Innovative Techniques for Large‐scale Seagrass Restoration Using Zostera marina (eelgrass) Seeds

The use of Zostera marina (eelgrass) seeds for seagrass restoration is increasingly recognized as an alternative to transplanting shoots as losses of seagrass habitat generate interest in large‐scale restoration. We explored new techniques for efficient large‐scale restoration of Z. marina using seeds by addressing the factors limiting seed collection, processing, survival, and distribution. We tested an existing mechanical harvesting system for expanding the scale of seed collections, and developed and evaluated two new experimental systems. A seeding technique using buoys holding reproductive shoots at restoration sites to eliminate seed storage was tested along with new techniques for reducing seed‐processing labor. A series of experiments evaluated storage conditions that maintain viability of seeds during summer storage for fall planting. Finally, a new mechanical seed‐planting technique appropriate for large scales was developed and tested. Mechanical harvesting was an effective approach for collecting seeds, and impacts on donor beds were low. Deploying seed‐bearing shoots in buoys produced fewer seedlings and required more effort than isolating, storing, and hand‐broadcasting seeds in the fall. We show that viable seeds can be separated from grass wrack based on seed fall velocity and that seed survival during storage can be high (92–95% survival over 3 months). Mechanical seed‐planting did not enhance seedling establishment at our sites, but may be a useful tool for evaluating restoration sites. Our work demonstrates the potential for expanding the scale of seed‐based Z. marina restoration but the limiting factor remains the low rate of initial seedling establishment from broadcast seeds.     

Factors Influencing Seedling Establishment Rates in Zostera marina and Their Implications for Seagrass Restoration

Selection of strategies to efficiently utilize limited seed supplies in efforts to restore the seagrass Zostera marina (eelgrass) requires a better understanding of the processes that limit seedling establishment at potential restoration sites. We investigated the effect of seed distribution timing on seedling establishment and tested for interactive effects of seed burial and distribution timing. We also investigated the effect of habitat type on seedling establishment by distributing Z. marina seeds inside and outside of established Ruppia maritima (widgeongrass) patches and examined mechanisms causing habitat differences by manipulating seed position (buried or unburied) and vulnerability to seed predators (unprotected or protected in packets). Seeds distributed on the sediment surface in the summer (July or August) produced fewer seedlings than seeds distributed in fall (October) in five of six trials over 3 years. Seed burial increased success rates for seeds distributed in summer at one of two sites tested, eliminating the effect of season, but reduced success at the other site. Seeds placed in R. maritima generally produced fewer seedlings than seeds in bare sand, and although seed burial and protection in packets increased success in bare sand at three of four sites, the effect was less consistent in R. maritima. We conclude that seed predation and physical interactions were influential in reducing seedling establishment in R. maritima, contrary to hypotheses positing a nursery role for existing vegetation. Efficient restoration efforts with Z. marina seeds should target unvegetated areas after summertime sources of mortality have diminished. Direct seed burial may enhance seedling establishment rates.     

Large‐Scale Zostera marina (eelgrass) Restoration in Chesapeake Bay,Maryland, USA. Part II: A Comparison of Restoration Methods in the Patuxent and Potomac Rivers

In response to systemic losses of submerged aquatic vegetation (SAV) in the Chesapeake Bay (east coast of North America), the U.S. Environmental Protection Agency's (EPA) Chesapeake Bay Program (CBP) and Maryland Department of Natural Resources (MD DNR) have considered SAV restoration a critical component in Bay restoration programs. In 2003, the CBP created the “Strategy to Accelerate the Protection and Restoration of Submerged Aquatic Vegetation in the Chesapeake Bay” in an effort to increase SAV area. As part of this strategy, large‐scale eelgrass (Zostera marina) restoration efforts were initiated in the Patuxent and Potomac Rivers in Maryland. From 2004 to 2007, nearly 4 million Z. marina seeds were dispersed over 10 ha on the Patuxent River and almost 9 million seeds over 16 ha on the Potomac River. Z. marina seedling establishment was consistent throughout the project (<4%); however, restored eelgrass survival was highly dependent on restoration site. Restoration locations on the Patuxent River experienced initial Z. marina seedling germination, but no long‐term plant survival. Restored Z. marina on the Potomac River has persisted and expanded, both vegetatively and sexually, beyond initial seeding areas. Healthy Z. marina beds now cover approximately five acres of the Potomac River bottom for the first time in decades. The differential success of Z. marina restoration efforts in the two rivers is evidence for the necessity of carefully considering site‐specific characteristics when using large‐scale seeding methods to achieve successful SAV restoration.     

