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Data Extent

Vegetation, rainfall simulation, and overland flow experiments before and after tree removal in woodland-encroached sagebrush steppe: the SageSTEP hydrology study

Paired large-plot rainfall simulations, Marking Corral, Nevada. Photo by USDA Agricultural Research Service, Northwest Watershed Research Center, Boise, Idaho, USA.

Introduction

Simulated rainfall and overland-flow experiments are useful for enhancing understanding of surface hydrologic and erosion processes, quantifying runoff and erosion rates, and developing and testing predictive quantitative models. This extensive dataset (1021 experimental plots) consists of rainfall simulation (1300 plot runs, 0.5 m2 to 13 m2 scales) and overland flow (838 plot runs, ~9 m2 scale) experimental plot data coupled with associated measures of vegetation, ground cover, and surface soil properties across point to hillslope scales. The data were collected at three woodland-encroached sagebrush (Artemisia spp.) rangelands in the Great Basin, USA, under undisturbed/untreated conditions and 1 yr to 9 yr following fire and/or mechanical tree-removal treatments. The methodology employed and resulting experimental data contribute to quantifying and understanding scale-dependent surface hydrologic and erosion processes for Great Basin woodlands and sagebrush rangelands before and after tree removal and for sparsely vegetated sites elsewhere. The dataset is a valuable source for developing and testing hydrology and erosion models for applications to diverse vegetation and ground cover conditions. Lastly, the series of repeated measures in the dataset for some sites over time provides a valuable dataset for exploring long-term landscape vegetation and hydrologic and erosion responses to various land management practices and disturbances.

Experimental Design

A suite of vegetation, soils, rainfall simulation, and overland flow experiments were conducted at three pinyon (Pinyon spp.) and juniper (Juniperus spp.) woodland study sites in the Great Basin, all of which were historically vegetated as sagebrush shrublands. The collective research is part of a larger study, the Sagebrush Steppe Treatment Evaluation Project (SageSTEP), aimed at evaluating ecological impacts of invasive species and woodland encroachment into sagebrush ecosystems and the effects of various sagebrush restoration practices (www.sagestep.org). Our study sites were selected from the larger SageSTEP study network. Site climatic, topographic, soils, and vegetation characteristics are provided in Table 1. Data collection spanned a 10 year period (2006-2015), with sample years varying by site. Vegetation and ground cover at the sites were sparse when the study initiated in 2006. Various tree-removal treatments (prescribed fire, tree cutting, tree shredding [bullhog]) were applied in late summer and autumn of 2006 at two sites (Marking Corral and Onaqui) to support study of the effectiveness of tree removal in re-establishing sagebrush vegetation and ground cover attributes and in reducing runoff and erosion. Wildfire burned a third site (Castlehead, 2007) before tree-removal treatments could be applied, and, therefore, served as a prescribed natural-fire tree-removal treatment at that site. In some years at all three sites, a cut-tree (downed tree) was placed across a subset of large-rainfall and overland-flow plot bases within various treatments to evaluate effects of downed trees on runoff and erosion processes. This additional treatment was applied to some plots in cut treatment areas at Marking Corral and Onaqui (2007 and 2015) and in unburned areas at Castlehead (2008 and 2009). The treatments and experimental design are explained in detail in Pierson et al. (2014, 2013, 2014, 2015) and Williams et al. (2014, 2018, 2019) and treatments at each site by year are shown in Table 2.

