Flow regulation affects temporal patterns of riverine plant seed dispersal: potential implications for plant recruitment

1. Changes to the natural flow regime of a river caused by flow regulation may affect waterborne seed dispersal (hydrochory), and this may be an important mechanism by which regulation affects riverine plant communities. We assessed the effect of altered timing of seasonal flow peaks on hydrochory and considered the potential implications for plant recruitment. 2. We sampled hydrochory within five lowland rivers of temperate Australia, three of which are regulated by large dams. These dams are operated to store winter and spring rains and release water in summer and autumn for agriculture. At three sites on each river, hydrochory was sampled monthly for 12 months using passive drift nets. The contents of the drift samples were determined using the seedling‐emergence method. 3. More than 33 000 seedlings from 142 taxa germinated from the samples. In general, more seeds and taxa were observed in the drift at higher flows. By altering the period of peak flows from winter–spring to summer–autumn, flow regulation similarly affected the period of peak seed dispersal. The effect of regulation on seed dispersal varied between taxa depending on their timing of seed release and whether or not they maintain a persistent soil seed bank. 4. Hydrochory in rivers is a product of flow regime and the life history of plants. By altering natural flow regimes and thus hydrochorous dispersal patterns, flow regulation is likely to affect adversely the recruitment of native plant species with dispersal phenologies adapted to natural flow regimes (such as many riparian trees and shrubs) and encourage the spread of non‐native (exotic) species. 5. Changes to hydrochorous dispersal patterns are an important mechanism by which altered flow timing affects riverine plant communities. Natural seasonal flow peaks (in this case spring) are likely to be important for the recruitment of many native riparian woody taxa.     

Seed dispersal in a polder after partial tidal restoration: Implications for salt‐marsh restoration

Question: The vegetation in a polder after partial tidal restoration does not resemble the targeted salt‐marsh vegetation. Is this difference in vegetation due to lack of dispersal or unsuitable abiotic conditions? What could be done for a better restoration of the site? Location: Northwestern France. Methods: Seeds were trapped at the single inlet of the polder with a 200‐μ m mesh net to estimate inputs of seeds from the bay. In parallel, seed dispersal was studied in the polder by placing Astroturf® seed traps on the surface of the sediment at three different elevations in three distinct areas. Abiotic conditions such as flooding frequency, water table level and soil salinity were monitored. Results: All but one species from the adjacent salt marshes were trapped at the inlet. Not all of these species were on the seed traps inside the polder. Seed dispersal was not homogeneous in the polder and seed trap content mostly discriminated in function of their elevation. Salinity and water logging at the bottom of the slope were very high compared to tolerance of most halophytes but decreased rapidly higher up the slope. Conclusions: The development of salt marsh target species is highly restricted by limited hydrochory inside the polder but also by unfavourable soil conditions induced by the actual hydrological regime. Halophytes are excluded at the bottom of the slope by abiotic conditions and out‐competed by sub‐halophytes higher up. In order to restore salt marsh vegetation inside the polder, a larger opening should be induced in order to increase the flooded surface, and diminish water logging and flooding frequencies.     

The role of mammals in maintaining plant species richness in a floating Typha marsh in southern Ontario

Animals are known to influence and sometimes help maintain plant species richness in terrestrial systems. This study investigated the effects of mammals in influencing plant species richness of a floating Typha marsh at Point Pelee National Park. The extent of use of the marsh by terrestrial mammals was documented by mapping mammal trails from air photographs. Trail densities ranging from 70 to 1550 m ha–1 in various areas of the marsh, provided evidence for widespread, and in some places frequent, mammal activity. Plant surveys indicated a pattern of increased species richness and frequency associated with these trails, particularly in late summer when Typha biomass increased off trails. Three mechanisms by which mammals might influence species richness: disturbance of the dominant Typha, nutrient enrichment, and seed dispersal, were investigated using field and lab experiments. Two types of disturbance, trampling and herbivory, at two levels of intensity were simulated within 2×2m plots with and without fertilizer added. Disturbance significantly affected species richness; high levels of trampling decreased while high levels of clipping increased species richness. Nutrients had no effect; there were no significant disturbance×nutrients interactions. The importance of seed dispersal by raccoon was studied by collecting raccoon scat from within the marsh, incubating scat in a growth chamber and comparing the species that emerged to those growing in the marsh. Although substantial numbers of viable seeds of terrestrial species were found in scat, only one of these species was actually part of the Typha mat community. We concluded that mammals do influence plant species richness in this marsh primarily through disturbance of the dominant Typha.     

