Seed Removal and Predation as Factors Affecting Seed Availability of Tree Species in Degraded Habitats and Restoration Plantings in Rainforest Areas of Queensland,Australia

The post‐dispersal removal or predation of seeds of native tree species was investigated in Queensland, Australia, at degraded habitats and rainforest restoration sites where direct seeding might be used to facilitate tree regeneration (old fields or open habitats, lantana thicket, rainforest edge, and 5‐ and 10‐year‐old restoration plantings). Seed removal/predation was assessed in relation to tree seed weight and canopy density of the habitats during the wet season period. Results indicated that seed removal/predation imposes limitations on seed availability, particularly for small seeded species. In most situations, larger seeds were less removed/predated, most likely due to the more limited range of large seed consumers. The use of large, hard‐coated seeds may potentially reduce seed loss in open situations (from both seed removal and desiccation), unless large seed consumers frequent the site. Canopy cover exerted an influence on seed removal/predation, though trends varied in relation to site and the time of season. Broadcast sowing of seed under planted tree canopies at the more advanced stages of closure may in some areas result in higher seed removal/predation. Likewise, seeding in areas dominated by woody weeds may result in high seed losses to consumers such as rodents. Results suggested that undertaking direct seeding to coincide with the maximal period of fruit production may in some situations be beneficial to minimize seed loss. Overall, site context, canopy cover, and species selection appear to be important considerations when aiming to reduce loss of seeds to animal seed consumers in restoration work.     

Restoring grassy woodland diversity through direct seeding: Insights from six ‘best‐practice’ case studies in southern Australia

Ecological restoration of grassy woodland ecosystems is now a significant landscape‐scale conservation objective throughout southern Australia. Technological improvements in direct seeding are now sufficiently well‐advanced to examine whether cost‐effective restoration of grassy woodlands is feasible. Consideration of six ‘best practice case studies shows substantial evidence of success. Further refinement of direct seeding techniques, in combination with native seed production systems, however, will be required into the future to meet the scale of woodland conservation targets and restore ecological function.     

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.     

The use of spatially patterned methods for vegetation restoration and management across systems

Widespread degradation of natural lands has created an urgent need for restoration. However, the high cost of conventional techniques limits the extent and success of restoration efforts. As a result, practitioners have developed new cost‐effective techniques. Spatially patterned restoration methods, where established clusters of plant species serve as propagule sources across a broad target area, have been proposed as practical restoration techniques. The spatial patterning is expected to reduce initial costs and provide ecological benefits such as increasing habitat heterogeneity. Over the past three decades, multiple spatially patterned restoration methods have emerged around the globe; however, it is unclear whether applications and theoretical foundations have been connected across methods. We conducted a literature review and bibliometric network analyses to (1) examine patterns in focal study systems, cost‐effectiveness, and ecological outcomes for spatially patterned restoration methods and (2) analyze connectivity among the bodies of literature associated with common spatially patterned restoration methods to identify knowledge gaps and synergies. We found the three most commonly studied methods are applied nucleation, slot seeding, and strip seeding. Applied nucleation studies mainly occurred in tropical forests and emphasized plant diversity and seed‐dispersing animal visitation. Slot‐seeding and strip‐seeding studies both primarily occurred in temperate grasslands and emphasized plant establishment and production. Applied nucleation and slot‐seeding approaches had distinct theoretical bases, as evidenced by patterns in reference citation, while strip‐seeding approaches did not draw from a unified body of literature. We discuss the need for full economic analyses and theoretical links between the different methods.     

Diminishing Returns from Higher Density Restoration Seedings Suggest Trade‐offs in Pollinator Seed Mixes

Native forbs have become a more central component of restoration programs, especially because of their role in supporting crop pollinators. This study evaluates the success of different native forb mixes and seeding rates using shared goals of restoration practitioners and agroecologists, namely percent native species cover, floral resources, native diversity, and cost‐effectiveness. At 6 sites with hedgerows adjacent to agricultural lands in California's Central Valley, we planted 3 native forb seed mixes at 3 seeding rates and monitored germination, percent cover, and floral resources for 2 to 3 years. We also evaluated the cost of the mixes based on seeding rates and original seed prices. More than mix type, relative seeding rate strongly affected germination, cover, and floral resource success. The relative benefits of seeding with more species diminished at higher seeding rates, especially when cost was considered. Cover increased significantly over the years but diversity declined sharply after the first year. Increased cover of target species was mainly due to the effect of 1 dominant species Grindelia camporum, common gumplant. We summarize data from a similar forb restoration study showing that the species that dominated in our mix‐and‐rate experimental sites also attracted the greatest diversity and abundance of pollinators. These findings highlight trade‐offs and balance‐points within restoration and pollination services goals. We offer suggestions on how to weigh those trade‐offs, given particular priorities and how native forb plantings can support combined goals of pollination services and restoration.     

