Research Projects
Assessing soil seed banks in north-central Missouri remnant prairies and a chronosequence of restored prairies
Period: March 1, 2020 - Present
Contact: Prairie Fork
Organization: University of Missouri Prairie Fork Trust, Missouri Department of Conservation, National Fish and Wildlife Foundation
Funding Source: PFCA
Objectives: Project Principal Investigator: Katherine Wynne
Team Members: Lauren Sullivan (MU), 1 undergraduate student (TBD)
Institution and/or Affiliation: University of Missouri, Division of Biological Sciences
Relationship of Proposal to the Long-term Goals of PFCA: Our proposed study will advance the long-term goals of Prairie Fork Conservation Area (PFCA) by providing knowledge on how seedling recruitment sources change throughout the restoration process, which is critical towards creating and maintaining diverse high-quality restorations. Additionally, data collected from the proposed study will be used to create seedling and seed identification resources that are beneficial to both educators and researchers at PFCA. Lastly, our proposed project will involve both graduate and undergraduate students interested in pursuing professional careers in plant and restoration sciences, furthering PFCA’s core mission of active learning.
Relationship of Proposal to PFCA Research Emphasis Areas (2019): Our proposed study on the soil seed bank dynamics in tallgrass prairie remnants and restorations of various ages will directly address PFCA’s research areas regarding the 1) “control and management of exotic plant species” and 2) “techniques, especially use of fire, to suppress the growth of warm-season grasses in order to encourage forb development within existing prairies”. By assessing the composition of the soil seed bank in restorations of various ages, we will identify whether exotic and undesirable ruderal species are accumulating in the seed bank or are diminishing over time. Soil seed banks can act as the last stronghold for invasive species, and disturbance events such as fire may increase their establishment (Rossiter et al. 2014). In contrast, soil seed banks may
similarly act as a refuge for native species in unfavorable environmental conditions and promote the long-term coexistence of species competing for shared resources via the ‘storage effect’ (Warner and Chesson 1985). Therefore, our study will also provide baseline knowledge on the persistence and regenerative potential of target prairie species after initial seed additions. Data obtained from this study are critical to answering some remaining questions from our previous PFCA funded work in 2019 quantifying the seed rain in these same prairies. The combined information from the seed rain and seed bank will provide a more complete picture of how new recruits (seeds) enter the prairie system and their fate following dispersal. This work will help determine where and what type of seeds are being lost from the system and could provide an answer to why restored prairie systems tend to become grass dominated.
Objectives: We have two research objectives: 1) describe the soil seed bank dynamics of tallgrass prairie restorations and compare them with mature remnant tallgrass prairie ecosystems, and 2) compare the composition of the seed bank to the seed rain collected in 2019 to determine what fraction of the seeds that fell last year can germinate as seedlings. In 2019, we completed a study quantifying the natural seed rain patterns in the last sizable remnant prairie in North- Central Missouri, Tucker Prairie, and at PFCA restored prairies of various ages. However, the post-dispersal fate of those seeds is unknown. Soil seed banks are natural storage reserves for ecosystems, where seeds remain dormant in the soil awaiting favorable conditions for establishment. Because soil seed banks act as a recruitment source, especially after disturbance events such as fire, assessing the species composition and abundance of seed banks is important in predicting the trajectory of community assembly during secondary succession. Understanding the role of soil seed banks in the community assembly of restored systems will help direct conservation decisions related to increasing forb diversity and controlling unwanted ruderal and
exotic species. Paired seed rain and soil seed bank studies conducted in tallgrass prairie ecosystems are limited (Rabinowitz and Rapp 1980, Schott and Hamburg 1997), and even fewer have investigated the relationship between seed rain and the soil seed bank in restored prairies (Kettenring and Galatowitsch 2011). Therefore, we propose to 1) assess and compare the soil seed bank in Missouri remnant prairies (Tucker Prairie and Marshall Diggs Conservation Area) and restored tallgrass prairies of various ages located at PFCA and 2) relate the soil seed bank to the seed rain measured in 2019. We aim to address the four following questions in our study:
1. How does the seed bank change through the restoration process?
2. How does the seed bank of restored prairies compare to remnant prairies?
3. Are there species present in the seed bank that are absent from the measured seed rain, and vice versa?
4. Does restoration reduce the abundance of exotic species in the seed bank over time?
Additionally, we also aim to challenge the hypothesis that succession primarily follows a deterministic pathway. Rather we predict that soil seed bank dynamics are mainly influenced by the seed rain rather than by a shared successional history.
