Patterns Of Seed Rain Research Articles

Lasting effects of avian‐frugivore interactions on seed dispersal and seedling establishment

Abstract The consequences of plant–animal interactions often transcend the mere encounter stage, as those encounters are followed by a chain of subsequent stages on the plant's reproductive cycle that ultimately determine fitness. Yet, the dissemination and recruitment stages of animal‐mediated seed dispersal are seldom analysed jointly, hindering a full understanding of the ecology of seed dispersal. We analyse the dispersal and recruitment of a fleshy‐fruited plant (Pistacia lentiscus), from fruit production to seedling survival up to their second year. We link early reproductive investment of individual plants to seedling recruitment and explore the role played by seed viability, the coterie of frugivores and microhabitat seed deposition. The proportion of viable seeds was generally low (mean = 34%) but highly variable among individual plants (range: 0%–95%). Seed viability did not seem to have a direct effect on individual plant's recruitment. We recorded 28 bird species feeding on P. lentiscus fruits or seeds. Their contribution to plant recruitment was mainly determined by their intensity of fruit consumption and probability to disperse viable seeds. Most frugivores presented non‐random microhabitat preferences, delivering uneven seed contributions to different sites. Post‐dispersal seed predation by rodents was the most limiting phase in P. lentiscus recruitment. Yet, microhabitats showing the lowest predation rates received the lowest seed rain. Hence, we found a decoupling of the dissemination and recruitment stages: most seeds do not arrive at the most suitable microhabitats. We estimate P. lentiscus plants need to produce c. 5 × 105 fruits to recruit a single seedling that survives to its second summer in our study site. Its success as a prevalent species in Mediterranean lowland landscapes relies on its high fecundity and thorough fruit removal and dispersal by a diversified frugivore assemblage, which compensates for the high seed unviability characteristic of this genus. Synthesis: Measuring the delayed, post‐dispersal outcomes of animal frugivory interactions may overturn inferences based on consumption observations only. Seed rain patterns are often decoupled from microhabitats' suitability for seedling recruitment. Hence, more integrative studies that encompass the entire plant reproductive cycle (from fruit production to seedling recruitment) are needed to fully understand frugivores' lasting contribution to plant regeneration in natural populations.

A review of natural and managed revegetation responses in two de-watered reservoirs after large dam removals on the Elwha River, Washington, USA

Large dam removals are increasing in frequency and the response of natural and managed revegetation is a critical consideration for managed restoration of dewatered reservoir landscapes post dam removal. The removal of two large dams on the Elwha River in 2011-2014 provides insight into reservoir revegetation. We review literature and datasets from 2012 through 2018, 1-6 years since reservoir dewatering, to compare pre-dam removal predictions on the Elwha to post-dam removal of natural revegetation, managed revegetation effects and invasive non-native vegetation response. Pre-dam removal hypotheses about natural revegetation did not predict species performance on reservoir sediments, seed rain patterns, or seed bank response. Sediment texture and landform affected multiple aspects of revegetation, including vegetation cover, species richness, woody stem densities and species composition. Reservoir drawdown timing influenced species composition and seedling densities. Predictions about managed revegetation effects were mixed. Planting trees and shrubs did not accelerate woody cover but did increase species richness. Seeding reduced non-native vegetation frequency and species richness, had no effect on vegetation cover on fine sediments, but increased vegetation cover on coarse sediments. Planting trees and shrubs during drawdown appeared to result in higher survival rates compared to plantings installed 1+ years post drawdown. Seeding Lupinus rivularis (riverbank lupine) on coarse sediments was successful and increased foliar nitrogen in planted conifers. Invasive non-native vegetation was correctly predicted to be more abundant in the Aldwell reservoir but did not preclude native species establishment in either reservoir, likely due to rapid establishment of native species and robust management that occurred before, during and after dam removal.

