Abstract
Sedges are a substantial and important component of many remnant tallgrass prairies but are often underrepresented in prairie restorations due to challenges associated with establishment, cost, and availability. Improving planting practices can mitigate some of these challenges, making it more cost-effective to include sedges in prairie restorations. In this study, we examine the effect of cold-moist stratification and perigynia removal on germination of 3 common and abundant upland sedge (Cyperaceae) species: plains oval or shortbeak sedge (Carex brevior (Dewey) Mack.), field oval or troublesome sedge (C. molesta Mack. ex Bright), and prairie or Bicknell’s sedge (C. bicknellii Britton). These species are highly practical candidates for prairie, roadside, and pollinator habitat restoration. We automated perigynia removal using a commercial brush machine to ensure applicability to large-scale restorations. Both stratification and perigynia removal improved total germination and germination speed, but there was no benefit to applying both treatments in combination. In general, stratification improved germination speed more than perigynia removal, but both treatments increased total germination by the end of the 84-d trials to comparable degrees. Stratification and perigynia removal were particularly beneficial for C. brevior and C. bicknellii, improving total germination by up to 40% in these species. Based on these results, we recommend fall seeding during restoration as a natural cold-moist stratification technique, and perigynia removal for spring-seeded restorations.
Carex production plots at the Tallgrass Prairie Center, Black Hawk County, Iowa.
CONVERSIONS
(°C × 1.8) + 32 = °F
2.54 cm = 1 in
25.4 mm = 1 in
Sedges (Carex spp. L. [Cyperaceae]) are a major component of tallgrass prairie and prairie wetland communities in the Midwestern US. Sedges can account for up to 25% of aboveground biomass in tallgrass prairies (Coppedge and others 1998) and 25 to 30% of total cover in prairie wetlands (Ashworth 1997; Aronson and Galatowitsch 2008). In spite of their prevalence, sedges are often omitted from prairie restoration projects because of low commercial availability. Protocols for the production, harvest, and cleaning of sedge seed have historically lagged behind those of native prairie grasses and forbs (Houseal and Smith 2010). Another reason for their omission is that sedges, when seeded, can be difficult to establish (Hipp 2008; Iannone and Galatowitsch 2008). Failure to establish sedges in prairie restoration projects could affect the ecosystem integrity and function of these restored plant communities. For example, prairie restorations are highly susceptible to weed invasion during their early stages (Zedler and Kercher 2004; Blumenthal and others 2005; Iannone and Galatowitsch 2008; Middleton and others 2010). Previous studies in wetlands have shown that the absence of sedges increases the likelihood of invasion by exotic cool-season grasses such as reed canarygrass (Phalaris arundinacea L. [Poaceae]) and smooth brome (Bromus inermis Leyss. [Poaceae]) (Budelsky and Galatowitsch 2000; Mulhouse and Galatowitsch 2003; Aronson and Galatowitsch 2008). Developing protocols that improve sedge establishment in prairie restorations would likely increase their use and could improve restoration outcomes.
Seed dormancy is a major obstacle to improving sedge establishment in prairie restorations. In many Carex species, freshly matured seeds display conditional dormancy (Schütz 1997, 1998, 2000; Schütz and Rave 1999; Kettenring and Galatowitsch 2007a, 2007b). In this state, seeds require stratification to germinate under most environmental conditions but can still germinate without stratification under a specific and narrower set of environmental conditions (Baskin and Baskin 1998). For example, Kettenring and Galatowitsch (2007a, 2007b) found that many Carex species germinate without stratification under summer temperatures (e.g., 27 °C [81 °F] days/15 °C [59 °F] nights), but that the same species germinate under a much wider range of temperatures when stratified. Other studies have shown that many Carex species also require light to germinate (for example, Baskin and others 1996; Schütz and Rave 1999; Schütz 2000; Kettenring and others 2006). Sedges may fail to establish in prairie restorations because earlier germinating prairie species and annual weeds limit light availability to sedges at their peak germination time (that is, mid-summer) (Kettenring and Galatowitsch 2007a, 2007b). Breaking conditional seed dormancy prior to sowing could increase sedge establishment in prairie restorations by reducing competition for light (Kettenring and Galatowitsch 2011).
