DOI: 10.5061/dryad.4qrfj6qkx
title: Data from: Greater biomass from Arctic greening absorbs increased grazing pressure from a large herbivore

description: Arctic warming is causing widespread “greening” of tundra ecosystems. What
 this means for plant-herbivore relations, including the grazing pressure
 herbivores exert on increasingly productive tundra ecosystems, is poorly
 understood. Svalbard is one of the fastest warming places on Earth, with
 concomitant increases in both forage biomass and reindeer numbers. In 11
 years between 1998 and 2023, we measured grass biomass and the proportion
 of shoots grazed in mesic grass-dominated tundra to evaluate whether
 increased forage biomass of grass absorbed the grazing pressure of more
 reindeer. Also, we used GPS data from adult female reindeer (2009-2023) to
 identify if grazing pressure was relieved by spillover into other
 habitats. During the study period, reindeer abundance, estimated by annual
 capture-mark-recapture, tripled, while grass biomass only doubled. Grazing
 pressure increased from 4% to 8%, which was lower than expected from the
 increased reindeer density. This discrepancy was not caused by spillover
 into other habitats, but rather by increased grazing in higher-biomass
 patches that have emerged with summer warming. Our findings support the
 notion that increased summer forage has contributed to Svalbard reindeer
 population growth, notably by making available higher biomass grass swards
 that allow for greater food offtake.
description: <em>Grazing data</em> In September
 1997, we established 13 plots (5 m ×5 m) in grass sward habitats in
 Semmeldalen, Savalbard to monitor grazing pressure on grasses. Plots were
 randomly selected among separate patches of varying shoot density of
 grasses in grass sward habitat and were &gt; 20 m apart from each
 other. In 2021 an additional 15 plots were established in grass sward
 habitat near the original plots. In late July and August (range: July 29 –
 August 24), we measured density of shoots and number of shoots grazed
 (only measuring true grasses and, thus, excluding rushes and sedges).
 Within each 5 m ×5 m plot, we sampled shoot density by randomly selecting
 15 subplots of 10 cm ×10 cm where we counted the number of grass shoots
 and the number of shoots grazed. Subplots were selected by tossing a 10 cm
 × 10 cm frame and counting the number of grazed and ungrazed grass shoots
 where it landed; thus, locations of subplots varied during each sampling
 period. To estimate the available grass biomass of a plot, we determined
 average shoot mass by collecting 25 randomly selected, ungrazed, grass
 shoots from within each 5 m × 5 m plot at each time of measurement. We
 dried shoot samples at 60 °C and placed them in a desiccator for a minimum
 of 48 hours before weighing them to the nearest mg to get the average mass
 per shoot. Mean shoot mass was then multiplied by shoot density and then
 multiplied by 100 (since measurements were taken at the 10 cm × 10 cm
 subplot) to estimate grass biomass within each plot
 (g/m<sup>2</sup>; biomass = shoot count × mean shoot mass ×
 100). Plots were monitored annually in 1998-2005 (except in 2003), 2010,
 and 2021-2023, for a total of 170 plot-level observations of grass biomass
 and grazing. 
 <em>Reindeer </em><em>population
 </em><em>and GPS-collar data</em>
 Since 1995, a sample of calves and adult female reindeer were
 captured and marked with a unique collar band and ear tags each spring
 (March-April; for details see Albon <em>et al.</em> 2017). All
 capture and handling was performed under licenses and permits issued by
 the Norwegian National Research Authority (license nr. 22/5068) and the
 Governor of Svalbard (license nr. 16/01632-25).  In late July and early
 August, an annual census of reindeer abundance was conducted. by observers
 walking through the valleys to record marked and unmarked animals.
