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Pastures and climate extremes: Impacts of cool season warming and drought on the productivity of key pasture species in a field experiment

Citation

Churchill, Amber et al. (2022), Pastures and climate extremes: Impacts of cool season warming and drought on the productivity of key pasture species in a field experiment, Dryad, Dataset, https://doi.org/10.5061/dryad.2fqz612qg

Abstract

Shifts in the timing, intensity and/or frequency of climate extremes, such as severe drought and heatwaves, can generate sustained shifts in ecosystem function with important ecological and economic impacts for rangelands and managed pastures. The Pastures and Climate Extremes experiment (PACE) in Southeast Australia was designed to investigate the impacts of a severe winter/spring drought (60% rainfall reduction) and, for a subset of species, a factorial combination of drought and elevated temperature (ambient +3 °C) on pasture productivity. The experiment included nine common pasture and Australian rangeland species from three plant functional groups (C3 grasses, C4 grasses and legumes) planted in monoculture. Winter/spring drought resulted in productivity declines of 45% on average and up to 74% for the most affected species (Digitaria eriantha) during the 6-month treatment period, with eight of the nine species exhibiting significant yield reductions. Despite considerable variation in species’ sensitivity to drought, C4 grasses were more strongly affected by this treatment than C3 grasses or legumes. Warming also had negative effects on cool-season productivity, associated at least partially with exceedance of optimum growth temperatures in spring and indirect effects on soil water content. The combination of winter/spring drought and year-round warming resulted in the greatest yield reductions. We identified responses that were either additive such that there was only as significant warming effect under drought (Festuca), or less-than-additive, where there was no drought effect under warming (Medicago), compared to ambient plots. Results from this study highlight the sensitivity of diverse pasture species to increases in winter and spring drought severity similar to those predicted for this region, and that anticipated benefits of cool-season warming are unlikely to be realised. Overall, the substantial negative impacts on productivity suggest that future, warmer, drier climates will result in shortfalls in cool-season forage availability, with profound implications for the livestock industry and natural grazer communities.

Usage Notes

Data included here include aboveground biomass summed across multiple harvests between June 1st 2019 and Nov 30th 2019 associated with nine pasture and rangeland species included at the Pastures and Climate Extremes field facility at the Hawkesbury Experiment Forest run by the Hawkesbury Institute for the Environment of Western Sydney University. Detailed methods on species establishment and experimental design can be found the associated publication, however briefly all aboveground biomass was clipped to 5cm using a sickle mower and hand-hand shears between 2-3 times during the winter and spring seasons. The weed fraction has been removed from this total, and all biomass was dried to constant mass prior to weighing.

File name: AGBiomassDryad

Column descriptions: SubPlotID (This provides a unique identifer for each individual subplot within the larger experiment- combining shelter, plot and subplot location information), SubPlotType (This is a three letter code linking the species grown in a subplot based on common names), SubPlotType2 (this is a three letter code linking the genus name for each species in a subplot), FxnlTyle (This is a functional group classification including 'C4 grass', 'C3 grass', and 'Legume', Water (drought treatment levels; drought- 60% reduction in precipitation and control- modelled precipitation based on the long-term average in Richmond, NSW), Temperature (warming treatment levels; elevated- +3 degrees C continuously relative to control plots, and Ambient- as measured in field for canopy and soil surface temperature), Group (factorial combination of Water and Temperature treatments to comprise four groups; aT-C, aT-D, eT-C, eT-D), Shelter (Factor describing the location of the sward among shelters; 1-6), Plot (placement within a shelter; numeric 1-8), Biomass (Aboveground biomass summer for a subplotID between June 1st and Nov 30th 2019; units are kg ha-1).

Supporting environmental data are also provided here, including soil volumetric water content (%; SoilMoisture_dailymean) and temperature (degrees C; SoilTemperature_dailymean) measurements from sensors installed in individual species swards. Canopy and soil surface temperatures were recorded at the treatment level and are included here (degrees C; CanopyTemperature_dailymean). Records for the air temperature  (AirTemp_dailymean) as well as relative humidity (RH_dailymean) and levels of photosynthetically active radiation (PAR; PAR_dailymean) inside and outside shelters are also included.