Large‐Scale Zostera marina (eelgrass) Restoration in Chesapeake Bay,Maryland, USA. Part I: A Comparison of Techniques and Associated Costs

The Chesapeake Bay, like many other temperate estuaries, has exhibited dramatic declines in the abundance of submerged aquatic vegetation (SAV) during the later half of the twentieth century. Because of the functions SAV serve in maintaining a healthy estuarine ecosystem, SAV restoration has become an important component of Chesapeake Bay restoration. Specifically, recent water quality improvements in areas from which populations of Zostera marina (eelgrass) have been extirpated have suggested that Z. marina restoration could succeed. Early restoration efforts involved transplanting Z. marina plants from healthy source beds to restoration locations, but this was labor intensive, time consuming, expensive, and potentially detrimental to donor beds. This multi‐year project investigated new techniques for large‐scale Z. marina seed collection and processing and compared two seed dispersal methods to evaluate cost effectiveness. Tens of millions of mature Z. marina seeds were collected through snorkeling, SCUBA, or with a mechanical harvester. Seed storage conditions and processing techniques were manipulated in order to maximize seed yield. Seeds were dispersed using two methods: spring seed buoys and fall seed broadcasts. Our costs for planting 1 ha of bottom with Z. marina seeds ranged from $6,674 to $165,699 depending on seeding density and dispersal method used. The average cost per Z. marina seed was $0.17. Interannual variations in seed collection yield and seed viability after summer storage had great impact on final costs. Our results suggest that the use of seeds for large‐scale Z. marina restoration offers a competitive advantage to more traditional transplanting methods.     

Seed use in the field: delivering seeds for restoration success

Seed delivery to site is a critical step in seed‐based restoration programs. Months or years of seed collection, conditioning, storage, and cultivation can be wasted if seeding operations are not carefully planned, well executed, and draw upon best available knowledge and experience. Although diverse restoration scenarios present different challenges and require different approaches, there are common elements that apply to most ecosystems and regions. A seeding plan sets the timeline and details all operations from site treatments through seed delivery and subsequent monitoring. The plan draws on site evaluation data (e.g. topography, hydrology, climate, soil types, weed pressure, reference site characteristics), the ecology and biology of the seed mix components (e.g. germination requirements, seed morphology) and seed quality information (e.g. seed purity, viability, and dormancy). Plan elements include: (1) Site treatments and seedbed preparation to remove undesirable vegetation, including sources in the soil seed bank; change hydrology and soil properties (e.g. stability, water holding capacity, nutrient status); and create favorable conditions for seed germination and establishment. (2) Seeding requirements to prepare seeds for sowing and determine appropriate seeding dates and rates. (3) Seed delivery techniques and equipment for precision seed delivery, including placement of seeds in germination‐promotive microsites at the optimal season for germination and establishment. (4) A monitoring program and adaptive management to document initial emergence, seedling establishment, and plant community development and conduct additional sowing or adaptive management interventions, if warranted. (5) Communication of results to inform future seeding decisions and share knowledge for seed‐based ecological restoration.     

Should I plant or should I sow? Restoration outcomes compared across seven riparian revegetation projects

To revegetate native plant communities, it is often cheaper to direct seed than to plant nursery‐grown stock. However, the outcomes of direct seeding can be quite variable, and it is unclear whether direct seeding or planting is more likely to facilitate the restoration of diverse plant communities. To address this question, we compared the outcomes of each method across several recent riparian revegetation projects where both direct seeding and tube‐stock planting were used. We surveyed riparian revegetation projects at seven sites within the greater Melbourne area that had been revegetated between 1 and 4 years previously. Sites were all on land previously used for agriculture or degraded public land and ranged in environmental and climatic conditions. Woody plant density, establishment of target species, species richness, species diversity (evenness) and plant heights were assessed. Direct seeding tended to result in higher plant densities and similar species richness, but lower rates of species establishment and diversity compared with planting. A median of 67% of target species established via direct seeding compared with 100% for planting, with direct seeded areas often dominated by one or two species. In general, overall revegetation outcomes were often driven by climatic and site factors, rather than revegetation method. We suggest that to achieve good restoration outcomes from revegetation in riparian areas, a bet‐hedging or combined approach using both sowing and planting may be the best strategy.     