  Population estimates were derived from  an integrated population model
 using these capture–mark–recapture data in winter and observations from
 the annual summer population census. Since 2009,
 between 12 and 48 captured adult females were fitted with GPS collars
 (Vectronic Aerospace GmbH) during capture events (see for details
 Loe<em> et al.</em> 2016), resulting in GPS data from 135
 different individuals. GPS collars remained on individuals for 1-7
 consecutive years (n = 419 animal years), recording locations at rates
 ranging between 1 and 10 h. In total, 319,774 GPS locations were recorded
 from 2009 to 2023.  
description: # Svalbard Reindeer Grazing and GPS data
 [https://doi.org/10.5061/dryad.4qrfj6qkx](https://doi.org/10.5061/dryad.4qrfj6qkx) ## Description of the data and file structure *Grazing data* In September 1997, we established 13 plots (5 m ×5 m) in grass sward habitats in Semmeldalen, Svalbard. Plots were randomly selected among separate patches of varying shoot density of grasses and were &gt; 20 m apart from each other. In 2021 an additional 15 plots were established in grass sward habitat near the original plots. In late July and August (range: July 29 – August 24), we measured density of shoots and number of shoots grazed (only measuring true grasses and, thus, excluding rushes and sedges). Within each 5 m ×5 m plot, we sampled shoot density by randomly selecting 15 subplots of 10 cm ×10 cm where we counted the number of grass shoots and the number of shoots grazed. Subplots were selected by tossing a 10 cm × 10 cm frame and counting the number of grazed and ungrazed grass shoots where it landed. We determined average shoot mass by collecting 25 randomly selected, ungrazed, grass shoots from within each 5 m × 5 m plot at each time of measurement. We dried shoot samples at 60 °C and placed them in a desiccator for a minimum of 48 hours before weighing them to the nearest mg to get the average mass per shoot. We used mean shoot mass to estimate grass biomass within each plot (g/m2; biomass = shoot count × mean shoot mass × 100). Plots were monitored annually in 1998-2005 (except in 2003), 2010, and 2021-2023, for a total of 170 plot-level observations of grass biomass and grazing. *Reindeer population estimates and GPS-collar data* Since 1995, a sample of calves and adult female reindeer were captured and marked with a unique collar band and ear tags each spring (March-April; for details see Albon *et al.* 2017).  In late July and early August, an annual census of reindeer abundance was conducted by observers walking through the valleys of Nordenskiöld Land to record marked and unmarked animals.  Population estimates were derived from  an integrated population model using these capture–mark–recapture data in winter and observations from the annual summer population census. Since 2009, between 12 and 48 captured adult females were fitted with GPS collars (Vectronic Aerospace GmbH) during capture events (see for details Loe* et al.* 2016), resulting in GPS data from 135 different individuals. GPS collars remained on individuals for 1-7 consecutive years (n = 419 animal years), recording locations at rates ranging between 1 and 10 h. In total, 319,774 GPS locations were recorded from 2009 to 2023.   ### Files and variables #### File: SvalbardReindeerGrazingData\_ArcticSceince2024.xlsx **Description:** Grass abundance and grazing in plots monitored in Semeldalen, Svalbard, 1998-2023, including estimates of reindeer abundance. ##### Variables PlotID - unique numeric/letter plot identifier Date - Date of measurement; mm/dd/yyyy tot.shoots - Total number of true grass shoots (excluding sedges and rushes) in 5 x 5 m plot m.shoots - Mean number of true grass shoots per 10 x 10 cm subplot tot.grazed - Total number of true grass shoots grazed in 5 x 5 m plot Plot_cat - F = fouling plot established 1998, including treated and control plots; GP = grazing plot established in grass swards in 2021 biomass_gm2 - Estimated biomass g/m2 of true grasses in the 5 x 5 m plot shoot.mass_g - Mean biomass (g) of a true grass shoot N.tot - Estimate of reindeer abundance in stud area #### File: GPSloc\_2009\_April2024.csv **Description:** GPS-location data from Svalbard reindeer 2009-2023. ##### Variables * id: unique animal ID * datetime: date and time of GPS location (UTC) * x: easting UTM (zone 33); reduced to precision equivalent to no more than 0.1 decimal degrees  * y: northing UTM (zone 33); reduced to precision equivalent to no more than 0.1 decimal degrees  * year: year of location * mon: month of location * day: day of location * hour: hour of location * julian: Julian day of location * idyear: unique identifier of animal ID and year ## Access information Other publicly accessible locations of the data: * GPS data are also available in Movebank (movebank.org; Svalbard Reindeer Project - Nordenskiöld; ID 2608802883). Data was derived from the following sources: * All data were collected by study investigators.