Cross-scale analysis reveals interacting predictors of annual and perennial cover in Northern Great Basin rangelands
Data files
Jan 21, 2024 version files 334.81 KB
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functionalcover_plotdata.csv
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functionalcover_shrubcategories_plotdata.csv
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README.md
Abstract
Exotic annual grass invasion is a widespread threat to the integrity of sagebrush ecosystems in Western North America. Although many predictors of annual grass prevalence and native perennial vegetation have been identified, there remains substantial uncertainty about how regional-scale and local-scale predictors interact to determine vegetation heterogeneity, and how associations between vegetation and cattle grazing vary with environmental context. Here, we conducted a regionally extensive, one-season field survey across burned and unburned, grazed, public lands in Oregon and Idaho, with plots stratified by aspect and distance to water within pastures to capture variation in environmental context and grazing intensity. We analyzed regional and local-scale patterns of annual grass, perennial grass, and shrub cover, and examined to what extent plot-level variation was contingent on pasture-level predictions of site favorability. Annual grasses were widespread at burned and unburned sites alike, contrary to assumptions of annual grasses depending on fire, and more common at lower elevations and higher temperatures regionally, as well as on warmer slopes locally. Pasture-level grazing pressure interacted with temperature such that annual grass cover was associated positively with grazing pressure at higher temperatures but associated negatively with grazing pressure at lower temperatures. This suggests that pasture-level temperature and grazing relationships with annual grass abundance are complex and context-dependent, though the causality of this relationship deserves further examination. At the plot-level within pastures, annual grass cover did not vary with grazing metrics, but perennial cover did; perennial grasses, for example, had lower cover closer to water sources, but higher cover at higher dung counts within a pasture, suggesting contrasting interpretations of these two grazing proxies. Importantly for predictions of ecosystem response to temperature change, we found that pasture-level and plot-level favorability interacted: perennial grasses had higher plot-level cover on cooler slopes, and this difference across topography was starkest in pastures that were less favorable for perennial grasses regionally. Understanding the mechanisms behind cross-scale interactions and contingent responses of vegetation to grazing in these increasingly invaded ecosystems will be critical to land management in a changing world.
README: Cross-scale analysis reveals interacting predictors of annual and perennial cover in Northern Great Basin rangelands
https://doi.org/10.5061/dryad.547d7wmfp
This dataset accompanies the Ecological Applications manuscript "Cross-scale analysis reveals interacting predictors of annual and perennial cover in Northern Great Basin rangelands." Data collection was led by Madelon Case and Lauren Hallett at the University of Oregon in 2021, funded by a cooperative agreement with USDA-ARS. Data were primarily collected via field surveys, with some annotated data from publicly available spatial datasets (as noted below). Contact mcase@usgs.gov or hallett@uoregon.edu with any questions.
Description of the data and file structure
unctionalcover_plotdata.csv
This file contains fractional cover data summarized by functional group from each field plot surveyed.
Column meanings:
PlotID - unique plot identifier for each field plot
FuncGroup - functional group code (AG = annual grass, F = forb, PG = perennial grass, S = shrub, T = tree)
cover - fractional vegetation cover of that functional group in that plot, determined from line-point-intercept transects
Pasture - code name for BLM pasture in which the plot was situated
WaterDist - distance (in meters) from focal livestock water source in pasture
Asp - aspect (N = north, S = south, flat = zero slope so no obvious aspect)
FireHistory - fire history category (Unburned = not burned for at least 25 years, Burned = burned in the last 4-25 years before survey)
fullwater - binary variable indicating whether focal water source contained water (1) or was dry (0) at time of sampling
Slope - slope of plot (in degrees)
Sand - soil sand content, from 4 homogenized cores taken in plot, analyzed at Oregon State University soil health lab (%)
Silt - soil silt content (%)
Clay - soil clay content (%)
C - total soil carbon content (%)
N - total soil nitrogen content (%)
ppt - mean annual precipitation (mm), from PRISM
tmean - mean annual temperature (degrees C), from PRISM
elev_ned - elevation above sea level (meters), from National Elevation Database
hli - heat load index derived from topographic data (scaled from 0 to 1, where a higher number means relatively more solar irradiation due to topographic position)
lastfire - year of most recent fire (year for Burned sites, 0 for Unburned sites)
Crested - binary logical variable for whether crested wheatgrass, Agropyron cristatum, was present in the plot (TRUE) or not (FALSE)
CattleDung - average number of cattle dung piles counted in a 2 x 25 m transect
logcattledung - log-transformed cattle dung count (log(CattleDung + 1))
functionalcover_shrubcategories_plotdata.csv
This file contains fractional cover data for shrubs only, split by whether shrubs were categorized as resprouting or non-resprouting after fire disturbance.
Column meanings are identical to those given above, except that there is no FuncGroup column (this file pertains only to the shrub group, S) and there is a Resprout column where 1 = resprouting and 0 = non-resprouting.
Sharing/Access information
Data were primarily field-collected by the research team. Please cite this dataset and the original published paper if the data are reused or shared in any way.
Climate data are derived from PRISM: PRISM Climate Group at Oregon State University
Elevation data are derived from NED: National Elevation Dataset (NED) (usda.gov)