Optimizing Graminoid Composition in Prairie Seed Mixes
Graminoid/forb balanced seed mixes have been shown to be both multifunctional and cost-effective, but the specific composition of graminoids in the seed mix will likely impact ecological outcomes. Seeding time also has been shown to impact grass establishment. Does graminoid diversty in seed mixes and timing of seeding effect native plant establishment and cost-effectiveness?
We installed a randomized study with a split plot design consisting of 8 prairie strips in 2020-2021. To assess the importance of graminoid diversity we compared seed a 5 Grass Mix that included 4 common warm season grasses and 1 common cool season grass (all planted at high rates), and a 16 Grass Mix that included 8 warm-season grasses, 2 cool-season grasses, 5 sedges, and one rush (all planted at low to moderate rates). We also included seeding time treatment, with treatments planted in the dormant season (Nov) or spring (May).
Based on first year data:
- The diverse graminoid seed mix produced more diverse stands
- By seeding prairie strips in the dormant season, higher quality habitat can be established at no additional cost
- More time is needed to assess the full effects of seed mix graminoid composition, hypothesized effects are not likely to appear immediately
Outcome Predictability in Prairie Establishment
Studies show that optimal reconstruction methods can improve ecological outcomes and cost effectiveness in prairie establishment. However, most studies are only performed at a single location and/or single planting year, and ecosystem processes can vary dramatically across space and time. Are the effects of prairie reconstruction methods consistently predictable across different planting sites and planting years?
We verified the consistency of results across two equivalent field experiments at different sites and planting years. We installed two randomized complete block experiments in northeastern Iowa in 2015 and 2018. We randomly assigned a combination of mowing and seed mix treatments to each plot. We assessed three seed mixes: an economy grass mix (21 spp., 3:1 grass-to-forb seeding ratio), a diversity mix (71 spp., 1:1 grass-to-forb), and a pollinator mix (38 spp., 1:3 grass-to-forb). We designed the mowing treatment as not mowing or mowing three times during the first year.
Based on two field experiments with two years of data:
- Seed mix design has a very strong, consistent effect on native plant establishment and resulting composition of prairie strips
- Even among different sites and planting years, planting a diverse, grass-forb balanced seed mix results in a stand with most multi-functionality
- While effects are sometimes short-term, establishment is consistently improved with frequent first year mowing
- Effects of many prairie reconstruction implementation methods are predictable
Assessing Surface and Drill Seeding Methods
Both broadcast and drill seeding methods are commonly employed to establish tallgrass prairie vegetation, but is one more cost effective than the other given the high price of seed? Does surface seeding favor small seeded species that may be easily be buried or rely on light to germinate?
We installed a pilot experiment with a completely randomized design consisting of four replicates in May 2019 .We randomly assigned a seeding method, surface seeding or drill seeding, to each plot (n = 8). We used a seed mix with 31 species of contrasting seed sizes, where we included small-seeded species (defined as having 1,058 seeds/g or greater) at approximately 10 times the rate of large-seeded species (defined as having 423 seeds/g or fewer).
Based on a pilot study with two years of data:
- Surface seeding is a more cost effective method than drill seeding when using a seed mix dominated by small seeded species
- Small seeded species were roughly twice as abundant in surface-seeded compared to drill-seeded treatments
- Both methods produced stands with similar native cover and species richness
- Seed should be sown in planting equipment that allows large seeded species to be drilled into the ground while small seeds are placed on the surface (most native seed drills can be modified or calibrated to achieve this)
Prairie Enhancement of Cool-season Grass Stands
Can roadsides dominated by cool-season grasses be enhanced by direct seeding and frequent first year mowing? This simplified management technique would reduce costs associated with weed control and site preparation, increase simplicity in equipment and skill requirements, add flexibility in planting options, and improve pollinator/monarch habitat and water quality in roadsides at comparatively low cost.
