Early scientists at the Desert Laboratory were pioneers in long-term ecological research. Successive generations of scientists continued the tradition by maintaining existing long-term studies and establishing new ones.
Perennial plants on vegetation plots established in 1906 and 1928 have been mapped (or, in the case of Area A, tallied) about once a decade. More than a dozen researchers have cooperated in the effort over the years. Mapping and monitoring of individual plants has made it possible to determine life spans of long-lived perennials, to follow fluctuations in establishment and mortality during wet and dry periods, and to study recovery of vegetation after a century of protection from domestic livestock.
The exact location of all saguaros on Tumamoc Hill and adjacent Sentinel Hill was mapped with a plane table in 1908. In 1964 Raymond Turner repeated this work on a slightly smaller scale, establishing four large plots on the north, south, east, and west aspects of Tumamoc Hill. He not only recorded locations of all saguaros on aerial photographs, he also their measured heights. Saguaros in these plots were mapped and measured again in 1970 and 1993. Betsy Pierson was in charge of the 1993 mapping and data analysis. These repeated censuses have made it possible to determine the relation between saguaro height and age at Tumamoc Hill, to calculate survivorship across all age classes, and to examine causes for fluctuations in population numbers during the twentieth century.
Permanent plots were established for the study of winter annuals in 1982. Using data gathered on these plots, Larry Venable and his graduate students have been able to test theoretical predictions about the way plants behave in variable environments.
Plots were also established for long-term study of blue paloverde, a common riparian tree in the Sonoran Desert. Maps made in 1907 and again in 1966 showed large losses in blue paloverde numbers, probably a response to drought and entrenchment of a major drainage channel. A third round of mapping in 1985 demonstrated a dramatic reversal of this decline. A series of wetter years promoted a substantial increase in blue paloverdes, especially along reaches where sediment accumulated, making a favorable environment for seedling establishment.