DOI: 10.5061/dryad.bb49h
title: Data from: Consequences of grazer-induced vegetation transitions on ecosystem carbon storage in the tundra

description: 1. Large herbivores can control plant community composition and, under
 certain conditions, even induce vegetation shifts to alternative ecosystem
 states. As different plant assemblages maintain contrasting carbon (C)
 cycling patterns, herbivores have the potential to alter C sequestration
 at regional scales. Their influence is of particular interest in the
 Arctic tundra, where a large share of the world’s soil C reservoir is
 stored. 2. We analysed how grazing mammals influence tundra vegetation and
 how grazer-induced vegetation shifts affect tundra C stocks, by resampling
 two sites located along pasture rotation fences in northern Norway. These
 fences have separated lightly grazed areas from heavily grazed areas (in
 close proximity to the fences) and moderately grazed areas (further away
 from the fences) for the past 50 years. 14 years earlier, the lightly and
 moderately grazed areas were dominated by dwarf shrubs, whereas heavy
 grazing had promoted the establishment of graminoid-dominated vegetation.
 Since then, both reindeer densities and temperatures have increased, and
 more time has passed for transient dynamics to be expressed. We expected
 that the vegetation and C stocks would have changed under all grazing
 intensities, but not necessarily in the same way. 3. At the site where
 relative reindeer numbers and trampling intensity had increased the most,
 graminoid-dominated vegetation was now also found in the moderately grazed
 area. At the other site, the dominant vegetation types under all grazing
 intensities were the same as 14 years earlier. 4. We show that the heavily
 grazed, graminoid-dominated, areas stored less C aboveground than the
 lightly grazed, shrub-dominated, areas. Yet, the belowground consequences
 of grazing-induced grassification varied between the sites: Grazing did
 not alter organic soil C stocks at the site where both evergreen and
 deciduous shrubs were abundant in the lightly grazed area, whereas heavy
 grazing increased organic soil C stocks at the site where the deciduous
 shrub Betula nana was dominant. 5. Our results indicate that despite the
 negative impacts of grazers on aboveground C storage, their impact on
 belowground C may even be positive. We suggest that the site-specific
 responses of organic soil C stocks to grazing could be explained by the
 differences in vegetation under light grazing. This would imply that the
 replacement of deciduous shrubs by graminoids, as a consequence of
 grazing, could be beneficial for C sequestration in tundra soils.
description: Ylanne_etal_2017_FunctEcol_dataThis file contains the carbon stock, vegetation abundance and soil data that is presented in the article "Consequences of grazer-induced vegetation transitions on ecosystem carbon storage in the tundra". The study sites Raisduoddar (69°31’29 N, 21°19’16 E; altitude 430–570 m asl) and Čearro (69°43’23 N, 21°37’45 E; altitude 540–570 m asl) are located in Northern Norway. In this file, Raisduoddar is referred to as Reisa. Other occuring acronyms are HG, MG and LG that represent the different grazing intensities found at the two sites. LG represents lightly grazed areas that are located 5 meters from the pasture rotation fence on the Winter grazing range. HG represent heavily grazed areas that are located 5 meters from the pasture rotation fence on the summer grazing range. MG represents moderately grazed areas, 100 m away from the fence on the summer grazing range. At each of the sites, we set eight transects perpendicular to the reindeer fence that cross all three grazing intensities.