*2.1. Study Area*

Our study used data collected in the Santa Rita Experimental Range (SRER) located about 30 km south of Tucson, AZ (Figure 1). SRER, founded in 1903, is the longest continuously active rangeland research facility in the United States [27]. The National Science Foundation (NSF) National Ecological Observation Network (NEON) has designated SRER as a terrestrial core site [28].

SRER is located in a semi-arid ecosystem with a bimodal precipitation distribution. The area receives 28 to 50 cm of rain annually with the majority of events occurring in the winter and summer. The average annual temperature is 20 ◦C. Cacti are common in the area due to a lack of extended freezing temperatures during the winter months [27].

Elevation levels range from 900 m in the northwest to 1400 m in the southeast. The vegetation composition consists of creosote (*Larrea tridentata)*, prickly pear(*Opuntia engelmannii*),cholla (*Cylindropuntia fulgida*), barrel cactus (*Ferocactus wislizeni*), mesquite (*Prosopis velutina*), palo verde (*genus Parkinsonia*), whitethorn acacia (*Acacia constricta*), yucca (*Yucca rostrata*), lotebush (*Ziziphus obtusifolia*), and various grasses [27].

The airplane-mounted hyperspectral AVIRIS (Airborne Visible-Infrared Imaging Spectrometer) exploration occurred in the northwest part of SRER, an ideal environment for cacti observed through a high occurrence of prickly pear and cholla cacti (Figure 1). The drone-based hyperspectral analysis occurred closer to the center of the SRER at an elevation of 1130 m. This area had plentiful prickly pear and barrel cacti. Due to the higher elevation and monsoon rains (collected in August 2021), the area had a substantial herbaceous cover of grasses and forbs.

**Figure 1.** We conducted this study at the Santa Rita Experimental Range (SRER), located about 30 km south of Tucson, Arizona. We identified cacti samples for the NEON AVIRIS imagery analysis using photos acquired with a DJI Mavic Pro multirotor in the northwest portion of the study area (black stars), an area with a high density of cacti. We collected drone-mounted hyperspectral imagery in the center of the SRER, where prickly pear and barrel cacti are plentiful (black circle).
