有生活力的种子,两种植物的种子只能形成短暂土壤种子库。     

Characteristic Change of Several Forest Landscapes Between 1896 and 1986 in Heilongjiang Province

The 16 tree species on Northeast China Transect (NECT) were analyzed from the change of geographical distribution, frequency and dominance pattern and the spatial correlation at landscape scale in 1986 and 1994. Pinus koraiensis Sieb. et Zucc. and Fraxinus rhynchophylla Hemsl. had spread rapidly towards west and east, respectively. The frontier form of species had close relation with its movement. The patch size of Pinus koraiensis, Populus davidiana Dode., Phellodendron amurense Rupr., Juglans mandshurica Maxim., Fraxinus mandshurica Rupr., Betula dahurica Pall., Picea koraiensis Nakai, Abies nephrolepis Maxim. and Larix olgeusis var. koreana Nakai decreased, however, Quercus mongolica Fisch., Betula costata Trautv., Acer mono Maxim., Tilia spp., Ulmus spp., Betula platyphylla Suk. and Fraxinus rhynchophylla increased. The frequency pattern of Populus davidiana, Betula platyphylla, Fraxinus rhynchophylla and Betula dahurica changed significantly. The dominance pattern of Populus davidiana, Tilia spp., Juglans mandshurica, Betula platyphylla, Betula dahurica and Abies nephrolepis changed significantly. The spatial correlation between Quercus mongolica and Betula dahurica, Betula costata and Picea spp., Betula costata and Abies nephrolepis, Picea spp. and Abies nephrolepis declined, however, the spatial correlation between Larix spp. and Betula platyphylla, Acer mono and Ulmus spp. increased.     

The evolutionary ecology of mast seeding in trees

The hypothesis that masting by trees is a defensive strategy which satiates seed predators in mast years and starves them in the intervening periods is tested in 59 sets of data on the seed production and pre-dispersal seed-predation of 25 tree species. Twenty-lour of the 59 data-sets support the hypothesis and show a statistically significant positive relationship between the proportion of seeds surviving the pre-dispersal stage and the log₁₀ of the crop size for the same year. Evidence that pre-dispersal seed survival increases with the length of the mast interval is poor.
A positive relationship between the strength of the masting habit and the maxintum observed pre-dispersal seed mortality in a sample of 15 tree species suggests that the masting habit is best developed in predator-prone species. A survey of seed crop frequencies in the woody plant flora of Nortli America shows masting species to be under-represented amongst shrubs and amongst trees which disperse their seeds in fleshy dispersal units. The selection pressures and evolutionary constraints which operate on the evolution of masting plants and their seed predators are discussed.     

中国东北样带树种（属）的空间特性及变化

对中国东北样带上１６个树种（属）在１９８６年与１９９４年景观水平的地理分布、出现频率、优势度及空间相关性等空间特性的分析得出,红松（Ｐｉｎｕｓ ｋｏｒａｉｅｎｓｉｓ Ｓｌｅｂ．ｅｔ Ｚｕｃｃ．）与花曲柳（Ｆｒａｘｉｎｕｓ ｒｈｙｎｃｈｏｐｈｙｌｌａ Ｈｅｍｓｌ．）分别是向西和向东扩展最快;种群的分布边界形态与该边界的移动有密切关系;红松、山杨（Ｐｏｐｕｌｕｓ ｄａｖｉｄｉａｎａ Ｄｏｄｅ．）、黄檗     

中国东北样带树种(属)的空间特性及变化

The 16 tree species on Northeast China Transect (NECT) were analyzed from the change of geographical distribution, frequency and dominance pattern and the spatial correlation at landscape scale in 1986 and 1994. Pinus koraiensis Sieb. et Zucc. and Fraxinus rhynchophylla Hemsl. had spread rapidly towards west and east, respectively. The frontier form of species had close relation with its movement. The patch size of Pinus koraiensis, Populus davidiana Dode., Phellodendron amurense Rupr., Juglans mandshurica Maxim., Fraxinus mandshurica Rupr., Betula dahurica Pall., Picea koraiensis Nakai, Abies nephrolepis Maxim. and Larix olgeusis var. koreana Nakai decreased, however, Quercus mongolica Fisch., Betula costata Trautv., Acer mono Maxim., Tilia spp., Ulmus spp., Betula platyphylla Suk. and Fraxinus rhynchophylla increased. The frequency pattern of Populus davidiana, Betula platyphylla, Fraxinus rhynchophylla and Betula dahurica changed significantly. The dominance pattern of Populus davidiana, Tilia spp., Juglans mandshurica, Betula platyphylla, Betula dahurica and Abies nephrolepis changed significantly. The spatial correlation between Quercus mongolica and Betula dahurica, Betula costata and Picea spp., Betula costata and Abies nephrolepis, Picea spp. and Abies nephrolepis declined, however, the spatial correlation between Larix spp. and Betula platyphylla, Acer mono and Ulmus spp. increased.     

