Mancos shale - favorite habitat of Mesa Verde cactus.
Funded by the US Fish and Wildlife Service through the Colorado Natural Areas Program, the study followed individually marked cactus plants over the period from 1986 to 2005. Each year, researchers measured every cactus stem in 3 different plots in southwestern Colorado, and recorded reproductive status and damage or mortality. A total of 1629 stems were measured. At least 30 cactus plants lived through the entire study period and were still going strong when last observed. Clearly, twenty years may not be long enough for the study of some long-lived species! Read the abstract here.
This little plant is about 4 cm (1.6 inches) in diameter, and probably at least 7 years old.