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.     

Seed Availability as a Limiting Factor in Forest Recovery Processes in Costa Rica

Abandoned pastures and secondary forests are increasingly prominent features of tropical landscapes. Forest regrowth on abandoned pastures is generally slow and virtually limited to regeneration from seeds from external sources, since agricultural activities alter site conditions. We hypothesize that seed availability is a major limiting factor in forest recovery on abandoned pastures. This hypothesis was tested by studying the seed bank, seed rain, and seed predation in a small pasture (1 ha) situated in a forest‐pasture mosaic in northwestern Costa Rica. The tree seed density in the pasture seed bank was much lower (21/m²) than the density in the seed bank of a neighboring secondary forest (402/m²). Within a period of five weeks, 23 tree seeds entered the pasture by seed rain. This number is low compared to densities found in closed forests but higher than densities reported in other studies where virtually no seeds were found beyond 20 m from the forest edge. Possibly the small size of the pasture with seed sources nearby and the small‐scale landscape mosaic enhance seed dispersal. Predation limits the seed density in pastures, with 42% of the woody species consumed by predators. The low seed density in the seed bank, and hampered recruitment combined with significant losses, pose severe restrictions to forest recovery on abandoned pastures. Moderate land use, and small sized clearings with seed sources nearby may increase the pace of recovery. Nevertheless, forest establishment may still take a considerable time. Thus, enlarging the available pool of species may be a worthwhile management strategy.     

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。     

Seed Rain Produced by Bats and Birds in Forest Islands in a Neotropical Savanna1

The high degree of isolation of forest “islands” relative to “continental” forested areas creates a naturally fragmented landscape in the savanna ecosystem. Because fragmentation can affect the intensity and quality of biological interactions (e.g., seed dispersal) we examined the abundance and species richness of seed rain produced by birds and bats in three different parts of forest islands (center, edge, and exterior) located at the Estación Biológica del Beni, Bolivia. Despite the fact that we found higher species density of seeds in the seed rain at the center of forest islands, when comparing species richness corrected for observed differences in density, species richness was higher at the edge of islands. The three parts of the islands did not differ in total number of seeds. Three genera (Byrsonima, Ficus, and Piper) contributed the most seeds to the seed rain. We found differences in the abundance of dispersed seeds probably because of the variation related with the disturbance line, where the savanna matrix interacts with the forest islands. Carollia perspicillata, Carollia brevicauda, and Sturnira lilium were the bats that contributed most to seed dispersal within forest islands, and Schistochlamys melanopis and Tyranneutes stolzmanni were the most important birds. The movement of seeds produced by bats and birds within forest islands of the savanna is crucial to assure the continuity of ecological process and dynamics of these forest islands.     

SPATIAL PATTERNS OF SEED DISPERSAL AND POSTDISPERSAL SEED PREDATION OF CRYPTANTHA FLAVA (BORAGINACEAE)

I examined the spatial patterns of seed dispersal and postdispersal seed predation of the semidesert perennial Cryptantha flava (A. Nels.) Payson (Boraginaceae) at two sites in north-eastern Utah. Most flowers mature only one seed (nutlet) which is permanently retained within a pubescent calyx. The calyx and enclosed seed abscise from the plant as a unit. These dispersal units are effectively dispersed by wind as evidenced by the highly directional seed shadows and the long distances some of them travel (up to 31.3 m). Potential seed predators at the sites include five species of rodents, of which Peromyscus maniculatus is the most common, and two species of ants, Pogonomyrmex occidentalis and an undescribed species of Conomyrma. There were no strong spatial patterns of postdispersal seed predation. More seeds were removed from dishes placed at the bases of fruiting adults than from dishes ≥ 1.0 m away in one of three experiments. More seeds were removed from under shrubs or clumps of grass than in the open in one of four experiments. After 3–4 days, there was a consistent tendency for more seed removal from high density (75 seeds per .25 m²) quadrats than from low density (75 seeds per 6.25 m²) quadrats, but the difference was not always significant. There was a similar nonsignificant difference between high- and low-density quadrats exposed for 21 days. The pubescent calyx greatly discourages seed predation by ants, and probably also reduces predation by rodents. In addition, by increasing the surface area of the dispersal unit, the calyx may facilitate dispersal by wind.     

