Diverse mix of native plant seed
Procuring Plant Material

 

Once you have determined which species you will use for your restoration project, you must then acquire the plant material. The two primary approaches utilize seed or outplanting of nursery-grown plants, though in some instances topsoil transfer or translocation of individuals may be useful. Seed can be collected in the field, but oftentimes commercially produced seed is needed. In any case, thought should be given to where plants are sourced from to ensure they will perform well at your site.

 

Wild Seed Collection

Although more labor-intensive than purchasing materials, collecting wild seed is a common restoration approach. Sometimes this may be the only option for procuring local seed of plant species that are targets for restoration. There are laws in place to protect wild and rare native plants in California. Do not collect materials without landowner permission or proper permits, and know the rules pertaining to seed collection and transfer.

Seed collection by hand

Seed collections should be conducted as close to the proposed planting location as possible [1] to ensure overlap between seeding conditions and germination requirements [2]. Seed collection can occur directly from the plant or from the ground (often the case for trees). Although seed collection should typically be conducted once the plant is dry, some studies have shown that seeds can be removed from green plants and stored until cured [3]. Plants exhibit a diversity of seed types and modes of dispersal, so collection techniques and timing should be optimized on a per species basis. For example, some seeds must be stripped or plucked from plants, while others can be beaten or shaken into trays, bowls, or tarps. Although these collection strategies are time consuming (and time sensitive for many species), data has shown that plant collected seed can demonstrate much higher viability than ground collected seed [4]. Seed processing (e.g., cleaning, storage, and testing) can also take substantial amounts of time and resources. Some general guidelines for seed collection, cleaning, and storage [5] include:

  1. Genetic Diversity: Collect seeds from at least 50 parent plants across the site to capture the full range of genetic diversity present.

  2. Timing and Monitoring: Closely monitor seed maturation to ensure collection occurs at the optimal time, as seed viability is directly tied to proper harvesting.

  3. Collection Techniques: Use appropriate techniques such as hand-stripping, clipping, or shaking seeds from plants, ensuring that at least 50% of seeds are left on-site to allow for natural regeneration.

  4. Seed Cleaning: After collection, clean seeds to remove debris, chaff, and damaged or non-viable seeds. This ensures high-quality seeds for restoration and reduces the introduction of pathogens or weed seeds. Use sieves, blowers, or hand sorting for, depending on seed size and type. Properly cleaning seeds enhances germination rates and long-term viability.

  5. Seed Testing: If possible, conduct seed testing to assess viability, purity, and germination rates before use in restoration projects. Testing ensures that high-quality, viable seeds are planted and can be used to identify appropriate treatments to enhance germination.

  6. Proper Storage: Store seeds under controlled conditions, avoiding high temperatures and moisture to maintain seed viability. Seeds should be kept in material that allows air in and should be stored in a cool and dry environment. Best practices for post seed collection suggests storing seed at -20 degrees C at low moisture conditions [6].

  7. Documentation: Thoroughly document collection locations and dates for each seed accession. These data can be used to inform future collections and evaluate success based on seed source.

Although this can be an issue with purchased seed as well, collected seed can often require exposure to environmental factors to overcome seed dormancy. These factors can be dissimilar across species living in the same region [7] and can include periods of heat, cold, moisture and physical scarification. Some species have also been shown to germinate and survive at higher rates when exposed to chemicals such as salicylic acid [8]. For species from fire-prone ecosystems, liquid smoke can be used to mimic the natural chemical cues produced by wildfire, thereby enhancing germination rates [9]. 

Mechanical seed collection 

Collecting large quantities of seed can be accomplished using mechanical methods such as brush, vacuum, and combine harvesting [10]. Hand collecting seed is more time consuming than bulk harvesting with machines. However, in addition to increased cost, the use of machines such as a combine or seed stripper, can result in harvests of materials associated with seed, such as leaves and stems. This reduces the amount of pure live seed per pound, subsequently requiring additional labor for cleaning the seed or increased pounds required for seeding. Moreover, weeds and other undesirable material is much more likely to contaminate collections when conducting bulk harvests. This approach also depends on having large, uniform stands of natives and is most appropriate in the context of native seed farming.

