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Buffelgrass invasion in the Sonoran Desert affects the regeneration of plant species and the diversity of plant communities. To study the impact of buffelgrass (Cenchrus ciliaris) invasion on the cactus Mammiliaria grahamii, we compare density, population structure and association with nurse plants between an undisturbed natural site and an adjacent buffelgrass invaded site, in the Sonoran desert, Mexico. As germination and establishment are important phases determining species survival, we also studied germination requirements of M. grahamii seeds under controlled conditions. Five 5 x 20 m plots were used to compare plant cover, density, population structure and association in each site. A total of 128 individuals in 500 m(2) were found in the natural area; 33 were in open areas and 95 under trees. About 71% of individuals under canopies were associated with two nurse species. In the invaded area 7 individuals were found under trees. M. grahamii seeds required light for germination, water potentials higher than - 0.6 MPa and temperatures above 25 degrees C. Seeds do not germinate after one minute exposure >= 100 degrees C. Results suggest that buffelgrass invasion affect cacti populations by changing the structure of a desert scrub, burning native plants, decreasing nurse plants, tree cover and changing microclimate. (C) 2016 Elsevier Ltd. All rights reserved.