Seed dynamics of resprouting shrubs in grassy woodlands: Seed rain,predators and seed loss constrain recruitment potential

Abstract Measuring the fate of seeds between seed production and seedling establishment is critical in understanding mechanisms of recruitment limitation of plants. We examined seed fates to better understand the recruitment dynamics of four resprouting shrubs from two families (Fabaceae and Epacridaceae) in temperate grassy woodlands. We tested whether: (i) pre‐dispersal seed predation affected seed rain; (ii) post‐dispersal seed predation limited seed bank accumulation; (iii) the size of the seed bank was related to seed size; and (iv) viable seeds accumulated in the soil after seed rain. There was a distinct difference in seed production per plant between plant families with the legumes producing significantly more seeds per individual than the epacrids. Seed viability ranged from 43% to 81% and all viable had seed or fruit coat dormancy broken by heat or scarification. Pre‐dispersal predation by Lepidopteran larvae removed a large proportion of seed from the legume seed rain but not the epacrids. Four species of ants (Notoncus ectatomoides, Pheidole sp., Rhytidoponera tasmaniensis and Iridomyrmex purpureus) were major post‐dispersal seed removers. Overall, a greater percentage of Hardenbergia (38%) and Pultenaea (59%) seeds were removed than the fleshy fruits of Lissanthe (14%) or Melichrus (0%). Seed bank sizes were small (<15 seeds m^?2) relative to the seed rain and no significant accumulation of seed in the soil was detected. Lack of accumulation was attributed to seed predation as seed decay was considered unlikely and no seed germination was observed in our study sites. Our study suggests that seed predation is a key factor contributing to seed‐limited recruitment in grassy woodland shrubs by reducing the number of seeds stored in the soil.     

木麻黄海防林种子雨的时空动态

为了解木麻黄(Casuarina equisetifolia)种子雨的时空间分布格局和萌发性能对其天然更新的影响,对海口木麻黄海防林种子雨的时空分布特征和种子雨的萌发动态进行了研究。结果表明,木麻黄种子落雨时间始于7月中旬,结束于次年4月中旬,持续长达9个月,期间种子雨年际平均密度为1 764.63 grain m~(-2)a~(-1);种子雨高峰期在12月上中旬,落种量占总散落量的43.38%;种子雨呈聚集分布,且种子雨密度与附近球果数量呈极显著正相关;种子雨萌发率较低,仅为11.31%,但由于种子雨密度较大,可萌发的种子雨密度仍然较大,为199.58grainm~(-2)a~(-1)。因此,种子数量和质量均不是制约木麻黄天然更新困难的主要障碍因子,但聚集分布特征使木麻黄种子在林内扩散能力十分有限。     

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.     

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.     

Spatial dynamics of <Emphasis Type="Italic">Ilex aquifolium</Emphasis> populations seed dispersal and seed bank: understanding the first steps of regeneration