Spatial–temporal distribution of ornithochorous seeds from an Elaeagnus umbellata community dominating a riparian habitat

The dispersal efficiency and potential distribution of ornithochorous seeds of Elaeagnus umbellata in a riparian habitat were evaluated to clarify this species' establishment site in relation to the disturbance regime of the floodplain. Fruit removal by avian frugivores was monitored using fruit bags, and the spatial distribution of excreted seeds was quantified by seed traps set randomly on a gravel bar as an isolated seed source in the Yoshino River throughout an autumn fruiting season. Although more than 45% of the fruits remained on the twigs in the fruit bags, almost all fruits on the control twigs without fruit bags were exploited by the beginning of January. The fruit removal rate and seed dispersal distance were positively correlated with an increase in wintering bird species and their abundance. Intact bird‐dispersed seeds of E. umbellata were trapped within a 400‐m range and damaged seeds were limited to traps set within 50 m from the seed source. Frugivore behavior, such as feces excretion on rocks near water drinking sites and perching on surrounding woodland, greatly influenced the spatial and temporal dispersal pattern of the seed rain. In the present study, the avian frugivores showed upstream seed dispersal; thus, in years with stochastic autumnal floods, secondary dispersal via hydrochory downstream may be facilitated. The intensive seed dispersal in E. umbellata indicates that the present distribution of parent trees in the restricted elevation range of the gravel bars is the result of survival through disturbance, rather than seed dispersal limitation.     

The role of hydrochory in structuring riparian and wetland vegetation

Hydrochory, or the passive dispersal of organisms by water, is an important means of propagule transport, especially for plants. During recent years, knowledge about hydrochory and its ecological consequences has increased considerably and a substantial body of literature has been produced. Here, we review this literature and define the state of the art of the discipline. A substantial proportion of species growing in or near water have propagules (fruits, seeds or vegetative units) able to disperse by water, either floating, submerged in flowing water, or with the help of floating vessels. Hydrochory can enable plants to colonize sites out of reach with other dispersal vectors, but the timing of dispersal and mechanisms of establishment are important for successful establishment. At the population level, hydrochory may increase the effective size and longevity of populations, and control their spatial configuration. Hydrochory is also an important source of species colonizing recruitment‐limited riparian and wetland communities, contributing to maintenance of community species richness. Dispersal by water may even influence community composition in different landscape elements, resulting in landscape‐level patterns. Genetically, hydrochory may reduce spatial aggregation of genetically related individuals, lead to high gene flow among populations, and increase genetic diversity in populations receiving many propagules. Humans have impacted hydrochory in many ways. For example, dams affect hydrochory by reducing peak flows and hence dispersal capacity, altering the timing of dispersal, and by presenting physical barriers to dispersal, with consequences for riverine plant communities. Hydrochory has been inferred to be an important vector for the spread of many invasive species, but there is also the potential for enhancing ecosystem restoration by improving or restoring water dispersal pathways. Climate change may alter the role of hydrochory by modifying the hydrology of water‐bodies as well as conditions for propagule release and plant colonization.     

