DOI: 10.5061/dryad.jh9w0vtn8
title: Data from: Forbs in Viking lands: The effect of disturbing dominant graminoids on recruitment in tundra grasslands

description: Grasslands, by definition, are dominated by graminoids. 
 Nevertheless, forbs also make up a substantial part of vascular plant
 diversity in grasslands and are important resources of mammalian
 herbivores. However, forb recruitment is constrained by successful
 dominant graminoids, limiting access to safe sites for germination.
 Disturbances created by herbivores can reduce graminoid dominance and
 favor forb recruitment. Here we hypothesize that intense disturbance, such
 as that caused by megaherbivores, promotes safe sites for forbs in such
 graminoid-dominated grasslands, whereas disturbance by today’s herbivores,
 such as small rodents, may not be sufficiently intense. We selected a
 total of 80 plots with either of four successful graminoid species in
 tundra grasslands of the Varanger Peninsula, Norway. The graminoid species
 were silicon-poor or rich, and of either mat- or bunch growth form. Plots
 were further selected in both rodent disturbed and undisturbed areas. We
 manually removed the dominant graminoid in half of the plots, mimicking
 megaherbivore disturbance by reducing both shading capabilities and
 belowground rhizome and root systems. Results show that forb recruitment
 was significantly enhanced one year following the manual removal of all
 four graminoids. This effect on forb recruitment was similar among the
 four graminoids even though they were associated with distinct plant
 communities. The rodent disturbance did not enhance forb recruitment. In
 plots with rodent disturbed graminoids, the manual removal enhanced forb
 recruitment only in plots with silicon-rich graminoids. Forb recruitment
 was further enhanced by higher levels of initial species richness, initial
 forb abundance and soil moisture. Our findings support the hypothesis that
 intense disturbance, simulating megaherbivore effects on dominant
 graminoids, significantly enhances forb recruitment.
description: This study was conducted in riparian grasslands along tributaries
 of the Bergebyelva river, Varanger Peninsula, Norway
 (70.30<sup>o</sup> N, 29.02<sup>o</sup>
 E).  The main treatment was manual disturbance of
 dominant graminoids that made up most of the vascular plant abundance in
 grassland vegetation plots. Both aboveground and belowground plant parts
 were removed, and in doing so most other vascular plants present in the
 plots were also disturbed. To test the extents to which small rodent
 disturbance, dominant graminoid growth form and dominant graminoid silica
 content affected the outcome of this manual disturbance, we established a
 nested study design in two riparian valleys (Torvhaugdalen, 70.31o N,
 29.08o E and Bearalveaijohka 70.29o N, 28.96o E) in July 2023. In both
 valleys, we identified substantial populations of the four dominant
 graminoids: the silica-rich bunch graminoid <em>Deschampsia
 cespitosa</em>, the silica-poor bunch graminoid <em>Carex
 nigra</em>, the silica-rich mat graminoid <em>Calamagrostis
 spp</em>. and the silica-poor mat graminoid <em>Anthoxanthum
 nipponicum</em>. For each dominant graminoid within each site, we
 identified areas with no visual signs of rodent disturbance and areas with
 high levels of rodent disturbance (hereafter denoted as
 <em>Non-rodent</em> and <em>Rodent
 Disturbed</em>). Disturbance was identified  by vegetation clipping,
 runways, and feces presence. In each area we established a minimum of two
 0.5m x 0.5m plots, or plot pairs. The plots representing a single pair
 were at least 0.5m from each other and plot pairs that were either
 Non-rodent or Rodent Disturbed were at least 7m from each
 other.  Initial plot conditions in July 2023 were
 determined by recording a list of all vascular plant species as a measure
 of species richness, estimating the percent cover per species, measuring
 plant height (in each plot quadrant), and assessing rodent disturbance
 intensity–percentage of the plot with graminoid clippings or runways and
 feces presence. After these initial recordings, we randomly chose one plot
 per pair for the manual disturbance. To simulate megaherbivory capable of
 disturbing both above- and belowground plant structures, we removed both
 above- and belowground biomass – breaking shade aboveground and rhizome
 and belowground root and rhizome networks (hereafter denoted
 <em>Manual</em>).  In July 2024, we
 revisited each plot, assessed percent cover per species and plant height
 as in 2023, and counted the number of seedlings in the plot (many
 seedlings had developed their first true leaf, allowing us to distinguish
 between forbs and other Dicotyledoneae plants - e.g., Salix shrubs). We
 did not register graminoid seedlings. This was because we could not
 differentiate clearly between true seedlings and regeneration from buds.
 Indeed, there were likely remains of rhizomes in the soil after the manual
 disturbance that have likely survived the winter.  We
 also sampled plot level abiotic information. We measured photosynthetic
 active radiation (PAR) at seedling height and above the vegetation canopy
 using the quantum sensor on a LiCOR 600 Porometer/Fluorometer (LiCOR
 Biosciences, Lincoln, Nebraska, USA) to determine the relative amount of
 light reaching seedlings. The PAR index ranged from 0 to 1, 1
 representing  a situation where all light reaches seedling. We further
 measured percent soil moisture using a SM150 soil moisture sensor (Delta-T
 Devices, Cambridge, UK), taking the mean of three measures per
 plot.  We calculated species richness and
 Simpson’s (1949) diversity index for each plot for initial conditions in 2023 before any manual treatment. We then estimated indices for species turnover in relation to species identity and dominance shifts, considering initial plot conditions in 2023 and change observed in 2024. We used the species exchange ratio based on richness (SERr) and abundance (SERa) per plot (Hillebrand et al. 2018) to evaluate species turnover per plot.
description: # Data from: Forbs in Viking lands: The effect of disturbing dominant
 graminoids on recruitment in tundra grasslands Dataset DOI:
 [10.5061/dryad.jh9w0vtn8](https://doi.org/10.5061/dryad.jh9w0vtn8) ##
 Description of the data and file structure Data used in "Forbs in
 Viking lands: The effect of disturbing dominant graminoids on recruitment
 in tundra grasslands". ### Files and variables #### File:
 Forb_recruitment_data_Celis_et_al_2024.csv ##### Variables * Valley:
 Locations of plots "TO" is Torvhaugdalen and "BE"
 is Bearalveaijohka * Graminiod_form: Graminoid form 'Mat' and
 'Bunch' * Silica_content: Silica content 'silica-poor'
 and 'silica-rich' * Dominant_graminoid: Species of dominant
 graminoid * Disturbance_treatment: Disturbance treatment
 'Non-rodent', 'Non-rodent + Manual',
 'Rodent', 'Rodent + Manual' * replicate: Replicate
 identifier * Dominant_graminoid_cover_2023: Percent cover of dominant
 graminoid * Forb_cover_2023: Percent cover of all forbs *
 Herbivore_disturbance_2023: Percent herbivory * Species_richness_2023:
 Number of species * Simpson_2023: Simpon's diversity index * SERr:
 Species Exchange ration based on species richness * SERa: Species Exchange
 ration based on species abundance * Soil_Moisture: Percent soil moisture *
 PAR_ratio: Photosynthetic active radiation ratio of incoming radiation
 that reaches seedlings.