One pre-sowing seed treatment that could improve sedge establishment in prairie restorations is cold-moist stratification, which increases overall germination rates in many Carex species (Budelsky and Galatowitsch 1999; Schütz and Rave 1999; Hoag and others 2001; Kettenring and Galatowitsch 2007a, 2007b). For example, Schütz and Rave (1999) found that cold-moist stratification (4 °C [39 °F] for 6 mo) increased germination rates in 28 of 32 Carex species tested. Cold-moist stratification can also hasten germination in Carex by widening the range of temperatures under which germination occurs (Kettenring and Galatowitsch 2007a, 2007b).
Another pre-sowing seed treatment that could improve sedge establishment in prairie restorations is perigynia removal. The perigynium is a sack-like structure that surrounds the seeds of true sedges. The perigynium can be removed with a razor blade (for example, Hough-Snee and Cooper 2011), forceps and sandpaper (for example, Hoag and others 2001), or a commercially available brush machine (for example, Houseal and Smith 2010). Previous studies have shown that perigynia removal increases overall germination rates in Nebraska sedge (C. nebrascensis Dewey; Hoag and others 2001), Pennsylvania sedge (C. pensylvanica Lam.; McGinnis and Meyer 2011), awlfruit sedge (C. stipata Muhl. ex Willd.; Hough-Snee and Cooper 2011), yellowfruit sedge (C. annectens (E.P. Bicknell) E.P. Bicknell.; Nelson and others 2018), and bottlebrush sedge (C. hystericina Muhl. ex Willd.; Nelson and others 2018). If cold-moist stratification and perigynia removal promote earlier germination and improve overall germination rates, then these pre-sowing seed treatments should increase sedge establishment in prairie restorations.
In this study, we examine the effects of cold-moist stratification and perigynia removal on germination in 3 upland Carex species: plains oval or shortbeak sedge (C. brevior (Dewey) Mack.), field oval or troublesome sedge (C. molesta Mack. ex Bright), and prairie or Bicknell’s sedge (C. bicknellii Britton). These species are highly practical candidates for prairie restoration projects because of their ubiquity in high-quality Midwestern tallgrass prairie remnants and prairie wetlands (Hipp 2008; Houseal and Smith 2010). Carex brevior and C. molesta are facultative hydrophytes, occurring in both wetland and non-wetland prairies. Carex bicknellii is a facultative upland species (USDA NRCS 2019). All 3 species are in the Ovales (Kunth.) tribe, with vegetative culms, gynecandrous spikes, and perigynia bearing marginal, epidermal wings (Hipp and others 2006). These species flower from April to June and fruit from June to July (Mohlenbrock 1999; Hipp 2008). We conducted germination trials to test the relative value of cold-moist stratification, perigynia removal, and their interactions as techniques for improving germination in these important but underused prairie restoration species.
Carex brevior achenes (fruit and seed) with intact perigynia.
MATERIALS AND METHODS
We obtained C. brevior, C. molesta, and C. bicknellii seed from the Tallgrass Prairie Center at the University of Northern Iowa, Cedar Falls, Iowa, USA. Seed from each species was collected from 17 to 31 remnant prairies across northern and central Iowa in 2006 (Houseal and Smith 2010). Seedlings from each population were greenhouse propagated and outplanted to establish seed increase plots at the Tallgrass Prairie Center (42.51052 N, 92.47560 W) in 2007 as described in Houseal and Smith (2010) and Houseal (2010). These collection and propagation methods were developed to ensure that the population of plants in the seed increase plots included a representative sample of the genetic diversity found in these Carex species across northern and central Iowa. Soils of the seed increase plots were a mixture of 391B Clyde-Floyd complex with 1–4% slopes and 83B Kenyon loam with 2–5% slopes (Web Soil Survey 2019).
