PS 42-55 - Seed arrival in grassland restorations alters the role of soil resources in structuring plant population size

Background/Question/Methods

To reestablish a native plant community, restoration practitioners often add seed, but the optimal seed mix design, including seeding rate, remains disputed. Seeding at higher rates can increase plant establishment rates and result in larger established populations; however, this relationship may become saturated, modified by environmental conditions such as soil moisture, and/or vary across species. To reduce unnecessary costs from these altered relationships and help optimize seed mixes, we asked: how do seeding rate and soil moisture independently and interactively affect plant density? Do these relationships differ among species?



To answer these questions, we manipulated seed arrival rate across a landscapes-scale soil gradient in a tallgrass prairie restoration experiment. Our experiment consisted of 5x5m plots seeded at eight densities and replicated across seven fields spanning a quantified soil moisture gradient. Within our experiment, we counted individuals of 12 focal species four years after seeding to quantify the extent to which seed arrival rate and soil moisture interactively structure plant population responses.

Results/Conclusions

Increasing the seeding rate increased abundance for 8 of the 12 species, and all species had higher abundances when seeded onto the drier soils. However, the relationship between plant abundance and soil moisture depended on the seeding rate and varied among species. For example, Schizachyrium scoparium (little bluestem) abundances declined as soil moisture increased, but this rate of decline was less when seeding rates were high. In contrast, Andropogon gerardii (big bluestem) abundances were highest on high moisture soils when seeding rates were high, but when seeding rates were low, abundances were highest on low moisture soils. Our results illustrate how seed arrival in grassland restorations alters the role of soil resources in structuring plant population size. These findings also inform seed mix design by illustrating the seeding rates that maximize plant establishment across soil resource conditions.