Comparison of three seed trap types in a chalk grassland: toward a standardised protocol

In a chalk grassland in north-western France, vegetation and seed rain were studied along two transects. We compared the efficiency of three types of seed traps (funnel traps, sticky traps, pots exposed in the field) to estimate the annual seed rain and to reveal various processes involved in plant community regeneration. Data were analysed to compare seed density, species richness and composition across seed traps and vegetation. Geostatistical analyses (semivariograms. were used to detect possible autocorrelation and to examine patterns of spatial variation in seed rain and vegetation. The results show that (1) funnel traps are most efficient (56 species, 8079 seeds.m^–2). (2) Each type of seed traps brings different information about the processes involved in seed dispersal and seedling establishment. Sticky traps help to understand import and export of seeds in a community through anemochory. Funnel traps may provide a measure of the auto-regeneration capacity of the vegetation through its local seed production. Pot traps integrate various processes involved between seed dispersal and seedling emergence. (3.) The exposition to environmental conditions generates marked spatial patterns in species richness measured in pots and in vegetation, selecting species able to survive. Pot traps indicate that numerous species producing seeds in standing vegetation are unable to establish in the field through seedling recruitment. Our study emphasizes the need of using different types of seed traps and spatial sampling configurations to assess the regenerative potential of standing vegetation and the various mechanisms involved in seed dispersal. A standardised protocol for seed rain sampling was finally developed.     

Seed rain into upland plant communities in Hong Kong, China

Hong Kong is an extreme example of tropical landscape degradation, with no substantial remnants of the original forest cover and a highly impoverished disperser fauna. Seed availability is a potential limiting factor in vegetation recovery in such landscapes. To assess the quantity and quality of the seed rain of woody taxa, seed traps were placed in the major upland vegetation types: fire-maintained grassland, shrubland, and secondary forest. Within the grassland site, traps were placed under isolated trees, isolated male and female shrubs of Eurya chinensis, and in the open. Seeds were collected every 2 weeks for 2 years. The seed rain was highest under female shrubs in grassland (6455 seeds m⁻² year⁻¹), where it was almost entirely confined to their fruiting period. Next highest were isolated trees (890 seeds), followed by male isolated shrubs (611 seeds), shrubland (558 seeds), forest (129 seeds) and open grassland (47 seeds). The number of seed taxa was highest in shrubland (59), followed by isolated trees (42), forest (42), female isolated shrubs (28), male isolated shrubs (15), and open grassland (9). The seed rain differed in species composition between the forest, shrubland, and grassland sites, while the differences within the grassland site were largely in terms of quantity. Birds (particularly bulbuls, Pycnonotus spp.) are known or inferred to be the major dispersal agents for 85% of the seed taxa trapped, 99% of the total number of seeds trapped, and 99.8% of the seeds trapped in the grassland site. Few taxa and of the total seeds were dispersed by wind and no seed taxa were definitely dispersed by fruit bats. The results suggest that even in the most degraded landscape the seed rain is adequate for the development of woody vegetation cover, but that human intervention will be needed for the restoration of plant diversity.     

Soil seed bank composition and diversity in a managed temperate deciduous forest

Little is known about the influence of forest management on the interaction between seed bank and aboveground vegetation. We surveyed seed banks and vegetation in 10 forest stands under similar abiotic conditions but submitted either to a coppice-with-standards treatment (n=5) or to a selective-cutting system (n=5). We analyzed species composition and diversity, community ecological profile, and distribution of taxa among different life forms, strategy, morphology and functional type categories. A total of 2085 seedlings (8296 seedsm^–2) germinated-corresponding to 28 species, among which Juncus effusus was the most abundant. Fifty-seven percent of the species were also recorded in the aboveground vegetation, the dominant species being Rubus fruticosus agg., but only 28% of the aboveground species were present in the seed bank. Our results suggest that (1) vernal geophytes and shade-tolerant perennials, which group most true forest species, are not incorporated in the seed bank, (2) parent plants of most seeds were present either in the stand in an earlier dynamic stage or apart from the stand and long-distance dispersed, (3) as expected, early-successional species are well represented in the seed bank, (4) forestry vehicles seem to be a major means of dispersion for stress-tolerant species normally found in forest lanes and wheel tracks. We conclude that seed banks contain species that have a potentially negative impact on the true forest flora and, thus, forest management should minimize soil disturbance and retain remnants of old-coppice woods to conserve disturbance-sensitive true forest species.     