SEED DYNAMICS OF ABIES BALSAMEA AND ACER SACCHARUM IN A DECIDUOUS FOREST OF NORTHEASTERN NORTH AMERICA

We studied the seed dynamics of Abies balsamea and Acer saccharum in a sugar maple-yellow birch forest of Québec, Canada. Seed rain was censused every week from spring to autumn in 1988 and 1989. The soil seed bank was sampled four times during the 1988 growing season. Abies seed rain varied significantly between 1988 and 1989. A total of 92.5 ± 7.0 seeds nr^-2 (mean ± 1 SE) were produced in 1988; 1989 seed production was null. Seed viability in 1988 averaged 31.5%. Dispersal during the winter period accounted for ca. 22% of the annual seed crop. The spatial dispersion pattern of the seed rain was contagious for the autumn period, but was not significantly different from random for the winter period. There was only a weak relationship in the spatial distribution of the seed rain between the autumn and winter periods. Abies did not maintain a persistent seed bank on the site; viable seeds were present on the soil only after seed dispersal had started. Postdispersal seed mortality was relatively high, ca. 70%. Acer seed rain started soon after the flowering period, but consisted at that time only of aborted, underdeveloped samaras. Viable seeds were disseminated from September through early winter. Dispersal during the autumn accounted for ca. 98% of the annual seed crop. There were significant differences between seed rain abundance of 1988 and that of 1989 (118.1 ± 9.5 samaras m^-2 and 158.9 ± 16.3 samaras m^-2 in 1988 and in 1989, respectively). Seed viability also varied significantly between the 2 years, i.e., 19% in 1988 and 5% in 1989. For both 1988 and 1989, samaras were contagiously dispersed over the site. There was a significant positive relationship between the spatial distribution of the seed rain in 1988 and that in 1989. Seed rain abundance was high mainly in the proximity of mature Acer trees. As for Abies, Acer did not maintain a persistent seed bank in the soil; viable seeds were present only in the autumn seed bank sampling, after seed fall had started. Postdispersal seed mortality was relatively low, i.e., 20%. Abies and Acer are quite similar in their regenerative traits, and these contrast sharply with those of Betula alleghaniensis, a regular member of this forest community. Differences in regenerative traits may contribute to the coexistence of these tree species considering the gap regime of the system studied.     

Resource limitation and pollen source (self and outcross) affecting seed production in two louseworts, Pedicularis siphonantha and P. longiflora (Orobanchaceae)

Two animal-pollinated hermaphrodite plants, Pedicularis siphonantha and P. longiflora , have been used to investigate factors limiting seed production in natural populations. To evaluate the potential seed abortion due to resources limitation, seed development has been observed and seed count conducted twice. Seed production per capsule has been compared when flowers have been removed and in a control group. Open pollination has been investigated and pollen supplementation undertaken to estimate the possibility of pollen limitation. Results show that seed abortion is frequent. Stigmatic pollen load is significantly higher than ovule number per ovary under open pollination for both species. Additional self and outcross pollen did not affect seed production. Flower removal significantly increases seed production per capsule, which indicates that seed production of the studied species is limited by available resources. To detect differences in seed production between flowers pollinated by self and outcross pollen, hand pollination of bagged flowers has also been conducted in natural populations of the two Pedicularis species. Compared with open pollination, hand-pollinating self-pollen decreases, while outcross pollen increases seed production per capsule. Such results suggest that inbreeding depression in the two self-compatible species may also result in partial seed abortion under open pollination if mixed pollen is deposited on the stigma. Our results also suggest that pollen interference plays an important role in low female fertility in the two Pedicularis species.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 83–89.