Drezner T. D., The keystone saguaro (Carnegiea gigantea, Cactaceae): a review of its ecology, associations, reproduction, limits, and demographics, Plant Ecology, 2014, 215(6):581-595, doi: 10.1007/s11258-014-0326-y
A review of saguaro ecology, nurse plants, variation in growth and reproductive maturity, population regeneration and interactions with Sonoran Desert animals. It synthesizes an extensive literature and emphasizes local conditions when interpreting age and population structure.