Seagrass restoration using seed ball burial in northern China

As seagrass bed restoration by seeding becomes more common, it is necessary to develop a simple and reliable method to improve the efficiency of seed-based restoration. In this study, we describe a novel method using seed ball burial for eelgrass restoration. Using this method, seeds were wrapped in a wet mud ball, which represented a transplant unit, and the balls were then buried in the sediment. Three experiments (proof of concept study, main study, and large-scale restoration) were conducted to test this method at three degraded sites (Rizhao, Qingdao, and Tangshan) with different environmental conditions. The density of seedlings and seedling shoots was 54 and 110 per m², respectively, in Rizhao, a site with coarser sediment and higher temperatures. Seedling survival in Qingdao reached 46.67 ± 9.46%. Relatively low seedling survival (26.67 ± 7.03%) in Tangshan was induced by local waves and currents. Seedling survival was also low (ca. 15% in April and 2% in July) at the large-scale restoration site , reflecting a mismatch between the environment at this site and the seed ball restoration method. In conclusion, our study provides evidence of the effectiveness of a novel seagrass seed planting method referred to as seed balls.     

The role of seedlings and seed bank viability in the recovery of Chesapeake Bay,USA, <Emphasis Type="Italic">Zostera marina</Emphasis> populations following a large-scale decline

The objective of this study was to quantify the spatial and temporal recolonization characteristics of Zostera marina beds in the lower Chesapeake Bay following large scale declines in the late summer of 2005. Transects were established and monitored monthly for changes in eelgrass abundance at three sites (two downriver, one upriver) in the York River from April–October 2006 and 2007. Measurements included percent bottom cover, above ground biomass, shoot density, shoot origin (seedling or vegetative), seed bank abundance and seed viability. During 2006, the eelgrass beds at all sites recovered with seedlings providing the largest proportion of the total shoot abundance. This trend shifted in 2007 and surviving vegetative shoots were the dominant component of shoot standing crop. A second consecutive decline related to low light conditions occurred during the summer of 2006 in the upriver site and recovery there was minimal in 2007. These results highlight that after a single die off event, seed germination with subsequent seedling growth is the principal method for revegetation in lower Chesapeake Bay Z. marina beds. However, no viable seeds remain in the seed bank during this first year of recovery and shoots produced by the seedling growth do not flower and produce seeds until their second year of growth. Therefore the seed-bank density is low and is not immediately replenished. This suggests that the resiliency of perennial Chesapeake Bay Z. marina populations to repeated disturbances is restricted and repeated annual stress may result in much longer term bed loss.     

Smoke, Mulch, and Seed Broadcasting Effects on Woodland Restoration in Western Australia

Smoke, canopy‐derived mulch, and broadcast seeds were used to maximize the establishment of Banksia woodland species in sand quarries in Western Australia. Smoke, particularly aerosol smoke, had a positive effect on total seedling recruitment. Pre‐mined (woodland) sites showed a 42‐fold increase in total germinants and a 3‐fold increase in the number of species with aerosol smoke application. Post‐mined (restored) sites showed only a 3.6‐fold increase in total germinants and a 1.4‐fold increase in the number of species. Two water‐based smoke chemicals, DC10 (pH 4.5) and SC63 (pH 2.5), increased seedling recruitment at both sites but were not as effective in stimulating recruitment as aerosol smoke. Neither of the chemicals were effective in significantly increasing species richness. Application of aerosol smoke directly to seeds as a pretreatment before broadcasting had no effect on seedling recruitment. Broadcasting of seeds onto restoration sites significantly increased seedling abundance and richness. Application of a single layer of mulch from the canopy vegetation after seed broadcasting gave optimum seedling recruitment. Two layers of mulch significantly reduced recruitment, as did applying mulch before seed broadcasting. For broad‐scale restoration, the application of smoke on newly restored sites would be more effectively achieved using smoke water sprayed over the soil surface. Species that do not recruit from replaced topsoil could be effectively recovered from broadcast seed rather than from mulch.     