Gardeners of the forest: hornbills govern the spatial distribution of large seeds

Seed dispersal by frugivores is vital to the maintenance of tree diversity in tropical forests. However, determining the influence of different frugivores over the distribution of their food plants is difficult, given the complexity of these interactions in the tropics. Consequently, most studies have been restricted to small scales, examining seed dispersal and establishment associated with nests, roosts or fruiting trees. Here, we evaluate the role of frugivorous hornbills in dispersing seeds at spatial scales of 1 ha. We monitored hornbills and seed rain at a tropical forest site in north‐east India. We quantified the abundance of hornbill food plants and recruits of large‐seeded plants. We estimated removal rates of dispersed, large seeds to determine post‐dispersal seed fate. We found that the distribution of large‐seeded canopy food plants influenced the distribution of the relatively abundant Rhyticeros undulatus. The overall distribution of hornbills resulted in spatially contagious seed rain patterns for the large‐seeded plant species. Patches with canopy food plants had a higher recruit diversity. Our results show positive feedback between distribution of rare but important hornbill food plants, hornbills and distribution of seeds and saplings of large‐seeded plants in the landscape. Widespread loss of hornbills due to hunting and habitat loss in the region have likely disrupted these feedback mechanisms that are critical for tree species regeneration.

Landscape configuration and frugivore identity affect seed rain during restoration

Seed dispersal is a critical ecological function provided largely by vertebrate frugivores in tropical forests. The seed dispersal events mediated by a frugivore species depend on the interaction between the frugivore's traits and landscape structure. Managers seeking to restore seed dispersal to degraded areas to facilitate passive regeneration must consider these interactions. We explore how the relationship between disperser traits and landscape configuration affects seed rain patterns by assessing two restoration goals: 1) high native seed dispersal into degraded areas and 2) low non‐native seed dispersal into intact areas. We developed an individual‐based, spatially‐explicit model, ‘Estimating Seed‐Animal‐Landscape Interactions' (eSALI), and applied it to the case study of Guam, a tropical island that experienced near‐total loss of animal‐mediated seed dispersal following extirpation of its vertebrate frugivores. We focus on two frugivorous bird species, såli Aplonis opaca and totot Ptilinopus roseicapilla, both candidates for rewilding on Guam but differ in their movement distances, gut passage times and habitat use. We simulated populations of both species in seven theoretical landscapes. These landscapes varied in the spatial configuration of intact and degraded forest patches, hosting native and non‐native plant species, respectively. Our results showed that seed rain pattern of the two frugivore species differed across scenarios. A clear tradeoff appeared between both restoration goals in all scenarios: while Såli moved overall more native seeds into degraded areas, they also moved more non‐native seeds into intact areas. Totot on the contrary minimized non‐native seed into intact areas at the expense of moving overall fewer native seeds in degraded areas. This tradeoff was also correlated to landscape configuration: lower heterogeneity minimized non‐native seed rain into intact patches while higher heterogeneity maximized native seed rain into degraded patches. Land managers should explore the interactions between dispersers and landscape configuration to identify ideal candidates for restoring ecological functions.

Extant fruit‐eating birds promote genetically diverse seed rain, but disperse to fewer sites in defaunated tropical forests

Abstract The world‐wide decline in populations of large‐bodied vertebrates due to deforestation and poaching threatens the persistence of animal‐dispersed plants by reducing long‐distance seed dispersal and generating aggregated seed rain patterns. We evaluated whether the composition of maternal trees contributing to the seed rain is also impacted by the loss of large frugivores. By combining molecular tools with a thorough sampling of the frugivore‐generated seed rain we quantified the number of seeds, richness of maternal progenies and number of maternal effective alleles in the seed rain of a tropical palm Euterpe edulis across ten Atlantic Forest remnants with varying levels of avian defaunation and density of palm conspecifics. Forest structure in defaunated areas was characterized by higher canopy openness. Defaunation did not affect the number of seeds dispersed or of effective alleles, but, together with palm density, was associated with higher numbers of maternal genotypes in the seed rain. This result suggests that medium‐sized birds may play an important role in mixing maternal genotypes where large‐sized frugivores have been extirpated. Defaunation, however, impacted the spatial distribution of seeds, with deposition sites in avian depauperated forests less likely to receive at least one seed. Synthesis. Our study suggests that medium‐sized frugivores contribute to maintaining the quantitative component of seed dispersal and local genetic diversity of a threatened tropical palm in human degraded forests and, therefore, may be important for guaranteeing the persistence of remnant animal‐dispersed plant populations under scenarios of rapid environmental change. The loss of large‐bodied frugivores, however, can disrupt longer dispersal events and strengthen the dispersal spatial limitation, with consequences for plant spatial distribution and fine‐scale genetic structure at the population level.