Sampling of various biological and physical attributes at each site was conducted at point, small-rainfall plot (0.5 m2), overland-flow plot (~9 m2), large-rainfall plot (13 m2), and hillslope plot (990 m2) scales. Surface soil texture (0-2 cm depth) was sampled as a point measure in microsites underneath tree canopies (tree coppices) and shrub canopies (shrub coppices) and in interspaces between plants within all treatment areas prior to treatments at Marking Corral and Onaqui (2006, 2008) and in unburned and burned areas at Castlehead (2008). Soil bulk density (0-5 cm depth) was sampled as a point measure on tree coppices, shrub coppices, and interspaces at each study site within all treatment areas 1-2 yr following treatments. Vegetation and ground cover were sampled at small-rainfall, large-rainfall, and overland-flow plot scales and at the hillslope scale before and after all treatments at Marking Corral and Onaqui and in unburned and burned areas at Castlehead. Sampling at the hillslope scale (site characterization plots) was conducted to characterize site-level vegetation and ground cover pre-treatment and over time post-treatment. The site characterization plots were installed and sampled in all treatment areas at Marking Corral and Onaqui prior to treatments in 2006 and left in place for sampling 1 yr (2007) and 9 yr (2015) post-treatment. Site characterization plots at Castlehead were installed and sampled in unburned and burned areas 1 yr post-fire (2008) and left in place for sampling 2 yr post-fire (2009). Vegetation and ground cover sampling on rainfall simulation and overland flow plots was employed to determine controls on surface hydrology and erosion processes and to characterize treatment effects on cover conditions at those plot scales. Vegetation and ground cover sampling on rainfall simulation and overland flow plots in untreated areas (control and unburned) and treated areas varied by site and year as shown in Table 2.

The rainfall simulations and overland flow experiments were conducted at the different plot scales to isolate specific runoff and erosion processes (Pierson et al., 2010; Williams et al., 2014). Rainfall simulations at the small plot scale were applied to quantify runoff and erosion solely by rainsplash and sheetflow (splash-sheet) processes. Each small plot was installed to occur on either a tree coppice, shrub coppice, or interspace microsite as described by Pierson et al. (2010) and Williams et al. (2014). Small plots were installed and sampled in controls and all other treatment areas at Marking Corral and Onaqui in 2006 prior to tree-removal treatments and were left in place for sampling 1 yr (2007), 2 yr (2008), and 9 yr (2015) post-treatment. Small plots were installed and sampled in unburned and burned areas at Castlehead 1 yr post-fire (2008) and left in place for subsequent sampling 2 yr post-fire (2009). Large plot rainfall simulations were employed to quantify runoff and erosion from the combination of splash-sheet and concentrated overland flow processes. Each plot was installed to occur on either a tree zone (tree coppice microsite and area just outside canopy drip line) or a shrub-interspace zone (intercanopy between trees) inclusive shrub coppice and interspace microsites (Pierson et al., 2010; Williams et al., 2014). Large plots were installed and sampled in all treatment areas at Marking Corral and Onaqui in 2006 prior to treatments (controls) and were removed following sampling. New plots were installed and sampled in treatment areas at those sites 1 yr post-treatment (2007) and were then removed. At Castlehead, large rainfall plots were installed and sampled in unburned and burned areas 1 yr post-fire (2008) and were then removed. Overland flow simulations at Marking Corral and Onaqui in 2006 and 2007 were conducted on large rainfall plots following the rainfall simulations. Overland flow simulations were also conducted in control and treated areas at Marking Corral and Onaqui in 2008, but those plots were not subjected to rainfall simulation. Overland flow simulations at Castlehead 1 yr post-fire (2008) were run on large rainfall simulation plots following rainfall simulations and 2 yr post-fire (2009) on newly installed plots without rainfall simulations. Overland flow plots run on large-rainfall simulation plots were bordered on all sides and contained a runoff collection trough at the plot base (Pierson et al., 2010, 2013, 2015; Williams et al., 2014). Overland flow simulations conducted independent of rainfall-simulation experiments were run on borderless plots with runoff collection trough at the plot base (Pierson et al., 2013, 2015; Williams et al., 2014, 2018, 2019).

