As the atmosphere warms, precipitation events become larger, but less frequent. Yet, there is fundamental disagreement about how increased precipitation intensity will affect vegetation. Walter’s two-layer hypothesis and experiments testing it have demonstrated that precipitation intensity can increase woody plant growth. Observational studies have found the opposite pattern. Not only are the patterns contradictory, but inference is largely limited to grasslands and savannas. We tested the effects of increased precipitation intensity in a shrub-steppe ecosystem that receives >30% of its precipitation as snow. We used 11 (8 m x 8 m) shelters to collect and redeposit rain and snow as larger, more intense events. Total annual precipitation was the same in all plots, but each plot received different precipitation event sizes ranging from 1 mm to 18 mm. Over three growing seasons, larger precipitation event sizes increased soil water availability, sagebrush (Artemisia tridentata) stem radius, and canopy greenness, decreased new root growth in shallow soils, and had no effect on herbaceous plant cover. Thus, we found that increased precipitation intensity can increase soil water availability and woody plant growth in a cold semi-arid system. Assuming that stem growth is positively correlated with shrub reproduction, establishment and spread, results suggest that woody plant encroachment observed around the world in the past 50 years may be explained in part by increasing precipitation intensity. Further, continued atmospheric warming that is likely to increase precipitation intensity may also potentially increase shrub encroachment in the future
Utah Agricultural Experiment Station
Utah State University
In June 2015, 14 plots, each 8 m x 8 m in size were established in a grid with at least 15 m between plots. Pre-treatment vegetation surveys and soil moisture measurements were taken until January 2016, when treatments were assigned randomly and applied through July 2018. Three plots were shelter-free controls and used to describe shelter effects. The remaining 11 plots were covered with 8 m x 8 m x 2.5 m (w x l x h) shelters. To allow a regression of vegetation responses across a wide range of precipitation event sizes, seven plots were assigned to different treatment levels (described below; Smith et al. 2014). Treatment levels were designed to create precipitation event sizes that could be expected with temperature changes from -1 to +10 °C relative to current temperatures.This resulted in minimum precipitation event sizes of 2, 3, 4, 8 and 18 mm for hypothetical temperature increases of 1 °C, 2 °C, 3 °C, 5 °C and 10 °C. To further expand our inference, one treatment designed to reflect precipitation intensity associated with -1 °C temperature change was added. In this treatment, irrigation was triggered manually multiple times per growing season depositing additional 1 mm events (hereafter referred to as the 1 mm treatment). All these treatments received the same total precipitation, and only differed in event size and frequency. Soil moisture, and above ground and below ground vegetation responses were measured in plots. When regressions were conducted the data was first averaged across plots by treatment, however, in the files provided here the plot level data is provide.
Hardware Ranch Wildlife Management Area, UT. 41° 36’ 53” N, 111° 34’ 1” W
See the README.txt file.
Environmental Sciences | Natural Resources and Conservation | Water Resource Management
This work is licensed under a Creative Commons Attribution 4.0 License.
Beard, K. H., & Kulmatiski, A. (2020). Determining How Increasing Precipitation Intensity Will Impact Rangelands in Utah. Utah State University. https://doi.org/10.26078/5B85-M736
Additional FilesREADME.txt (9 kB)
soil-moisture_diviner.csv (323 kB)
soil-moisture_229.csv (404 kB)
plant-cover.csv (3 kB)
stem-growth.csv (421 kB)
NDVI_twice-monthly.csv (11 kB)
NDVI_continuous.csv (68 kB)
roots.csv (72 kB)