Synchrony of Seed Dispersal, Hydrology and Local Climate in a Semi-arid River Reach in California

The temporal availability of propagules is a critical factor in sustaining pioneer riparian tree populations along snowmelt-driven rivers because seedling establishment is strongly linked to seasonal hydrology. River regulation in semi-arid regions threatens to decouple seed development and dispersal from the discharge regime to which they evolved. Using the lower Tuolumne River as a model system, we quantified and modeled propagule availability for Populus fremontii (POFR), Salix gooddingii (SAGO), and Salix exigua (SAEX), the tree and shrub species that dominate near-channel riparian stands in the San Joaquin Basin, CA. A degree-day model was fit to field data of seasonal seed density and local temperature from three sites in 2002–2004 to predict the onset of the peak dispersal period. To evaluate historical synchrony of seed dispersal and seasonal river hydrology, we compared peak spring runoff timing to modeled peak seed release periods for the last 75 years. The peak seed release period began on May 15 for POFR (range April 23–June 10), May 30 for SAGO (range May 19–June 11) and May 31 for SAEX (range May 8–June 30). Degree-day models for the onset of seed release reduced prediction error by 40–67% over day-of-year means; the models predicted best the interannual, versus site-to-site, variation in timing. The historical analysis suggests that POFR seed release coincided with peak runoff in almost all years, whereas SAGO and SAEX dispersal occurred during the spring flood recession. The degree-day modeling approach reduce uncertainty in dispersal timing and shows potential for guiding flow releases on regulated rivers to increase riparian tree recruitment at the lowest water cost.     

The dispersal and deposition of hydrochorous plant seeds in drainage ditches

1. Surface water is an important dispersal vector for wetland plant species. However, most previous studies on hydrochory (i.e. water dispersal) have focused on ecosystems with relatively rapid water flow. Therefore, there is a need to study such dispersal in slow‐flowing or stagnant waterbodies, such as drainage ditches, which might act as dispersal corridors between habitat patches. 2. To gain insight into the mechanisms by which seeds are transported in drainage ditches, the effect of the velocity of wind and water on the rate of transport of floating seeds of three wetland species (Carex pseudocyperus L., Iris pseudacorus L. and Sparganium erectum L.) was investigated. Furthermore, in release and retrace experiments with painted C. pseudocyperus seeds, a number of factors potentially determining the probability of seed deposition were investigated. 3. Net wind speed was found to be the main factor determining the rate at which seeds are transported in drainage ditches. No relation between water flow at middepth in the ditches and seed transport was found. Wind speed and flow at the water surface were positively related. The effect of wind speed on the rate of transport of floating seeds was greater for S. erectum seeds, because a greater ratio of their volume protrudes from the water, than for C. pseudocyperus and I. pseudacorus seeds. 4. The principal factors that determine seed deposition were aquatic plant cover, ditch slope and indentations in the ditch bank. Seeds changed direction if the wind direction changed, or if there was a bend in the ditch. The final pattern of deposition was related to mean net wind speed. Mean transport distance after 2 days varied between 34 and 451 m. 5. Unlike in rivers, seed transport in ditches was determined by wind speed and direction, enabling multidirectional seed dispersal. We conclude that in slow‐flowing waters, wind is a more important driver for hydrochorous seed transport than the flow of water. This sheds a new light on hydrochory and has important consequences for the management of otherwise fragmented wetland remnants.     

Hydrodynamics and seed dispersal in the lower Amazon

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丹江口库区滩涂与入库支流植被与土壤种子库: 水传播潜力探讨

为了探索库区滩涂与入库支流土壤种子库与植被的关系, 以及物种通过水传播扩散的潜力, 对丹江口库区内4条支流及其入库滩涂的地表植被和土壤种子库进行了调查。结果显示, 支流地表植被和种子库的物种多样性高于库区滩涂, 汉江库区滩涂和支流的地表植被与种子库均有较高的物种相似性。DCA排序和TWINSPAN聚类可以明显地将支流的植被和种子库样方与滩涂的植被和种子库样方分到不同的样方组, 结合物种排序图可以清楚地发现, 流入汉江库区支流的植被和种子库的物种组成与滩涂的植被和种子库的物种组成有密切联系。汉江库区滩涂0-15 cm的土层内都有种子萌发, 而丹江库区种子库中只有狗牙根(Cynodon dactylon)一种植物, 且仅存在于0-5 cm土层。研究结果表明, 繁殖体通过支流向滩涂的水传播作用对植被建立有积极贡献。     