Seed bank versus seed rain in the regeneration of a tropical pioneer tree

Summary We used the tropical pioneer tree, Cecropia obtusifolia to evaluate the relative importance of different sources of seeds in the regeneration of species that depend on ephemeral sites. We studied seed production in a population established in a 5 ha plot, and dispersal, dormancy and seed predation in two recent treefall gaps (<1 year-old), two building or successional forest patches (10–15 since disturbed), and two mature forest patches (>35 years since disturbed) for a one year period at Los Tuxtlas (Mexico). Flowers and fruits were counted at monthly intervals. Annual fecundity per tree ranged from 1.4×10⁴ to 1.4×10⁷ seeds. Seeds were continuously available on the trees and on the ground. Average annual seed rain per m² (as measured by 0.5×0.5 m seed traps) varied from 184 to 1925 among the six sites. Distance to nearest seed source and patch type explained more than 60% of the seed rain variation among sites. Soil seed density, estimated by counting seeds from ten samples (78.5 cm²×10 cm deep) collected from each site in October and January, ranged among the six sites from 269 to 4485 seeds per m² in January and from 204 to 5073 in October. Soil seed viabilities were much lower (17.1% in October and 5.1% in January) than those of rain seeds (48.26%). Annual survivorships of 2.2% were estimated for seeds artificially sown on the soil surface of a gap and a mature patch, and 3.75% in a building patch. In two other experiments seed removal rates ranged from 27% to 98% in 4 days. Removal rates were significantly higher in gap and mature patches than in building patches. Ants (Paratrechina vividula) and grasshopper nymphs (Hygronemobius. sp.) were the main predators. We draw three main conclusions from our data: (1) Pathogens and predators determine low survivorship of C. obtusifolia's seeds in the soil and a rapid turnover rate (1.07 to 1.02 years) of its seed bank; (2) a continuous and copious seed production and an abundant and extensive seed rain replenish the soil seed pool in patches with different disturbance ages at least up to 86 m from nearest source; (3) more than 90% of the seeds contributing to C. obtusifolia seedling recruitment in gaps are less than one year-old. We discuss our results in the context of previous similar studies for tropical forests.     

Ficus seed shadows in a Bornean rain forest

Due to their copious seed production and numerous dispersers, rain forest fig trees have been assumed to produce extensive and dense seed shadows. To test this idea, patterns of seed dispersal of two species of large hemiepiphytic fig tree were measured in a Bornean rain forest. The sample included four Ficus stupenda and three F. subtecta trees with crop sizes ranging from 2,000 to 40,000 figs (400,000 to 13,000,000 seeds). Seed rain out to a distance of 60 m from each study tree was quantified using arrays of seed traps deployed in the understory. These trees showed a strongly leptokurtic pattern of dispersal, as expected, but all individuals had measurable seed rain at 60 m, ranging from 0.2 to 5.0 seeds/m². A regression of In-transformed seed rain density against distance gave a significant fit to all seven trees' dispersal patterns, indicating that the data could be fitted to the negative exponential distribution most commonly fitted to seed shadows. However, for six of seven trees, an improved fit was obtained for regressions in which distance was also In-transformed. This transformation corresponds to an inverse power distribution, indicating that for vertebrate-dispersed Ficus seeds, the tail of the seed rain distribution does not drop off as rapidly as in the exponential distribution typically associated with wind dispersed seed shadows. Over 50% of the seed crop was estimated to fall below each fig tree's crown. Up to 22% of the seed crop was dispersed beyond the crown edge, but within 60 m of the tree. Estimates of the maximum numbers of seeds which could have been transported beyond 60 m were 45% for the two largest crops of figs, but were under 24% for the trees with smaller crops. Seed traps positioned where they had an upper canopy layer above them were associated with higher probabilities of being hit by seeds, suggesting that vertebrate dispersal agents are likely to perch or travel through forest layers at the same level as the fig crown and could concentrate seeds in such areas to some degree. The probability of a safe site at 60 m from the fig tree being hit by seeds is calculated to be on the order of 0.01 per fruiting episode. Fig trees do not appear to saturate safe sites with seeds despite their large seed crops. If we in addition consider the rarity of quality establishment sites and post-dispersal factors reducing successful seedling establishment, hemiepiphytic fig trees appear to face severe obstacles to seedling recruitment.     