The objective of this study was to analyse quantitatively the spatial distribution of holly (Ilex aquifolium L.) seed rain and seed bank, and to detect the relationships between these consecutive processes. We measured seed dispersal by birds and fallen fruits, and also density and viability of seed bank in two Ilex populations in central Spain. Analysis was made distinguishing the following microhabitats: holly woodland, edge of holly woodland, open grassland 10 m and 100 m from the woodland, fleshy fruit shrubs, dry fruit shrubs, and adjacent non-holly woodland. Spatial distribution of dispersed and in-soil seeds was measured by the clumping index. Seed rain and seed bank under holly woodlands were significantly higher than in the other microhabitats. Forest edges and fleshy fruit shrubs were the next microhabitats with the highest seed rain and seed bank density. Interannual and interlocality variations were not significant. The relative importance of the different dispersal methods varied between microhabitats, with a similar support of bird dispersed seeds and fallen fruits within the woodland and a greater influence of cattle dispersal in open areas. Seed spatial aggregation was significant in both dispersed seeds and soil seeds from holly woodlands and the edge of the forest. Aggregation under shrubs, grasslands and the adjacent forests evidenced a general random distribution of holly seeds (only in some cases clumping index was significant). Quantitative differences between seed rain and seed bank are important. Post-dispersal seed predation did not modify seed rain distribution, which was mirrored in the seed bank pattern. These two phases of holly regeneration had a heavy spatial influence, determined by the landscape structure and activity of the dispersal agents, that reflects a differential recruitment potential. Comparisons between both populations suggest that in the southern locality (Robregordo) holly has a weaker capacity to colonize open areas, and a stronger recruitment limitation due to propagule availability.     

Reproductive potential and seedling establishment of the invasive alien tree Schinus molle (Anacardiaceae) in South Africa

Schinus molle (Peruvian pepper tree) was introduced to South Africa more than 150 years ago and was widely planted, mainly along roads. Only in the last two decades has the species become naturalized and invasive in some parts of its new range, notably in semi‐arid savannas. Research is being undertaken to predict its potential for further invasion in South Africa. We studied production, dispersal and predation of seeds, seed banks, and seedling establishment in relation to land uses at three sites, namely ungrazed savanna once used as a military training ground; a savanna grazed by native game; and an ungrazed mine dump. We found that seed production and seed rain density of S. molle varied greatly between study sites, but was high at all sites (384 864–1 233 690 seeds per tree per year; 3877–9477 seeds per square metre per year). We found seeds dispersed to distances of up to 320 m from female trees, and most seeds were deposited within 50 m of putative source trees. Annual seed rain density below canopies of Acacia tortillis, the dominant native tree at all sites, was significantly lower in grazed savanna. The quality of seed rain was much reduced by endophagous predators. Seed survival in the soil was low, with no survival recorded beyond 1 year. Propagule pressure to drive the rate of recruitment: densities of seedlings and sapling densities were higher in ungrazed savanna and the ungrazed mine dump than in grazed savanna, as reflected by large numbers of young individuals, but adult : seedling ratios did not differ between savanna sites. Frequent and abundant seed production, together with effective dispersal of viable S. molle seed by birds to suitable establishment sites below trees of other species to overcome predation effects, facilitates invasion. Disturbance enhances invasion, probably by reducing competition from native plants.     

Seed to seedling transitions in successional habitats across a tropical landscape

Recognition that tree recruitment depends on the balance between seed arrival and seedling survival has led to a surge of interest in seed‐dispersal limitation and seedling‐establishment limitation in primary forests. Virtually unaddressed are comparisons of this balance in mature and early successional habitats. We assessed seed rain and seedling recruitment dynamics of tree species in primary forest, secondary forest and pasture released from grazing in a tropical agricultural landscape. Seed to seedling ratios (seed effectiveness; Φ_i) for 43 species in southern Mexico determined differences in the extent to which seeds produced seedlings by habitat, life history, and dispersal mode. Reproductive potential as estimated by the transition from seed rain to seedling recruitment, differed by habitats, and varied dramatically by life history and dispersal mode. Expected recruit densities (E_it) were higher for animal‐dispersed than wind‐dispersed species, and for non‐pioneer than pioneer species. Non‐pioneers and animal‐dispersed species had higher expected relative recruit abundance (ε_it) in primary forest (median of 4 seeds recruit^?1) whereas in secondary forest wind‐dispersed pioneers had the highest expected relative recruit abundance (median of 16 seeds per recruit). In pastures, wind‐dispersed pioneer species were most successful with many more seeds per recruit (median of 291) than both forest habitats. Seeds per recruit (Φ_i) appeared to decrease with increase in seed mass for 43 species for which data were available (r = –0.55, P < 0.001). This was associated with a negative correlation of Φ_i with seed size in primary forest (r = –0.50, P = 0.08 for 13 species); Φ_i was not correlated with seed size in secondary forest (n = 16) or pasture (n = 14). Metrics of seeds per recruit, expected recruit density and expected relative recruit abundance dramatically illustrate differences in barriers to recruitment in successional habitats.     