Effects of edge/interior and patch structure on reproduction in Zostera marina L. in Chesapeake Bay,USA

We examined the effects of location (patch edge vs. interior) and shoot density (individual, patchy, continuous) on reproduction in three natural and two transplanted Chesapeake Bay (USA) stands of the submerged marine angiosperm Zostera marina L. (eelgrass; Zosteraceae). There were no edge effects on demographic-based reproductive effort or reproductive output (propagule production), and patch structure (individual, patchy, continuous) alone never accounted for the majority of variability in any metric. Transplant site was the most important predictor of eelgrass reproduction response, and relationships among metrics were predictable within sites. Our results suggest that, in Chesapeake Bay eelgrass, environmental factors acting at a regional scale (km) have a stronger impact on reproductive investment than those at a patch scale (1–10 m). Since tradeoffs between clonal and sexual production are mediated primarily by exogenous environmental factors, site selection may be more critical than transplant configuration for producing self sustaining stands, and achieving long-term restoration success.     

The Role of Habitat and Herbivory on the Restoration of Tidal Freshwater Submerged Aquatic Vegetation Populations

Submerged aquatic vegetation (SAV) has declined precipitously throughout coastal areas and its reestablishment has long been an important objective of coastal management. We investigated restoration success of Vallisneria americana (wild celery) using seeds, seed pods, and whole shoot transplants at sites in the Chesapeake Bay in the United States where historical aerial photography has indicated that the species once grew. In addition, we evaluated habitat conditions and established herbivore exclosures to assess the impacts of water quality, sediment conditions, and grazers on planting success. Whole shoot transplants resulted in the most rapid cover of the bottom, but required greater planting effort. Direct dispersal of individual seeds was generally more successful than dispersal of intact seed pods, resulting in more rapid initial seedling growth. Overall, 100% bottom cover of whole shoot transplant plots could be reached in approximately 3 years, despite light attenuation coefficients (K_d) of 3.0 to 4.0. Transplants at shallow depths (<0.5 m) were able to rapidly grow and elongate to the surface at mid‐to‐low tidal heights. Transplants were successful in both muddy (8% organic) and sandy (<2%) substrates. Using mesh exclosures to protect the plants from herbivory was critical to restoration success. Although water quality and other habitat conditions are important for SAV growth and survival, restoration in the unvegetated areas studied here was limited by grazing of initial recruits. The establishment of protected founder colonies of sufficient size to withstand initial grazing pressures may be required to reestablish SAV in similar areas.     

Growing Zostera marina (eelgrass) from Seeds in Land‐Based Culture Systems for Use in Restoration Projects

The use of aquaculture systems to grow the seagrass Zostera marina (eelgrass) from seeds for restoration projects was evaluated through laboratory and mesocosm studies. Along the mid‐Atlantic coast of North America Z. marina seeds are shed from late spring through early summer, but seeds typically do not begin to germinate until the late fall. Fall is the optimal season to plant both seeds and shoots in this region. We conducted studies to determine if Z. marina seeds can be induced to germinate in the summer and seedlings grown in mesocosms to a size sufficiently large enough for out‐planting in the fall. Seeds in soil‐less culture germinated in the summer when held at 14°C, with percent germination increasing with lower salinities. Cold storage (4°C) of seeds prior to planting in sediments enhanced germination and seedling survival. Growth rates of seedlings were significantly higher in nutrient enriched estuarine sediments. Results from preliminary studies were used in designing a large‐scale culture project in which 15,000 shoots were grown and out‐planted into the Potomac River estuary in the Chesapeake Bay and compared with an equal number of transplanted shoots. These studies demonstrate that growing Z. marina from seeds is an alternative approach to harvesting plants from donor beds when vegetative shoots are required for restoration projects.     