Landscape structure mediates zoochorous-dispersed seed rain under isolated pasture trees across distinct tropical regions

Isolated pasture trees play an important role in forest recovery within fragmented tropical landscapes by attracting seed dispersers and facilitating seedling growth. However, studies with conflicting results have led to confusion about what drives variation in zoochorous-dispersed seed rain patterns under isolated tree canopies. To assess the role of landscape and biological factors impacting zoochorous-dispersed seed rain under isolated pasture trees across three tropical regions of the world. We measured seed dispersal under 144 isolated pasture trees found in 12 fragmented tropical and sub-tropical landscapes in Australia, Colombia and Nigeria. Using linear mixed effect models, we modeled seed diversity, abundance, richness and evenness as functions of the biological features and landscape context of isolated trees. Throughout all regions, the amount of woody vegetation surrounding trees in pastures was negatively related to rainforest seed diversity, evenness and abundance. Seed diversity and evenness increased significantly with the distance of isolated trees to forest fragments in the Australian sub-tropics, but elsewhere, seed diversity and evenness tended to decline with distance to forest, though not significantly. Our results suggest that the tree composition of landscapes surrounding isolated pasture trees is important for influencing zoochorous-dispersed seed rain, regardless of the region studied. Our study highlights the prominent role of landscape-scale, rather than local-scale factors on seed dispersal to isolated pasture trees, while providing strong evidence that early stage successional processes involving isolated pasture trees are similar throughout global tropical regions.

Rainforest seed rain into abandoned tropical Australian pasture is dependent on adjacent rainforest structure and extent

AbstractIt is well known that the recovery of abandoned tropical pastures to secondary rainforest benefits from the arrival of seeds from adjacent rainforest patches. Less is known, however, about how the structural attributes of adjacent rainforest (e.g. tree density, canopy cover and tree height) impact seed rain patterns into abandoned pastures. Between 2011 and 2013, we used seed traps and ground seed surveys to track the richness and abundance of rainforest seeds entering abandoned pastures in Australia's wet tropics. We also tested how seed rain diversity is related to the distance from forest, the proportion of forest cover in the landscape and several structural attributes of adjacent forest patches, specifically average tree height, canopy cover, tree species richness and density. Almost no seeds were captured in elevated pasture seed traps, even near forest remnants. Abundant forest seeds were found in ground surveys but only within 10 m of forest edges. In ground surveys, seeds from wind‐dispersed species were more abundant, but less species rich, than animal‐dispersed species. A survey of pasture seedling recruits suggested that some forest seeds must be dispersing more than 10 m into pasture at very low frequencies, but only a few species are establishing there. Recruits were predominantly animal‐dispersed not wind‐dispersed species. In addition to distance from forest and the proportion of forest within a 100‐ to 200‐m radius of sampling sites, the richness and density of adjacent forest trees were the most important factors for explaining the probability of seed occurrence in abandoned pastures. Results suggest that without some restoration assistance, the recovery of abandoned pastures into secondary rainforest in Australia's tropical rainforests will likely be limited, at least in part, by a very low rate of seed dispersal away from forest edges and by the diversity and density of trees in adjacent remnant forests.

Sleeping-tree fidelity of the spider monkey shapes community-level seed-rain patterns in continuous and fragmented rain forests

Abstract:Repeated use of sleeping trees (STs) by frugivores promotes the deposition and aggregation of copious amounts of seed, thus having key implications for seed dispersal and forest regeneration. Seed-rain patterns produced by this behaviour likely depend on the frequency of use of these sites, yet this hypothesis has been poorly tested. We evaluated community-level seed-rain patterns produced by the spider monkey (Ateles geoffroyi) over 13 mo in latrines located beneath 60 STs in the Lacandona rain forest, Mexico. Because this primate is increasingly ‘forced’ to inhabit fragmented landscapes, we tested whether sleeping-tree fidelity (STF) differed among sites and between continuous and fragmented forests. We also tested whether seed-rain patterns were associated with STF within each site and forest type. STF was highly variable among STs (average = 7 mo, range = 1–12 mo), but did not differ among study sites or forest types. STF was positively associated with seed abundance, species diversity and species turnover. Nevertheless, STF tended to be negatively related to seed community evenness. These results are likely due to the most frequently used STs being in areas with greater food density. Our results demonstrate that site fidelity shapes community-level seed-rain patterns and thus has key ecological implications.

