Santa Rita Experimental Range NEON / SRER

The Santa Rita Experimental Range, located in the massive Sonoran Desert, is characterized by a semi-arid, hot climate. Winters are short and mild, while summers are long and hot. The mean annual temperature is 19.3°C (67°F). The Sonoran Desert is wetter than most deserts, and SRER has a mean annual precipitation of 346.2 mm (13.6 in.) each year. Precipitation has a bimodal distribution in this region, with gentle, quenching rains in the winter and fierce thunderstorms during the summer monsoons. However, there are many months between the wet seasons, so both plants and animals in the area are adapted to arid conditions. The lack of prolonged freezing temperatures in winter means that columnar cacti and other large succulents are common. During any season, diurnal temperature swings of up to 32°C (~59°F swing) are common. [9] [12] [13]

The SRER is located at the foothills of the Santa Rita Mountains. The range itself consists of some isolated foothills but is mostly comprised of gently sloped alluvial fans cut by canyons and arroyos. The geology of SRER is characterized by undivided sand and gravels. [1] [6]

The soils found at SRER are those typical of desert regions - they are mostly composed of alluvial deposits from the Santa Rita Mountains, with alluvial caps covering approximately 95% of the region. The soil subgroup Typic Torrifluvents, within Entisols, are commonly found in NEON plots at SRER. Higher-elevation soils have higher organic content, less salt, and lower temperature than soils at lower elevations. [1]

Arroyos and gullies are common within the experimental range, representing the alluvial fan dominated area. Runoff flows to the west and northwest into the Santa Cruz River. [1]

The dominant vegetation found in an area is highly dependent on elevation. For example, densities of velvet mesquite (Prosopis velutina) and cholla cactus (Cylindropuntia spp.) are greatest at elevations between 975 - 1100 m (3200 - 3600 ft.), but creosote bush (Larrea tridentata) dominates at elevations lower than 975 m (3200 ft.). Vegetation at the site is dominated by drought-resistant, thorny species. This includes a mix of short trees, shrubs, cacti and other succulents, perennial grasses, and annual forbs. [1] [2]

There are many distinctive faunae found in the Santa Rita Experimental Range. One of the most interesting mammals in the region is the carnivorous grasshopper mouse (Onychomys torridus). These mice eat everything from large insects to other mice and even scorpions. Grasshopper mice have evolved to not feel the pain of bark scorpion venom, so even if they get stung by their prey, they don’t feel the lasting, burning pain most vertebrates associate with scorpion stings. This allows the mouse to take advantage of an otherwise inaccessible food source and survive in the harsh desert environment. [8]

Established in 1903 by the U.S. Forest Service, the Santa Rita Experimental Range was managed by USDA until around 1988 when control was handed over to the University of Arizona. Establishment of the SRER to study rangelands over time was prompted by several severe droughts at the end of the 1800s that completely wiped out some ranchers in the region and exposed the delicate nature of arid rangelands. When research on SRER first started, the land was badly degraded by the grazing of unregulated cattle. Subsequently, the area was fenced off and grazing prohibited until 1915. This gave scientists time to study forage plants on the range, including their phenology and carry capacity for grazing, and how to restore the denuded landscape for future grazing. Over time, the focus of research at SRER has shifted from rangeland and cattle management to more general studies about ecology, climate change, and environmental restoration. [1] [4] [7]

Control of the experimental range changed hands in 1988 and is now hosted by the University of Arizona. Both the College of Agriculture and Life Sciences and the School of Natural Resources at the University of Arizona use this site as an outdoor laboratory to test pressing questions about ecology, climate change, range management, and wildfire. The mission of the School of Natural resources at the SRER is "To advance research and education on the ecology and management of desert rangelands through the secure, long-term access to research areas, state-of-the-art facilities, new discoveries, and research legacies." The SRER is considered a world-class facility because since its inception over 100 years ago scientists have kept meticulous records of their research, resulting in a huge repository of information about arid grasslands and how to manage them. [3] [4] [11]

Plots for SRER were established in January 2015, and terrestrial sampling began in early 2016. The final instrumentation suite was installed in April 2017.