Seed conglomeration: a disruptive innovation to address restoration challenges associated with small‐seeded species

Small‐seeded species are an integral component of many natural systems. However, small‐seeded species are often omitted from restoration projects due to limited flow through seeders, low broadcast distance, and inconsistent seeding rates. To address these problems, we developed a novel technique within a rotary coater that allows for the conglomeration of small, low‐purity seeds using a combination of clay, compost, water, and a polymer binder. We used Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), which has a seed size of approximately 1 mm or less, as a model species to evaluate the technology. We demonstrated improved flowability of conglomerates over untreated (control) seeds through measurements of the Hausner ratio (8% decrease), the angle of repose (21% decrease), and delivery through a broadcast seeder. Seeding rates of conglomerated seed were more consistent than control seed over rugged terrain. Conglomerates were also broadcast 2.2 times further than control seed, which may mitigate the overall cost of implementing this technology. Laboratory trials demonstrated that the final germination of conglomerated seed averaged 15% higher than control seed. Field trials at two sites demonstrated that seedling emergence was similar for control and conglomerated seed. With no deleterious effects observed from the conglomeration treatment, additional research is merited for using conglomerates as a platform to apply various additives, such as fungicides, plant growth hormones, fertilizers, and biologicals. The potential outcomes of these strategies may have a significant impact on future seeding attempts by improving seed delivery and increasing overall seeding success.     

Near‐natural methods promote restoration of species‐rich grassland vegetation—revisiting a road verge trial after 9 years

The present loss of species‐rich grasslands makes it vital to restore these valuable habitat types, including novel habitat variants such as road verges. Due to the lack of knowledge on long‐term outcomes of restoration initiatives, well‐designed studies comparing different restoration methods are needed. In this study, we examined fine‐scale vegetation recovery patterns over 9 years in a field experiment with several near‐natural restoration methods (adding local seed mixtures, transferring hay from local grasslands using hard or light raking, and natural regeneration) in a road verge. We compared this to standard revegetation (hydroseeding species‐poor commercial seed mixtures). We found major temporal changes in vegetation restored by local seed or hay transfer, before it gradually became more similar to the donor grasslands and seed mixtures, which served as references for the experiment. Natural (spontaneous) regeneration with seed dispersal from surroundings gave similar results, whereas areas revegetated using standard methods became more dissimilar to the reference sites during the study period. The main variation in species composition reflected the contrast between local donor grasslands and seed mixtures and the species‐poor early successional grasslands. We conclude that near‐natural methods (hay transfer and seeding) successfully restored species‐rich grassland, including road verges. This study underlines the importance of comparing several treatments over a sufficiently long period to assess their success in restoring species‐rich grassland.     

Effectiveness of seed sowing techniques for sloped restoration sites

Practitioners are challenged with choosing among many potentially effective methods for sowing seed in ecological restoration projects to achieve sufficient native plant establishment. We tested the effectiveness of seed sowing techniques on moderate and steep slopes in a Mediterranean climate by measuring native seedling density immediately following germination, as well as plant density, recruitment success, and soil movement through the second growing season. We calculated cost effectiveness of different methods as the native plant density per dollar spent sowing seed. While all sowing techniques resulted in significant native establishment compared with unseeded controls, hydro seeding on moderate slopes was the most cost effective (native seedlings established per dollar spent). Although all steep‐sloped seeding techniques resulted in high densities of native species, all methods also resulted in significant soil loss. Shrubs preferred hand seeding followed by jute netting on steep slopes, while forbs reached greatest densities with hydro seeding on moderate slopes. Seedlings of species with heavy seeds were present in greater densities than species with lighter seeds in imprint sowing treatments. The “best” seed sowing technique varied depending on slope and metric of success (native density, species richness, shrub density, or forb density). Different combinations of slope, technique, and success metric resulted in significantly different project costs, which implies opportunities for savings given careful decision‐making relative to mitigation needs on heterogeneous landscapes. Evaluations of techniques for restoring slopes are limited, yet critical for expanding the area capable of being restored and the application of limited conservation funding.     