Functional responses to edge effects: Seed dispersal in the southern Atlantic forest, Argentina

Recent studies have advanced our understanding of the mechanisms behind population and community responses to edge effects. However, functional responses remain poorly explored. Seed dispersal is a key process in ecosystem functioning, and edge effects may alter patterns of seed dispersal through changes in dispersers’ behavior and environmental conditions. Here, we test predictive models of edge effects and habitat suitability on seed dispersal by considering different scenarios given by differences in the dispersal agent (wind and vertebrate dispersal), and the contrast between habitats of native southern Atlantic forest and tree plantations that occur across the entire area of influence of the edge. We fit our data to non-linear theoretical models to explore the response of seed rain to three general patterns of response to edge effects and differences on habitat suitability: (1) monotonic (sigmoid or exponential) (seed rain is higher in one of the habitats), (2) unimodal (seed rain shows either a maximum or a minimum near the edge, with or without differences on habitat suitability between adjacent habitats) and (3) neutral response (seed rain is constant across the ecotone). We estimated abundance and richness of wind- and vertebrate-dispersed seeds using seed traps, and measured vegetation structure in four different edges between native forest and tree plantations (from recent to mature plantations). Edge effects affected seed rain patterns depending on both the degree of vegetation contrast between habitats and the dispersal agent. Wind-dispersed seeds showed a monotonic response to most edges, whereas responses of vertebrate-dispersed seeds varied among edges (monotonic, unimodal and neutral), consistent with the dispersers’ behavior. High contrast edges (forest-recent plantation) showed unimodal edge response, while those created by low contrast edges (forest-mature plantation) exhibited monotonic responses (sigmoid). Differences on habitat suitability on vertebrate-dispersed seeds increased with edge contrast, while richness and abundance of vertebrate-dispersed seeds in the habitat interior showed the opposite pattern. The abundance of wind-dispersed seeds inside the studied habitats increased with edge contrast. The current analytical framework developed to explore responses of populations and communities to edge effects successfully described the response of seed dispersal. Furthermore, edge effects affected seed dispersal patterns differently depending on the dispersal agent and the contrast between habitats. Our findings contribute to the understanding of forest regeneration processes and may help increase the effectiveness of restoration efforts.

Contagious deposition of seeds in spider monkeys' sleeping trees limits effective seed dispersal in fragmented landscapes.

The repeated use of sleeping sites by frugivorous vertebrates promotes the deposition and aggregation of copious amounts of seeds in these sites. This spatially contagious pattern of seed deposition has key implications for seed dispersal, particularly because such patterns can persist through recruitment. Assessing the seed rain patterns in sleeping sites thus represents a fundamental step in understanding the spatial structure and regeneration of plant assemblages. We evaluated the seed rain produced by spider monkeys (Ateles geoffroyi) in latrines located beneath 60 sleeping trees in two continuous forest sites (CFS) and three forest fragments (FF) in the Lacandona rainforest, Mexico. We tested for differences among latrines, among sites, and between forest conditions in the abundance, diversity (α-, β- and, γ-components) and evenness of seed assemblages. We recorded 45,919 seeds ≥5 mm (in length) from 68 species. The abundance of seeds was 1.7 times higher in FF than in CFS, particularly because of the dominance of a few plant species. As a consequence, community evenness tended to be lower within FF. β-diversity of common and dominant species was two times greater among FF than between CFS. Although mean α-diversity per latrine did not differ among sites, the greater β-diversity among latrines in CFS increased γ-diversity in these sites, particularly when considering common and dominant species. Our results support the hypothesis that fruit scarcity in FF can ‘force’ spider monkeys to deplete the available fruit patches more intensively than in CFS. This feeding strategy can limit the effectiveness of spider monkeys as seed dispersers in FF, because (i) it can limit the number of seed dispersers visiting such fruit patches; (ii) it increases seed dispersal limitation; and (iii) it can contribute to the floristic homogenization (i.e., reduced β-diversity among latrines) in fragmented landscapes.

