Prairie Restoration Experiment Research Articles

An Ecological Restoration Experiment on a High School Campus

We established a tallgrass prairie restoration experiment on a high school campus in Kansas. This easily accessible natural environment provides students and teachers many options including scientific research, artistic ventures, or simply relaxing in nature. Our restoration project has four main objectives: (1) practicing science; (2) increasing prairie habitat; (3) fostering a sense of place by getting students outside; and (4) facilitating community collaboration. Here, we present an overview of our restoration as a general model that is adaptable for a variety of ecosystems and circumstances.

Seasonal Shifts in Diversity and Composition of a Tallgrass Prairie Restoration Have Implications for Sampling Time

<h3>ABSTRACT</h3> Restorations change across the growing season. Because of this, the point in the season that a restoration is sampled may affect the conclusions reached based on the sample. In this study, we explore seasonal changes in a prairie restoration experiment in eastern Kansas and investigate how these changes affect observed composition, biodiversity, and the effects of seeding density treatment on the plant community based on when, and how completely, vegetation is sampled. Free State Prairie was established in 2014 to test the effects of forb seeding density on forb establishment, diversity, and restoration success. We compared absolute cover data collected in early June and early September 2019 to each other and to combined data. We found changes in both composition and biodiversity from early-to-late in the season. Sown forbs decreased in cover and richness, while sown grasses increased in cover and richness. Nonsown species did not change in cover but decreased in richness. Neither individual sample fully represented the overall composition or biodiversity of the community. We detected a significant negative effect of forb seeding density on diversity in June, and with combined data, but not in September. As sampling time can affect both broad patterns of composition and diversity and observed results of establishment and management techniques, sampling multiple times in a year will provide the fullest and most accurate picture of the community. When multiple samples are impractical, sampling time should be selected carefully based on the phenology of the restoration and the variables of interest.

The effects of dispersal, herbivory, and competition on plant community assembly.

Dispersal is a key process in community assembly but is often considered separately from downstream assembly processes (e.g., competition, herbivory). However, dispersal varies by species and can interact with other assembly processes through establishment as species enter communities. Here, we sought to distinguish the role of dispersal in community assembly and its interaction with two biotic assembly processes: competition and herbivory. We used a tallgrass prairie restoration experiment that manipulated the competitive and herbivore environments while allowing for natural dispersal and establishment from a diverse regional species pool into areas of low diversity. Dispersal, competition, and herbivory all influenced local communities. By tracking the spread of four target species across the plots, we found interspecific and intraspecific differences in establishment patterns, with herbivores influencing the number of individuals present and the distances species moved. At the community level, only dispersal and competition significantly influenced alpha diversity, but all three processes additively influenced community composition. There was also evidence of herbivore-competition and herbivore-colonization trade-offs in our experiment. Some species that could tolerate herbivory were less likely to establish in competitive environments, while others that could tolerate herbivory were more likely to disperse greater distances. More work is needed to understand the contexts under which dispersal variation affects community assembly and its synergy with other processes.

Selection on convergent functional traits drives compositional divergence in early succession of a tallgrass prairie restoration experiment

