Seed source impacts germination and early establishment of dominant grasses in prairie restorations

Background/Question/Methods

Restoration managers select seed from a variety of sources for restoration projects. Purchasing non-local seed may be easier and cheaper than gathering seeds from local sources. But if the purchased seed is not of the local ecotype, land managers risk poor establishment in the short-term and outcrossing between local and non-local ecotypes, genetic swamping, and losing local genetic diversity in the long-term. However, using seeds from local sources may not be advantageous if populations are inbred or maladapted to the managed restoration environment.

Three dominant warm-season prairie grass species from remnant, restoration, and nursery sources were planted as seeds and plugs into experimental plots located at three established prairie restorations in rural western Minnesota. The goals were to determine the extent to which (1) seed source and (2) restoration site influence seedling germination and growth in established prairie restorations. Also I measured the extent to which (3) establishment and growth differs between seedlings planted as plugs (greenhouse-seedlings) and those grown from seed in the field (field-seedlings).

Results/Conclusions

(1) Seed source impacted germination and survival in all seedlings, except for Sorghastrum nutans field-seedlings. Generally, Andropogon gerardii and Bouteloua curtipendula nursery seeds had the highest germination and growth, followed by restoration seedlings, and remnant seedlings.

(2) In field-seedlings, germination, survival, and growth differed among restoration sites, however results were species specific. The effect of seed source on germination of Sorghastrum field-seedlings varied among sites, as evidenced by a significant interaction term, indicating that Sorghastrum may be particularly sensitive to environmental variation. In greenhouse-seedlings of all species, only leaf length differed among sites.

(3) Germination was 3-12 times higher for greenhouse-seedlings than for field-seedlings. However, once seedlings were established in the restoration sites, mortality was low in all species: less than 1% for field-seedlings and 9-13% for greenhouse-seedlings.

Both seed source and restoration practices have an important impact on germination and performance during establishment. Sensitivity to restoration practices vary among dominant warm-season grasses, making it inappropriate to consider them ecological equivalents. Germination likely limits restorations that sow seeds directly. These results highlight some of the important factors that managers should consider when selecting seeds for restoration projects.