Relationships among the seed rain,seed bank and vegetation of a Hawaiian forest

Abstract. Hawaiian ecosystems are prone to invasion by alien plant species. I compared the seed rain, seed bank, and vegetation of a native Hawaiian forest to examine the potential role that seed ecology plays in allowing alien species to invade native forest. Absolute cover of seed plants in the forest was 126 %, annual seed rain was 5 713 seeds m^-2 yr^-1, and the mean density of seedlings emerging from the seed bank averaged across four seasons was 1 020/m². The endemic tree Metrosideros polymorpha was the most abundant species in the vegetation, seed rain and winter seed bank. Overall, native seed plants comprised 95 % of the relative cover in the vegetation and 99 % of the seeds in the seed rain, but alien species comprised 67 % of the seeds in the seed bank. Alien species tended to form persistent seed banks while native species formed transient or pseudo-persistent seed banks. Dominance of the seed bank by alien species with persistent seed banks suggests that aliens are favorably placed to increase in abundance in the vegetation if the forest is disturbed.     

Revegetation of an artificial cut-slope by seeds dispersed from the surrounding vegetation

We examined a method for revegetation of cut-slopes in Tochigi, Japan, using only natural plant dispersal from the surrounding vegetation. We examined plant establishment in six plots in a cut-slope in bedrock (inclination: 65°, direction: S45°W) treated with various types of netting and fertilizer. We surveyed the plant communities, individual trees, and seed rain on the cut-slope, as well as the plant community on the undisturbed upper slope. Revegetation method using polyethylene netting with fertilizer and water-retention material was the most effective. The resulting plant community was dominated by Pinus densiflora, with a cover of 49.0±11.4% after 5 years. This plant community consisted of 19 species, including ten tree species and a density of 26.2 trees/m². Revegetation method using palm-fiber netting with fertilizer also resulted in high plant cover after five years, although little revegetation grew on this plot in the earlier years. The roughness of the palm fiber may have inhibited revegetation. Application of fertilizer was essential for the success of this natural revegetation method. In addition, the revegetated plant community was strongly influenced by seed rain from the vegetation of the upper slope. The number of trees that became established was much lower than the number of tree seeds that were dispersed, possibly because of the absence of soil. We recommend that soil is allowed to accumulate or that a base of material to facilitate plant growth is added. Successful revegetation was achieved even under the harsh conditions of this cut-slope.     

Small mammal seed consumption in the Karoo,South Africa: further evidence for divergence in desert biotic processes

Summary Annual seed consumption by a small mammal community in the semi-arid Karoo, South Africa, was calculated using population, biomass and dietary estimates and published estimates of field metabolic rate. The community comprised a macroscelid elephant shrew Macroscelides proboscideus, and two rodents Gerbillurus paeba and Desmodillus auricularis. Only G. paeba consumed seed during the study, and then in low amounts (annual mean = 0.4% of diet, insects = 53%, herbage = 47%), with M. proboscideus and D. auriocularis consuming mainly insects (88%) and herbage (90%), respectively. Energy requirements for the G. paeba population averaged 568 kJ ha^–1 day^–1. Total seed consumption was estimated to be 140 g ha^–1, or 155 000 seeds ha^–1 which represents 0.5% of the annual seed production for this site. These levels of granivory by small mammals are significantly lower than those recorded for North American deserts, and raises the question as to why granivory varies between these systems. These findings also refute the hypothesis that as a result of the harshness and similarity of physical conditions in deserts, the properties of desert communities are convergent.     