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.     

Seed Banks in Savanna,Forest Fragments,and Continuous Forest Edges Differ in a Tropical Dry Forest in Madagascar

Rapid deforestation has fragmented habitat across the landscape of Madagascar. To determine the effect of fragmentation on seed banks and the potential for forest regeneration, we sampled seed viability, density and diversity in 40 plots of 1 m² in three habitat types: forest fragments, the near edge of continuous forest, and deforested savanna in a highly fragmented dry deciduous forest landscape in northwestern Madagascar. While seed species diversity was not different between forest fragments and continuous forest edge, the number of animal‐dispersed seeds was significantly higher in forest fragments than in continuous forest edge, and this pattern was driven by a single, small‐seeded species. In the savanna, seeds were absent from all but three of the 40 plots, indicating that regeneration potential is low in these areas. Several pre‐ and post‐dispersal biotic and abiotic factors, including variation in the seed predator communities and edge effects could explain these findings. Understanding the extent to which seed dispersal and seed banks influence the regeneration potential of fragmented landscapes is critical as these fragments are the potential sources of forest expansion and re‐connectivity.     

准噶尔盆地东南缘梭梭种子雨特征

为了研究梭梭种子散布规律,通过布设种子雨收集器结合室内实验分析,对准噶尔盆地东南缘梭梭种子雨特征进行了研究。研究显示:(1)梭梭种子雨的累积密度达到平均189粒/m2,其中有活力种子占约80%;(2)种子散布的高峰集中在11月初到11月15日时间段,其落种量占整个种子雨的65%。其后种子雨密度随时间逐渐减小;(3)整个种子雨过程,不同时期散落的种子雨质量存在差异,表现为不同时期散落种子的萌发率呈现出先增大后减小的趋势;(4)变异函数分析表明,梭梭种子雨在8.12 m的有效变程内,种子雨具有明显的空间格局,其由空间自相关和随机因素引起的空间异质性各占50.0%。准噶尔盆地东南缘梭梭种子雨密度大且质量较高,同时其时空分布异质性较高,这些特征均将影响梭梭种群的分布格局和种群更新。     

Patterns of Seed Dispersal and Dispersal Failure in a Hawaiian Dry Forest Having Only Introduced Birds

Dry forests are among the most endangered natural communities in the Hawaiian Islands. Most have been reduced to isolated trees and small forest fragments in which native tree species reproduce poorly. The replacement of native birds by introduced generalists may be contributing to dry forest decline through modification of seed dispersal patterns. To document seed dispersal by introduced birds, we conducted foraging observations on fleshy-fruited trees and measured seed rain under trees and in adjacent open areas for 1 year in a dry forest dominated by native trees. Although trees covered only 15.2 percent of the study area, 96.9 percent of the bird-dispersed seeds were deposited beneath them. The Japanese white-eye (Zosterops japonicus) was the principal dispersal agent. Among bird-dispersed seeds, those of the invasive tree Bocconia frutescens accounted for 75 percent of all seeds collected beneath trees (14.8 seeds/m²/yr) and the invasive shrub Lantana camara accounted for 17 percent. Although nearly 60 percent of the reserve's native woody species possess fleshy fruits, introduced birds rarely disperse their seeds. Native trees accounted for <8 percent of all bird-dispersed seeds and are consequently experiencing dispersal failure by falling directly under parent trees. Smaller-seeded non-native plants, in contrast, may be benefiting from dispersal by introduced birds. Current dispersal patterns suggest that these readily disseminated non-native plants may eventually replace the remaining native flora.     