Abstract Plant biodiversity is often partitioned into taxonomic diversity (species composition and abundance), phylogenetic diversity (breadth of evolutionary lineages) and functional diversity (resource‐use strategies or physical traits). Evaluating the effects and interplay of these dimensions can provide insights into how assembly processes drive compositional changes in plant communities. However, teasing apart the effects of different biodiversity dimensions is challenging in observational studies or retrospective analyses. To evaluate how plant phylogenetic and trait history shape community establishment and turnover in restoration of a species‐rich North American tallgrass prairie, we conducted an experiment with 127 species planted in assemblages representing three levels of phylogenetic diversity (PD) and two of functional trait diversity (FD), holding starting species richness (SR) fixed. We tested whether PD and FD of planted assemblages predicted species diversity, compositional turnover and selection on functional traits. Rank order of initial functional and phylogenetic diversity levels was maintained throughout the experiment, but neither diversity measure correlated positively with species richness by the end of the experiment. Phylogenetic and taxonomic beta diversity increased among all treatments. This increase in compositional beta diversity was associated with directional selection on phylogenetically dispersed functional traits. A set of functional traits associated with competitiveness in tallgrass prairies predicted species' cover for all survey years: stem dry matter content, leaf dry matter content, vegetative height and rhizomatous growth. Although all plots collectively converged on a similar suite of functional traits, functional beta diversity increased among high‐FD plots. Synthesis. Neither higher functional nor phylogenetic diversity maintained higher species richness (SR) over time in our study. Although SR was not maintained, higher levels of PD and FD were. Both types of diversity shaped the rate at which plots changed in composition over time, with high diversity treatment plots increasing in beta diversity. Selection for traits convergent across the tree of life drove phylogenetic and compositional divergence among plots. While optimization of site‐specific functional traits may be most important for maintaining higher SR, our work implies that planting higher initial PD and FD may make grassland restorations more adaptable to site conditions that may be difficult to predict.

Depth Profile of Soil Carbon and Nitrogen Accumulation over Two Decades in a Prairie Restoration Experiment

Prairies converted from agriculture are known to accumulate carbon (C) and nitrogen (N) and are an important contribution to terrestrial C sequestration. However, estimates of decadal accumulation rates of C and N and their vertical distribution in the soil profile are highly variable among studies, in part due to the lack of repeated inventories of soil C and N stocks over long time periods. We determined the depth profile of soil C and N accumulation and bulk density following the transition from agriculture to planted prairie. Using 13 contiguous plantings with similar land-use histories, planted sequentially from 1995 to 2007, we sampled soil C, N, and bulk density three times over the course of two decades (2000, 2010, and 2019), combining a chronosequence approach with repeated inventories through time. In the top 20 cm of the profile, we found consistent accumulation of C and N, corresponding to 58% (0–10 cm) and 29% (10–20 cm) increases in soil C concentrations and 3.18% (0–10 cm) and 2.7% (10–20 cm) increases in soil N concentration over 19 years. In contrast, we found no change in C or N concentrations at 20–65 cm depth. A chronosequence approach did not detect C or N accumulation in any single sample year. Rather, initial soil C and N content appeared to be the best predictor of final concentrations. Our results suggest that the majority of C and N accumulation is occurring in the top portion of the profile and that restored prairies continue to sequester C two decades after initial planting.

Application of remote sensing technology to estimate productivity and assess phylogenetic heritability.

PREMISEMeasuring plant productivity is critical to understanding complex community interactions. Many traditional methods for estimating productivity, such as direct measurements of biomass and cover, are resource intensive, and remote sensing techniques are emerging as viable alternatives.METHODSWe explore drone‐based remote sensing tools to estimate productivity in a tallgrass prairie restoration experiment and evaluate their ability to predict direct measures of productivity. We apply these various productivity measures to trace the evolution of plant productivity and the traits underlying it.RESULTSThe correlation between remote sensing data and direct measurements of productivity varies depending on vegetation diversity, but the volume of vegetation estimated from drone‐based photogrammetry is among the best predictors of biomass and cover regardless of community composition. The commonly used normalized difference vegetation index (NDVI) is a less accurate predictor of biomass and cover than other equally accessible vegetation indices. We found that the traits most strongly correlated with productivity have lower phylogenetic signal, reflecting the fact that high productivity is convergent across the phylogeny of prairie species. This history of trait convergence connects phylogenetic diversity to plant community assembly and succession.DISCUSSIONOur study demonstrates (1) the importance of considering phylogenetic diversity when setting management goals in a threatened North American grassland ecosystem and (2) the utility of remote sensing as a complement to ground measurements of grassland productivity for both applied and fundamental questions.

Rapid adaptation (or not) in restored plant populations.