Establishment of Fabaceae Tree Species in a Tropical Pasture: Influence of Seed Size and Weeding Methods

The successful establishment of trees in pastures may be related to species, seed size, and weed control treatments. This study experimentally evaluated the emergence, establishment after 2 years, and growth of individuals of 7 tree species with different seed sizes sowed under three weeding methods (no weeding, grasses clipped, and grasses removed). The experiment was carried out in a tropical abandoned pasture in Midwestern Brazil, dominated by the exotic invasive grass Urochloa brizantha. The effect of seed size on seedling emergence was significant and was more intense in the no weeding and weeding treatment plots than in grasses clipped. Furthermore, an increase in seed size resulted in an increase in the probability of establishment of tree species, although this pattern also differed among weeding treatments. The increase in seed size reflected negatively on tree growth in the absence of grasses, whereas in the presence of grasses there was an inverse relationship. The experimental results suggested that the use of seeds of different sizes for direct seeding in pastures is a possible strategy of Fabaceae tree species reintroduction in pastures within the Cerrado. Fabaceae species with seeds larger than 100 mg can establish in areas with no weeding, whereas species with seeds smaller than 50 mg can establish preferentially in areas with weeding, growing faster than larger ones. Thus, weeding strategies can determine the success of direct seeding of different species in restoration projects of tropical pastures.     

Polycross Seed of Genetically Diverse Smooth Cordgrass (Spartina alterniflora) for Erosion Control and Habitat Restoration

Although seed‐based planting is common in crop systems, it is relatively a new concept in coastal erosion control and habitat restoration. This paper discusses the potential use of seed‐based revegetation to accommodate large‐scale erosion control using a highly diverse population of smooth cordgrass (Spartina alterniflora) from controlled polycross to attain desirable genetic diversity suitable for habitat restoration. Seed‐based restoration provides a more versatile alternative approach to the current clonal revegetation technique in many regions, including the Gulf Coast of the United States. The objectives of this study were to (1) describe seed production and cultural aspects of the polycross population and (2) discuss the potential use of polycross seeds for direct seeding applications and other innovative restoration approaches using seed‐derived planting materials. The polycross population was produced using 15 genetically diverse and high‐seed producing smooth cordgrass lines selected from native populations. The average seed set of the polycross population was 58.5 ± 6.3% with an average germination rate of 82.2 ± 9%. As comparison, Vermilion, the only available smooth cordgrass cultivar, has a seed set of 20.6 ± 5% and a germination rate of 35 ± 8%. The average yield of S. alterniflora seed from the polycross population was 277.5 kg/ha, which is equivalent to approximately 26 million viable seeds. Seed can be stored in 100% humidity at a temperature of 2 ± 1°C for 6–9 months.     

Recovery after African Olive invasion: can a ‘bottom‐up’ approach to ecological restoration work?

African Olive (Olea europaea ssp. cuspidata) is a densely crowned evergreen small tree, native to eastern Africa that is highly invasive in areas where it has been introduced, including Hawaii and Australia. Invasion by African Olive threatens Cumberland Plain Woodland, a critically endangered grassy eucalypt woodland from western Sydney, Australia, through the formation of a dense mid‐canopy excluding the regeneration of native species. We established a 3‐year field experiment to determine the effectiveness of direct seeding and fire, as techniques for early stage restoration of a 2 ha historically cleared and degraded Cumberland Plain Woodland site after the removal of African Olive. Direct seeding was able to re‐establish a native perennial grass cover which was resistant to subsequent weed invasion and could be managed as an important first stage in woodland restoration with fire and selective herbicide. Fire was able to stimulate some germination of colonising native species from the soil seed bank after 15 years of African Olive invasion; however, germination and establishment of native shrubs from the applied seed mix was poor. We propose a ‘bottom‐up’ model of ecological restoration in such highly degraded sites that uses a combination of direct seeding and stimulation of the soil seed bank by fire, which could be applicable to other degraded grassy woodland sites and plant communities.     

Forest restoration is more than firing seeds from a drone

We are witnessing a rapid increase in news sending the message that drone seeding is a promising technological solution to implement forest restoration at large spatial scales. However, there are neither reports regarding success nor peer-reviewed studies to support these assertions. Once in the ground, the seeds and the seedlings and saplings that they generate have to face biotic and abiotic hazards that can strongly reduce regeneration potential. Successful forest restoration, therefore, cannot be achieved by simply dropping seeds from the air. We summarize some aspects to take into account before considering drone seeding as an efficient and widely applicable technology for forest restoration. A first step should be to increase the precision of drone seeding—contrary to the current massive firing of seeds—in order to concentrate the efforts in the best microsites for establishment and reduce the number of seeds needed and the cost of the whole operation.     

Protecting direct seeded grasses from herbicide application: can new extruded pellet formulations be used in restoring natural plant communities?