Uncoupled spatiotemporal patterns of seed dispersal and regeneration in Pyrenean silver fir populations

Silver fir (Abies alba) reaches its southwestern distribution limit (rear edge) in the Pyrenees, where it forms highly fragmented populations threatened by drought-induced die-off. Therefore, we need a better knowledge of regeneration patterns and processes (seed production and dispersal, regeneration niche) of such rear-edge stands to assist their long-term conservation. Seed rain patterns were studied in two structurally contrasting sites: an even-aged pure stand (Las Eras) and an uneven-aged mixed silver fir-beech (Fagus sylvatica) stand (Gamueta) over 8 and 12years, respectively. Seed production experienced a greater synchrony in years of high seed production than when crops were low, suggesting masting behavior in both sites. Seed inverse modeling methods resulted in dispersal curves differing between sites, with estimates of mean dispersal distances of 9.9 and 21.5m for the pure and mixed stands, respectively. Long-term sampling of seed dispersal and production was complemented with an analysis of silver fir regeneration niche. Seed and seedling patterns were spatially uncoupled, emphasizing the relevance of microsite filtering of regeneration. Understory light environment was the main factor explaining seedling emergence and mortality. Our study provides a mechanistic basis and a methodological approach for understanding the colonization ability of Pyrenean rear-edge silver fir stands and similar tree populations.

Frugivore Behavioural Details Matter for Seed Dispersal: A Multi-Species Model for Cantabrian Thrushes and Trees

Animal movement and behaviour is fundamental for ecosystem functioning. The process of seed dispersal by frugivorous animals is a showcase for this paradigm since their behaviour shapes the spatial patterns of the earliest stage of plant regeneration. However, we still lack a general understanding of how intrinsic (frugivore and plant species traits) and extrinsic (landscape features) factors interact to determine how seeds of a given species are more likely to be deposited in some places more than in others. We develop a multi-species mechanistic model of seed dispersal based on frugivore behavioural responses to landscape heterogeneity. The model was fitted to data from three-years of spatially-explicit field observations on the behaviour of six frugivorous thrushes and the fruiting patterns of three fleshy-fruited trees in a secondary forest of the Cantabrian range (N Spain). With such model we explore how seed rain patterns arise from the interaction between animal behaviour and landscape heterogeneity. We show that different species of thrushes respond differently to landscape heterogeneity even though they belong to the same genus, and that provide complementary seed dispersal functions. Simulated seed rain patterns are only realistic when at least some landscape heterogeneity (forest cover and fruit abundance) is taken into account. The common and simple approach of re-sampling movement data to quantify seed dispersal produces biases in both the distance and the habitat at which seeds arrive. Movement behaviour not only affects dispersal distance and seed rain patterns but also can affect frugivore diet composition even if there is no built-in preference for fruiting species. In summary, the fate of seeds produced by a given plant species is strongly affected by both the composition of the frugivore assemblage and the landscape-scale context of the plant location, including the presence of fruits from other plants (from the same or different species).

Chuva de sementes de espécies lenhosas florestais em mosaicos de floresta com Araucária e campos no Sul do Brasil

Mecanismos de dispersão de diásporos e recrutamento de plântulas evitam a competição intra-específica e possibilitam a colonização de novos ambientes. Em áreas de transição entre florestas e vegetação campestre esses processos não são aleatórios, e sim associados muitas vezes a indivíduos lenhosos isolados em tais áreas de campo ou a formações arbustivas. No sul do Brasil, as Florestas com Araucária formam mosaicos com áreas campestres e observa-se o avanço da floresta sobre os campos. O estudo teve como objetivo avaliar a chuva de sementes de espécies lenhosas florestais associadas a áreas de ecótonos de Floresta com Araucária e campos e a indivíduos lenhosos isolados na matriz campestre. Os estudos foram realizados no Centro de Pesquisas e Conservação da Natureza Pró-Mata PUCRS, em São Francisco de Paula, RS, em vegetação campestre excluída de fogo e de pastejo há 16 anos, circundada por florestas. A chuva de sementes foi avaliada mensalmente por um período de oito meses com o uso de coletores que foram posicionados em ecótonos de floresta e campos com diferentes fisionomias e sob indivíduos lenhosos isolados na matriz campestre. Tais ambientes foram comparados através de análise de variância univariada e multivariada para verificar padrões de chuva de sementes. Os resultados indicaram que a dispersão de sementes em áreas campestres ocorre preferencialmente associada a indivíduos isolados de Araucaria angustifolia e a formações arbustivas de Baccharis uncinella e que tais ambientes funcionariam como extensões de condições mais semelhantes à floresta na matriz campestre.