Landscape-scale variation in the seed banks of floodplain wetlands with contrasting hydrology in China

1. At a local scale, the species composition, diversity and spatial variation of wetland plant communities are determined primarily by spatial and temporal heterogeneity in their environments. Less is known about variation at a landscape‐level. The floodplain of the Changjiang (Yangtze) River in China includes hydrologically connected, subtropical wetlands with different hydrological characteristics. 2. We examined seed‐bank species composition and richness in marshes of two contrasting hydrological types: permanent marshes, fed by local runoff, and lakeshore marshes more closely connected to the regulated river. Lakeshore marshes are flooded annually to depth of approximately 1 m and during flooding they support an alternate, aquatic vegetation type. The soil seed bank in March was a comparative estimator of species diversity. At the beginning of the growing season it included seeds from both phases of alternating vegetation types associated with the annual hydrological cycle. 3. A regional pool of 101 species was detected in the seed banks of six wetlands associated with the river and its tributaries: 56 occurred in permanent marshes and 59 in lakeshore marshes, with only 15 common to both. Species rarefaction curves indicated that more species occurred in permanent than lakeshore marshes at equal numbers of individuals sampled. However, the more heterogeneous lakeshore seed banks were estimated (Chao 2) to have greater total species richness (81) than permanent marsh (60). 4. Analysis using Sørensen's coefficient of similarity and DCA ordination revealed complex variation, with much greater differences between hydrological types than within them, irrespective of geographical distance. The types also differed significantly in the composition of four functional groups of species. 5. Despite the potential for dispersal of propagules via the annually pulsing river system (hydrochory), at a regional and landscape scale, diversity is maintained largely by large‐scale temporal hydrological heterogeneity and smaller scale spatial and topographic heterogeneity.     

Experimentation,modelling, and simulation of hydrochory in an Amazonian river

1. Seed transport by hydrochory is a key mechanism of long-distance dispersal constrained by attributes of the seed and hydrodynamics of the river, influenced by seasonal precipitation and hydrological pulses. However, the extent to which a hydrodynamic model can predict seed dispersal influenced by a tributary is unknown.
2. The study was conducted along a 10-km stretch of the Falsino River in Amapá, Brazil. Hydrodynamic parameters from the 2021 rainy season were used to calibrate a three-dimensional numerical model (SisBaHia) and simulate hydrochory of Macrolobium bifolium, a widely distributed species in the Amazon floodplains. This model was coupled with a Lagrangian dispersal model to estimate the average transport distance of the fruit plume. The simulated results were compared statistically with those of dispersal quantified in the field.
3. The field experiment coincided with the maximum hydrological pulse, providing with a maximum potential distance of longitudinal dispersal fruit of c. 10 km in 2 hr. The orders of magnitude of the mean plume transport (observed and numerically simulated centre of mass) were compatible with each other over six longitudinal tracking sections (4.0% ≤ estimated × observed error ≤ 16.5%). Different channel stretches had distinct hydraulic characteristics that influenced spatial dispersal dynamics and are likely to be factors influencing the distribution of M. bifolium in these environments.
4. The present research is a contribution to understanding fluvial hydrodynamics and hydrochory by M. bifolium, whose seed dispersal syndrome is an adaptive characteristic that might explain its abundance and richness in these Amazonian riparian zones. We used M. bifolium as a model species to understand the role of seasonal flood pulse and fluvial hydrodynamics related to hydrochory favouring.

     

Seed Dispersal and Seedling Emergence in a Created and a Natural Salt Marsh on the Gulf of Mexico Coast in Southwest Louisiana, U.S.A.