Restoration of native plant communities through direct seeding often experience low seedling establishment success rates, partly due to competition with invasive weed species. To improve seeding success, herbicides can be applied to control weed competition, however, this can have negative impacts on the seeded species. Activated carbon (AC) can be incorporated into newly developed seed enhancement technologies to adsorb herbicides and increase seedling tolerance. This study expands upon research completed to date, by developing new formulations of extruded pellets containing AC, aiming to provide increased protection to seeded species and increase herbicide selectivity. We tested six extruded pellet formulations, which included two pellet formula variations, and three quantities of AC, to examine the impact on emergence (without herbicide) and mortality (with herbicide) of Lolium rigidum Gaudin (annual ryegrass). Extruded pellet formulations containing a superabsorbent polymer (3%) and AC (10%) did not impede emergence (79%), in the absence of herbicide, similar to the non‐pelleted seeds (81%). This extruded pellet formulation increased seedling tolerance to Simazine (a pre‐emergent, soil applied herbicide) application, with mortality reduced from 96% in non‐pelleted seeds, and 77% in pellets containing no AC, to 22% in pellets containing AC. The results from this study demonstrate that AC extruded pelleting can be used as a restoration seeding technology by protecting seeds from the negative effects of pre‐emergent herbicide applications. Field evaluations with native seeds will mark an important step forward to ensure seed enhancement technology options, such as AC extruded pelleting, are available for restoring natural plant communities in restoration programs.     

Collection and production of native seeds for ecological restoration

The global push to achieve ecosystem restoration targets has resulted in an increased demand for native seeds that current production systems are not able to fulfill. In many countries, seeds used in ecological restoration are often sourced from natural populations. Though providing seed that is reflective of the genetic diversity of a species, wild harvesting often cannot meet the demands for large‐scale restoration and may also result in depletion of native seed resources through over harvesting. To improve seed production and decrease seed costs, seed production systems have been established in several countries to generate native seeds based on agricultural or horticultural production methods or by managing natural populations. However, there is a need to expand these production systems which have a primary focus on herbaceous species to also include slower maturing shrub and tree seed. Here we propose that to reduce the threat of overharvest on the viability of natural populations, seed collection from natural populations should be replaced or supplemented by seed production systems. This overview of seed production systems demonstrates how to maximize production and minimize unintended selection bias so that native seed batches maintain genetic diversity and adaptability to underpin the success of ecological restoration programs.     

Review of seed pelletizing strategies for arid land restoration

Arid lands face numerous restoration challenges due to infrequent and irregular precipitation which impacts plant germination, growth, and survival. Abundant seed predators, harsh surface conditions, and native seeds often poorly suited to mechanical distribution compound restoration challenges. Seed pellets (a.k.a. pods, seed balls, and seed bombs), an aggregation of clay, soil, water, and multiple seeds, have the potential to reduce some of the challenges. However, no formal guidelines based on an aggregated research review exist. Available publications, both peer‐reviewed and any public domain, were reviewed. Of the 24 publications found (some describing multiple tests), seed pellets tested on rangelands had 9 negative effects, 10 neutral effects, and 8 positive effects. Greenhouse testing showed five negative effects, two neutral effects, and four positive effects. Forest systems had three neutral effects and two positive effects. Advantages in mechanical distribution were not well quantified and other effects were lumped together in germination and seedling establishment totals. The use of pelleted seed would benefit from a more mechanistic understanding of the interaction between the pellets and the systemic constraints. As long as the pellets themselves do not greatly reduce germination or establishment, they appear a potentially viable method for improving seed distribution and seeding efficiency, protecting seeds, and adding amendments. While the evidence is far from conclusive, seed pellets may also hold some advantages in increasing germination and establishment.     

Community‐based native seed production for restoration in Brazil – the role of science and policy

• Large‐scale restoration programmes in the tropics require large volumes of high quality, genetically diverse and locally adapted seeds from a large number of species. However, scarcity of native seeds is a critical restriction to achieve restoration targets.
• In this paper, we analyse three successful community‐based networks that supply native seeds and seedlings for Brazilian Amazon and Cerrado restoration projects. In addition, we propose directions to promote local participation, legal, technical and commercialisation issues for up‐scaling the market of native seeds for restoration with high quality and social justice.
• We argue that effective community‐based restoration arrangements should follow some principles: (i) seed production must be based on real market demand; (ii) non‐governmental and governmental organisations have a key role in supporting local organisation, legal requirements and selling processes; (iii) local ecological knowledge and labour should be valued, enabling local communities to promote large‐scale seed production; (iv) applied research can help develop appropriate techniques and solve technical issues.
• The case studies from Brazil and principles presented here can be useful for the up‐scaling restoration ecology efforts in many other parts of the world and especially in tropical countries where improving rural community income is a strategy for biodiversity conservation and restoration.