Past studies of the effects of stratification and perigynia removal on Carex germination have used both freshly harvested (Schütz and Rave 1999; McGinnis and Meyer 2011) and stored seed (Hoag and others 2001; Jones and others 2004). Most prairie restoration projects use stored seed (Jones and others 2004), but fresh seed is used in some circumstances. We conducted germination trials using stored seed for C. brevior and C. molesta, and fresh seed for all 3 species (C. brevior, C. molesta, and C. bicknellii). We did not perform germination trials on stored C. bicknellii seed because of limited availability.
We combine-harvested ripe seed from the seed increase plots in late June 2010 for the stored seed trials and early July 2011 for the fresh seed trials. All seed was air-dried, rough-cleaned, and air-screen cleaned twice using a Westrup seed cleaner (type LA-LS, No. LALS-0106) following Houseal (2007) with minor adjustments based on trial and error (see Table 1 for settings). We cleaned the machine prior to use and between species to avoid contamination. Seed used in the stored seed trials was placed in resealable plastic bags and refrigerated (7.0–7.5 °C [44.6–45.5 °F]) for 10 mo, which is consistent with typical restoration practices for native tallgrass prairie plant species (Houseal 2007).
Westrup air-screen cleaner (type LA-LS, No. LALS-0106) settings for seed treatments.
We employed a 2 × 2 factorial design for the germination trials with stratification and perigynia removal as factors. Each treatment group—control (C), stratified (S), perigynia removed (P), and stratified and perigynia removed (SP)—was replicated 4 times for each species × seed type (fresh or stored) group.
To remove the perigynia, we passed the seed through a Westrup brush machine (type LA-H, No. LAH-0105, medium brush, 6.5 RPM, #10 [2 mm (0.08 in)] drum screen, 6.35 mm [0.25 in] gate opening) 2 times (Houseal 2007). Once the perigynia were removed, seed was passed through the air-screen cleaner to remove any loose perigynia material (see Table 1 for settings). We cleaned both machines thoroughly prior to use and between species. We examined treated seed under magnification to ensure no visible damage to the seed had occurred during perigynia removal.
For the cold-moist stratification treatment, we placed seeds between pieces of distilled water-moistened blue blotter paper (10.2 × 10.2 cm [4.0 × 4.0 in]) in clear polystyrene containers (11.0 × 11.0 × 3.5 cm [4.3 × 4.3 × 1.4 in]) (Hoffman Manufacturing, model 156C) with tight-fitting lids for 28 d at 7.0 to 7.5 °C [44.6–45.5 °F] and 37 to 41% RH.
Westrup brush machine used to remove perigynia from Carex seeds.
Carex brevior seeds shown with and without perigynium.
Cold-moist stratified Carex brevior seeds with intact perigynia ready to enter the germination chamber.
We hand-selected 100 seeds for each replicate and examined seed to ensure that the perigynia was either completely intact or removed, as required for each treatment. We positioned the seed of each replicate into 10 rows of 10 on blotter paper moistened with distilled water in the bottom of a clear polystyrene container with a tight-fitting lid. We placed the containers into a Percival Scientific Intellus germination chamber (model 130L) set to 12-h days (30 °C [86 °F]) and 12-h nights (15 °C [59 °F]). The arrangement of the containers in the chamber was haphazardly selected and changed frequently throughout the trials. The stored seed germination trials began on 19 April 2011, and the fresh seed germination trials started 1 September 2011.
We defined germination as the presence of a radicle and coleoptile visible to the naked eye (Schütz and Rave 1999). In the stored seed trials, we checked seed for germination every day for 24 d, then every other day through day 42, then every 6 d through day 84. In the fresh seed trials, we checked seed every day for 30 d, then every other day through day 48, then every 6 d through day 84. At the end of the trials, we inspected every seed that did not germinate for viability by gently pinching them with forceps. We assumed that any soft, empty seeds were nonviable and excluded them from germination calculations (Baskin and Baskin 1998; Schütz and Rave 1999). Based on these criteria, no more than 5 nonviable seeds had to be removed from any replicate.