Methods

Vegetation and Soil Measurements
Detailed explanations of vegetation, ground cover, and soils sampling at each plot scale are provided in Pierson et al. (2010, 2013, 2014, 2015) and Williams et al. (2014, 2018, 2019) and are briefly summarized here. All trees > 0.5 m height on each site characterization plot were tallied and measured for tree height and crown diameter. The respective total number of trees and crown diameters were then used to determine live tree density (number per hectare) and canopy cover on each site characterization plot. The number of live shrubs ( 5 cm height) and live tree seedlings (5-50 cm height) on each site characterization plot were quantified using 3 belt transects, 2 m wide × 30 m long. Percent foliar and ground cover by cover type on each site characterization, large-rainfall plot, and overland-flow plot were quantified using line-point intercept methodologies along 5 to 9 transects spanning the full length of the respective plot. Sample point spacing along each transect varied from 10-20 cm (216-295 points/plot) on large-rainfall and overland-flow plots and 50 cm (300 points/plot) on site characterization plots (Pierson et al., 2010, 2013, 2015; Williams et al., 2014, 2018, 2019). Ground surface roughness was also quantified on each large-rainfall and overland-flow plot using a survey level line and incremented stadia rod (Pierson et al., 2010). Distances between plant bases (basal gaps) and plant canopies (canopy gaps) in excess of 20 cm were measured along each line-point transect on large-rainfall and overland-flow plots and used to determine the percentage of the sampled transects on each respective plot with gaps in various gap size classes (Pierson et al., 2010, 2013, 2015; Williams et al., 2014, 2018, 2019). Percent foliar and ground cover by cover type and ground surface roughness on small-rainfall plots was quantified using point frame methods with 5-cm × 10-cm grid spacing (105 points/plot) (Pierson et al., 2010; Williams et al., 2014). A mean litter depth was derived on each small-rainfall plot based on 4 evenly spaced litter depth measurements along each of two plot edges perpendicular to the hillslope contour. The aggregate stability of the soil surface for each small-rainfall plot was determined immediately prior to rainfall simulation using a modified sieve test (Pierson et al., 2010). Soil water repellency at 0-, 1-, 2-, 3-, 4-, and 5-cm soil depths for each small-rainfall simulation plot was quantified immediately prior to rainfall simulation using the Water Drop Penetration Time (WDPT) procedure (Pierson et al., 2010, 2014; Williams et al., 2014, 2018, 2019). Soil moisture was measured for all rainfall simulation and overland flow simulations by gravimetric sample taken immediately prior to the respective simulation (Pierson et al., 2010; Williams et al., 2014). Portions of these samples had to be discarded in various years due to failed seals on soil cans.

Rainfall Simulations
Rainfall was applied to small- and large-rainfall plots at target rates of 64 mm h-1 (dry run) and 102 mm h-1 (wet run) for 45 min. The dry run was applied on uniform dry antecedent soil moisture conditions, and the wet run began within 30 min following the dry run. Rainfall was applied to small-rainfall plots using a portable oscillating-arm rainfall simulator fitted with 80-100 Veejet nozzles (Meyer and Harmon, 1979; Pierson et al. 2010, 2013, 2014; Williams et al., 2014, 2018, 2019). Rainfall was applied to large-rainfall plots using a Colorado State University (CSU) type rainfall simulator (Holland, 1969; Pierson et al. 2010, 2013, 2015; Williams et al., 2014) with stationary sprinklers elevated 3.05 m above the soil surface. Raindrop size (2 mm) and kinetic energy (200 kJ ha-1 mm-1) of simulated rainfall were within approximately 1 mm and 70 kJ ha-1 mm-1 respectively of values reported for natural convective rainfall (Holland, 1969; Meyer and Harmon, 1979). The total amount of rainfall applied to each small-rainfall plot was obtained by integrating the pan catch of a 5-min calibration run prior to each rainfall simulation. Total applied rainfall was estimated on plots where vegetation prevented placement of calibration pans. Estimated rainfall amount was calculated as the average of all calibrations for the respective simulation date. Total rainfall applied to large-rainfall plots was determined from the average of six plastic depth gages placed on a uniform grid within each plot. Timed samples of small-rainfall and large-rainfall plot runoff were collected at 1-min to 3-min intervals throughout each 45-min simulation and analyzed for runoff volume and sediment concentration. Runoff from direct rainfall on the large-plot collection troughs (trough catch, see Fig. 1) was estimated by sampling collection trough runoff before plot-generated runoff occurred. Cumulative runoff and sediment were obtained for each runoff sample by weighing the sample before and after drying at 105°C. Sample weights were adjusted to account for trough catch. A mean runoff rate (mm h-1 and L min-1) was calculated for each sample interval as the interval runoff divided by the interval time. Sediment discharge (g s-1) for each sample interval was derived as the cumulative sediment for the sample interval divided by the interval time. Sediment concentration for each sample interval was calculated by dividing cumulative sediment by cumulative runoff (g L-1). Some field samples were discarded from the final dataset due to laboratory errors or issues identified in the field notes (i.e., spillage, bottle overrun, etc.).