We established three research sites testing native plant establishment with and without mowing in three different Iowa counties (Benton, Linn, Fayette) consisting of experiment plots paired with demonstration plantings. We used a diverse prairie seed mix with 71 species and standardized seeding rates for milkweed species. We conducted site-preparation by mowing and removing the duff layer in April 2017, then seeded using a no-till drill in late April. We conducted establishment mowing every three weeks from June 1- August 30.
Based on our first year of data:
- Most prairie species established poorly when seeded (no-till drilled) into established stands of non-native grasses
- Milkweed seedlings emerged at sufficient densities to create monarch habitat (> 0.6 plants/m2) with minimal site preparation (duff removal only) and no follow-up management, but it is still unknown whether that translates to adult milkweed establishment
- First year mowing does not reduce competition enough for sufficient native seedling establishment- initial herbicide is likely necessary
Building Multifunctional, Cost-effective Prairies
Many conservation programs are highly specified in their restoration objectives, and program design (enhance pollinators or halt surface erosion for example) may focus entirely on optimizing one ecological metric at the expense of others. Can multifunctional seed mixes be designed to meet many objectives at once, or is continuing single objective optimization the most effective conservation strategy? What is the most cost-effective way to do it?
We established a randomized complete block experiment testing seed mix designs typical in CRP plantings (grass to forb seeding rate ratios, site customization) with and without mowing in northeastern Iowa. We assessed an economy grass mix ($130/ac, 21 spp., 3:1 grass-to-forb seeding ratio), a diversity mix ($291/ac, 71 spp., 1:1 grass-to-forb), and the pollinator mix ($368/ac, 38 spp., 1:3 grass-to-forb). We conducted site-preparation by disking and cultivating the site and seeded using a no-till drill in late April 2015. We conducted establishment mowing three times during the first year, but did no other management afterwards.
Based on four years of data:
- Expensive, forb-dominated seed mixes produce high pollinator forage, but also have excessive bare ground and perennial weed cover
- Inexpensive, grass-dominated seed mixes produce high native cover and stem density, but little pollinator forage
- Diverse, moderately priced grass/forb balanced seed mixes produce floral resources comparable to forb-dominated mixes, and native cover and stem density comparable to grass dominated mixes with high cost-effectiveness
- Frequent first year mowing accelerated establishment, leading to more ecosystem functioning over a typical 10 year contract.
- Research Highlights: Increasing Cost-Effectiveness of Nutrient Reduction Practices Using Perennial Native Vegetation
- Year 1 Preliminary Technical Report
- Year 2 Research Summary
- Year 3 Technical Report
Reconstructing Cost-effective, Multifunctional Prairies on Dry Marginal Lands
Paired with incentive-based conservation programs, converting farmland on marginal soils to native perennial vegetation may represent a viable conservation land-use choice for many farm owners, but there is a need to better understand how site soils influence establishment outcomes and how seed mixes can be designed to be adaptive to those influences. How does seed mix design, specifically the effect of species habitat matching to soils, affect plant establishment, ecosystem function, and cost-effectiveness in dry marginal lands?
We established a small completely randomized experiment testing seed mix design (soil moisture customization) on dry (sandy) marginal lands. We assessed two mixes- a mix using species adapted to dry soils, and a mix using species adapted to medium soils (developed using the Tallgrass Prairie Seed Calculator, tallgrassprairieseedcalculator.com). We did minimal soil preparation, and seeded the experiment using a no-till drill in late November 2017.
Based on two years of data:
- Key prairie species establish well even in dry conditions. Native warm and cool season grasses establish well in marginal dry soil, along with important summer and fall flowering forbs.
- Seed mixes customized for dry soils result in more ecological functionality at similar price. Dry adapted forb species established better than their medium to wet soil counterparts, resulting in more functional groups present. The entire spring forb functional group was missing from the non-customized mix.
- Cost-effectiveness of native perennial vegetation comparable in productive vs marginal soils. Number of plants produced from one dollar of seed is similar for many native grass and forb species in medium and dry soils.