Justification: Tallgrass prairies are among the most imperiled ecosystems in the world (Samson et al. 2004). Although once a dominant ecosystem, less than 1% of 6 million hectares of tallgrass prairie remains intact in Missouri (Samson and Knopf 1994). Due to the alarming loss in North American grasslands, considerable efforts have been made to convert agricultural land back into tallgrass prairie ecosystems. However, prairie restorations and reconstructions have yet to fully emulate the structure and function of remnant, “virgin” prairies (e.g. Baer et al. 2002, Martin et al. 2005, Barak et al. 2017, Newbold et al. 2019). Restorations also tend to lose biodiversity over time (e.g. Barak et al. 2017). Warm-season grasses often dominate restorations, resulting in the
displacement of desired native forb species (Baer et al. 2002, Dickson and Busby 2009) and decline in floristic quality (Newbold et al. 2019). For these reasons, further understanding of the mechanisms related to the recruitment and long-term persistence of forbs, especially “conservative” species, are warranted to create high-quality restorations that safeguard ecosystem services and meet conservation goals.
Seedling recruitment occurs when seeds from the seed rain are incorporated into the soil seed bank, and can remain dormant in the soil for many years. Even after being displaced from the above-ground flora, species may persist for years in the seed bank awaiting conditions favorable for establishment (e.g. Rabinowitz 1981, Schott and Hamburg 1997, Jakobsson et al. 2006). Additionally, soil seed banks may act as genetic reservoirs that help to maintain genetic variation in plant populations (Templeton and Levin 1979, Schulz et al. 2018). Soil seed banks also assist with the rapid regeneration of vegetation in gaps created by disturbance (Kalamees and Zobel 2002). Although seed banks may provide a refuge for native species, exotic species also tend to accumulate in seed banks (D’Antonio and Meyerson 2002, Gioria and Pyšek 2016). Disturbance including fire may increase the establishment of unwanted ruderal and invasive species lurking in the soil seed bank (Rossiter et al. 2014). Therefore, understanding seed bank dynamics is critical towards assessing the regenerative potential of native prairie species and the invasion potential of exotic species following disturbance events such as fire.
Expected Benefits and Outcomes: Our proposed research on soil seed banks aligns with PFCA’s core mission by 1) providing baseline knowledge on how critical sources of seedling recruitment via the soil seed bank change throughout the restoration process and 2) determining whether restorations are comparable to remnant prairies. Due to the limited nature of paired seed rain and seed bank studies in restored prairie ecosystems, our study will provide rare insight into
these processes. We also have the unique opportunity to revisit a fundamental soil seed bank study conducted in a Missouri remnant tallgrass prairie by Rabinowitz (1981) and assess how the soil seed bank has changed 39 years later. Furthermore, identification of the species present in the soil seed bank can inform management decisions. For example, decisions regarding supplementary seed additions of desired native species or concerning the control of noxious invasive species such as Lespedeza cuneata (Zylka et al. 2016).
Besides providing baseline data beneficial towards management decisions, we plan on furthering the educational mission of PFCA by compiling information garnered from this study and the 2019 seed rain study into a north-central Missouri tallgrass prairie seed and seedling guide. Because this high-quality photographic guide is primarily based on species found in PFCA restorations, and other available guides are very low quality, it will act as a valuable resource for educators, volunteers, and researchers who plan to work at PFCA and other grasslands in the state. Additionally, we plan on training an undergraduate student in the Freshman Research in Plant Sciences (FRIPS) Program at the University of Missouri in restoration ecology and plant identification, increasing the educational benefit of PFCA. We are also more than happy to share our research and knowledge about tallgrass prairie plants at PFCA educational events.
Background and Rationale: Since starting her PhD in June 2019, lead PI Katherine has been revisiting a seminal grassland seed rain study conducted by Rabinowitz and Rapp (1980) to quantify seed rain patterns in a remnant prairie (Tucker Prairie) and at a chronosequence of restored prairies located at PFCA. Preliminary analyses suggest that prairies exhibit clear temporal patterns of seed rain, where seed dispersal peaks once in the late spring/early summer and again in the early fall (Fig. 1). In general, restored prairies had higher abundances of seeds
falling than the remnant, where significantly more seeds fell in younger restorations. However, there are strong differences in the species composition of the seed rain between remnant and restored prairies. These differences indicate that seed rain could be altering the community assembly process, and could be further emphasized should there be differences in which seeds are emerging from the seed bank. Seed rain studies conducted in grassland systems are relatively rare and studies that combine seed rain with soil seed banks are even more exceptional. Pairing the previous work on seed rain with the proposed research on seed bank dynamics will contribute towards further understanding the relationship between seed rain and the soil seed bank and their combined role in the assembly of tallgrass prairie plant communities.
Figure 1. Seed rain patterns in a remnant (Tucker Prairie) and chronosequence of reconstructed prairies located at PFCA. Seed rain data for the remnant in 1980 was obtained from Rabinowitz and Rapp (1980). We are currently in the process of completing our identification of seeds from our seed rain samples from 2019.