Overland Flow Simulations
Computer-controlled flow regulators (Pierson et al., 2010, 2013, 2015; Williams et al., 2014, 2018, 2019) were used to apply concentrated flow release rates of 15, 30, and 45 L min-1 to each overland-flow plot. Flow was routed through a metal box filled with Styrofoam pellets, to dissipate kinetic energy, and was released through a 10-cm wide mesh-screened opening at the base of the box (Pierson et al., 2010). Each flow release on each plot was applied for 12 min from the same release-point location, approximately 4 m upslope of the collection trough apex. Release rate progression was consecutive from 15 L min-1 to 45 L min-1. Flow samples were collected at varying intervals (commonly 2-min intervals) for each 12-min simulation at each release rate. Flow samples were weighed, oven-dried at 105°C, and then re-weighed to determine runoff rate and sediment concentration. As noted above for rainfall simulation samples, a small number of runoff samples were discarded due to various lab and field issues. Runoff and sediment variables for each release rate were calculated for an 8-min time period beginning at the time of runoff initiation. The 8-min runoff and sediment variables were calculated as described for the 45-min rainfall simulations. The velocity of runoff was measured by releasing a concentrated salt solution into the flow and using electrical conductivity probes to track the mean transit time of the salt over a known flow path length (Pierson et al., 2010, 2013, 2015; Williams et al., 2014, 2018, 2019). The width, depth, and total rill area width (TRAW) of flowing water were measured along flow cross-sections 1 m, 2 m, and 3 m downslope from the release point. TRAW represents the total width between the outermost edges of the outermost flow paths at the respective cross section (Pierson et al. 2010). Overland flow simulations run on large-rainfall simulation plots (Marking Corral and Onaqui - 2006 and 2007, Castlehead - 2008) were conducted approximately two hours after respective rainfall simulations. Overland flow simulations on plots not subjected to rainfall simulation (Marking Corral and Onaqui - 2008, 2015, Castlehead - 2009) were run on soils pre-wet with a gently misting sprinkler (Pierson et al., 2013, 2015; Williams et al., 2014, 2018, 2019).

Resulting Data

The resulting collective dataset of 1021 experimental plots contains vegetation, ground cover, soils, hydrology, and erosion data collected across multiple spatial scales, diverse cover and surface conditions, three study sites, and five different study years. The collective dataset contains 57 plots at the hillslope scale (site characterization plots), 528 small-rainfall plots, 146 large-rainfall plots, and 290 overland-flow plots. The hydrology and erosion experiments yielded time series datasets for small-rainfall plot, large-rainfall plot, and overland-flow plot simulations. Some time series hydrographs and sedigraphs from rainfall and overland flow simulations were excluded due to various equipment failures. The final time series datasets consist of 1020 small-rainfall, 280 large-rainfall, and 838 overland-flow plot run hydrographs and sedigraphs, not excluding plots without runoff. Restricting the data to plots that generated runoff results in 749 small-rainfall, 251 large-rainfall, and 719 overland-flow plot simulation hydrographs and sedigraphs. Overall, the hydrology and erosion time series dataset amounts to 2138 hydrographs/sedigraphs including plots with zero runoff and 1719 hydrographs/sedigraphs for plots that generated runoff.

Field experiments and data management were conducted as part of the Sagebrush Steppe Treatment Evaluation Project (SageSTEP, (www.sagestep.org) funded by the US Joint Fire Science Program, US Department of Interior (USDI) Bureau of Land Management, and US National Interagency Fire Center. This dataset is contribution number 134 of the Sagebrush Steppe Treatment Evaluation Project.

FieldValue
Tags
Modified
2019-10-02
Release Date
2019-09-05
Identifier
163e5ad0-34c1-4f3f-9e83-8f59c7b7d845
Spatial / Geographical Coverage Area
POINT (-116.7775 42.447222)
POINT (-115.114167 39.454722)
POINT (-112.473333 40.211667)
Spatial / Geographical Coverage Location
Idaho, Nevada, Utah, USA
Publisher
Ag Data Commons
Temporal Coverage
May 26, 2006 to September 10, 2015
License
Data Dictionary
Contact Name
Williams, C. Jason
Contact Email
Public Access Level
Public
Program Code
005:040 - Department of Agriculture - National Research
Bureau Code
005:18 - Agricultural Research Service