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.

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.

Seeds are a critical and limited resource for restoring biodiversity and ecological function to degraded and fragmented ecosystems. Cleaning and quality testing are two key steps in the native seed supply chain. Optimizing the practices used in these steps can ensure seed quality. Post‐collection handling of seeds can have a profound impact on their viability, longevity in storage, and establishment potential. The first section of this article describes seed cleaning, outlines key considerations, and details traditional and novel approaches. Despite the growth of the native seed industry and the need for seed quality standards, existing equipment and standards largely target agricultural, horticultural, and commercial forestry species. Native plant species typically have complex seed traits, making it difficult to directly transfer existing cleaning and quality standards to these species. Furthermore, in ecological restoration projects, where diversity is valued over uniformity crop standards can be unsuitable. We provide an overview and recommendations for seed quality testing (sampling, purity, viability, germinability, vigor), identity reporting, and seed transfer as well as highlight the need to implement internationally recognized standards for certification for native seeds. Novel and improved cleaning and testing methods are needed for native species from a range of ecosystems to meet the challenges and goals of the United Nations Decade on Ecosystem Restoration. The guidelines outlined in this article along with others in the Special Issue of Restoration Ecology “Standards for Native Seeds in Ecological Restoration” can serve as a foundation for this critical work.

There is a clear need to maximize the genetic diversity of plant material used in restorations to ensure restored populations are equipped to handle current and future conditions. This increasingly translates to focused efforts to intentionally increase the genetic diversity of seed sources in production and/or restoration settings. For example, multiple populations may be brought together to create plant materials with more genetic diversity than is present in any single population. Recent literature showing minimal risk of outbreeding depression and extensive benefits of genetic rescue has helped justify this approach, with the exception of mixing populations with fixed chromosomal differences. In these cases, extensive loss of fertility may occur after mixing. Some types of incompatible chromosomal differences are difficult to detect and therefore have unknown occurrence and distribution within and among species. However, the most extreme form of chromosomal differences-intraspecific ploidy variation (IPV)-is relatively easy to quantify with current technology and known to be fairly common in angiosperms. To encourage more systematic consideration of IPV in native plant restoration, we used available data on IPV to estimate its incidence in 115 species widely used for restoration in the United States. Over one-third have IPV. Additional focused research is needed to understand the consequences of IPV for restoration, particularly given the current trend toward mixing natural collections for materials development and use. We provide recommendations to explicitly incorporate the reality of IPV into the production and use of genetically diverse plant materials for restoration.Key words: chromosomal differences, genetic diversity, intraspecific ploidy variation, mixed-source native plant materials development and use, outbreeding depression Implications for Practice• Intraspecific ploidy variation (IPV) was found in one-third of 115 common restoration species in the United States, highlighting the importance of incorporating it in restoration sourcing decisions.• For species with IPV, declines in seed set and offspring fitness are likely when populations with different ploidy levels are planted together. To minimize these negative consequences for species with known or suspected IPV, the ploidy of populations being considered for mixing should be investigated using flow cytometry, and individuals with different cytotypes should not be mixed in production beds or restoration settings.• If IPV is suspected but not known for all populations being mixed, small trial plots should be used to identify and mitigate potential fitness consequences before mixing over large scales.

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Tallgrass prairie is among the most endangered ecosystems in North America. High-diversity restorations protect remnant habitat and expand native communities. Excluding land acquisition, the most expensive step in restoration is procuring seed. Given this cost, managers want to maximize seedling establishment. Native species that flower and ripen early in the growing season are included in a diverse seeding mix but as a group they have not successfully established. For early-maturing species, the practice of storing seeds in a cold room from harvest until sowing in the dormant season effectively eliminates exposure to the summer conditions seeds would naturally have in the wild. In this study, we compared the effect of summer sowing timing and winter sowing timing on establishment in field conditions. In August 2004 and December 2004, we broadcast a seed mix of seven early-maturing species: Antennaria plantaginifolia (L.) Richardson. (Pussy toes), Arabis lyrata L. (Sand cress), Carex swanii (Fernald) Mack. (Downy green sedge), Hymenopappus scabiosaeus L'Hér. (Old plainsman), Lupinus perennis L. ssp. perennis var. occidentalis S. Watson. (Wild lupine), Phlox bifida Beck. (Sand phlox) and Hesperostipa spartea (Trin.) Barkworth. (Porcupine grass). We collected data on establishment and reproductive success at 12 time points from June 2005 until October 2008. Species established one growing season sooner when planted at the summer sowing time, and diversity in the summer sowing plots was higher after 4 years. Quicker establishment may have benefits such as providing early competition from weeds that may outweigh additional effort required to ensure timely planting.

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