Major funding from the National Science Foundation allowed us to add a rainfall experiment to our plots in 2014. The precipitation plots in the Carrizo Valley are used to assess the potential impacts of climate change on native and invasive species in the Carrizo Plain National Monument. To accurately simulate the effects of climate change on plant-animal interactions, the study applies precipitation manipulations by applying precipitation treatments to the paired kangaroo rat exclosures and control plots on 18 pre-existing plots. By varying precipitation levels, the study examines the effects of climate change on vegetation and giant kangaroo rats in the Carrizo Plain.
Brekke, L. D., N. L. Miller, K. E. Bashford, N. W. T. Quinn, and J. A. Dracup. 2004. Climate change impacts uncertainty for water resources in the San Joaquin River Basin, California. Journal of the American Water Resources Association 40:149-164.
Cayan, D., E. Maurer, M. Dettinger, M. Tyree, K. Hayhoe, C. Bonfils, P. Duffy, and B. Santer. 2006. Climate scenarios for California. California Climate Change Center, Sacramento.
Maurer, E. P., and P. B. Duffy. 2005. Uncertainty in projections of streamflow changes due to climate change in California. Geophysical Research Letters 32.
Thorne, J., R. Boynton, L. Flint, A. Flint, and T.-N. g. Le. 2012. Development and application of downscaled hydroclimatic predictor variables for use in climate vulnerability and assessment studies. California Energy Commission, Publication number:CEC-500-2012-010.
18 sites were identified for the precipitation plot experiment and precipitation treatments were applied to the paired kangaroo rat exclosures and control plots. These sites are comprised of 6 blocks, divided into three separate sites (each separated by ~ 500 m, each containing paired enclosure and non-enclosure plots) which comprise a block. Within each block, one site was randomly assigned as a precipitation control, and precipitation treatments are not applied to either plot. On the second site, a rainout shelter was constructed over the kangaroo rat exclosure, and water is transported from the shelter to the kangaroo rat control plot on that site. The third site receives the reverse treatment, with a rainout shelter constructed over the kangaroo rat control plot and water transported to the exclosure.
Precipitation plots are approximately 10mx10m. Rainout shelters were constructed over rainfall reduction plots, using a design whereby shelters intercept a portion of each rainfall event. Based on recent climate projections for California (Cayan et al. 2006), rainfall will be reduced by 50% on rainfall reduction plots, and water will be collected from shelters and added to rainfall addition plots, thus increasing precipitation by 50%. We manipulate rainfall through both additions and reductions because downscaled climate models deviate on whether future rainfall in the region will increase or decrease over the next century (Brekke et al. 2004, Maurer and Duffy 2005, Thorne et al. 2012). Our experiment will thus mimic expected changes by producing higher highs and lower lows within a reasonable range of predicted future climate scenarios.
Shelters consist of a steel frame that supports an array of clear acrylic v-shaped shingles that passively reduce each rainfall event by ~50% . Shingles have high light transmission, a low yellowness index, and are UV transparent. The low edge of the shelter is oriented towards the prevailing winds to minimize blow-in, and the shelter will extend 1 m beyond the edge of the plot. The holding tank is large enough to contain runoff from an hour-long downpour (1 cm of water falling on the shelter). This water is subsequently applied to the water addition plots using solar-powered water pumps, hose lines, and a sprinkler in the center of the plot. To accurately simulate the effects of climate change on plant-animal interactions, we conduct precipitation manipulations at a large enough scale to reduce artifacts that could be created by small scale changes in kangaroo rat movement.