Cache site selection by chipmunks (Tamias spp.) and its influence on the effectiveness of seed dispersal in Jeffrey pine (Pinus jeffreyi)

The effectiveness of Jeffrey pine (Pinus jeffreyi) seed dispersal performed by seed-caching yellow pine chipmunks (Tamias amoenus) and lodgepole chipmunks (Tamias speciosus) was compared to that of wind dispersal in the Sierra Nevada of western Nevada. Wind-dispersed seeds typically fall under or near the parent tree. Chipmunks removed 90 and 97% of 1064 radioactive seeds from each of two simulated wind-dispersed seed shadows in less than 24 h. Wind-dispersed seeds were deployed within 12 m of the two source trees, but chipmunk caches were found from 2–69 m from the trees. Chipmunks carried nearly all seeds away from source trees, greatly reducing the density of seeds under and near source trees. Caches contained from 1–35 seeds and most were buried 7–21 mm deep. Chipmunks cached in open bitterbrush shrubland with mineral soils much more than expected and cached in closed-canopy Jeffrey pine and lodgepole pine forests with thick needle litter much less than expected. Many Jeffrey pine seedlings and saplings grow in the bitterbrush habitat and few grow in the pine forests. Ten and 20% of the original caches survived until April, the time of seed germination, at the two sites. The movement of wind-dispersed seeds is random relative to environmental variables important in seedling survival, and the wind in coniferous forests cannot quickly bury seeds. The quality of seed dispersal rendered by chipmunks was superior to that provided by the wind because the chipmunks quickly harvested seeds on the ground, moved them away from source trees, and buried them in the ground in habitats and microhabitats where they were more likely to establish new seedlings. The increased quality of seed dispersal provided by animals relative to the wind may help explain why over twenty species of pines have evolved seeds and cones that are adapted for dispersal by seed-caching animals.     

Seed rain and advanced regeneration in a tropical rain forest

By comparing seed rain, seedling and sapling community structures we assessed the possible role played by vertebrate seed dispersal as a structuring factor in advanced regeneration of closed-canopied sites in the tropical rain forest of Los Tuxtlas, Mexico. Seed weight, initial morphology of seedlings and species abundance were also analyzed to determine if these traits influenced the probability of establishment in the shade.About half of the seed species falling in five closed forest sites (25×25 m) during one year came from fruiting trees growing within the sites (local seeds) and half from fruiting trees found outside the sites (immigrant seeds). Seeds of liana and upper-canopy species were over-represented among immigrant seeds compared with seeds of understory tree species. This probably reflects the activity of frugivorous arboreal mammals, bats, and birds. Species with immigrant seeds had both a lower abundance and a narrower spatial distribution than locally produced seeds. Therefore, immigrant seeds showed higher diversity values than locally produced seeds.Average seed size and the proportion of epigeous seedlings were similar in local and immigrant species. Under closed-canopied sites, factors affecting community organization seem to operate selectively, favoring the establishment of large-seeded, local abundant species in the advanced regeneration. However, the fact that some saplings of immigrant species were found in the plots suggest that a slow species infiltration may be occurring leading to a slow shift in the advanced regeneration species composition. We propose that the influence of seed dispersal on advanced regeneration structure depends on the disturbance history of the patches where seeds land.     

Mechanisms of plant regeneration during succession after shifting cultivation in eastern Amazonia

The role of seed bank, seed rain, and regeneration from seedlings and sprouts after swidden agriculture was compared in 5-, 10- and 20-year-old secondary forest and in a primary forest in Bragantina, Pará, Brazil. The seed bank (0–5 cm soil depth) was largest in the 5-year-old forest (1190 ± 284 seeds m⁻²) and decreased nearly ten-fold with age to 137 ± 19 seeds m⁻² in the primary forest. The highest seed rain was in the 5-year-old forest (883 ± 230 seeds m⁻² year⁻¹) and the least in the primary forest (220 ± 80 seeds m⁻² year⁻¹). Large plants (≥5 cm dbh) had more individuals and species that regenerated from sprouts than from seeds and the most abundant tree species in the secondary forest stands of all ages appear to be maintained by sprouting. The smaller individuals (≥1 m tall, <5 cm dbh) in the 5-year-old forest were mainly from sprouts, but those in the older secondary forests originated mainly from seeds. These results show that at the beginning of succession, although many species can be introduced to swidden fallow from seed bank and seed rain, it is the sprout that is the main source of recruits of primary forest species in secondary forests in Bragantina.     