Testing Broadcast Seeding Methods to Restore Urban Forests in the Presence of Seed Predators

Forest restoration in urban areas often occurs in isolation from remnant forest, limiting the chances for recolonization by native species. Plants with bird‐dispersed seeds can be particularly vulnerable to dispersal limitation and regeneration can be further impeded by non‐native seed predators. We used a factorial experiment to investigate broadcast seeding as a method to reintroduce trees with large seeds and fleshy fruits into early successional forests. We assessed rates of seed and fruit loss, germination and seedling establishment in three seed treatments: (1) caging to exclude introduced mammalian seed predators; (2) removal of fleshy fruit pericarp; and (3) placing seeds in nutritionally enriched clay balls. Across all species (Beilschmiedia tawa, Elaeocarpus dentatus, and Litsea calicaris) seeds and fruits accessible to mammalian predators suffered significantly greater loss (58%) than those protected by cages (4%). However, seed and fruit loss in the presence of predators was reduced to only 35% across all species by the treatment combining the removal of fruit flesh and clay ball application to seeds. Establishment of B. tawa seedlings after 1 year was significantly enhanced by the clay ball treatment (12% of seeds sown vs. 6% without clay balls). Very low establishment rates were recorded for E. dentatus and L. calicaris. Broadcast seeding was found to be a viable method of improving regeneration of large‐seeded late successional trees and may be a cost‐effective alternative to planting saplings. Seedling establishment can be improved with fruit flesh removal and clay ball treatments, especially in the presence of mammalian seed predators.     

Effects of the pericarp on imbibition,seed germination,and seedling establishment in seeds of <Emphasis Type="Italic">Hedysarum scoparium</Emphasis> Fisch. et Mey

Four independent experiments were designed to investigate the effects of the pericarp on seed imbibition, dehydration, germination, seedling establishment, and seed longevity in the field in seeds of Hedysarum scoparium Fisch. et Mey. The results showed that the presence of the pericarp decreased seed imbibition rates in the first 6 h, but the seeds attained significantly higher final water content after 24 h of soaking. The pericarp caused seed dormancy, and removal of the pericarp improved the germination percentage to 90 from 44%. In the pot experiment, where the level of moisture was maintained at field capacity (control), seeds with the pericarp removed had significantly improved seedling establishment. However, no statistical differences were observed in seedling establishment when the experiment was repeated under dry conditions at 40% of the field water capacity. The seedling biomass derived from seeds without the pericarp was much higher in the control but the trend was reversed under dry conditions. For seed longevity, 2 months burial in the field killed almost all seeds without the pericarp, while more than 70% of the seeds with the pericarp intact remained viable. These results indicated that the pericarp was beneficial for seedling establishment and seed longevity in arid environments. The results of this study may have practical application in grassland restoration in dry areas, especially for aerial seeding, which has been extensively used in the northern part of China.     

The Role of Currents and Waves in the Dispersal of Submersed Angiosperm Seeds and Seedlings

We tested the hypothesis that currents, waves, and sediment grain size affect the dispersal of seeds and seedlings of the submersed angiosperms Ruppia maritima, Potamogeton perfoliatus and Stuckenia pectinata. Seed settling velocities and initiation of motion of seeds and seedlings and distance transported were quantified on four sediment types under a range of currents and waves in a flume. The rapid settling velocities of R. maritima and S. pectinata seeds and the increased settling velocity of P. perfoliatus in currents above 8 cm/second suggest that primary dispersal of these species is localized to the general area colonized by their parents. Once settled within a bed, seeds are exposed to weak currents and waves, and are likely to be subject to sediment deposition which may further limit dispersal. In contrast, in restoration projects, the absence of vegetation is likely to make seeds more vulnerable to grazing and transport, and may contribute to the lack of plant establishment. If seeds germinate without being buried, they are susceptible to secondary dispersal at relatively low current velocities and small wave heights due to the drag exerted on the cotyledon. Sand grains tend to stick to the seed coat and rootlet of P. perfoliatus seedlings, perhaps a mechanism to reduce the chances of being displaced following germination. These data reveal the close links between sediment, water flow, and submersed angiosperm seedling establishment; these parameters should be considered when using seeds for restoration of submersed angiosperms.     

