Damage in a Saguaro (carnegiea Gigantea) Population in the El Pinacate and Gran Desierto De Altar Biosphere Reserve, Sonora, Mexico

The saguaro is an endemic and emblematic columnar cactus of the Sonoran Desert that offers refuge and food to different species. Climate change and increased ultraviolet exposure are threatening this species. Although reports of an increase in "epidermal browning" in saguaro populations in the United States have been published, to the best of our knowledge, no studies of this or other types of damage to Mexican saguaro populations are available. The present research is the first report of its kind performed in a saguaro population in the El Pinacate and Gran Desierto de Altar Biosphere Reserve (Sonora, Mexico). Seven types of damage were evaluated and classified in saguaro stems: cactus cortical scaling (CCS = epidermal browning), girdling, shell, exposed root, eyelet, termite tubes, and topping cuts. In addition, an anatomical comparison of healthy and CCS-damaged tissues is presented. Shell was the most frequent type of damage (91% of individuals), followed by CCS (73%). Girdling occurred mainly in small organisms. Shell, exposed root, eyelet, and termite tubes tended to occur more frequently in larger organisms, whereas CCS tended to be more evenly distributed among differently sized individuals. Of all individuals, 3.3% were undamaged, 89.2% were moderately damaged, and 7.5% were highly damaged. CCS damage causes differences in the composition of the tissues, as well as in stomata distribution, thus compromising the photosynthetic function of the stem. The snapshot of the state of the individuals provided in the present study highlights the need for longer-term studies considering the long life cycle of the saguaro to develop conservation strategies.