DOI: 10.5061/dryad.7m0cfxq71
title: Herbivores override climate control of grassland production in Yellowstone National Park

description: Understanding the factors regulating temporal variation in grassland
 annual aboveground net primary production (ANPP) is dominated by studying
 the effects of climate, particularly water, in ungrazed grassland.
 However, the overwhelming majority of the Earth’s grasslands are grazed by
 large herbivores, which have large effects on ANPP and interact with
 climate in unknown ways. Here we analyzed an eight-year data set of ANPP
 across a 26-year period that included widely variable climatic conditions
 and consumption rates by herds of elk (Cervus elaphus), bison (Bison
 bison), and pronghorn (Antilocapra americana) at 25 grassland sites in
 Yellowstone National Park (YNP). We found that ANPP was primarily a
 positive function of consumption rate and secondarily affected by a
 nonlinear temperature effect, with ANPP declining in hot years. Water
 balance (WB, a measure of soil moisture available to plants) did not
 affect ANPP. Examining the difference between grazed minus ungrazed
 (fenced) ANPP (i.e., grazer stimulation) at 13 grassland sites revealed
 that herbivores increased average ANPP by 20%, with variation across sites
 and years driven by the amount grazed, temperature, and interactions of
 temperature with local environment and WB. We found a surprising negative
 main effect of WB on ANPP stimulation, likely because grazing ameliorated
 moisture stress in dry years by reducing transpirational moisture loss.
 Our results demonstrate that Yellowstone grazers override the
 well-documented positive effect of moisture on grassland ANPP, which
 highlights the need to understand how together climate and herbivory
 regulate production in the world’s other grassland ecosystems.
description: # Herbivores override climate control of grassland production in
 Yellowstone National Park Dataset DOI:
 [10.5061/dryad.7m0cfxq71](10.5061/dryad.7m0cfxq71) ## Description of the
 data and file structure The data file incudes eight years of plant
 aboveground biomass data spanning three decades (1988-1989, 1999-2001,
 2012-2014) to examine how variation in local climate, soil chemistry, and
 grazing intensity affect aboveground production in grasslands of YNP that
 are grazed by large migratory herds of wild ungulates.  In each of the
 eight years, aboveground production (g m-2), consumption (g m-2 removed)
 and climatic conditions for sequential sampling intervals during the April
 to September growing season were determined at 25 grazed grasslands.  In
 addition, ANPP was calculated for fenced (ungrazed) grassland at 13 of the
 sites. ### Files and variables #### File: YNP\_data\_abridged.csv
 **Description:** Here we synthesize eight years of data spanning three
 decades (1988-1989, 1999-2001, 2012-2014) to examine how variation in
 local climate, soil chemistry, and grazing intensity affect aboveground
 production in grasslands of YNP that are grazed by large migratory herds
 of wild ungulates.  In each of the eight years, aboveground production (g
 m-2), consumption (g m-2 removed) and climatic conditions for sequential
 sampling intervals during the April to September growing season were
 determined at 25 grazed grasslands.  In addition, ANPP was calculated for
 fenced (ungrazed) grassland at 13 of the sites. ##### Variables * yr: Year
 sample was collected * end.date: date of end of sampling interval *
 juldate: Day of year sample was collected * sample.: The numerical
 sampling interval during each year * site: Site name * trt: The treatment
 codes associated with each sample.  *te* refers to samples taken inside
 temporary exclosures in grasslands, and *pe* refers to those taken inside
 permanent exclosures in grasslands.  *ste* refers to samples of herbaceous
 vegetation growing under individuals of sagebrush (*Artemisia tridentata)
 *that had been fenced from grazing with temporary exclosures and *sgr*
 refers to samples collected under individuals of sagebrush that had not
 been protected from grazing. Sagebrush occurred at only two sites, lsg and
 usg. * quadrat.: Quadrat number * totshtbiom:  Aboveground plant biomass
 (g m^2) of the sample * soilc: 0 -10cm soil total carbon * soiln: 0 -10 cm
 soil total nitrogen * clay:  Percent clay in 0-10 cm soil * silt: Percent
 silt in 0-10 cm soil * days.1: Number of days of the sampling interval *
 prismint.ppt: The total precipitation (mm) during the sampling interval
 derived by PRISM * prismint.temp: The mean temperature (Celsius) during
 the sampling interval derived by PRISM * prism.pptday: Average daily
 precipitation (mm) during the sampling interval derived by PRISM *
 wy.prism: Water year precipitation (mm) derived by PRISM * gsppt.prism:
 Total growing season precipitation (mm) derived by PRISM * Pwy.prism:
 Total water year precipitation (mm) for the previous year derived by PRISM
 * Pgsppt.prism:  Total growing season precipitation (mm) for the previous
 year derived by PRISM * Pgstemp.prism:  Mean temperature (Celsius) during
 the previous year derived by PRISM * siteelevation: Elevation (meters) of
 site * spei: The standardized evaporation index (mm) derived by PRISM *
 watbal: Water balance (mm) derived by PRISM * pet: Potential Evaporation
 (mm) derived by PRISM #### File: latitudes.csv **Description:** This file
 is required to run PRISM on the data set. ##### Variables * site: Site
 name * latitude: Latitude of site * longitude: Longitude of site ##
 Code/software The data are in CVS files and the following code to read the
 data are in R Markdown format. Note that both data files are required to
 run the code (YNP climate-grazing analysis.R) which  processes ecological
 field data to calculate monthly and annual aboveground net production
 (ANP) and herbivore consumption (C) across sites and years.