Limited effectiveness of artificial bird perches for the establishment of seedlings and the restoration of Brazil’s Atlantic Forest

Brazil’s Atlantic Forest biome is severely degraded and fragmented throughout its range. Developing effective techniques to restore pasture and agriculture back to native vegetation is therefore a priority for legal and conservation purposes. In this study, we evaluate the ability of artificial bird perches to enhance the arrival of new seeds and seedling establishment in a degraded, semi-deciduous seasonal portion of the Atlantic Forest in southern Brazil. Specifically, we assess the influence of previous land use and habitat types on the abundance, species richness and ecological traits of bird-dispersed seeds, as well as on seedling establishment. Eight sampling sites were established, each containing one unit with seed traps and restoration plots under artificial perches and one similar unit without the perches. These sites were located in pasture and agriculture, distributed between riparian and sub-montane areas. Monthly sampling was conducted over two years between December 2005 and November 2007, resulting in the evaluation of 25,755 seeds and 56 endozoochoric seed species. The most abundant species were the pioneers Cecropia pachystachya Trécul and Solanum americanum Mill. Experimental units with perches received significantly more seeds than control units. Moreover, seed arrival was higher in sub-montane areas and on former pasture sites. Species richness followed a similar pattern of higher seed arrival, but there was no effect of vegetation type. Ecological characteristics of seeds were associated with land use type: former pastures received more tree seeds and pioneer species than expected by chance. Seedling establishment was very low in all treatments, with only eight seedlings established in perch plots by the end of the experiment. We conclude that despite artificial perches significantly increasing the arrival of endozoochoric seeds onto degraded lands, seedling establishment is drastically limited in these areas, compromising the efficacy of this technique for restoration purposes.     

Consequences of Seed Origin and Biological Invasion for Early Establishment in Restoration of a North American Grass Species

Local, wild-collected seeds of native plants are recommended for use in ecological restoration to maintain patterns of adaptive variation. However, some environments are so drastically altered by exotic, invasive weeds that original environmental conditions may no longer exist. Under these circumstances, cultivated varieties selected for improved germination and vigor may have a competitive advantage at highly disturbed sites. This study investigated differences in early establishment and seedling performance between wild and cultivated seed sources of the native grass, Poa secunda, both with and without competition from the invasive exotic grass, Bromus tectorum. We measured seedling survival and above-ground biomass at two experimental sites in western Montana, and found that the source of seeds selected for restoration can influence establishment at the restoration site. Cultivars had an overall advantage when compared with local genotypes, supporting evidence of greater vigor among cultivated varieties of native species. This advantage, however, declined rapidly in the presence of B. tectorum and most accessions were not significantly different for growth and survival in competition plots. Only one cultivar had a consistent advantage despite a strong decline in its performance when competing with invasive plants. As a result, cultivated varieties did not meet expectations for greater establishment and persistence relative to local genotypes in the presence of invasive, exotic species. We recommend the use of representative local or regional wild seed sources in restoration to minimize commercial selection, and a mix of individual accessions (wild, or cultivated when necessary) in highly invaded settings to capture vigorous genotypes and increase the odds native plants will establish at restoration sites.     

