Germination information for common Arizona restoration species

Seed-based ecological restoration is an approach used to revegetate damaged and disturbed habitats by spreading seed with the expectation that germination will occur and plants will become established and flourish. Although restoration can enhance the health and productivity of landscapes by reinvigorating ecosystem services both directly and indirectly, successful restoration is difficult to achieve – particularly in arid systems (Copeland et al. 2018). Germination is a well known bottleneck to plant growth that prohibits successful restoration (James at al. 2011).

General information about germination likelihood and requirements would provide critical information that managers need to make decisions about which species to prioritize for restoration. We assessed a series of commonly used restoration species and their germination using basic lab and greenhouse tests. Species we tested included the grasses Aristida purpurea (purple three awn), Bouteloua gracilis (blue grama), Bouteloua rothrockii (six-weeks grama), Elymus elymoides (squirreltail), Pascopyrum smithii (western wheatgrass), Poa secunda (Sandberg bluegrass), and Vulpia octoflora (six-weeks fescue); and the forbs/shrubs Atriplex canescens (four-wing saltbush), Baileya multiradiata (desert marigold), Dalea candida (white prairie clover), Ericameria nauseosa (rubber rabbitbrush), Krascheninnikovia lanata (winterfat), Linum lewisii (prairie flax), Machaeranthera tanacetifolia (Tahoka daisy), Penstemon palmeri (Palmer’s penstemon), Plantago ovata (psyllium), Senna covesii (desert senna), and Sphaeralcea ambigua (desert globemallow). The seeds were purchased from Granite Seed in spring 2022, and were stored at room temperature for five months, then in cold storage until germination tests began in winter 2023. Seeds were sown in pots in a greenhouse in groups of 20 of the same species. They were provided sunlight and water daily in room temperature conditions. For species that had low germination in the greenhouse and/or documented (from our previous work) or suspected dormancy requirements (e.g. Atriplex canescens, Baileya multiradiata, Bouteloua rothrockii, Penstemon palmeri, Senna covesii, and Sphaeralcea ambigua) we also assessed effect of scarification (swiping each seed across sandpaper) and/or cold/moist stratification on germination (placing seeds in petri dishes with moist filter paper in a refrigerator for 40 days) (Dunn 2011). The experiment was conducted over a single month.

All the shrubs we tested, Atriplex canescens, Ericameria nauseosa, and Krascheninnikovia lanata; as well as grass Bouteloua rothrockii, and forb Senna covesii demonstrated low germination (<25%). Grasses Aristida purpurea, Bouteloua gracilis, Pascopyrum smithii, Poa secunda, and Vulpia octoflora; and forbs Baileya multiradiata, Linum lewisii, Penstemon palmeri, and Sphaeralcea ambigua demonstrated moderate germination (25-70%).  Finally, grass Elymus elymoides, and forbs Dalea candida, Machaeranthera tanacetifolia, and Plantago ovata demonstrated high germination (>70%; Table 1). Attempts to break dormancy through scarification and/or cold/moist stratification did not enhance germination for Atriplex canescens, Bouteloua rothrockii, or Senna covesii, but did improve germination for Baileya multiradiata, Penstemon palmeri, and Sphaeralcea ambigua.

Table 1. Common native restoration species and their percent germination. In the dormancy tested column, a “no” means the seeds were grown in the greenhouse, while “stratification” or “scarification + stratification” means the species were stratified in cool/moist conditions, and/or scarified with sandpaper, in order to break dormancy. Grasses are noted in green while forbs/shrubs are noted in black color.

Although our study highlights species that might provide more utility for restoration based on their high germination, managers should be aware that many factors can drive differences in germination. These include variety, quality of seed, the presence of a seedcoat, storage conditions, temperature and moisture availability. For instance, the seeds in this study were stored at room temperature for five months, and may have had higher percent germination if they had been kept in cold storage. Our data can be used as a guide, but performing small batch germination tests for restoration species of interest is always recommended. Considering some of the significant differences in germination found between untreated and treated (e.g. approached to break dormancy) seeds, growers and practitioners should always explore the utility of pre treating seeds in some way to enhance germination. NRCS ‘Plant Guides’ often describe seed pre treatment requirements to break dormancy. For more information on restoration and to develop a plant list, visit Ecorestore.arizona.edu.

Copeland SM, Munson SM, Pilliod DS, Welty JL, Bradford JB, Butterfield BJ (2018) Long-term trends in restoration and associated land treatments in the southwestern United States. Restoration Ecology 26: 311-322

Dunn B (2011) Improved germination of two Sphaeralcea A. St.-Hil. (Malvaceae) species with scarification plus stratification treatments. Native Plants Journal 12: 13-17

James JJ, Svejcar TJ, Rinella MJ (2011) Demographic processes limiting seedling recruitment in arid grassland restoration. Journal of Applied Ecology 48: 961-969

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