Resources

References

  1. Lippitt, L., Fidelibus, M.W. and Bainbridge, D.A. (1994). Native Seed Collection, Processing, and Storage for Revegetation Projects in the Western United States. Restoration Ecology, 2: 120–131. https://doi.org/10.1111/j.1526-100X.1994.tb00049.x
  2. Smith, S.E., Riley, E., Tiss, J.L. and Fendenheim, D.M. (2000). Geographical variation in predictive seedling emergence in a perennial desert grass. Journal of Ecology, 88: 139–149. https://doi.org/10.1046/j.1365-2745.2000.00436.x
  3. Scotton, M., & Ševčíková, M. (2017). Efficiency of mechanical seed harvesting for grassland restoration. Agriculture, Ecosystems & Environment, 247, 195–204. https://doi.org/10.1016/j.agee.2017.06.040
  4. Phillips, R. (1992). Environmental factors contribute to acorn quality: Elevation, on- or off-tree collection influence the viability of blue oak acorns. California Agriculture, 46(5), 30–32. PDF
  5. Linington, S., & Manger, K. (2014). Seed bank design: Cold rooms for seed storage (Technical Information Sheet, 12). Kew Royal Botanic Gardens. PDF
  6. Kildisheva, O.A., Erickson, T.E., Madsen, M.D., Dixon, K.W. and Merritt, D.J. (2019). Seed germination and dormancy traits of forbs and shrubs important for restoration of North American dryland ecosystems. Plant Biology, 21: 458–469. https://doi.org/10.1111/plb.12892
  7. Pedrini, S., Stevens, J. C., & Dixon, K. W. (2021). Seed encrusting with salicylic acid: a novel approach to improve establishment of grass species in ecological restoration. PLoS One, 16(6), e0242035. https://doi.org/10.1371/journal.pone.0242035
  8. Keeley, J. E., McGinnis, T. W., & Bollens, K. A. (2005). Seed germination of Sierra Nevada postfire chaparral species. Madroño, 52(3), 175–181. https://doi.org/10.3120/0024-9637(2005)52[175:SGOSNP]2.0.CO;2
  9. Pedrini, S., Gibson-Roy, P., Trivedi, C., Gálvez-Ramírez, C., Hardwick, K., Shaw, N., Frischie, S., Laverack, G. and Dixon, K. (2020). Collection and production of native seeds for ecological restoration. Restoration Ecology, 28: S228–S238. https://doi.org/10.1111/rec.13190

Translocation

Although more labor-intensive than purchasing materials, plant materials collected in the field can be an effective method for achieving restoration goals. This can include translocating entire plants or using cuttings of species that can be propagated vegetatively. For example, the translocation of salvaged plants has been successful for restoring coastal sage scrub in southern California [1] and Mojave Desert plant communities [2]. Plants can be directly transferred from donor sites to areas being restored or cared for in a nursery setting prior to transplanting. Transplanting during the growing season will ensure that plants are in good condition and more likely to survive. Keep in mind that pretreatments prior to transplanting (such as soaking tree cuttings) [3] might be necessary for transplant success. Practitioners should be mindful of potential negative impacts that removal of plants could have on donor sites. This method is an excellent restoration approach for rescuing native plants at “doomed” sites that are slated for development or resource extraction.

California has laws regarding the collection of native plants in addition to federal laws. Do not collect materials without landowner permission or proper permits, and know the rules pertaining to plant collection and transfer.

Resources

References

  1. Bowler, P. A. (2000). Ecological restoration of coastal sage scrub and its potential role in habitat conservation plans. Environmental Management, 26, S85–S96. https://doi.org/10.1007/s002670010064
  2. Abella, S. R., Chiquoine, L. P., Newton, A. C., & Vanier, C. H. (2015). Restoring a desert ecosystem using soil salvage, revegetation, and irrigation. Journal of Arid Environments, 115, 44–52. https://doi.org/10.1016/j.jaridenv.2015.01.003
  3. Schaff, S. D., Pezeshki, S. R., & Shields, F. D., Jr. (2002). Effects of pre-planting soaking on growth and survival of black willow cuttings. Restoration Ecology, 10, 267–274. https://doi.org/10.1046/j.1526-100X.2002.02035.x

Topsoil Transfer

Topsoil transfer is another approach that can be used as an alternative to seeding or transplanting. In this method, the upper horizon of the soil profile which contains the native seed bank is collected and spread across the restoration site. This method is widely used in mine-site restoration, though success can be highly variable [1]. Direct soil transfer is preferable to storage, as over time stockpiling can reduce the number of viable seeds in the soil [2] and have negative impacts on beneficial soil biota that are important for plant growth [3]. One potential pitfall in this approach is that the mixing of topsoil during transfer may bury some seeds too deep to emerge, thereby diluting the native seed bank [4], and other supplemental restoration techniques may be required. Care should also be taken to ensure that seeds of invasive plant species are not transferred to the restoration site during this process, and plans should be in place for weed control if nonnatives do emerge [5]. When a recipient restoration site has a pre-existing seed bank of weeds, applying a thick layer of native topsoil (greater than 5 cm) can effectively suppress non-native seed emergence and reduce invasive plant cover [6].