File name: SoilMoisture_dailymean

Column descriptions: Date (Date of measurement YEAR-MO-DA), SubPlotID (This provides a unique identifer for each individual subplot within the larger experiment- combining shelter, plot and subplot location information, SubPlotType2 (this is a three letter code linking the genus name for each species in a subplot), Group (factorial combination of Water and Temperature treatments to comprise four groups; aT-C, aT-D, eT-C, eT-D), Water (drought treatment levels; drought- 60% reduction in precipitation and control- modelled precipitation based on the long-term average in Richmond, NSW), Temperature (warming treatment levels; elevated- +3 degrees C continuously relative to control plots, and Ambient- as measured in field for canopy and soil surface temperature), Location (refers to the placement of the sensor in the soil column where 'upper' measures 0-15cm and 'lower' measures 15-30cm depth), Shelter (Factor describing the location of the sward among shelters; 1-6), Plot (placement within a shelter; numeric 1-8), Subplot (refers to directional placement within a plot; letters A-D), SM_Mean_per (daily mean volumetric soil water content, units expressed as %), SM_Mean_se (daily standard error of volumetric soil water content, units expressed as %).

File name: SoilTemperature_dailymean

Column descriptions: Date (Date of measurement YEAR-MO-DA), SubPlotID (This provides a unique identifer for each individual subplot within the larger experiment- combining shelter, plot and subplot location information, SubPlotType2 (this is a three letter code linking the genus name for each species in a subplot), Group (factorial combination of Water and Temperature treatments to comprise four groups; aT-C, aT-D, eT-C, eT-D), Water (drought treatment levels; drought- 60% reduction in precipitation and control- modelled precipitation based on the long-term average in Richmond, NSW), Temperature (warming treatment levels; elevated- +3 degrees C continuously relative to control plots, and Ambient- as measured in field for canopy and soil surface temperature), Location (refers to the placement of the sensor in the soil column where 'upper' measures 0-15cm and 'lower' measures 15-30cm depth), Shelter (Factor describing the location of the sward among shelters; 1-6), Plot (placement within a shelter; numeric 1-8), Subplot (refers to directional placement within a plot; letters A-D), ST_mean (daily mean soil temperature, units are degrees C), ST_se (daily standard error of soil temperature, units expressed as degrees C).

File name: CanopyTemperature_dailymean

Column descriptions: Date (Date of measurement YEAR-MO-DA), PlotID (Factor describing the Shelter and Plot location of the measurement), Shelter (Factor describing the location of the sward among shelters; 1-6), Water (drought treatment levels; drought- 60% reduction in precipitation and control- modelled precipitation based on the long-term average in Richmond, NSW), Temperature (warming treatment levels; elevated- +3 degrees C continuously relative to control plots, and Ambient- as measured in field for canopy and soil surface temperature), IR_Mean (daily mean canopy and soil surface temperature, units are degrees C), IR_se (daily standard error of canopy and soil surface temperature, units expressed as degrees C).

File name: AirTemp_dailymean

Column descriptions: Date (Date of measurement YEAR-MO-DA), Shelter (Factor describing the location of the sward among shelters; 1-6), Location (Factor describing whether the sensor is located 'inside' or 'outside' the rainout shelters covering the PACE field facility, AirTemp_Daily (daily mean air temperature, units are degrees C), AirTempse (daily standard error of air temperature, units expressed as degrees C).

File name: RH_dailymean

Column descriptions: Date (Date of measurement YEAR-MO-DA), Shelter (Factor describing the location of the sward among shelters; 1-6), Location (Factor describing whether the sensor is located 'inside' or 'outside' the rainout shelters covering the PACE field facility, Humidity_Daily (daily mean relative humidity, units are %), Humidityse (daily standard error of relative humidity, units are %).

File name: PAR_dailymean

Column descriptions: Date (Date of measurement YEAR-MO-DA), Shelter (Factor describing the location of the sward among shelters; 1-6), Location (Factor describing whether the sensor is located 'inside' or 'outside' the rainout shelters covering the PACE field facility, PAR_Daily (daily mean PAR, units are micromoles m-2), PARse (daily standard error of PAR, units expressed as micromoles m-2)

Funding

Meat and Livestock Australia, Award: P.PSH. 0793

Dairy Australia, Award: C100002357

Western Sydney University