Mismatches between the traits of a colonizing population and a novel habitat can generate strong selection, potentially resulting in rapid adaptation. However, for most colonization events, it can be difficult to detect rapid adaptation or distinguish it from nonadaptive evolutionary changes. Here, I take advantage of a replicated prairie restoration experiment to compare recently established plant populations in two closely located restored prairies to each other and to their shared source population to test for rapid adaptation. Using a reciprocal transplant experiment six years after the populations were established, I found that one restored plant population showed evidence of adaptation, outperforming the other restored population when grown at its home site. In contrast, I detected no evidence for adaptation at the other site. These findings demonstrate that while rapid adaptation can occur in colonizing plant populations, it may not be the rule. Better understanding of when adaptation may or may not occur in these contexts may help us use evolution to our advantage, potentially improving establishment of desirable species in restored habitats.

Soil heterogeneity increases plant diversity after 20 years of manipulation during grassland restoration.

The "environmental heterogeneity hypothesis" predicts that variability in resources promotes species coexistence, but few experiments support this hypothesis in plant communities. A previous 15-yr test of this hypothesis in a prairie restoration experiment demonstrated a weak effect of manipulated soil resource heterogeneity on plant diversity. This response was attributed to a transient increase in richness following a post-restoration supplemental propagule addition, occasionally higher diversity under nutrient enrichment, and reduced cover of a dominant species in a subset of soil treatments. Here, we report community dynamics under continuous propagule addition in the same experiment, corresponding to 16-20yr of restoration, in response to altered availability and heterogeneity of soil resources. We also quantified traits of newly added species to determine if heterogeneity increases the amount and variety of niches available for new species to exploit. The heterogeneous treatment contained a factorial combination of altered nutrient availability and soil depth; control plots had no manipulations. Total diversity and richness were higher in the heterogeneous treatment during this 5-yr study due to higher cover, diversity, and richness of previously established forbs, particularly in the N-enriched subplots. All new species added to the experiment exhibited unique trait spaces, but there was no evidence that heterogeneous plots contained a greater variety of new species representing a wider range of trait spaces relative to the control treatment. The richness and cover of new species was higher in N-enriched soil, but the magnitude of this response was small. Communities assembling under long-term N addition were dominated by different species among subplots receiving added N, leading to greater dispersion of communities among the heterogeneous relative to control plots. Contrary to the deterministic mechanism by which heterogeneity was expected to increase diversity (greater variability in resources for new species to exploit), higher diversity in the heterogeneous plots resulted from destabilization of formerly grass-dominated communities in N-enriched subplots. While we do not advocate increasing available soil N at large scales, we conclude that the positive effect ofenvironmental heterogeneity on diversity can take decades to materialize and depend on development of stochastic processes in communities with strong establishment limitation.

Are two strategies better than one? Manipulation of seed density and soil community in an experimental prairie restoration

Restoration practitioners have a variety of practices to choose from when designing a restoration, and different strategies may address different goals. Knowledge of how to best use multiple strategies could improve restoration outcomes. Here, we examine two commonly suggested strategies in a single tallgrass prairie restoration experiment: increased forb sowing density and prairie soil inoculation. We designed a study with two different forb seeding densities. Within these densities, we transplanted seedlings into 1‐m2 plots that had been grown in either a whole prairie soil inoculum or sterilized prairie soil. After 4 years, we found positive effects of both high forb sowing density and inoculation treatments on the ratio of seeded to nonseeded plant cover in these plots, and negative effects of both treatments on nonseeded plant diversity. No effects of either treatment were seen on seeded plant diversity. Each strategy also affected the plant community in different ways: high forb sowing density increased seeded forb richness and decreased native nonseeded plant cover, while inoculation decreased non‐native cover, and tended to increase average successional stage of the community. These effects on restoration outcome were typically independent of each other, with the result that plots with both manipulations had the most positive effects on restoration outcomes. We thus advocate the combined use of these restoration strategies, and further studies which focus on both seeding and soil community manipulation in restoration.