Dung beetle activity affects rain forest seed bank dynamics and seedling establishment

Dung beetles relocate vertebrate feces under the soil surface, and this behavior has many ecological consequences. In tropical forests, for example, seeds defecated by mammals that are subsequently buried by dung beetles are less likely to suffer predation. While the effects of dung beetles on the fate of defecated seeds have been relatively well studied, their effect on seeds already buried in the soil has not. To contribute to fill this gap, we designed a study with three objectives: (a) Describe the vertical re‐distribution of soil seeds that occurs due to dung beetle activity; (b) Determine if beetle activity favors establishment of seedlings from the soil seed bank; and (c) Determine if the effect of dung beetles is stronger in sites of recurrent mammal defecation. We carried out three complementary field experiments, one with artificial seeds (plastic beads) of three sizes buried at known depths, one with two species of seeds buried at those same depths, and one with the natural soil seed bank in sites of single vs. recurrent defecation. Buried beads were moved by dung beetles along the vertical axis, both upwards (9.5%) and downwards (11.5%); smaller beads were more frequently moved downwards while the contrary occurred for larger beads. Dung beetle activity caused an increase in seedling establishment, both from experimentally buried seeds and from the natural seed bank. Defecation recurrence had no effect on seedling establishment. We conclude that dung beetle activity affects seed bank dynamics with important consequences for seedling establishment in tropical forests.Abstract in Spanish is available with online material.     

Genetic effects of eelgrass restoration efforts by fishers' seeding to recover seagrass beds as an important natural capital for coastal ecosystem services

The reestablishment of seagrass vegetation is a vital part of recovering coastal marine ecosystem services. Historically the Hinase area was a famous for the fishing by coastal pound netting in eelgrass beds, but this practice was progressively displaced with oyster farming due to an enormous decline in seagrass vegetation. For several decades, the local fishers' cooperative has worked to restore eelgrass beds by a seeding method. Through these efforts, seagrass vegetation in their fishing area has increased to about half of their previous area. This study examined the effect of long-term seeding by fishers on the recovery of eelgrass beds in the Hinase area, based on analysis of eelgrass genetic structure using microsatellite markers. Specimens for the DNA analysis were collected from each of all eelgrass meadows that the fishers conducted sowing eelgrass seeds as well as from the source sites where they collected the seeds. The results found that restored beds in the study area have high genetic diversity comparable to natural ones. The multiple regression analysis revealed that a combined model of seedling intensity and geographic distance (R² = .457) better explained genetic structure across our sampling sites than models of seedling intensity (R² = .092) or geographic distance only (R² = .344). This supports that the eelgrass seeds they sowed did not disturb the genetic structure but rather supplemented natural dispersal, suggesting that the fishers' seeding did not develop nonnatural seagrass meadows but certainly contributed to the recovery of natural seagrass meadows.     

Restoring Eelgrass (Zostera marina L.) Habitats Using a Simple and Effective Transplanting Technique

Eelgrass beds in coastal waters of China have declined substantially over the past 30 years. In this study, a simple new transplanting technique was developed for eelgrass (Zostera marina L.) restoration. To assist in anchoring single shoots, several rhizomes of rooted shoots were bound to a small elongate stone (50–150 g) with biodegradable thread (cotton or hemp), and then the bound packet was buried at an angle in the sediments at a depth of 2–4 cm. This stone anchoring method was used to transplant eelgrass in early November 2009 and late May 2010 in Huiquan Bay, Qingdao. The method led to high success. Three month survivorship of the transplanted shoots at the two transplant sites was >95%. From April 20 to November 19, 2012, the following characteristics of the 2009 and 2010 transplanted eelgrass beds were monitored: morphological changes, shoot density, shoot height, leaf biomass, and sediment particle size. Results showed that the sexual reproduction period of the planted eelgrass was from April to August, and vegetative reproduction reached its peak in autumn. Maximum shoot height and biomass were observed in June and July. After becoming established, the transplanted eelgrass beds were statistically equal to natural eelgrass beds nearby in terms of shoot height, biomass, and seasonal variations. This indicates that the transplant technique is effective for eelgrass restoration in coastal waters.     

