Saguaro flowers from April into June, the hottest time of year in the Sonoran Desert of North America. Stored water used in flower production and vegetative growth is replenished by the North American Monsoon soon after flowering. However, climate change models predict that the northern region of the Sonoran Desert will become significantly hotter and drier over the next century. The monsoon has been weak in recent years, and observations indicate that saguaro have lost their turgidity, turned lighter green, and suffered damage at the tips of stems where flowers are produced. Our objective was to determine water costs associated with reproductive effort in order to predict effects of climate variation on saguaro regeneration. Across six long-term monitoring sites varying in temperature and precipitation across Arizona, USA and Sonora, Mexico, we estimated total bud, flower, and fruit production, measuring water content of sub-samples of reproductive structures at each stage. We predicted that cooler and wetter sites would utilize more water because they would make more flowers. However, due to higher evaporative demands, the proportional water cost of reproduction would be greater in hotter and drier sites.
Results/Conclusions
Preliminary results suggest that the amount of water entering the system has a strong effect on flower production. This research will help elucidate how much water saguaro are using for reproduction relative to their total water budget. Given that the Sonoran Desert is likely becoming hotter and drier, the water cost of reproduction is going to be an important consideration for land managers moving forward. Plants will push their available resources to their physiological limits in order to reproduce; depending on water availability, reproduction during some years or to some extent could become detrimental to saguaro in the future. Saguaro have a minimum amount of water they must conserve in order to survive, and continually producing flowers, regardless of the climate conditions, could push them over that limit. If saguaro are not adapting to these changes in temperature and water availability the future of this flagship Sonoran Desert plant could be grim.