Early regeneration dynamics related to seed dispersal and seedling emergence can contribute to differences in species composition among a created and a natural salt marsh. The objectives of this study were to determine (1) whether aquatic and aerial seed dispersal differed in low and high elevations within a created marsh and a natural marsh and (2) whether seedling emergence was influenced by marsh, the presence of openings in the vegetation, and seed availability along the northern Gulf of Mexico coast. Aerial seed traps captured a greater quantity of seeds than aquatic traps. Several factors influenced aquatic and aerial seed dispersal in a created and a natural salt marsh, including distance from the marsh edge, cover of existing vegetation, and water depth. The natural marsh had a high seed density of Spartina alterniflora and Distichlis spicata , the low-elevation created marsh had a high seed density of S. alterniflora , and the high-elevation created marsh had a high seed density of Aster subulatus and Iva frutescens . The presence of adult plants and water depth above the marsh surface influenced seed density. In the natural marsh, openings in vegetation increased seedling emergence for all species, whereas in the low-elevation created marsh, S. alterniflora had higher seedling density under a canopy of vegetation. According to the early regeneration dynamics, the future vegetation in areas of the low-elevation created marsh may become similar to that in the natural marsh. In the high-elevation created marsh, vegetation may be upland fringe habitat dominated by high-elevation marsh shrubs and annual herbaceous species.     

A keystone ant species promotes seed dispersal in a “diffuse” mutualism

In order to understand the dynamics of co-evolution it is important to consider spatial variation in interaction dynamics. We examined the relative importance of ant activity, diversity and species identity in an ant seed dispersal mutualism at local, regional and continental scales. We also studied the determinants of seed dispersal rates and dispersal distances at eight sites in the Eneabba sandplain (29.63 S, 115.22 E), western Australia to understand local variation in seed dispersal rate and distance. To test the generality of the conclusions derived from the eight local sites, we established 16 sites along a 1650-km transect in western Australia, covering 11° of latitude and a six-fold increase in rainfall, at which we sampled the ant assemblage, estimated ant species richness and ant activity and observed the removal rate of myrmecochorous seeds. We also assessed the importance of ant species identity at a continental scale via a review of studies carried out throughout Australia which examined ant seed dispersal. Among the eight sandplain shrubland sites, ant species identity, in particular the presence of one genus, Rhytidoponera, was associated with the most dispersal and above average dispersal distances. At the landscape scale, Rhytidoponera presence was the most important determinant of seed removal rate, while seed removal rate was negatively correlated with ant species richness and latitude. Most ant seed removal studies carried out throughout Australia reinforce our observations that Rhytidoponera species were particularly important seed dispersers. It is suggested that superficially diffuse mutualisms may depend greatly on the identity of particular partners. Even at large biogeographic scales, temporal and spatial variation in what are considered to be diffuse mutualisms may often be linked to variation in the abundance of particular partners, and be only weakly – or negatively – associated with the diversity of partners.     

Gastrointestinal passage time of seeds ingested by captive Japanese martens <Emphasis Type="Italic">Martes melampus</Emphasis>

The time it takes for ingested seeds to pass through the gut of animals is an important aspect of endozoochorous seed dispersal because it influences seed dispersal distance. Variations in the physical characteristics of seeds, such as their weight, volume, and specific gravity, can affect their movement through the gastrointestinal system of a given animal. We conducted feeding experiments with captive Japanese martens, Martes melampus (n = 4), at Toyama Municipal Family Park Zoo, central Japan to examine the effects of the physical characteristics of seeds on their passage times. The mean (±SD) transit time, mean retention time, and time of last appearance of four different types of commercial seeds were 2.6 ± 0.3 h (range 0.6–5.4), 9.7 ± 1.1 h (3.8–17.3), and 23.8 ± 3.1 h (12.2–51.8), respectively. All of these values are greater than those found during previous experiments conducted with mustelids. Similar to previous studies, however, none of these passage time variables was correlated with the physical characteristics of seeds. Our results thus indicate that martens disperse seeds of different plant species, whose size, volume, and specific gravity all fall within the range of those used in the present study, from parent plants at similar distances.     

