DOI: 10.5061/dryad.pg4f4qrnc
title: Size-selective exclusion of mammals and invertebrates differently affects grassland plant communities depending on vegetation type

description: Human-caused loss of vertebrate and invertebrate animals, defaunation, is
 increasing, and potentially affects plant community structure of diverse
 grassland ecosystems worldwide. We experimentally simulated defaunation
 using size-selective fences to progressively exclude large-, medium- and
 small-sized mammals, and invertebrates from two subalpine vegetation types
 in the Swiss National Park (SNP): intensively grazed short-grass and
 moderately grazed tall-grass vegetation. We assessed plant community
 properties yearly from 2009 to 2013, and examined treatment effects on
 plant community structure in the two grassland types. In the short-grass
 vegetation, the exclusion of large mammals increased total plant biomass,
 while the exclusion of large and medium-sized mammals increased total,
 grass and forb biomass compared to when all animals had access. These
 increases became stronger when also invertebrates were excluded. The
 exclusion of all mammals and invertebrates increased biomass of grasses by
 205%, forbs by 100% and total plant biomass by 118% compared to when all
 animals had access, hence enhancing relative biomass of grasses from 43.6%
 to 60%, changing plant species composition and lowering richness of forbs
 by 16%, the number of plant families by 13% and family-level Shannon
 diversity by 23%. In contrast to these significant community-level
 responses found in the short-grass vegetation, there was no evidence that
 the size-selective exclusion of animals altered the plant community
 structure of the tall-grass vegetation. The contrasting results were due
 to the difference in plant community composition prior to our experiment,
 which were related to differences in quantity and quality of forage and in
 grazing intensities of herbivores between the two grassland types.
 Synthesis. Our results showed that different-sized animals, in particular
 large mammals and invertebrates, contributed to maintain the plant
 community structure in the short-grass vegetation, highlighting the
 importance of multiple, functionally different animal groups for ecosystem
 functioning and stability. In contrast to the short-grass vegetation, we
 could not detect such a top-down control by animals in the tall-grass
 vegetation. Our results suggest that potential defaunation effects on
 grassland plant community structure depend on the degree of grazing
 pressure release and grassland vegetation type.
description: <b>1 </b><b>Study area</b>
 The study was conducted in<b> </b>subalpine
 grasslands in<b> </b>the Swiss National Park (SNP). The SNP is
 located in the central Alps, and covers an area of 172
 km<sup>2</sup> ranging from 1350 to 3170 m above sea level
 (a.s.l.), with mean annual precipitation of 826 ± 112 mm and mean annual
 temperature of 0.9 ± 0.5°C (mean ± SD, 2009 - 2013; MeteoSchweiz, 2014).
 Forests (50 km<sup>2</sup>), alpine grasslands (33
 km<sup>2</sup>) and subalpine grasslands (approximately 3
 km<sup>2</sup>) cover around 50% of the SNP (Risch et al.,
 2013), the rest is dominated by rock and scree. The underlying bedrock of
 the subalpine grasslands is dolomite. Since its
 foundation in 1914, the SNP has been protected from human disturbances (no
 livestock grazing, no hunting, no fishing, no camping, or no off-trail
 hiking). The subalpine grasslands are comprised of homogeneous patches
 (usually &gt;1 ha) of short- and tall-grass vegetation, which
 developed mainly because of differences in land-use history and grazing by
 domestic livestock and wild ungulates over several centuries (Schütz et
 al., 2003, 2006). Soon after banning cattle in 1914, red deer
 (<i>Cervus elaphus </i>L.) re-migrated into the SNP and
 started to preferentially graze where cattle formerly rested overnight and
 soils became enriched in nutrients, creating what we today call
 short-grass vegetation (Schütz et al., 2003). Tall-grass vegetation
 developed where cattle frequently grazed, but not rested before the
 foundation of the SNP. These areas became depleted of soil nutrients. The
 vegetation, therefore, is less nutrient-rich, hence, red deer graze these
 areas with much lower intensity (Schütz et al., 2003).<i>
 </i> The aboveground animals found in our study
 area can be divided into four groups (Risch et al., 2013): (1) large
 mammalian herbivores (30–150 kg; mainly red deer and chamois
 <i>Rupicapra rupicapra</i>), (2) medium mammals (3–6 kg; e.g.
 alpine marmot <i>Marmota marmota and</i> mountain hare
 <i>Lepus timidus</i>), (3) small mammals (30–100 g; small
 rodents such as <i>Clethrionomys </i>spp., <i>Microtus
 </i>spp. and <i>Apodemus </i>spp.), and (4)
 invertebrates (&lt; 5 g; e.g. grasshoppers, caterpillars and
 leafhoppers). At present a total of 26 species of large to small wild
 mammals can be found in the SNP (see Risch et al., 2018), with large
 mammalian predators (wolf, bear or lynx) being absent or non-resident
 during our experiment. Reptiles, amphibians and birds are scarce in the
 subalpine grasslands. See Risch et al. (2018) for a full list of
 invertebrate species captured in the SNP in summer 2013.