Spatial and temporal dynamics of Phytolacca americana seed rain under Robinia pseudoacacia forest in Lingshan Bay National Forest Park, Shandong, China.

Aims Phytolacca americana is a serious invasive plant species, which has harmed biodiversity and arboreal regeneration in coastal protective forests in Shandong Province. Our objective was to reveal its mechanism of reproduction and dispersal in order to provide guidance for controlling its invasion. Methods To study the spatial and temporal pattern of seed rain of P. americana, we conducted field surveys under Robinia pseudoacacia forest in Lingshan Bay National Forest Park from September to December 2008. We established five transects at 15 m intervals from forest edge to forest interior and within each transect set up 30 samples (1 m × 1 m) to survey seed densities. We also chose eight mother plants of P. americana at 10 m intervals in each transect and placed seed traps (30 cm × 30 cm × 10 cm) at 11 sample points at every 30 cm surrounding them. We collected fallen seeds one or two days. One-way ANOVA was used to test the diversity. Important findings The quantities and densities of seed rain were 1 846–2 273 seeds and 621–1 382 seeds per square meter, respectively, and values decreased from forest edge to interior. In five transects, the average seed rain densities were 33.64%–60.80% of reproduction, and the total average seed rain density accounted for 49.52% of seed reproduction densities; the rest was removed by firewood collecting and seed predation by animals. Seed rain began in mid September and ended in late December, and it occurred on forest edges before forest interiors. There were two seed-rain peaks in late October and mid December, and maximum intensities were 32 and 59 seeds per square meter per day, respectively. The dispersal distance of seed rain decreased from forest edge to forest interior. The same pattern existed with increasing distance from mother plant. The maximal dispersal and weighted mean distances were 210–180 cm and 94.32–63.03 cm, respectively; the average weighted mean 翟树强等: 灵山湾国家森林公园刺槐林下垂序商陆种子雨时空动态 1237 doi: 10.3773/j.issn.1005-264x.2010.10.013 distance was 81.00 cm. Phytolacca americana seed rain had obvious spatio-temporal heterogeneity. Findings were important to predict the invasive potential of P. americana and the trend in community structure.

Effects of bamboo stands on seed rain and seed limitation in a rainforest

Bamboos often negatively affect tree recruitment, survival, and growth, leading to arrested tree regeneration in forested habitats. Studies so far have focused on the effects of bamboos on the performance of seedlings and saplings, but the influence of bamboos on forest dynamics may start very early in the forest regeneration process by altering seed rain patterns. We tested the prediction that the density and composition of the seed rain are altered and seed limitation is higher in stands of Guadua tagoara (B or bamboo stands), a large-sized woody bamboo native from the Brazilian Atlantic Forest, compared to forest patches without bamboos (NB or non-bamboo stands). Forty 1 m 2 seed traps were set in B and NB stands, and the seed rain was monitored monthly for 1 year. The seed rain was not greatly altered by the presence of bamboos: rarefied seed species richness was higher for B stands, patterns of dominance and density of seeds were similar between stands, and differences in overall composition were slight. Seed limitation, however, was greater at B stands, likely as a resulted of reduced tree density. Despite such reduced density, the presence of trees growing amidst and over the bamboos seems to play a key role in keeping the seeds falling in B stands because they serve as food sources for frugivores or simply as perches for them. The loss of such trees may lead to enhanced seed limitation, contributing ultimately to the self-perpetuating bamboo disturbance cycle.