Spatial distribution of soil seed banks of three African savanna woody species at two contrasting sites

In southern African savannas, bush encroachment is a major problem for range managers. However, little is understood of the actual regeneration processes leading to it, and in particular the role of soil seed banks. The horizontal (between microsites) and vertical (with depth in litter and soil) distribution of soil seed banks of the microphyllous woody species, Acacia tortilis, A. nilotica and Dichrostachys cinerea (all legumes of the Mimosoideae), were quantified in an area with low intensity grazing (reserve), and a bordering cattle farm with high intensity grazing (farm). Species differed in seed bank densities between microsites and sites. Seed densities for all species were highest below parent tree canopies and decreased with distance beyond the canopy, and with soil depth. D. cinerea had the smallest seed bank associated with parent trees, particularly on the farm (8 vs. 1643 seeds/tree on the reserve), A. tortilis had the largest (6357, 31910), with A. nilotica intermediate (1789, 1906). The proportion of current (recently fallen) versus old (1 year old) seeds differed between species and sites. These species form at least short-term persistent seed banks with the old seeds largely representing the persistent seed bank. Seed densities in the open (inter-canopy) and those dispersed under either of the other two (non-parental) study species were much lower than those associated with parent trees. The latter were mostly found under the acacias (single-stemmed) rather than D. cinerea (multistemmed). Total seed store per parent plant increased with plant size (best fits were mostly power curves of canopy area). A large proportion of intact seeds were viable, namely 81–84% for A. tortilis, 68–77% for A. nilotica and 63–78% for D. cinerea, with no differences between sites. Viability tended to increase with depth of burial, except for A. nilotica seeds at the 3–5 cm depths on the farm. At the landscape scale there were 1.5 million and 140000 A. tortilis seeds/ha on the reserve and farm respectively, with corresponding values of 2000 and 31000 for D. cinerea, and 23000 and 86000 for A. nilotica.     

Spatial and Temporal Variation of Seed Rain in the Canopy and on the Ground of a Tropical Cloud Forest

Spatial and temporal patterns of seed rain impact plant fitness, genetic and demographic structure of plant populations, and species' interactions. Because plants are sessile, they rely on biotic and abiotic dispersal agents to move their seeds. The relative importance of these dispersal agents may shift throughout the year. In tropical forests, seed dispersal of epiphytes constitutes a major but hitherto unknown portion of seed rain ecology. For the first time, we report on patterns of seed rain for both epiphytic and terrestrial plants across an entire year in a Neotropical montane forest. To examine seed rain, we placed traps in the canopy and on the ground. We analyzed seed dispersal syndrome (bird, mammal, wind) and plant habit (epiphyte, liana, shrub, small tree, large tree) across all seasons of the year (dry, misty, wet). We found that the community of species collected in canopy traps was significantly different from the community in ground traps. Epiphytes were the most common plant habit found in canopy traps, while large trees were most common in ground traps. Species with bird‐dispersed seeds dominated all traps. Species richness was significantly higher during the dry season in ground traps, but did not vary across seasons in canopy traps. Our results highlight the distinct seed rain found in the canopy and on the ground and underscore the importance of frugivores for dispersing both arboreal and terrestrial plants in tropical ecosystems.     

Seed dynamics during forest succession in Costa Rica

Soil seed banks and current seed inputs each play a role in tropical succession. We compared the abundance and floristic composition of seeds from these two sources at a Costa Rican site by germinating seeds from the soil, measuring seed inputs for 3 yr, and monitoring the earliest colonists in a forest clearing.There were an estimated 6800 viable seeds/m² in the soil of 3.3-yr-old vegetation, 9500 seeds/m² in 11-yr-old vegetation, and 7000 seeds/m² in a 75-yr-old forest. An estimated 10100 seeds/m² fell on the soil surface of the young successional vegetation during 3 yr and 3700 seeds/m² fell during that same time in the forest.Locally produced seeds accounted for about 75% of the seed input to the soil surface early in succession. Seeds dispersed out of young successional vegetation increased the quantity and species richness of the seed input and storage in an adjacent forest. Much of the species richness of the young successional vegetation resulted from seeds dispersed there from other communities by animals.Deforestation stimulated germination of most seeds in the surface soil of the old forest, including seeds of the dominant canopy tree. The recruitment of seedlings from the soil seed bank numerically overwhelmed that from post-disturbance seed rain and sprouts.We evaluated patterns of soil seed storage during succession and predicted the ability of vegetation of differing ages to respond to disturbance. Immediately after disturbance the number of seeds in the soil plummeted due to mortality, low inputs, and germination. As the vegetation regrew, the soil seed bank increased to a peak after 4 to 7 yr, then gradually decreased to its pre-disturbance size. High-frequency pulses of disturbance should result in reduced species richness, dominance by species with long-lived seeds, and fast recovery by seedling recruitment from the soil seed bank.Journal series number 6459 from the Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611, USA.Reprint requests to J. J. E. at Florida.     