 <b>2 Experimental design </b> In
 early May 2009, we established eighteen fencing setups (referred to as
 random factor 'Fence' in the Statistical Analysis section) in
 six subalpine grasslands (random factor 'Grassland') located
 across the SNP at elevations ranging from 1975 to 2300 m a.s.l. There were
 two fencing setups per vegetation type (short-grass vs. tall-grass) in
 each of the three large grasslands, and one fencing setup per vegetation
 type in each of the three small grasslands. Hence, we established nine
 fencing setups in short-grass vegetation and nine in tall-grass vegetation
 in a paired design (Fig. S1). The fencing setups were left in the field
 for five consecutive growing seasons (May 2009 - October 2013), but to
 protect them from snow damage and avalanches they were temporarily
 dismantled in late October every year, and reconstructed in early May of
 the following year, immediately after snowmelt. For a
 detailed fencing protocol see Risch et al. (2013). Briefly, each fencing
 setup consisted of a 2.1 m tall and 7 × 9 m large main fence and we
 established five<i> </i>2 × 3 m plots that simulated the
 size-selective exclusion treatments (Fig. S1). The 'LMSI' plot
 was located at least five meters away from the main fence (i.e., control
 plot; 2 × 3 m) and gave access to large (L), medium (M) and small (S)
 mammals, and invertebrates (I). The main fence consisted of wooden posts
 and electrical wires mounted at regular intervals between 0.5 and 2.1 m to
 keep large mammals out. Note that the bottom wire (0.5 m) was not
 electrified to allow smaller mammals to enter safely. Within each main
 fence, we randomly established four 2 × 3 m treatment plots one meter from
 the main fence line to avoid edge effects and separated by one meter
 walkways: (1) the ‘MSI’ plot remained unfenced and gave access to medium
 (M) and small (S) mammals and all aboveground dwelling invertebrates (I);
 (2) the 'SI' plot was surrounded by an electrical fence with 10
 × 10 cm mesh size and allowed small (S) mammals and invertebrates (I) to
 enter; (3) the 'I' plot was surrounded by 2 × 2 cm mesh-sized
 metal fence, double-folded at the bottom 50 cm, which only allowed
 invertebrates (I) to enter; and (4) the 'None' plot was
 surrounded by a 1.5 × 2 mm mesh-sized mosquito net and covered with a
 mosquito mesh-lined roof to exclude all vertebrate and invertebrate
 animals (Fig. S1). We built additional six 'micro-climate
 control' exclosures (one in each of the six main grasslands; see
 Risch et al., 2013, 2018 for the construction details) with a comparable
 micro-climate to the 'None' plots, but also a comparable feeding
 pressure by invertebrates to the 'I' plots. As discussed in
 detail in Risch et al. (2013, 2018), differences in plant and soil
 properties between the 'I' and the 'None' treatments
 were not due to the exclosure design (mesh and roof) of the
 'None' exclosure, but a function of animal exclusions.
 <b>3 Vegetation characteristics</b>
 We collected plant data in a total of 90 plots (18 × 5). We
 quantified vegetation characteristics yearly at peak biomass (July) in
 predetermined, randomly assigned 1 × 1 m subplots within each 2 × 3 m plot
 over five consecutive growing seasons (2009 - 2013). We assessed plant
 community composition by identifying all vascular plants to species level.
 We estimated percentage cover of each species and assigned each species to
 one of five plant functional groups: forbs, grasses, sedges, legumes, or
 woody species. We measured aboveground biomass
 (g/m<sup>2</sup>) of each plant functional group (see Table 1)
 using the canopy intercept method (Frank & McNaughton, 1990).
 Total aboveground plant biomass (i.e., biomass of live shoots,
 'BM.shoots') was defined as the sum of biomass of all five plant
 functional groups. As woody species were rare and their biomass
 negligible, we did not further analyse their responses to the exclusion
 treatments. For each plot and study year, we calculated
 different plant diversity measures: overall species richness (total number
 of plant species), Shannon diversity (exponential of Shannon entropy),
 plant family richness (number of taxonomic families), family-level Shannon
 diversity, and richness of each plant functional group. We also calculated
 Rao’s quadratic entropy (Laliberté, Legendre, & Shipley 2014),
 which accounts for both species relative abundance and traits, as an
 overall measure of plant functional diversity (FDq). Species traits that
 we considered here were taxonomic family, functional group, and ecological
 indicator values for moisture, pH, nutrients, light and temperature
 (Landolt et al., 2010; Table S4). Life span was not included in the trait
 dataset because over 95% of species recorded in our study are
 perennials.
description: The dataset was used for analyses in the following journal
 article: Wang, X., Schütz, M., & Risch, A. C. (2021)
 Size-selective exclusion of mammals and invertebrates differently affects
 grassland plant communities depending on vegetation type, Journal of
 Ecology. Users of the dataset should cite the journal
 article AND the Dryad Dataset Repository. To correctly understand and use
 the dataset, it is suggested to read the METHODS of this research (see
 above). For further information, please contact:
 anita.risch@wsl.ch