DOI: 10.15482/usda.adc/30801848
title: Data from: Mixed effects of drought on species-level traits and plant composition in the United States mixed-grass prairie

description: Komatsu, Porensky, Reinhart, Wilcox, and Koerner conducted a randomized complete block design with five drought treatments replicated three times per block within grazing treatment paddocks (40.4×30.5 m), and with three blocks (80.8×61.0 m) at one site in Montana and one site in Wyoming. The three grazing treatments included a light, moderate, and heavy grazing regime. The drought treatments included five levels: 0% (control), 25%, 50%, 75%, and 99% rainfall reduction to mimic a range of different realistic drought scenarios, achieved with 3×4 m rain-out shelters erected over 2×2 m plots (Figure 1c). Within each grazing paddock, there were two control treatments (0% rainout). Rainfall reduction treatments were applied during the growing season from May to October in 2019 and 2020, except during a short period when cattle grazed in each paddock in July in WY and August in MT. Then from 2021-2023 no drought treatments were applied to any plots (recovery). Prior to the experimental setup, all cattle grazing treatment paddocks were grazed using conventional practices of moderate summer grazing. Three cattle grazing treatments were randomly assigned within each block. Cattle grazing treatments consisted of destock, stable, and heavy cattle grazing, where forage utilization was manipulated each year of the experiment at levels consistent with three common regional livestock drought management strategies. In destock cattle grazing paddocks, forage utilization was 50% during the drought in years 1 and 2 (2019, 2020, respectively) and 30% during recovery years 3 and 4 (2021, 2022, respectively). The stable cattle grazing treatment consisted of forage utilization at 50% during drought and recovery (2019-2022). The heavy cattle grazing treatment consisted of forage utilization at 50% during the first drought year (year 1, 2019), 70% during the second drought year (year 2, 2020) and the first year of recovery (year 3, 2021), and 50% during the second year of recovery (year 4, 2022). To manipulate cattle grazing, beef cattle (<i>Bos taurus</i>) herds were allowed into paddocks in July in WY and August in MT and grazed freely until appropriate forage utilization was met, measured using a visual obstruction pole (Robel <i>et al.</i>, 1970).Data were collected by Bloodworth, Komatsu, Porensky, Reinhart, Vaarre-Lamoureux, Wilcox, and Koerner. We measured foliar plant community composition using the pin-drop method in a designated 1 m<sup>2 </sup>subplot within each 2×2 m plot (Frost et al. 2023) during peak growing season in each year of the experiment (2019-2023). We also collected plant functional traits on each site’s top 90% of plant species based on the plant species composition (percent cover) data measured, as described above, in years prior to trait measurements (2019-2021). Functional trait data were collected once in 2022 on nine individuals of each species found in ambient rainfall conditions at each site. C3 graminoid and forb trait measurements were collected in May and C4 graminoid and shrub trait measurements were collected in late June. Traits included plant height, leaf thickness, leaf dry matter content (LDMC), leaf area, and specific leaf area (SLA). Plant height was measured to the tallest stretched vegetative point. Leaf thickness of the second fully expanded leaf from the top was measured using a micrometer caliper (0.25-0.01 mm United Scientific PMSET04 Precision Measuring Micrometer Caliper). Using the same leaf, LDMC was measured as the dry weight of the leaf (dried at 60°C for at least 1 week) divided by the wet weight of the leaf. Again, using the same leaf, we measured leaf area using ImageJ (Rasband 2021). SLA was calculated by dividing the leaf area by the dry weight of the leaf.Using the same collection techniques we collected plant functional traits (plant height, leaf thickness, LDMC, leaf area, and SLA) on three common grasses and two common forbs at each site from areas within the experimental blocks that received ambient rainfall. The focal plant species in WY were <i>Bouteloua </i><i>gracilis</i>, <i>K</i><i>oeleria </i><i>macrantha</i>, <i>Pascopyrum </i><i>smithii</i>, <i>Logfia arvensis</i>, and <i>Vicia americana</i>. The focal plant species in MT were <i>Bromus</i> <i>arvensis</i>, <i>Hesperostipa </i><i>comata</i>, <i>K</i><i>oeleria </i><i>macrantha</i>, <i>Sphaeralcea coccinea</i>, and<i>Tragopogon dubius</i>. For each plant species, we collected nine individuals from across blocks during peak growing season (late June or early July) of 2019-2022. Leaf thickness was not collected in 2020. <i>L. arvensis</i> leaves were too small for the scale used and therefore measurements that used leaf weight (LDMC and SLA) are not reported for <i>L. arvensis</i>.Yearly precipitation levels in this study were obtained from local precipitation gauges (within 2 miles of the site) for the WY site and from a NOAA weather station in Miles City, MT (within 15 miles of the site) for the MT site. Precipitation was calculated as the total precipitation from October of the previous year through the month when measurements were collected. In 2019, 2021, and 2022, measurements were collected in June. In 2020 due to delays because of the COVID-19 Pandemic measurements were collected in July.<br>Within Excel files:sites are listed as FK (Fort Keogh Livestock Range and Research Laboratory in Miles City, Montana) and TB (Thunder Basin Ecoregion in Bill, Wyoming).Block, paddock, and plot: randomized complete block design.Slope: scale 1-6 with 1 being the flattest and 6 being the steepest slope.Rainfall reduction & drought: 0, 25, 50, 75, or 99% rainfall reduction on plotgrazing category: L refers to low grazing utilization (30%), M refers to moderate grazing utilization (50%), H refers to heavy grazing utilization (70%). 5 letters denote 5 years of grazing treatmentgrazing treatment: general treatment name (stable, heavy, restock)livestock_util_2019, 2020, 2021: 30%, 50%, or 70% utilizationaerial_basal: Aerial or Basal relatives cover measurements (aerial refers to amount of vegetation at tallest height, basal refers to amount of vegetation near the surface of the ground).Native_introduced: N=native, I=introducedAnnual_perennial: P=perennial, A=annualMerged_Traits_FK_2022 and Merged_Traits_TB_2022: paddock is LG (equivalent to MLLMM grazing category), MG (equivalent to MMMMM), and HG (equivalent to HHMMM)<br>