Digging deep for diversity: riparian seed bank abundance and species richness in relation to burial depth

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Shrub invasion into subalpine vegetation: implications for restoration of the native ecosystem

The ability of plant communities to recover after non-native species invasion will depend upon the nature of their soil seed bank and seed rain characteristics. This study assessed changes in the soil seed bank and seed rain associated with the invasion of the non-native shrub Cytisus scoparius in subalpine vegetation. Soil seed bank and seed rain composition, density and richness were investigated at three areas of different stages of invasion: (i) recent (8–10 years), (ii) mature (15–16 years) and (iii) long-term (25 years). There were few changes in seed bank composition or richness regardless of invasion stage. By contrast, the seed rain composition, richness and density was substantially different within long-invaded areas. Very few seeds were able to colonise the dense barrier characteristic of larger, more mature C. scoparius stands. Some prominent herbs from the native vegetation were under-represented or absent from the seed bank, both in invaded and uninvaded areas. Laboratory germination experiments demonstrated that most native species germinate easily, which may imply a transient seed bank, rather than a persistent one. The majority of herbaceous and shrub species were capable of resprouting vegetatively. Therefore, regeneration appeared more reliant on the bud and tuber bank than a persistent soil seed bank. The dominance of graminoid species and C. scoparius rather than other herbaceous, shrub or tree species suggests that the regenerating vegetation will be dominated by grass species and/or C. scoparius. Hence, in areas where long-invaded C.␣scoparius stands are present the recovery of native subalpine vegetation maybe difficult. Recovery may only be possible through wind dispersal from the surrounding intact vegetation or through actively reseeding the area. This study highlights the importance of early intervention in invasive species management.     

The role of Japanese macaques (Macaca fuscata) as endozoochorous seed dispersers on Kinkazan Island, northern Japan

We studied the characteristics of seeds within faeces, an important aspect of endozoochorous seed dispersal, in Japanese macaques Macaca fuscata inhabiting Kinkazan Island, northern Japan. We intermittently collected faecal samples from 1999 to 2009 (N = 1294) and examined the rate of seed occurrence, species/life-form composition, number of seeds, and their intact rate. Seeds were found within faecal samples during every month, but their characteristics changed monthly: the rate of seed occurrence and the number of plant species within faecal samples were greater in summer and fall, and the intact rate and number of intact seeds observed within single faecal samples were also higher during these seasons than spring and winter. These results suggest that Japanese macaques on Kinkazan act as seed dispersers in summer and fall and that they disperse intact seeds into wider areas within the forest through defecation. During the study period, we observed seeds from a total of 35 plant species from 22 families in our samples. In addition to those of woody plants, we also observed seeds from as many as 12 herbaceous plants, for which sympatric sika deer (Cervus nippon) have historically been considered the sole seed dispersal agents. The intact rate of seeds was significantly negatively correlated with the seeds’ mean cubic diameter, and this relationship was strengthened for non-fleshy fruits. We also conducted regional comparisons of the characteristics of defecated seeds in order to address whether regional variations in the diet of the macaques affect their efficacy as seed dispersers, both in terms of quantity and quality. Macaques living in the natural habitats of Kinkazan and Yakushima dispersed more seeds of tall tree species than do macaques inhabiting the human-altered areas of in Shimokita and Kashima. The number of plant species represented within single faecal samples also varied geographically, being greater in Yakushima. This pattern likely resulted from Yakushima's warm temperate climate, as the other three study sites occur in the cool temperate region. Our results suggest that the composition of seeds dispersed by Japanese macaques is not rigid, but is determined instead by the vegetation found in a given habitat.     