Spatiotemporal patterns of seed dispersal in a wind‐dispersed Mediterranean tree (Acer opalus subsp. granatense): implications for regeneration

Seed dispersal can severely limit the quantity of plant recruits and their spatial distribution. However, our understanding of the role of dispersal in regeneration dynamics is limited by the lack of knowledge of seed deposition patterns in space and time. In this paper, we analyse the spatiotemporal variability of seed dispersal patterns in the Mediterranean maple, Acer opalus subsp. granatense, by monitoring seed rain along two years at a broad spatial scale (2 mountain ranges, 2 populations per range, 4 microhabitats per population). We quantified seed limitation and its components (source and dispersal limitation), and explored dispersal limitation in space by analysing dispersal distances, seed aggregation, and microhabitat seed distribution. Acer opalus subsp. granatense was strongly seed‐limited throughout the gradients explored, being always dispersal limitation much higher than source limitation. The distribution of seeds with distance from adult individuals was leptokurtic and right‐skewed in all populations, being both kurtosis and skewness higher the year of the highest seed production. Dispersal distances were shorter than expected by random in the four populations, which suggests distance‐limited dispersal. Dispersal patterns were highly aggregated and showed a preferential direction around adults. At the microhabitat scale, most seeds accumulated under adult maples. However, there were no more seeds under trees and shrubs other than maple than in open interspaces, implying that established vegetation does not disrupt patterns of seed deposition by physically trapping seeds. When compared with patterns of seedling establishment, limited dispersal ability and inter‐annual spatial concordance in seed rain patterns suggest that several potentially safe sites for recruitment have a very low probability of receiving seeds in most maple populations. These findings are especially relevant for rare species such as Acer opalus subsp. granatense, and illustrate how dispersal studies are not only crucial for our understanding of plant population dynamics but also to provide conservation directions.

Modelling seed dispersal to predict seedling recruitment: Recolonization dynamics in a plantation forest

The extend to which seed dispersal influences seedling recruitment is of major importance for forest dynamics. In non-equilibrium situations, seed dispersal might be of even further importance as it is a major determinant of the rate and composition of secondary succession. We modelled primary seed dispersal in a planted pine–spruce stand intensively recolonized by Abies alba and Fagus sylvatica, an ecological situation commonly found throughout southern Europe. We then evaluated the role of primary seed dispersal in seedling emergence and recruited seedling density. Using a seed trap experiment and inverse modelling methods, we calibrated short- and medium-distance seed dispersal functions. The relationship between the density of dispersed seed, the density of emerging seedlings and microsite characteristics were assessed using generalized linear models. The cumulative distribution function of seedling-to-nearest-adult distances made it possible to test the concordance between seed rain patterns and seedling spatial distributions. Seed production was highly variable between years for A. alba and F. sylvatica. Seed dispersal was shown to be locally restricted (median dispersal distance of 13.2–19.2 m for A. alba depending on the year and 6.49 m for F. sylvatica). Model prediction was considerably increased when seed production was directly assessed (and not indirectly estimated using diameter, for example). The number of A. alba seedlings that emerged in 1999 was positively correlated with the number of seeds dispersed in 1998 and with the local density of Picea abies adults, and negatively correlated with grass cover. The spatial distribution of seedlings was less aggregated around adult trees than expected from seed dispersal models, but significantly different from random beyond 6 m to the nearest adult for F. sylvatica and 26 m for A. alba. Thus, seed rain patterns are only partially responsible for recruitment dynamics in our model forest. Our study demonstrates that inverse modelling methods are well suited for the study of seed dispersal at the local scale, especially when a direct count of seed production can be made, and are therefore of particularly high interest in forests where several successional stages are present.

Extensive hydrochory uncouples spatiotemporal patterns of seedfall and seedling recruitment in a ‘bird‐dispersed’ riparian tree