Evaluating Dispersal Limitation in Passive Bottomland Forest Restoration

Dispersal limitation can retard natural establishment of desirable species on restoration sites, especially where landscapes are fragmented, but dispersal limitation is assumed to become less critical with time as early colonists become reproductively mature. Distribution patterns of recruiting trees in a 20‐year‐old passively restored bottomland in northeast Louisiana suggested persistent dispersal limitation in some bottomland hardwood species and influence of dense shrub patches on colonization. To test these hypotheses, we measured seed rain as a function of distance to seed source and association with shrub cover. Seed rain of the wind‐dispersed Fraxinus pennsylvanica was highest near the forest edge, except where mature recruits occurred. Although shrub presence did not influence dispersal of F. pennsylvanica, its negative influence on probability of occurrence in the sapling layer suggests that shrub cover may limit its regeneration. The bird‐dispersed Crataegus viridis and Ilex decidua were found in the seed rain and as reproductive individuals within the field; neither had a positive relationship with shrub presence. Dispersal of heavy‐seeded Quercus spp. and Carya aquatica was limited to within 20 m of the forest edge. These results imply that dispersal limitation is diminishing in wind‐ and bird‐dispersed species with maturation of in‐field recruits and that shrub patches may influence these patterns. Heavy‐seeded species, however, remain restricted to field edges that directly abut a seed source. If canopy closure by wind‐ and bird‐dispersed species precedes dispersal of heavy‐seeded species into the field, establishment of Quercus and Carya spp. may remain low for the foreseeable future.     

Does proximity to a mature forest contribute to the seed rain and recovery of an abandoned agriculture area in a semiarid climate?

Proximity to forests contributes to the recolonisation of anthropogenic‐disturbed areas through seed input. We evaluated the role of proximity to a mature forest in the recolonisation of an agricultural area that has been abandoned for 18 years and is currently a young forest. Seed rain was monitored at fixed distances from the mature forest. The type of surface recolonisation (germination versus resprouting) and the reproductive season were measured in both forests. The majority of plants recolonising the young forest originated from seed germination. Proximity to the mature forest contributed to the seed rain in the young forest; however, 18 years has not provided sufficient time for the recolonisation of 80 species present in the mature forest. Some species shared between forests differed in their fruiting season and seed dispersal. The seed rain had a total species richness of 56, a total density of 2270 seeds·m^?2·year^?1 and predominance of self‐ and wind dispersal. A significant reduction in seed rain with increasing distance from the mature forest was observed. The young forest contained 35 species not observed in the mature forest, and the floristic similarity between the two forests was 0.5, indicating that the two forests are floristically distinct.     

Impacts of secondary seed dispersal and herbivory on seedling survival in Aesculus turbinata

Abstract. Aesculus turbinata is a tree species with large seeds (6.2 g mean dry weight). We studied the demography of its seeds and seedlings in a temperate deciduous forest in northern Japan to elucidate the ecological significance of large seeds with special reference to herbivory and secondary dispersal. Both seed and seedling stages suffered greatly from herbivores. Seedling herbivory was important judged from experiments with shoot clipping and hypogeal cotyledon removal. However, some seedlings survived through re-sprouting after herbivory. Survival rate and percentage resprouting seedlings were lower than those with remaining cotyledons, though seedling size was not affected. This suggests that stored resources in hypogeal cotyledons are working as a kind of ‘risk hedge’ against severe aboveground shoot clipping experienced by A. turbinata. The spatial distribution of seedlings was expanded via seed scatter-hoarding by rodents. Seedling survival rate was higher within canopy gaps than under closed canopy, indicating that canopy gaps are safe sites for establishment, and was negatively correlated with seedling density. Therefore, secondary seed dispersal in this species seems to be effective in ‘finding’ safe sites and in ‘escaping’ density-dependent mortality. The large seeds and seedlings of A. turbinata are attractive to herbivores, but the high resistance of seedlings to herbivory due to large reserves and the effective secondary dispersal appear to mitigate these disadvantages.