Enhanced germination of artificial seeds by marine cynobacterial extract

Summary We have developed an improved artificial seed system by using a hot-water extract from a marine cyanobacterium, Synechococcus sp. NKBG 042902. Carrot somatic embryos (Daucus carota L.) were divided into two size categories (> 800 m and 425–800 m). High frequency germination (91%) was obtained using the large somatic embryos encapsulated in calcium alginate gel containing 400 mg 1^–1 of extract. This compares to 35% without addition of the extract. A non-dialysate fraction of the extract showed strong germination-promoting activity compared with a dialysate fraction. The germination frequency of artificial seeds containing 100 mg 1^–1 of non-dialysate fraction was more than 90%. Almost all germinating artificial seeds developed into plantlets within 4 days. We also achieved high frequency germination (60%) of artificial seeds encapsulating small somatic embryos (425–800 m) that contained 100 mg 1^–1 of non-dialysate (control 9%). Although the small somatic embryos showed a lower germination frequency than the large embryos, the plantlet development process in these seeds was far more vigorous. Such a high germination frequency has not previously been reported for a carrot artificial seed system.     

浙江古田山自然保护区常绿阔叶林种子雨的时空变异

木本植物种子产量的时间和空间变化格局对植物更新以及群落组成和结构有着重要影响, 是种子雨研究的一个重要方面。2006年6月在古田山亚热带常绿阔叶林24 hm²样地布置了130个面积为0.5 m²的种子雨收集器, 每周收集一次。利用4年的种子雨数据, 研究了种子雨的时间和空间变异。主要结果如下: (1)共收集到124227粒成熟种子, 属于29科51属63种, 每月降水量与平均每月种子数、物种数均呈显著负相关; (2)种子产量在每年干季(秋季)有明显的高峰, 有10个物种在湿季扩散种子, 不同物种结实物候起始和终止时间有差异; (3)基于4年的种子雨数据, 几乎所有物种的种子雨均存在很大的年际变异, 收集到的所有物种的种子产量年际变异系数的中位数为1.72; (4)种子雨在不同收集器之间有很大的变异, 变异系数的中位数为8.06; 几乎所有物种的空间变异都远远大于时间变异, 这可能是由于母树的稀有性、种子传播距离的差异, 以及地形等因素造成。通过与巴拿马Barro Colorado Island 50 hm ²样地108个物种种子产量的年际变异系数相比较, 古田山种子雨数据支持了高纬度地区种子产量变异高于低纬度地区的假说。     

文峪河上游华北落叶松林的种子雨、种子库与幼苗更新

华北落叶松林下更新不良,为探究其制约因素,开展了山西省文峪河上游5个华北落叶松林分的种子雨、土壤种子库和幼苗更新的研究。结果表明:(1)华北落叶松种子主要集中于9—10月散落。2011年为华北落叶松种子丰年:种子产量高,种子雨密度达(961.93±377.40)粒/m2;种子质量高,完整种子占(89.31±16.13)%。2012年为种子平年,种子产量低,种子雨密度为(252.73±115.12)粒/m2。华北落叶松种子雨主要源于毗邻树木,华北落叶松纯林和落叶松云杉林的种子雨密度显著高于其他3个针阔混交林。(2)土壤种子库主要由上年种子雨组成,2012年4月的土壤种子库密度为(695.18±297.23)粒/m2,完整种子占(59.73±9.56)%。种子自然萌发前,约(78.98±24.76)粒/m2具发芽力,基本可满足更新需要。但种子活力保持期少于2 a,只能形成短期持久土壤种子库。(3)华北落叶松更新不良,种子年后仍难以实现幼苗建成,当年生幼苗的出现频度平均为1.6%,且林下难以存活。幼苗发生与种子储量关联性不强,种源条件不是制约华北落叶松更新的主要因素。     

