Abstract ID: 3.9559 | Accepted as Talk | Talk/Oral | TBA | TBA

The giant columnar cactus Trichocereus pasacana is an iconic species of the Salar de Uyuni (3600 m), Bolivia’s second most visited tourist site. These cacti can reach up to 9 meters in height, making them the tallest plants in an area that is almost devoid of trees. Trichocereus serves as a crucial resource for local inhabitants, providing materials for construction and craftsmanship. The densest populations of Trichocereus are primarily found on the islands within the salar, which have historically been sheltered from human activity. We analyzed the spatial distribution of Trichocereus, monitored the stem temperature of individuals from both dense and sparse populations over several years, and modeled the daily minimum temperature and heat balance of the stems. Individuals from sparse populations often experienced sub-zero minimum temperatures during the austral winter, while those in denser populations were 3°C to 5°C warmer. The giant cactus can survive night frosts as long as its succulent stem has stored sufficient heat during the day, and nighttime atmospheric conditions prevent excessive heat loss. However, these conditions are frequently unmet in wind-exposed sites, where isolated individuals are pushed to the limit of their thermal tolerance. We discussed the future of the giant columnar cactus and its sustainable use in the context of climate change in the altiplano, as well as the increasing human pressure resulting from tourism and mining activities.