Does genetic diversity of restored sites differ from natural sites? A comparison of <Emphasis Type="Italic">Vallisneria americana</Emphasis> (Hydrocharitaceae) populations within the Chesapeake Bay

The goal of ecological restoration is to re-establish self-sustaining ecosystems that will resist future perturbation without additional human input. We focus here on the re-establishment of submersed aquatic macrophyte beds in the restoration of the Chesapeake Bay estuary. Degraded environmental conditions are often to blame for poor bed establishment, but genetic factors could also be contributing to low survival. We quantified the effect of restoration practices on genetic diversity in the submersed aquatic plant species Vallisneria americana Michx. (Hydrocharitaceae) in the Chesapeake Bay. In 2007, we collected 440 shoots from 8 restored/natural site pairs and 4 restoration stock repositories, and genotyped those individuals at 10 microsatellite loci. Restoration practices do not appear to negatively impact genetic diversity, and basic measures of genetic diversity within restored sites overlap with natural sites. However, small population size of restored sites, significant inbreeding coefficients within 3 sites, and low overlap of allele composition among sites provide cause for concern. These problems are relatively minor, and we propose several corrections that would alleviate them altogether. Managers should be encouraged by our findings as well as the current state of the genetic diversity within V. americana restoration efforts.     

Experimental demography of the rare Gentianella germanica: seed bank formation and microsite effects on seedling establishment

The persistence of populations of short-lived species requires regular reproduction and seedling establishment. A persistent seed bank can buffer populations against extinction in unfavourable years. We experimentally investigated seed fate in Gentianella germanica, an endangered biennial species characteristic for species-rich nutrient-poor calcareous grasslands in central Europe. We studied the effect of experimental gaps on seedling establishment from sown seeds and the fate of seeds buried in bags over two years. In December 1993 experiments were established at seven calcareous grassland sites in the Swiss Jura mountains. In spring 1994 seedlings emerged in all plots where seeds had been sown, including previously unoccupied patches. This suggests that limited dispersal within sites contributes to small population sizes. Significantly more seedlings emerged at sites with current populations of G. germanica than at unoccupied sites (5.95% vs 3.40%). Because this difference was not explained by germinations from the natural seed bank it indicates differences in habitat quality. Clipping of the vegetation and disturbance of the soil reduced vegetation cover in the following spring and enhanced seedling emergence. In undisturbed plots 4.5% of seeds sown produced a seedling in spring 1994, whereas in plots with clipped vegetation 9.9% and in disturbed plots 12.7% produced seedlings (p>0.01). This suggests that management measures which create gaps in the vegetation (e.g. grazing) could positively influence population size and persistence of G. geymanica. On average, we recovered 7.55% viable seeds after one year of burial in bags, and 4.05% after two years, indicating that G. geymanica has a persistent seed bank. The demographic data indicate that the number of viable seeds in the seed bank exceeds the number of established plants in a population at least by a factor of 20. Restoration of extinct populations of the species from the seed bank may thus be possible if appropriate management measures are taken within a few years.     

Small vertebrate granivores reduce seedling emergence in native tallgrass prairie restoration

High seed cost and low rates of establishment make tallgrass prairie restorations challenging and expensive endeavors. Typical seedling emergence rates in prairie restorations are approximately 10% and the causes of seed mortality are poorly understood. In this study, we examined the impact of small vertebrate granivores on prairie restoration by comparison of seedling emergence in open (sham) versus closed exclosures at three newly restored sites. To assess other causes of seed loss, we also tracked seed fates at one prairie restoration site. We coated seeds of four prairie species with fluorescent dye, placed them under closed exclosures, and monitored their fate (emerging seedling, partially germinated, nongerminated/viable, and nongerminated/nonviable) over a 5‐month period. On average, 9.6 more seedlings/m² emerged in the closed than the opened exclosures, suggesting that small vertebrate granivores reduce seedling emergence in prairie restoration. Granivores influenced the composition of the emerging community but did not preferentially consume large‐seeded species. In the seed‐tracking experiment, we found that greater than 70% of seeds were lost within 30 days of sowing, that seed recovery and viability both decreased with time in soil, and that seed fates differed between species. Collectively, our results indicate that small vertebrate granivores are an important cause of seed loss in prairie restoration, but unidentified belowground (e.g. fungal decomposition, invertebrate predation) and environmental (wind, rain) factors account for a greater proportion of total seed loss. Until these causes of seed loss are better understood, high seed costs will persist and continue to impede prairie restoration.