广西靖西西南桦天然林种子雨的时空动态

以一片西南桦(Betula alnoides)天然林和一个西南桦独立单株为研究对象, 通过收集散种期内与林分或母树不同距离的种子以及测定风速和风向, 研究了西南桦群落和个体水平上种子雨的时空动态及其与风速和风向的关系。结果表明: 群落水平上, 西南桦种子散布的初始期、高峰期、消退期分别历时11天、32天和40天, 而个体水平上则为9天、25天和26天。高峰期内群落和个体水平的散种量分别占其总量的83.1%和68.7%, 而且白天的种子雨密度高于夜间; 西南桦个体白天种子雨密度最大的时段为12:00-16:00, 与此时段内风速较高有关。在个体水平上, 距离母树0-30 m范围内散落的种子占总散种量的79.6%; 而在群落水平上, 距离林缘0-45 m范围内集中了总散种量的81.2%。西南桦种子散布具有方向性, 无论个体还是群落水平上不同方向间种子雨密度差异极显著(p < 0.01), 与散种期内的主要风向有关; 而且种子雨密度与风速亦呈极显著正相关关系。研究结果将有助于揭示西南桦天然更新动态和更新机制, 亦为开展西南桦人工促进天然更新提供理论依据。     

Composition and seasonal dynamics of seed rain in broad-leaved Korean pine (Pinus koraiensis) mixed forest in Changbai Mountain, China

To explore the composition and spatio-temporal dynamics of seed rain in broad-leaved Korean pine (Pinus koraiensis) mixed forest, 150 seed traps were set up in a 25 hm2 plot in Changbai Mountain. Seeds, fruits, anthotaxy and others in seed traps were collected, identified and divided into 4 types. From 2005 to 2006, we collected 47 different types. Total number of seeds and fruits was 121291, including 23147 mature seeds and fruits (19.1% of the total). Tilia amurensis and Fraxinus mandshurica, with the most seeds and fruits, accounted for 90% of the total. The analysis on seasonal dynamics of seed rain showed that there were the largest number of seeds and fruits between July and October, which were composed of immature seeds and fruits. In mid-October, mature seeds and fruits reached their peak, but immature seeds and fruits still accounted for high proportion. There were 91 traps that contained 100–200 mature seeds and fruits, and one trap without any mature seed or fruit. The largest number of species found in a trap was 7, and usually 3 or 4 species were found in most of the traps. There were obvious relationships between spatial patterns of mature seeds and fruits and their parent trees, indicating that their mature seeds and fruits were not dispersed far from their parent trees.     

The importance of seed reserves for seedling performance: an integrated approach using morphological,physiological, and stable isotope techniques

To investigate how seed reserves affect early seedling performance, we conducted a factorial greenhouse experiment using Lithocarpus densiflora (Tanoak). Seedlings were grown from large (5.8±0.7 g) and small (3.2±0.4 g) seeds and, following shoot emergence, seeds were either removed or left attached. Seedlings were harvested for quantification of biomass and ¹³C at seven time periods following seed removal (2, 4, 8, 16, 32, 64, 128 days) and seedling photosynthesis was measured three separate time periods (2–4, 49–82, 95–128 days after seed removal). Biomass increased for all seedlings, but the increase was significantly larger for seedlings with attached seeds than with removed seeds. Seed removal just after shoot emergence significantly decreased seedling biomass, but seed removal 64 days after shoot emergence had no effect on seedling biomass. Seedling photosynthesis per unit leaf area varied by time and seed presence, but not by seed size. At the first period, seedlings with attached seeds had significantly higher photosynthetic rates than seedlings with removed seeds, at the second period there was no effect of seed removal, and at the third time period seedlings with attached seeds had significantly lower photosynthetic rates than seedlings with removed seeds. Despite temporal variation in photosynthesis per unit leaf area, seedlings with attached seeds always had significantly greater leaf area than seedlings with removed seeds, resulting in significantly higher total plant photosynthesis at all three time periods. The ¹³C values of both the leaves and roots were more similar to that of the seed for seedlings with attached seeds than for seedlings with removed seeds, however, seed removal and seed size strongly affected root ¹³C. This study demonstrates that seed reserves have important effects on the early growth, physiology, and ¹³C of L. densiflora seedlings.