Statistical Analysis
We defined 3 variables to describe the shape of the cumulative germination curve. First, we defined total germination as the percentage of seed that successfully germinated at the end of each 84-d germination trial. Calculations were based on 100 seeds per treatment replicate, corrected for seed viability. Corrections were minor since viability was 95% or greater in all cases. Second, we defined time to germination onset as the day on which the first seed germinated in a germination trial. This is a measure of “lag time” prior to the start of germination. Finally, we defined time to 50% germination as the day on which a given germination trial achieved ≥50% germination. This measure can be conceptualized as the median amount of time a seed requires to germinate and is thus a measure of germination speed that incorporates initial lag time. We calculated these 3 variables for each germination trial replicate and analyzed the resulting values using analysis of variance (ANOVA) and Tukey’s HSD pairwise comparisons of means.
To graphically visualize germination curves, we fit an asymptotic nonlinear function with offset using the formula:
where yi is the germination percentage on day xi, A is a parameter for the asymptotic total germination rate, lrc is the natural log of the rate constant parameter, and c0 is a parameter representing time to germination onset.
Prior to analysis, we assessed all data for normality and homogeneity of variance. When residuals were non-normal, we checked whether ANOVA was robust to the departure from normality by comparing ANOVA results to a nonparametric ANOVA (Aligned Rank Transform [ART]). In almost all cases, ANOVA was found to be robust to normality departures, as is often true (Schmider and others 2010), so the ANOVA results were reported. Two exceptions were found, and in these cases we applied the Box-Cox transformation to normalize the data. This resulted in log-transforming one response variable (time to 50% germination for stored C. brevior seed). Box-Cox transformation failed to adequately normalize data for one other response variable (total germination for stored C. molesta seed). In this case, we used Aligned Rank Transform to analyze the data. All statistical analyses were done using R version 3.5.2 (R Development Core Team 2019), and asymptotic curves were fit using the SSasympOff function in R. We defined significance as P < 0.05 and marginal significance as 0.05 < P < 0.10.
RESULTS
Total germination of untreated (control) seed ranged from 56.4% for stored C. brevior to 93.0% for stored C. molesta (Figure 1). In general, both seed treatments (cold-moist stratification and perigynia removal) increased total germination and germination speed (Table 2). In most cases, the effects of stratification were greater than perigynia removal, and the combined treatment effects were not additive.
Effects of cold-moist stratification and perigynia removal seed treatments on total germination of 3 tallgrass prairie Carex species.
Effects of cold-moist stratification and perigynia removal seed treatments on total germination, time to germination onset, and time to 50% germination of 3 tallgrass prairie Carex species.
Total Germination
For stored C. brevior seed, both stratification and perigynia removal increased total germination by approximately 40%, with no additive effect of the combined treatment (Table 2, Figure 1). For stored C. molesta seed, both treatments produced a significant but modest increase (~5%) in total germination (Table 2), though post-hoc tests were unable to sufficiently resolve the modest differences (Figure 1).
For fresh C. brevior seed, perigynia removal resulted in the largest increase in total germination; however, the benefit of perigynia removal was less pronounced when the seeds were also stratified, as indicated by the significant SP term (the interaction between stratification and perigynia removal; Table 2). Stratification alone also resulted in a small increase in total germination, but there was no added benefit when both treatments were combined (Table 2, Figure 1). For fresh C. molesta seed, only stratification resulted in a small significant increase in total germination. For fresh C. bicknellii seed, perigynia removal increased total germination by 34% and stratification resulted in a marginally significant 27% increase in total germination, but applying both treatments in combination did not result in any significant additional increase.
