Precipitation events have been predicted and observed to become fewer, but larger as the atmosphere warms. While many studies have tested the effects of precipitation amount, few studies have tested the effects of precipitation intensity on plant growth. The few studies that have been done suggest that precipitation intensity can have large effects on plant growth, and in particular on woody plant growth. However, due to the difficulties of manipulating snow, the effects of precipitation intensity in cold climates is poorly understood. Yet, climate change has been faster in cold than warm systems. Here, we manipulated rain and snow event sizes using 8 m by 8 m shelters in a sagebrush-dominated, rangeland ecosystem in northern Utah. All precipitation was collected and returned to plots at rates expected under -1, 0, 1, 2, 3, 5 and 10 degree Celsius warming. Total precipitation quantity was the same in all plots. We measured above- and belowground vegetation and soil moisture responses to these treatments.
Results/Conclusions
Experimental shelters did not change temperature, but soil moisture increased with precipitation intensity. After two years of treatment, sagebrush (Artemisia tridentata) stem-growth increased, but plant composition and grass cover remained unchanged. Results support the idea that more deeply-rooted plants will benefit from increased precipitation intensity, if increased precipitation intensity decreases interception or ‘pushes’ water deeper into the soil. Thus, while shrub encroachment that has been observed in systems around the world in the past 50 years has been attributed to changes in fire, grazing and CO2, our results suggest that increased precipitation intensity may also encourage shrub encroachment. We believe this is one of the first studies to address plant responses to increases in precipitation intensity in ecosystems that receive snow. Results suggested that intact shrub-dominated systems can respond rapidly (< 2 year) to changes in snow and rain intensity. This study did not manipulate temperature, so the interacting effects of temperature and precipitation intensity are unclear, but precipitation intensity alone is expected to increase shrub and ecosystem growth by decreasing interception and ‘pushing’ precipitation deeper into the soil.