Resources

References

  1. Scoles-Sciulla, S. J., & DeFalco, L. A. (2009). Seed reserves diluted during surface soil reclamation in eastern Mojave Desert. Arid Land Research and Management, 23(1), 1–13. https://doi.org/10.1080/15324980802598698
  2. Golos, P. J., Dixon, K. W., & Erickson, T. E. (2016). Plant recruitment from the soil seed bank depends on topsoil stockpile age, height, and storage history in an arid environment. Restoration Ecology, 24, S53–S61. https://doi.org/10.1111/rec.12389
  3. Valliere, J. M., D’Agui, H. M., Dixon, K. W., Nevill, P. G., Wong, W. S., Zhong, H., & Veneklaas, E. J. (2022). Stockpiling disrupts the biological integrity of topsoil for ecological restoration. Plant and Soil. https://doi.org/10.1007/s11104-021-05217-z
  4. Fowler, W. M., Fontaine, J. B., Enright, N. J., & Veber, W. P. (2015). Evaluating restoration potential of transferred topsoil. Applied Vegetation Science, 18, 379–390. https://doi.org/10.1111/avsc.12162
  5. Dixon, P. J. (2018). Assessment of topsoil salvage and seed augmentation in the restoration of coastal sage scrub on Santa Catalina Island, California. Western North American Naturalist, 78(4), 711–721. https://doi.org/10.3398/064.078.0412
  6. Schmidt, K. T., Maltz, M., Ta, P., Khalili, B., Weihe, C., Phillips, M., Aronson, E., Lulow, M., Long, J., & Kimball, S. (2020). Identifying mechanisms for successful ecological restoration with salvaged topsoil in coastal sage scrub communities. Diversity, 12(4), 150. https://doi.org/10.3390/d12040150

Purchasing

When it’s not feasible to collect seed on site or from nearby areas, purchasing plant materials either as seed or nursery stock becomes necessary. While potentially expensive, this option offers several advantages, including clear knowledge of the source populations (most of the time), ease of procurement, and the opportunity to support local businesses. Since species can vary greatly in their tolerance to biotic and abiotic factors depending on their origin [1], it’s important to choose plant materials from sites with similar climatic and soil conditions to the revegetation area whenever possible [2]. This will increase the likelihood of establishment success as well as long-term persistence of restored communities. Understanding your climate zone is critical when selecting the right materials, such as through the use of seed transfer zones. Many native seed and plant suppliers can offer recommendations based on climate zones. 

When purchasing seed, pay attention to purity values, which drive pounds per acre needed for seeding. Seed quality is determined by its ‘Pure Live Seed’ or PLS value, which is a function of purity, germination and dormancy. PLS varies across and even within species. For example, forbs are expected to have lower PLS values because they often have a complex dormancy mechanism. Keep in mind that critical information associated with germination and dormancy break is unknown for many native plants [3]. However, similar plants (e.g. phylogenetically close) often have similar requirements [4], which can be a helpful guide.

Resources

California native seed suppliers

References

  1. Hufford, K. M., & Mazer, S. J. (2003). Plant ecotypes: genetic differentiation in the age of ecological restoration. Trends in Ecology & Evolution, 18(3), 147–155. https://doi.org/10.1016/S0169-5347(03)00002-8
  2. McKay, J. K., Christian, C. E., Harrison, S., & Rice, K. J. (2005). “How local is local?”—a review of practical and conceptual issues in the genetics of restoration. Restoration Ecology, 13(3), 432–440. https://doi.org/10.1111/j.1526-100X.2005.00058.x
  3. Ladouceur, E., Jiménez-Alfaro, B., Marin, M., De Vitis, M., Abbandonato, H., Iannetta, P. P. M., Bonomi, C., & Pritchard, H. W. (2018). Native seed supply and the restoration species pool. Conservation Letters, 11: e12381. https://doi.org/10.1111/conl.12381
  4. Seglias, A. E., Williams, E., Bilge, A., & Kramer, A. T. (2018). Phylogeny and source climate impact seed dormancy and germination of restoration-relevant forb species. PLoS One, 13(2), e0191931. https://doi.org/10.1371/journal.pone.0191931

*Mentions of specific companies or products are for educational purposes only and not intended as endorsements.

Seed Farming

There is currently insufficient native seed to meet the growing demand of ecological restoration [1]. For large-scale and long-term restoration initiatives, native seed farming is one approach for ensuring adequate plant material that also minimizes impacts on wild populations [2]. This requires land and resources for growing native plants and harvesting and processing seed. There are several organizations and commercial growers in California that have undertaken large-scale seed production, such as Heritage Growers, Hedgerow Farms, and S&S Seeds. In addition to supplying commercially available seed (see Purchasing), some operations may be able to provide seed bulking services. Smaller scale seed farms may be an option in some instances, particularly for species that are high conservation priorities and for which it is difficult to collect sufficient seed in the wild. For example, In the highly modified and fragmented San Joaquin Valley, local genotypes are largely unavailable for commercial purchase, and the scarcity of remnant native vegetation makes it difficult to collect enough seed for large-scale restoration efforts. To address this challenge, local seed was collected and used to establish a field nursery specifically for seed production [3].