Time to Germination Onset
For stored C. brevior and C. molesta seed, stratification reduced time to germination onset from approximately 8 d (controls) to 5 d (Table 2, Figure 2). Perigynia removal slightly reduced time to germination onset compared to controls, and the combined treatments produced results identical to stratification alone.
Effects of cold-moist stratification and perigynia removal seed treatments on time to germination onset of 3 tallgrass prairie Carex species.
For fresh seed, both seed treatments reduced time to germination onset relative to controls, but stratification reduced it to a greater degree than did perigynia removal (Table 2). Stratification reduced time to germination onset from 9.8 to 6.5 d in C. brevior, from 8.3 to 5.3 d in C. molesta, and from 13.0 to 7.8 d in C. bicknellii (Figure 2). In C. bicknellii only, the combined treatment reduced time to germination onset to a greater degree than either stratification or perigynia removal alone (Figure 2.)
Time to 50% Germination
Stratification greatly reduced time to 50% germination for stored seed (Table 3). Stratified seed reached 50% germination approximately 7 times faster (9.3 d) than did the control seed (65.3 d) in C. brevior and 2 times faster (5.8 d) than control seed (12.0 d) in C. molesta (Table 3, Figure 3). Perigynia removal did not significantly reduce time to 50% germination in stored C. brevior but did reduce the time in C. molesta, although post hoc tests were unable to sufficiently resolve the slight differences in means (Figure 2). The effects of the combined treatment were comparable to stratification alone (Table 3).
Effects of cold-moist stratification and perigynia removal seed treatments on time to 50% germination of 3 tallgrass prairie Carex species.
Influence of pre-sowing seed treatments on time to 50% germination (days) for fresh and stored seed of 3 tallgrass prairie Carex species.
For fresh seed, both seed treatments generally reduced time to 50% germination, but the benefit of each pre-sowing seed treatment varied by species (Table 2). For C. brevior, perigynia removal reduced time to 50% germination compared to the control (from 19.8 to 13.3 d), while stratification had a smaller effect (Table 3, Figure 3). For C. molesta, both seed treatments reduced time to 50% germination compared to the control, but the effect of stratification (from 12.3 to 7.8 d) was greater than that of perigynia removal (from 12.3 to 9.8 d; Table 3, Figure 3). For C. bicknellii, both seed treatments reduced time to 50% germination from 35.0 to approximately 18.5–19 d (Table 3, Figure 3).
DISCUSSION
Both cold-moist stratification and perigynia removal increased total germination of these 3 upland prairie sedge species. Applying both pre-sowing seed treatments did not produce higher total germination than applying either pre-sowing seed treatment individually. The effect of stratification or perigynia removal was most pronounced in C. brevior and C. bicknellii, whereas C. molesta displayed greater than 90% germination regardless of treatment or seed type (stored or fresh). Collectively, our total germination results suggest that 1) stratification or perigynia removal can improve sedge germination and potential sedge establishment in prairie restoration; 2) stratification and perigynia removal are particularly beneficial for sedge species with low germination rates and for restorations that use stored seed; and 3) restoration practitioners should apply either stratification or perigynia removal but not both techniques.
Hastening germination could be key to improving sedge establishment in prairie restorations. Many sedge species require light for germination (Baskin and others 1996; Schütz and Rave 1999; Schütz 2000; Kettenring and others 2006). Sedges that germinate slowly in prairie restorations would likely emerge into a low-light, competitive environment that would hinder establishment (Williams and others 2007). Our results show that both cold-moist stratification and perigynia removal hasten germination in these Carex species. Stratification reduced time to germination onset and time to 50% germination in all species and seed types, and perigynia removal hastened germination in all groups except stored C. brevior. In addition to enhancing light availability, hastening germination can reduce the likelihood of other seed hazards, such as predation, loss due to flooding or burial, and loss of viability (Budelsky and Galatowitsch 1999; van der Valk and others 1999; Jones and others 2004). Our results indicate that cold-moist stratification is generally a superior technique to perigynia removal for hastening sedge germination in prairie restorations. Although perigynia removal hastened germination in fresh Carex seed, most Midwestern prairie restorations use commercially available seed, which generally has been stored.
