Germination syndromes and their relevance to rangeland seeding strategies in the intermountain western United States

Authors: Hardegree, Stuart; Sheley, Roger; JAMES, JEREMY - University Of California; Reeves, Patrick; Richards, Christopher; Walters, Christina; Boyd, Chad; Moffet, Corey; Flerchinger, Gerald

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2019
Publication Date: 3/1/2020
Citation: Hardegree, S.P., Sheley, R.L., James, J., Reeves, P.A., Richards, C.M., Walters, C.T., Boyd, C.S., Moffet, C., Flerchinger, G.N. 2020. Germination syndromes and their relevance to rangeland seeding strategies in the intermountain western United States. Rangeland Ecology and Management. 73(2):334-341. https://doi.org/10.1016/j.rama.2019.11.004.
DOI: https://doi.org/10.1016/j.rama.2019.11.004

Interpretive Summary: Sagebrush/bunchgrass rangelands in the western US are being transformed to invasive annual grass communities after wildfire. These plant communities are very difficult to rehabilitate or restore after disturbance given the extremely high annual and seasonal variability in precipitation and temperature. Short term field studies in rangeland seeding are difficult to interpret as they don't usually survey the variability in conditions that can be expected in the field. We simulated cumulative germination response of native perennial and introduced annual grasses as if they had been planted during any week in the last 57 years and determined that two general strategies might increase the probability of initial seedling establishment in these systems: 1) plant as late in the fall as possible in order to avoid premature germination and seedling death during the winter; and 2) plant as diverse a seed mix as possible to ensure that some seeds are available for germination during any period of seedbed favorability during the late fall, winter and spring. Seed mix diversification can be achieved by increasing the number of species in the seed mix, increasing the number of seed-lots of individual species in the seed mix, or using artificial methods to broaden the germination response of planted seeds. Late fall planting and diversification of the seed mix can be expected to increase the probability of seedling emergence and successful first-year establishment and improve overall restoration efforts on millions of acres of public and private rangeland in the Intermountain western US.

Technical Abstract: Rangelands in the western US exhibit extremely high temporal variability in seedbed microclimate and this variability contributes to poor establishment success of revegetation species that are typically planted in the fall. We conducted long-term simulations of cumulative germination as a function of planting date and identified alternative germination syndromes based on population-level responses to environmental variability. These germination syndromes reveal ecologically significant differences, but also, noteworthy similarities in species and seed-lot response that can inform rangeland restoration planning and management. Seed germination may occur much sooner than assumed under the traditional paradigm of fall-planting/spring-emergence in the Intermountain western US. Hence, it does not appear to be a bottleneck for successful establishment in most years. Instead, simulations of germination response support recent hypotheses that post-germination/pre-emergent mortality may be the larger contributor to poor seedling establishment. Our data support two general strategies to improve the likelihood of seedling survival into the spring: seeding as late as possible in the fall and active diversification of potential germination syndromes within a given seed mix. Consistent application of these strategies could increase the probability that some seed are always available to take advantage of any pulse of seedbed favorability in the late fall, winter or early spring.