DOI: 10.5061/dryad.d7wm37qb2
title: Data from: Bison grazing in eastern tallgrass prairie does not alter plant diversity after five years

description: North American tallgrass prairie evolved with regular fire set by
 Indigenous people and grazing from large herbivores, including the plains
 bison (Bison bison). In contrast to the uniform effects of
 prescribed fire, bison graze selectively, creating increased heterogeneity
 in the landscape. We examined plant community responses to reintroduced
 bison grazing in high-diversity native and restored tallgrass prairie in
 Illinois, USA. We evaluated plant community diversity and structure in
 paired grazed and ungrazed (fenced) plots. After 5 y of grazing at a
 relatively low target stocking rate of 1 animal unit per 5.2 ha (13
 acres), there were no differences in plant community diversity,
 composition, nonnative: native species ratio, or visual obstruction
 readings between grazed and ungrazed plots. An interaction exists (or was
 found) between plant community type and grazing in which grazed savanna
 plots had greater grass relative abundance compared to ungrazed plots.
 Ongoing monitoring will evaluate long-term trends.
description: Nachusa Grasslands is located near Franklin Grove, Illinois
 (41.8837068N, 89.3424108W) and is owned and managed by The Nature
 Conservancy (TNC). Nachusa consists of more than 1600 ha of native prairie
 remnants, restored prairies, savannas and woodlands, and wetlands. To
 examine the impact of bison grazing on plant communities, twenty-two 10 m
 3 18 m fenced plots (exclosures) and paired unfenced plots were
 established prior to bison reintroduction (Fig. 1). Fences are electrified
 metal wire. The plots are stratified to represent the habitat types at
 Nachusa (Table 1). There are six sampling sites on native prairie (n=3 in
 the north unit, n=3 in the south unit), six sampling sites on older
 plantings (n=3 in the north unit, n=3 in the south unit), four sampling
 sites on newer plantings (n=3 in the north unit, n=1 in the south unit),
 and three sampling sites on savannas (n=in the south unit). This
 unbalanced design results from uneven representation of these habitat
 types across the preserve. We used a stratified random approach to placing
 exclosures on the landscape within each habitat type. For each exclosure,
 three 12.5 m permanent transects inside the fence (ungrazed) are paired
 with three transects of the same length outside the fence (grazed)
 (Supplemental Fig. S1). Transect lines are located at least 2 m from fence
 lines and each transect is 3 m from the adjacent transect.
 Quarter-square-meter quadrats are placed on the east side of each transect
 line at five regular intervals (0–0.5 m, 3–3.5 m, 6–6.5 m, 9–9.5 m, and
 12–12.5 m) for a total of 15 quadrats in each grazed and ungrazed
 plot. Within each 0.25 m2 quadrat, we identified all
 species rooted in the sub-plot and visually estimated their percent cover
 for a total of 570 surveyed quadrats. Plots were sampled regardless of
 whether they had been grazed recently. Plant nomenclature follows Wilhelm
 and Rericha (2017). Plant community composition and cover were determined
 in the north unit in 2014 (pre-bison), 2017, and 2019. In the south unit,
 data were collected in 2015 (pre-bison), 2018, and 2020. Because the bison
 were introduced to the north unit in fall 2014 and the south unit in fall
 2015, this corresponds to year zero, three, and five for each grazing
 unit. In 2014, Daubenmire cover classes (Daubenmire 1959) were used
 instead of percent cover. Class 1 is 0–5% coverage, class 2 is 5–25%,
 class 3 is 25–50%, class 4 is 50–75%, class 5 is 75–95%, and class 6 is
 95–100%. To include the 2014 data in our analyses, we converted the
 2015–2020 data to Daubenmire classes and then transposed all data to
 percent cover midpoints. In 2019 and 2020, aboveground
 plant visual obstruction readings (VOR) were recorded near the time ofpeak
 biomass (late August) in each plot using a Robel pole (Robel et al. 1970;
 Benkobi et al. 2000).