Techniques that improve sedge germination should enhance ecological outcomes in prairie restorations. Weed invasion is a major concern with any wetland or prairie restoration project. Studies on wetland restoration have shown that invasive species, such as reed canarygrass, can quickly dominate the plant community if they become established (Galatowitsch and van der Valk 1996; Green and Galatowitsch 2001; Mulhouse and Galatowitsch 2003; Kettenring and Galatowitsch 2007b). The presence of reed canarygrass hinders sedge performance (Wetzel and van der Valk 1998) and establishment (Budelsky and Galatowitsch 2000) thereby reducing the overall quality of the restoration. Studies on prairie restoration have shown that rapid establishment of cool-season grasses limits invasion by Canada thistle (Cirsium arvense (L.) Scop. [Asteraceae]) (Larson and others 2013). If sedge seeds germinate earlier in the spring and with greater frequency, then their establishment and long-term presence could reduce the likelihood of weed invasion in prairie restorations through inhibitory priority effects.
Management Implications
As a pre-sowing seed treatment, cold-moist stratification of seed in a controlled laboratory setting is currently impractical at the scale required for most prairie restoration projects. Further, cold-moist stratified seed would be wet and difficult to sow using seed drills, which rely on flowability of dry materials to function properly. Broadcast seeding of wet seeds may be possible, though the binding likely to occur with other seeds would preclude precision in seed mix sowing. However, in temperate climates fall seeding can be used to implement natural cold-moist stratification. Kettenring and Galatowitsch (2011) found that unstratified sedge seed established at much higher rates in fall-seeded compared to spring-seeded prairie wetland restorations. Fall seeding has also been advocated for sedge establishment in the restoration of utility meadows on degraded grasslands (Phillips-Mao 2017). In prairie restorations specifically, Larson and colleagues (2011) found that different suites of species establish in fall-seeded versus spring-seeded tallgrass prairie restorations. Many seeds fail to germinate immediately in spring-seeded restorations, which places them at risk of burial, predation, or fungal attack for a full year until they receive their germination cue (Chambers and MacMahon 1994). For sedges, most emergence in wetland restorations occurs within the first year (Kettenring and Galatowitsch 2011), further emphasizing the importance of pre-sowing seed treatments that break dormancy. The natural cold-moist stratification of a fall-seeded restoration should promote sedge germination earlier in the spring when there is less competition for light, thus increasing the likelihood of successful establishment.
From a practical standpoint, perigynia removal is a more versatile pre-sowing seed treatment than cold-moist stratification. This technique could be used in prairie restoration regardless of seeding method (broadcast or drill) or seeding time (fall or spring). However, removing the perigynia of bulk seed requires a brush machine. Therefore, this pre-sowing seed treatment would likely need to be performed by the seed producer. While the benefits of perigynia removal were generally smaller than those of cold-moist stratification, the former still increased total germination and germination speed relative to no pre-sowing seed treatment. Therefore, we advocate perigynia removal in spring-seeded restorations where natural cold-moist stratification is not possible.
Although in general we found cold-moist stratification and perigynia removal both substantially improved germination, this result was true to varying degrees among the 3 Carex species. Carex molesta, for example, exhibited high total germination even in untreated (control) seed, leaving little room for improvement through stratification or perigynia removal. By contrast, total germination in untreated stored C. brevior was lower than any other untreated seed, and as a result we observed the largest benefits of stratification and perigynia removal treatments in this species. Similarly, seed storage had a varying influence on treatment effectiveness in the 3 species. These findings suggest that the benefit of stratification or perigynia removal are likely to vary among species, and we recommend testing the benefits of stratification or perigynia removal before extending these results to other Carex species.