Summary Initial recruitment is by far the most variable and least predictable phase of the plant life cycle. Its dynamics remain little known, particularly in complex seed dispersal systems and over multiple reproductive cycles. Seeds of the tree Frangula alnus are usually dispersed by frugivorous birds. Mediterranean populations, however, are mostly restricted to riparian forests, and their seeds may be re‐distributed during the winter by elevated stream water flow. Strength and frequency of peak discharges vary greatly from year to year. I investigated spatiotemporal variation of initial recruitment by monitoring fruit production, seedfall and seedling emergence over 4 years along permanent transects in two F. alnus populations growing along small mountain streams in southern Spain. Seedling abundance varied greatly among years and independently of fruit or primary seedfall abundance. Spatial distributions of both seedfall and seedling emergence were highly consistent among years. Bird‐mediated seedfall density decreased exponentially with both increasing distance from the nearest fruiting tree and the decrease of its crop size. Seedling emergence was, however, uncoupled in space from the previous year's seedfall, both across single sample points and entire 60‐m transects. Dispersal experiments with seed mimics revealed that flooding caused secondary dispersal of much of the population seed pool over several scores of metres. Seed re‐distribution by water appears to override patterns of primary (bird‐generated) seedfall and to determine spatial patterns of seedling recruitment. Seedling emergence is, however, more stable across years than would be expected given the unpredictability of rainfall (and thus stream flow), suggesting that seed deposition may be primarily determined by relatively stable microsite characteristics. The dynamics of seed rain patterns are of critical importance for plant population demography and spatial structures. The finding that even complex, multistep dispersal systems may produce remarkably consistent year‐to‐year distributions of recruits has important implications for the interpretation of long‐term patterns of riparian plant regeneration at the landscape level and resulting conservation management.

Fruiting trees as dispersal foci in a semi-deciduous tropical forest.

Quantification of seed rain patterns is an initial step toward explaining variation in plant recruitment, and consequently, organization of forest communities. Spatially contagious patterns of seed deposition, where seeds are patchily dispersed with some sites receiving relatively high densities and others receiving low densities of seeds, may be a common phenomenon for which we have very little knowledge. For example, prior feeding events by frugivores (monkeys and birds) combined with transport and dispersal of seeds to other fruiting trees may result in the contagious deposition of non-conspecific seeds below them. Here, we examined whether fruiting trees act as dispersal foci in the semi-deciduous tropical rainforest of the Dja Reserve, Cameroon. Seed rain was sampled below the canopies of nine tree species: three typically dispersed by large, frugivorous birds, three dispersed by monkeys, and three dispersed by wind. We found no evidence that monkeys generate spatially contagious patterns of seed rain under fruiting trees at which they feed. However, we found that rates of deposition of non-conspecific seeds and species richness of seeds delivered by birds (hornbills and turacos) were significantly greater during fruiting than non-fruiting periods, and significantly greater under fruiting individuals of bird-dispersed tree species than under fruiting individuals of monkey- or wind-dispersed tree species. Additionally, during fruiting periods, the composition of non-conspecific seed rain under bird-dispersed tree species was more similar to other bird-dispersed trees than to monkey- or wind-dispersed tree species. The contagious dispersal of non-conspecific seeds to fruiting, bird-dispersed trees leads to higher seed densities under fruiting trees than those caused by local seed production. Non-conspecific seeds deposited in high densities may experience increased seed mortality even far from parent trees if predators are generalists. Alternatively, in the absence of complete density-dependent mortality, contagious seed dispersal could result in associations among species dispersed by the same dispersal agent.

Community seed rain patterns and a comparison to adult community structure in a West African tropical forest

We examined the seed rain throughout a twelve month period in a lowlandtropical forest in Cameroon, West Africa, 1996–97. Traps (0.5m2, n = 216) were erected throughout a 25km2 area in 24 randomly placed clusters of nine trapseach. Fruits and seeds that landed in traps were collected every 7–10daysand classified by species and dispersal type. More than 32,000 seeds fromapproximately 200 species fell into the traps, an average of 297 seedsm−2 yr−1 Thirty species represent 82%of the total seed rain while an additional 175 species comprise the remaining18%. When we compared the adult community to the seed rain community within thesame plots, we found no apparent correlation between seed rain patterns andadult community structure for this year of study. Furthermore, only 49% of theadult tree community produced and dispersed seed into traps in this year. Morethan 100 species (52%) found in the seed rain represented long-distanceimmigrant seed rain. Seed rain was highly variable at several scales, bothspatially and seasonally, although seeds arrived in traps during eachcollectionperiod. Cluster analyses showed that traps within plots were seldom moresimilarto one another than traps between plots. While 82% of the tree species in thecommunity are thought to be animal dispersed, only 28% of all seeds that fellinto traps had been obviously “handled” (bitten, chewed, or passed)by animals. Tests for fruit and seed removal by predators or dispersers found5%or less removal rate from traps.