A herbivory-induced increase in the proportion of floating seeds in an invasive plant

It is important to determine the factors prompting seed dispersal because for plant species seed dispersal is the only opportunity to disperse into a new habitat. Previous studies showed that the maternal stress, such as high density and low nutrient levels, induces the adaptive plastic increase of the dispersal ability in seed heteromorphic plants. In this study, we examined whether herbivory can change the relative proportion of dispersal-related seed heteromorphism (floating or non floating seeds) in an invasive weed Ambrosia artemisiifolia. Because A. artemisiifolia often distributes in the riparian habitat, floating seeds might contribute to the long distance dispersal by hydrochory. Floating ability and seed weight were compared between plants damaged by a specialist herbivore Ophraella communa and undamaged plants. The damaged plants produced lighter and more likely floating seeds than the undamaged plants. However, multi-regression analysis revealed that the probability of floating was affected by seed weight but was not affected by herbivore treatment (damaged vs. undamaged plants). These results suggest that the increased proportion of floating seeds was not a direct response to the herbivore signal but an indirect response through the herbivore's effect on the reduction of seed weight. Plants damaged by herbivores might not only decrease seed production and quality but also increase the dispersal ability. These responses in dispersal ability against the herbivores might contribute to the spread of invasive plants.     

Rapid Seed Bank Development in Restored Tidal Freshwater Wetlands

Studies of seed bank development have rarely been included in evaluations of wetland restoration. We compared the seed bank of a recently restored tidal freshwater marsh in Washington, D.C., Kingman Marsh, with seed banks of another restored site (Kenilworth Marsh) and two reference marshes (Dueling Creek and Patuxent Marsh). The density and richness of emerging seedlings from Kingman Marsh seed bank samples increased from less than 4 seedlings and 2 taxa/90-cm² sample in 2000 (the year of restoration) to more than 130 seedlings and 10 taxa/90-cm² sample in 2003. The most important seed bank taxa at Kingman Marsh included Cyperus spp., Juncus spp., Lindernia dubia , Ludwigia palustris , and the non-native Lythrum salicaria . These taxa are not abundant in most mid-Atlantic tidal freshwater marshes but are almost identical to those described for a created tidal freshwater wetland in New Jersey. Seed banks of both the restored sites contained few seeds of several important species found at the reference sites. Flooding had a significant negative effect on emerging seedling density and taxa density, suggesting that slight decreases in soil elevation in restored wetlands will dramatically decrease recruitment from the seed bank. Because seed banks integrate processes affecting growth and reproduction of standing vegetation, we suggest that seed banks are a useful metric of wetland restoration success and urge that seed bank studies be incorporated into monitoring programs for restored wetlands.     

Harvester ants modify seed rain using nest vegetation and granivory

1. In annual plant communities, the seed bank determines each generation's potential emergence and any factor that influences it could alter community structure. Harvester ants are common seed predators that may cause seed sources and seed rain composition to vary. 2. In semi‐arid shrubland of the Negev desert of Israel, we hypothesised that the positive effects of dense vegetation on nests of the harvester ant Messor ebeninus Sant. would outweigh reduction by granivory. 3. To test whether nests were seed sources, we removed vegetation on 10 of 20 sampled nests prior to seeding. We tested the interaction between seed sources and granivory by locating seed traps at three locations: nests, foraging trails, and unvisited areas. Trapped seeds were recorded during spring and summer dispersal. Plant recruitment from the altered seed bank was recorded the following spring. 4. During April, seeds were more abundant near nests than the other locations and at uncut compared with cut nests. Foraging trails had fewer species and higher equitability compared with nests or unvisited areas. May and June to August had highest species richness at nests, but richness of cut and uncut nests were similar. Ordination of plant recruitment showed slightly lower vegetation community variation by diminished species in the cut seed bank. 5. While intact nest vegetation initially had high abundance of locally deposited seeds, it apparently blocked wind‐dispersed seeds later in the summer. Conversely, granivory reduced seed species richness only on trails and decreased dominance structure by preferential removal of some species.