Water manipulation
The long-term mean total rainfall for West Perenjori Nature Reserve in the growing season from June to October (inclusive) is 174.1 mm (± 6.2 mm standard error, Bureau of Meteorology 2021, 105-year means). As there had been an average amount of precipitation preceding the growing season in 2020, we aimed to alter rainfall by 50% such that typical dry and wet years were represented.
To reduce water availability, we built rainout shelters based on the design by Gherardi and Sala (2013, see Figure S1 for design details). We erected the rainout shelters in mid-August after tallying emergence and thinning interaction neighbourhoods. This allowed an average amount of rainfall to cue emergence across all plots, after which the experimental water manipulation was imposed until seed collection.
To increase water availability, we transferred the water collected from the rainout shelters onto the water addition plots within three days of each rainfall event. We added the water slowly using a watering can to prevent run-off and recorded the amount added. Throughout the growing season, there was 109.8 mm of rainfall across approximately six rainfall events (Bureau of Meteorology 2021). In total, watered plots each received an extra 29.9-38.8 L of water (27-35% increase) compared to ambient plots.