One possible way to favor the establishment and persistence of forbs in restorations is by manipulating the assembly history of plant communities. Priority effects, or the timing and order of species arrival, have been shown to strongly alter the trajectory of community assembly (Fukami 2015). Because priority effects operate via niche preemption and modification, where early-arriving species may either increase or limit the colonization potential of subsequent species, species addition according to natural dispersal phenology could result in reconstructions with greater biodiversity (Fukami 2015). Consequently, studying priority effects in a natural context can provide the critical understanding necessary to create high-quality tallgrass prairie reconstructions that maintain biodiversity. Although demonstrated in experimental settings, previous experimental treatments have only examined priority effects in broad functional groups (e.g. forbs and grasses) or a subset of early-arriving species (e.g. Körner et al. 2008, Martin and Wilsey 2012). It has yet to be established whether priority effects act in accordance with natural temporal patterns of seed dispersal and seed storage. However, baseline ecological data on natural dispersal patterns and seed storage in tallgrass prairies are needed to inform this experimental project. Our proposed study on soil seed bank dynamics will address these gaps in knowledge and make this experiment possible.
Methods:
Study Sites and Experimental Design: To compare soil seed bank dynamics with seed rain dynamics, we will use the same sites as our 2019 study quantifying natural patterns of seed rain, which was conducted at the 59-ha remnant claypan tallgrass prairie, Tucker Prairie, and three PFCA tallgrass prairie restorations seeded in 2004, 2013, and 2016. Additionally, we will extend our study to include one of the scattered remnant claypan tallgrass prairies (≤ 4 ha in total) at Marshall Diggs Conservation Area (MDCA). Except for at MDCA, we will obtain one soil core (10 x 10 x 10 cm; 1000 cm3) from the center of each transect established in the 2019 seed rain
study (10 transects per site) to allow for comparison between the soil seed bank and seed rain. Because seed rain was not collected from MDCA, we will randomly select 10 locations to collect soil samples in a remnant MDCA prairie. Overall, this will result in 10 soil samples per site, for a total of 50 samples.
After the removal of non-seed plant material (e.g. roots and rhizomes) and air-drying, we will homogenize and then spread soil samples in plastic germination trays to a depth of 1 cm.
Trays (n = 50) will be placed in a greenhouse and watered when dry. We will check germination 1-2 days per week and identify and subsequently remove germinated seedlings. When germination stops and seedlings are identified, samples will be stirred and monitored for any additional germination in case seeds were in an unfavorable location for germination. We will end the study once there is a 3-week period without germination in post-stirred samples.
Data Analysis: To determine the effect of restoration on the abundance of viable seeds present in the soil seed bank, we will conduct a linear mixed-effects model predicting seedling abundance using the fixed effect site type (restoration or remnant) and the random effect transect ID. A similar linear mixed-effects model will be used to instead predict exotic species abundance to determine if restorations reduce the abundance of exotic species over time. Species compositional differences between remnant and restored prairie soil seed banks will be analyzed with a permutational analysis of variance (PERMANOVA) using Bray-Curtis dissimilarity.
Likewise, another PERMANOVA will be conducted to determine whether there are compositional differences between the soil seed bank and soil seed rain. Compositional differences will then be visualized using non-metric multidimensional scaling.
Schedule and Duration: We anticipate collecting soil seed bank samples in late March before dispersal activity from early-maturing plant species begins. Sample collection will take approximately 1-2 days at field sites. Germinating the samples will take anywhere between 6 to 12 months. We expect preliminary results to be available in September 2020 and final results by April 2021.
Information Transfer: We plan on completing one peer-reviewed publication from our proposed study. Furthermore, we plan on presenting our findings on soil seed bank and seed rain dynamics at the 2021 Ecological Society of America conference in Long Beach, CA.
Previous Funded Research by PFCA: PFCA generously funded a study conducted in 2019 by the Sullivan lab to quantifying patterns of seed rain between remnant and restored prairies.
References:
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Barak, R. S., E. W. Williams, A. L. Hipp, M. L. Bowles, G. M. Carr, R. Sherman, and D. J. Larkin. 2017. Restored tallgrass prairies have reduced phylogenetic diversity compared with remnants. Journal of Applied Ecology 54:1080–1090.
D’Antonio, C., and L. A. Meyerson. 2002. Exotic plant species as problems and solutions in ecological restoration: A synthesis. Restoration Ecology 10:703–713.
Dickson, T. L., and W. H. Busby. 2009. Forb Species Establishment Increases with Decreased Grass Seeding Density and with Increased Forb Seeding Density in a Northeast Kansas, U.S.A., Experimental Prairie Restoration. Restoration Ecology 17:597–605.
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Gioria, M., and P. Pyšek. 2016. The Legacy of Plant Invasions: Changes in the Soil Seed Bank of Invaded Plant Communities 66:40–53.
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