Plant Community Changes During the First 10 Years of a Tallgrass Prairie Restoration Experiment

The relationship between seeding mixtures and establishment of tallgrass prairie plantings was examined in experimental plots established in 2007. Native grass and wildflower seed mixtures, representing four functional groups (C4 grasses, C3 grasses, nitrogen-fixing species, and late-flowering composites), were sown at five levels of richness/seeding density - 4, 8, 12, 16, and 20 species—in 900-m2 plots. Annually, evenness, and total cover and species richness for target (seeded) and non-target (resident) species were measured for the decade from 2007–2016. During the establishment period, eight years received average to above average precipitation; two years experienced drought. Plots seeded with 16 and 20 species achieved 100% target cover by the second year; plots seeded with 12 species had 100% target cover by the fourth year. Plots seeded with 8 or more species had less non-target cover than 4-species plots by the third year, a pattern that persisted for the remainder of the study. Target species ri...

Sowing density effects and patterns of colonization in a prairie restoration

AbstractA cost‐effective approach in plant restorations could be to increase sowing density for species known to be challenging to establish, while reducing sowing density for species that easily colonize on their own. Sowing need not occur evenly across the site for rapidly dispersing species. We explored these issues using a prairie restoration experiment on a high‐school campus with three treatments: plots sown only to grasses (G plots), to grasses and forbs (GF1), and to grasses and forbs with forbs sown at twice the density (GF2). In year 2, GF1 and GF2 plots had higher diversity than G plots, as expected, but GF2 treatments did not have twice the sown forb cover. However, high forb sowing density increased forb richness, probably by reducing stochastic factors in establishment. Cover of nonsown species was highest in G plots and lowest in GF2 plots, suggesting suppressive effects of native forbs on weedy species. Colonization of G plots by two sown forbs (Coreopsis tinctoria and Rudbeckia hirta) was apparent after 2.5 years, providing evidence that these species are self‐sustaining. Colonization was greater in edges than in the central areas of G plots. Through construction of establishment kernels, we infer that the mean establishment distance was shorter for R. hirta (6.7 m) compared to C. tinctoria (21.1 m). Our results lead us to advocate for restoration practices that consider not only seed sowing but also subsequent dispersal of sown species. Furthermore, we conclude that restoration research is particularly amenable for outdoor education and university‐high school collaborations.

Burning reveals cryptic plant diversity and promotes coexistence in a California prairie restoration experiment

Grassland and prairie restoration projects in California often result in long‐term establishment of only a few native plant species, even when they begin with a diverse seed palette. One explanation for the disappearance of certain native species over time is that they are excluded through competition. If so, management that reduces interspecific competition may favor “subordinate” natives and promote greater native species diversity in restored communities. Potential management approaches to accomplish this goal include intraspecific spatial aggregation during seeding and prescribed fire. However, no studies have experimentally evaluated the effects of fire on a controlled (restoration) species pool or the interaction between fire and spatial aggregation. In a previous California prairie restoration experiment, we demonstrated that aggregated plantings protected competitively subordinate species from exclusion and increased community diversity for three years. However, native species richness declined throughout the study, and the benefits of aggregated seeding had begun to disappear by the third year. For the present study, we resurveyed the experimental plots five years after seeding and in the following year carried out controlled burns on half of the plots. The four subordinate species and one of the previously dominant species continued to decline and essentially disappeared aboveground during years four and five. However, burning in year five decreased the cover of dominant natives, triggered the reappearance of the three subordinate species that had disappeared or nearly disappeared in previous years, and increased diversity of the restored community. Seeding treatments (aggregated or interspersed) did not significantly affect community‐level responses to the burning treatment. These results confirm that although initial intraspecific aggregation may promote species coexistence in the short term, re‐establishing disturbance regimes can allow coexistence over a longer time scale by revealing and potentially renewing seed bank diversity.