Establishing reliable and economically viable seed production systems with native plants requires a significant amount of time and resources. In addition to collecting wild seed and establishing plants in the field, operations must include plans for seed cleaning and testing. This also requires the capacity and appropriate facilities for seed storage.

It is important to include ample genetic variation when seed farming by propagating individuals from a variety of maternal plants. Native plants cultivated for multiple generations could lead to unintentional changes in plant traits (i.e., domestication syndrome), so farmed populations should be replenished with new wild-collected genotypes regularly to maintain genetic diversity and mitigate artificial selection [4].

Resources

References

  1. Harrison, S. P., Atcitty, D., Fiegener, R., Goodhue, R., Havens, K., House, C. C., Johnson, R. C., et al. (2023). An assessment of native seed needs and the capacity for their supply. Washington, DC: The National Academies Press. https://doi.org/10.17226/26618
  2. Pedrini, S., Gibson-Roy, P., Trivedi, C., Gálvez-Ramírez, C., Hardwick, K., Shaw, N., Frischie, S., Laverack, G., & Dixon, K. (2020). Collection and production of native seeds for ecological restoration. Restoration Ecology, 28: S228–S238. https://doi.org/10.1111/rec.13190
  3. Conrady, M., Lampei, C., Bossdorf, O., Hölzel, N., Michalski, S., Durka, W., & Bucharova, A. (2023). Plants cultivated for ecosystem restoration can evolve toward a domestication syndrome. Proceedings of the National Academy of Sciences, 120(20), e2219664120. https://doi.org/10.1073/pnas.2219664120
  4. Borders, B. D., Cypher, B. L., Ritter, N. P., & Kelly, P. A. (2011). The challenge of locating seed sources for restoration in the San Joaquin Valley, California. Natural Areas Journal, 31(2), 190–199. https://doi.org/10.3375/043.031.0213

*Mentions of specific companies or products are for educational purposes only and not intended as endorsements.

Provenancing

When procuring plants of seeds for restoration, it is important to make informed decisions about where these are sourced from (i.e., provenance) based on the location and environmental conditions of the restoration site. The prevailing paradigm in restoration ecology has been “local is best”, where local seed is assumed to perform best due to local adaptation to site conditions [1]. There is evidence to support this approach, though local adaptation is not always present or detected in plant populations [2]. Using local seed offers practical advantages, such as the ability to collect it directly from the restoration site, reducing logistical complexities. More importantly, it minimizes the risk of introducing non-local genotypes that may be poorly adapted to the site’s environmental conditions. By using local seed, practitioners also avoid the potential for unintended gene flow into local populations, which could disrupt the genetic integrity and diminish the adaptive traits that have evolved over time in response to local conditions. It is also important to collect from a range of maternal plants in order to maintain genetic diversity in restored plant communities. 

For many restoration projects, local plant material may be unavailable. In such cases, practitioners can use data on climate, soil type, and elevation to identify appropriate regions for seed collection or purchase. This ensures that the selected seeds are well-suited to the environmental conditions of the restoration site [3]. Seed transfer zones can be informed by factors beyond just climate. For instance, considering the fire history of a region can help prioritize areas where seed conservation and collection are most needed [4]. 

Practitioners should carefully weigh the pros and cons of using non-local genotypes. For example, gene swamping is likely more of a risk in rare species with limited distributions as compared to widespread species.

Resources

References

  1. McKay, J. K., Christian, C. E., Harrison, S., & Rice, K. J. (2005). “How local is local?”—A review of practical and conceptual issues in the genetics of restoration. Restoration Ecology, 13, 432–440. https://doi.org/10.1111/j.1526-100X.2005.00058.x
  2. Bucharova, A., Durka, W., Hölzel, N., Kollmann, J., Michalski, S., & Bossdorf, O. (2017). Are local plants the best for ecosystem restoration? It depends on how you analyze the data. Ecology and Evolution, 7, 10683–10689. https://doi.org/10.1002/ece3.3585
  3. Richardson, B. A., & Chaney, L. (2018). Climate-based seed transfer of a widespread shrub: population shifts, restoration strategies, and the trailing edge. Ecological Applications, 28, 2165–2174. https://doi.org/10.1002/eap.1804
  4. Barga, S. C., Kilkenny, F. F., Jensen, S., Kulpa, S. M., Agneray, A. C., & Leger, E. A. (2023). Not all seed transfer zones are created equal: using fire history to identify seed needs in the Cold Deserts of the western United States. Restoration Ecology, 31, e14007. https://doi.org/10.1111/rec.14007