description: # Bison Grazing in Eastern Tallgrass Prairie Does Not Alter Plant
 Diversity after Five Years
 [https://doi.org/10.5061/dryad.d7wm37qb2](https://doi.org/10.5061/dryad.d7wm37qb2) ## Description of the data and file structure Article: Bison grazing in eastern tallgrass prairie does not alter plant diversity after five years Journal: Natural Areas Journal 44(4) Authors: Jennifer Chakravorty, John Herrington, Elizabeth Bach ([elizabeth.bach@tnc.org](mailto:elizabeth.bach@tnc.org)) DOI: [doi.org/10.3375/2162-4399-44.4.215](https://doi.org/10.3375/2162-4399-44.4.215) NachusaBisonExclosureDiveAbund.csv: These data summarize species and functional group diversity observed at Nachusa Grasslands. Columns include: plotyear, graze (G=grazed, UG=ungrazed), community (new, old, remnant, savanna), year since burn, year, fern, forb, grass, rush, sedge, shrub, tree, vine, grass-forb ratio, shannon diversity, native cover, non-native cover, year since bison. Values for functional groups are percent cover. Grass-forb ratio is ratio of grass cover to forb cover. Shannon diversity is the calculated shannon diversity value at the plot level. Native and non-native are mean cover values for native and non-native species. Rows are plots. These data are used to generate Figs. 2 and 3 in Chakravorty et al. 2024. NachusaBisonExComm2014-20.csv: These data present the raw observed plant species cover in each plot across all plots and years. Sub-plots were pooled to generate the plot-level data. Columns are: community, grazing status, siteID, plot, year, and plant species. Rows are plots. These data are used to generate Fig. 4 and Supplemental Table 1 in Chakravorty et al. 2024. These data are observed plant community composition with and without grazing in the first 5 years since bison (Bison bison) were reintroduced at The Nature Conservancy's Nachusa Grasslands. Nachusa Grasslands is located near Franklin Grove, IL (41.883706°N, -89.342410°W) and is owned and managed by The Nature Conservancy (TNC). Nachusa consists of more than 1,600 ha of native prairie remnants, planted restored of prairies, savannas and woodlands, and wetlands. In 2014, American bison (Bison bison) were reintroduced to Nachusa Grasslands in a phased approach. An initial 30 animals were released onto ~200 ha (the north unit) in fall 2014 and grazed exclusively in the north unit for the 2015 growing season. In addition to 20 calves born in spring 2015, an additional 20 adult animals joined the herd in fall 2015 and the grazing area was expanded to include the 400-ha south unit. Since winter 2015/16, the herd has had full access to the entire 600 ha grazing area. After 2018, the herd has been managed at approximately 100 animals overwinter, with new calves increasing its size each growing season. To examine the impact of bison grazing on plant communities, twenty-two 10 m x 18 m bison fenced in exclosures were constructed and installed prior to bison reintroduction. The plots are stratified to represent the habitat types at Nachusa Grasslands. All treatment areas, but one, were included in areas that had been burned within 2 years of sampling. Where possible, locations of exclosures were chosen randomly within each community type. In cases where contiguous hectares of a community were sparse, as was the case for some of the exclosures located in remnant communities, exclosures had to be placed where adequate space was available. For each exclosure, three 12.5-meter permanent transects inside the fence (ungrazed) are paired with three transects of the same length outside the fence (grazed). Transect lines are located at least 2 m from fence lines and each transect is 3 m from the adjacent transect. Quarter-square-meter quadrats are placed on the east side of each transect line at five regular intervals – 0-0.5 m, 3-3.5 m, 6-6.5 m, 9-9.5 m, and 12-12.5 m – for a total of fifteen quadrats in each grazed and ungrazed plot. Please see Chakravorty et al. 2024 for full experimental details, including maps of the preserve and experimental design schema. ### Files and variables #### File: NachusaBisonExclosureDivAbund.csv **Description:** These data summarize species and functional group diversity observed at Nachusa Grasslands. These data are used to generate Figs. 2 and 3 in Chakravorty et al. 2024. ##### Variables * plot_year: plot and year data was observed * graze: grazing status, G=grazed, UG=ungrazed * community: habitat type, new=newer planting, old=older planting, remnant=native prairie, savanna=savanna (see Table 1) * years_since_burn: year since last prescribed fire * year: year data were observed * fern: percent cover of observed ferns * forb: percent cover of observed forbs * grass: percent cover of observed grasses - note several observations of Poa not identified to species * rush: percent cover of observed rushes * sedge: percent cover of observed sedges - note some sedges not identified to species * shrub: percent cover of observed shrubs * tree: percent cover of observed trees * vine: percent cover of observed vines * grass_forb: ration of grass cover to forb cover * shannon: Shannon's diversity index * native: mean percent cover of native plant species * non_native: mean percent cover of non-native plant species * ratio_non_native: ratio of mean native to non-native plant species cover * bison_year: year since bison reintroduction #### File: NachusaBisonExComm2014-20.csv **Description:** These data present the raw observed plant species cover in each plot across all plots and years. Sub-plots were pooled to generate the plot-level data. These data are used to generate Fig. 4 and Supplemental Table 1 in Chakravorty et al. 2024. ##### Variables * community: habitat type, new=newer planting, old=older planting, remnant=native prairie, savanna=savanna (see Table 1) * graze: grazing status, G=grazed, UG=ungrazed * siteID: Nachusa management site identification number * plot: plot identification number * year: year data were observed * Acalypha.virginica: observed percent cover of this plant species * Acer.saccharinum: observed percent cover of this plant species * Achillea.millefolium: observed percent cover of this plant species * Agalinis.tenuifolia: observed percent cover of this plant species * Agastache.scrophulariaefolia: observed percent cover of this plant species * Ageratina.altissima: observed percent cover of this plant species * Agrimonia.parviflora: observed percent cover of this plant species * Agrimonia.pubescens: observed percent cover of this plant species * Agrostis.hyemalis: observed percent cover of this plant species * Agrostis.stolonifera: observed percent cover of this plant species * Allium.cernuum: observed percent cover of this plant species * Ambrosia.artemisiifolia: observed percent cover of this plant species * Ambrosia.psilostachya: observed percent cover of this plant species * Ambrosia.trifida: observed percent cover of this plant species * Amorpha.canescens: observed percent cover of this plant species * Amorpha.fruticosa: observed percent cover of this plant species * Amphicarpaea.bracteata: observed percent cover of this plant species * Andropogon.gerardii: observed percent cover of this plant species * Anemone.canadensis: observed percent cover of this plant species * Anemone.cylindrica: observed percent cover of this plant species * Anemone.quinquefolia: observed percent cover of this plant species * Anemone.virginiana: observed percent cover of this plant species * Angelica.atropurpurea: observed percent cover of this plant species * Antennaria.neglecta: observed percent cover of this plant species * Antennaria.plantaginifolia: observed percent cover of this plant species * Argemone.albiflora: observed percent cover of this plant species * Aristida.purpurascens: observed percent cover of this plant species * Arnoglossum.atriplicifolium: observed percent cover of this plant species * Arnoglossum.plantagineum: observed percent cover of this plant species * Artemisia.campestris.subsp..caudata: observed percent cover of this plant species * Artemisia.campestris.subsp..caudata.subsp..caudata: observed percent cover of this plant species * Asarum.canadense: observed percent cover of this plant species * Asclepias.incarnata: observed percent cover of this plant species * Asclepias.syriaca: observed percent cover of this plant species * Asclepias.verticillata: observed percent cover of this plant species * Asclepias.viridiflora: observed percent cover of this plant species * Astragalus.canadensis: observed percent cover of this plant species * Baptisia.lactea: observed percent cover of this plant species * Baptisia.leucophaea: observed percent cover of this plant species * Botrychium.dissectum: observed percent cover of this plant species * Bouteloua.curtipendula: observed percent cover of this plant species * Brickellia.eupatorioides: observed percent cover of this plant species * Bromus.inermis: observed percent cover of this plant species * Calamagrostis.canadensis: observed percent cover of this plant species * Campanula.aparinoides: observed percent cover of this plant species * Campanulastrum.americanum: observed percent cover of this plant species * Cardamine.pensylvanica: observed percent cover of this plant species * Carex.emoryi: observed percent cover of this plant species * Carex.haydenii: observed percent cover of this plant species * Carex.hystericina: observed percent cover of this plant species * Carex.lacustris: observed percent cover of this plant species * Carex.pellita: observed percent cover of this plant species * Carex.scoparia: observed percent cover of this plant species * Carex.spp: observed percent cover of this plant species * Carex.stipata: observed percent cover of this plant species * Carex.stricta: observed percent cover of this plant species * Carex.trichocarpa: observed percent cover of this plant species * Carex.vulpinoidea: observed percent cover of this plant species * Castilleja.sessiliflora: observed percent cover of this plant species * Catalpa.speciosa: observed percent cover of this plant species * Celtis.occidentalis: observed percent cover of this plant species * Chamaecrista.fasciculata: observed percent cover of this plant species * Chelone.glabra: observed percent cover of this plant species * Chenopodium.album: observed percent cover of this plant species * Chondrosum.hirsutum: observed percent cover of this plant species * Circaea.canadensis: observed percent cover of this plant species * Cirsium.arvense: observed percent cover of this plant species * Cirsium.discolor: observed percent cover of this plant species * Comandra.umbellata: observed percent cover of this plant species * Conyza.canadensis: observed percent cover of this plant species * Coreopsis.palmata: observed percent cover of this plant species * Coreopsis.tripteris: observed percent cover of this plant species * Cornus.racemosa: observed percent cover of this plant species * Crataegus.mollis: observed percent cover of this plant species * Crocanthemum.canadense: observed percent cover of this plant species * Cuscuta.glomerata: observed percent cover of this plant species * Cuscuta.gronovii: observed percent cover of this plant species * Cyperus.esculentus: observed percent cover of this plant species * Cyperus.filiculmis: observed percent cover of this plant species * Cyperus.strigosus: observed percent cover of this plant species * Dactylis.glomerata: observed percent cover of this plant species * Dalea.candida: observed percent cover of this plant species * Dalea.purpurea: observed percent cover of this plant species * Danthonia.spicata: observed percent cover of this plant species * Daucus.carota: observed percent cover of this plant species * Desmodium.canadense: observed percent cover of this plant species * Desmodium.illinoense: observed percent cover of this plant species * Dianthus.armeria: observed percent cover of this plant species * Dichanthelium.implicatum: observed percent cover of this plant species * Dichanthelium.oligosanthes: observed percent cover of this plant species * Dichanthelium.perlongum: observed percent cover of this plant species * Dodecatheon.meadia: observed percent cover of this plant species * Doellingeria.umbellata: observed percent cover of this plant species * Drymocallis.arguta: observed percent cover of this plant species * Echinacea.pallida: observed percent cover of this plant species * Elaeagnus.umbellata: observed percent cover of this plant species * Eleocharis.elliptica: observed percent cover of this plant species * Eleocharis.erythropoda: observed percent cover of this plant species * Eleocharis.palustris: observed percent cover of this plant species * Elymus.canadensis: observed percent cover of this plant species * Elymus.virgin: observed percent cover of this plant species ## Code/software Code in this repository was built and finalized in RStudio(version: 2023.09.1) running R 4.3.1. NachusaBisonPlots_Analysis_final.R: This file applies linear mixed-effects models to compare plant richness, Shannon's diversity, grass:forb ratio, non-native:native ratio, and visual obstruction readings (VOR). It also produces the graphs showing these results (Figures 2, 3, and S2 in Chakravorty et al.). It uses packages lme4 (v. 1.1-34) and tidyverse (v. 2.0.0). NachusaBisonExclosure_NMDS_final.R: This file applies multivariate statistics to visualize and analyze plant community data (Figures 4 and S3 in Chakravorty). It uses packages tidyverse (v. 2.0.0), vegan (v. 2.6-4), and ggplot2 (v. 3.4.3). All analyses were performed in RStudio (R Core Team 2020; RStudio Team 2020). Differences in the Shannon-Weiner Diversity Index (H0), average percent cover of grasses to forbs and nonnative to native species, and VOR were tested using linear mixed-effects models in the nlme package (lme function) (Lokonon et al. 2019; Pinheiro et al. 2020). The Shapiro-Wilk test was used to assess normality of the data and the Levene’s test was used to test for equal We graphed dissimilarities between plant community species composition using nonmetric multidimensional scaling (NMDS) (Prentice 1977). Differences in species composition and functional group composition were further tested for using PERMANOVA in the vegan package in R (adonis function, Bray-Curtis dissimilarity matrix) (Anderson and Walsh 2013; Oksanen et al. 2020). Community type, year surveyed, grazing treatment, and the interaction between these were used as fixed factors. Post hoc analyses included PERMANOVA models constrained by habitat type or years since bison introduction. We carried out a secondary regression analysis to understand whether years since burning had an impact as a covariate using the vegan package in R (envfit function) (Dixon 2003; Oksanen et al. 2020). Prescribed fire is a regular management practice at Nachusa and time since last fire was consistently #2 y across all habitats. All code is openly accessible with this dataset.