Sedges would be useful species in restoration projects for which short stand stature is desired, such as roadside prairie restorations (Smith 1998; Houseal and Smith 2000; Brandt and others 2015). Restoring native vegetation on roadsides can provide numerous ecosystem services and functions, for example, reducing soil erosion, improving water quality, reducing the need for herbicide use, and providing habitat for wildlife (summarized in Brandt and others 2015), but short-statured plants like sedges that provide these services without obscuring motorists’ vision are preferable to tall C4 grasses. Demand for sedge seed for roadside restoration projects has increased in recent years (Nemec 2019), highlighting the growing interest in these underutilized species. Sedges would also be useful in the restoration of pollinator habitat. Grasses are typically seeded at low rates in pollinator habitat plantings to reduce competition with native forbs; however, this practice can result in stands with high amounts of bare ground and low resistance to weed invasion (for example, Dickson and Busby 2009). The use of short-statured sedges could allow practitioners to 1) increase the graminoid component of pollinator habitat seed mixes without the threat of light competition to forbs and 2) potentially increase the ecosystem services that pollinator habitat provides (Meissen and others 2019).
Future Directions
We performed germination trials in this study under constant light and temperature (12-h days at 30 °C [86 °F], 12-h nights at 15 °C [59 °F]). Previous research has shown that many sedge species germinate without stratification under high summer temperatures (for example, 27 °C [81 °F] d / 15 °C [59 °F] nights), similar to the conditions applied in our study (Kettenring and Galatowitsch 2007a, 2007b). Cold-moist stratification and perigynia removal are known to widen the range of temperatures under which sedge germination occurs in a variety of sedge species (Budelsky and Galatowitsch 1999; Schütz and Rave 1999; Hoag and others 2001; Nelson and others 2018). Future studies should examine whether perigynia removal and stratification widen the range of temperatures under which germination occurs in these species to the same extent. Widening the range of germination temperatures may provide insurance against climatic anomalies or climate change reducing germination success in the early stage of a restoration. These results would provide more insight into the comparable value of the 2 pre-sowing seed treatments for prairie restoration. In addition, a study on the impact of fall- versus spring-seeding on species establishment in tallgrass prairie restoration is currently being conducted by researchers at the Tallgrass Prairie Center (Cedar Falls, Iowa, US). Two of the seed mixes used in this study contain sedge species, and preliminary results suggest that first-year sedge establishment is higher in fall-seeded than in spring-seeded restorations (Meissen 2019).
CONCLUSIONS
Carex brevior, C. molesta, and C. bicknellii are good candidates for a wide variety of prairie restoration projects. They were specifically selected for this study because of their ubiquity in high-quality Midwestern tallgrass prairie remnants (Hipp 2008; Houseal and Smith 2010). The high rates of germination observed for all 3 species in this study further highlight their potential for restoration. Our results show that cold-moist stratification is a superior technique to perigynia removal for hastening germination, but both techniques improve total germination and germination speed relative to no pre-sowing seed treatment. Management decisions about whether to implement pre-sowing seed treatments will likely depend on their perceived value relative to the cost (time, labor, and equipment) of implementing them. Targeted application of pre-sowing seed treatments to those Carex species or seed types exhibiting poor germination, particularly those with higher seed prices, may improve establishment likelihood and reduce overall project costs. Based on our results, we recommend fall seeding of C. brevior, C. molesta, and C. bicknellii as the best approach to improving their establishment in Midwestern prairie restorations and perigynia removal as the best approach for restorations seeded in the spring.
ACKNOWLEDGMENTS
Funding for this project was provided by the 2010 Wetlands II Project through the Iowa Natural Resource Conservation Service of the United States Department of Agriculture and by the Tallgrass Prairie Center at the University of Northern Iowa. We thank Justin Meissen and an anonymous reviewer for critical reviews of the manuscript.
Footnotes
Photos by Christina Boeck Crew and Greg Houseal, Tallgrass Prairie Center