Soil Properties and Spatial Processes Influence Bacterial Metacommunities within a Grassland Restoration Experiment

AbstractMetacommunity theory proposes that a collection of local communities are linked by dispersal and the resulting compositions are a product of both niche‐based (species sorting) and spatial processes. Determining which of these factors is most important in different habitats can provide insight into the regulation of community assembly. To date, the metacommunity organization of heterotrophic soil bacteria is largely unknown. Spatial variation of soil bacterial communities could arise from (1) the resource heterogeneity produced by plant communities through root exudation and/or litter inputs; (2) the heterogeneity of soil environmental properties; and (3) pure spatial processes, including dispersal limitation and stochastic assembly. Understanding the relative importance of these factors for soil bacterial community structure and function could increase our ability to restore soil communities. We utilized an ongoing tallgrass prairie restoration experiment in northeastern Kansas to assess if restoring native plant communities produced changes in bacterial communities 6 years after restoration. We further examined the relative importance of the spatial heterogeneity of plant communities, soil properties, and pure spatial effects for bacterial community structure in the old‐field restoration site. We found that soil bacterial communities were not influenced by plant restoration, but rather, by the local heterogeneity of soil environmental properties (16.9% of bacterial community variation) and pure spatial effects (11.1%). This work also stresses the idea that restoring bacterial communities can take many years to accomplish due to the inherent changes that occur to the soil after cultivation and the time it takes for the re‐establishment of soil quality.

Fast, easy measurements for assessing vital signs of tall grassland

Abstract We present a small set of measurements for monitoring the recovery of tallgrass ecosystems. The measures incorporate indices of water retention, nutrient cycling, primary production, and the condition of the plant community. Careful novices can make the measurements in a few minutes per sample with simple tools. Our measurements are intended for tallgrass restorations on degraded pastures or former croplands in situations where budgets are tight and neither experienced botanists nor skilled specialists are available for data collection (e.g. restorations that rely on volunteers for data collection, grazing lands whose managers seek improved ecological condition, or sites monitored by novice students). We searched the literature for grassland condition measures that did not require substantial time per measurement, specialized equipment or expert judgments, field tested candidate measurements at six sites that spanned an extreme range of ecological condition, and eliminated those that did not correspond to expert assessments of site condition, that suffered from technical problems, or that depended on recent weather or subtle judgments. We then tested whether different workers could confidently apply the remaining measurements, and used them to assess the condition of 11 fields involved in a prairie restoration experiment. The recommended measurements are presence of bare ground, abundance of five important native perennial grass species, and abundance of two invasive species. These measurements are analogous to vital signs. They provide basic information on the condition of a site rapidly and inexpensively, and can alert analysts to situations that warrant more detailed evaluation.

Effects of timing of prescribed fire on the demography of an invasive plant, spotted knapweed Centaurea maculosa

Summary Prescribed burning is a key tool used in prairie and savanna restoration projects. The timing and frequency of prescribed fires are important variables to consider because they can differentially affect the survival of individual plant species, including noxious exotic species. We used annual censuses and population matrix analysis to evaluate the demographic consequences of burning on populations of the invasive species spotted knapweed Centaurea maculosa in a Michigan, USA, prairie restoration experiment. We compared spring, summer and autumn burns at two frequencies: annually (2000–03) and in alternate years (2001, 2003). We examined the effects of different seasons and frequencies of prescribed fire on the survival, growth and reproduction of C. maculosa populations, and used life‐table response experiments and elasticity analyses to determine how season of fire affects population growth rates. We found that annual summer burning was the only treatment that significantly reduced overall population growth rates. The life‐table response experiment analysis indicated which life stages contributed the most to changes in population growth rates under the different treatments. The summer burn treatments reduced population growth by reducing reproduction. The different burn treatments altered the elasticity structure of populations, but in general reproduction of adults as well as survival of non‐reproductive adults and juveniles remained important in all treatments. This indicates that future attempts to control C. maculosa should focus on combinations of treatments targeting these life stages. Synthesis and applications. Management decisions regarding prescribed burning in grassland restoration projects should consider the responses of individual species already present in the system. In particular, it is important to consider the effects of burning on noxious invasive species that may or may not have different life histories and responses to fire compared with native species. Population matrix modelling provides a more complete picture of the effects of management on population responses compared with other measures based only on community composition and relative abundance. Depending on the goals of a restoration, non‐traditional management options, such as summer burning in mid‐west USA prairies, may be effective management tools for the control of invasive species.