In 1903, Volney Spalding, a retired botany professor from the University of Michigan, joined the staff of the fledgling Desert Laboratory. One of his first acts was to establish 19 plots on the Desert Laboratory grounds. Most were 100 square meters in size. He mapped the locations of all perennial plants within the plots and, when he retired from the Desert Laboratory several years later, turned the maps over to Forrest Shreve, the well-known desert ecologist. As well as mapping some of the Spalding plots in 1910, 1928, and 1936, Shreve established some new ones: Area A, a polygon about 557 square meters in size for the study of seedling survival, and Area B, a set of 8 contiguous plots, each 10 meters by 10 meters. Locations of some of the original plots were lost over the years, and one or two others were inadvertently destroyed by road construction. Ten of the Spalding plots as well as Areas A and B are still extant and still being monitored by Desert Laboratory researchers.
Maps made at decadal intervals have made it possible to follow changes in numbers of perennial plants as climate has fluctuated. The maps have revealed other kinds of changes too, some of them unexpected. The above illustration shows canopies of two woody plants, creosote bush (blue) and white ratany (red), on plot 16 between 1928 and 2001. Both species are long-lived. White ratany is a root parasite on creosote bush but its demands are probably not heavy enough to kill its host under normal circumstances. On plot 16 however, creosote bush has declined and white ratany has increased, especially since 1948. The replacement of one by the other was probably promoted by a combination of severe drought in the mid-twentieth century and a type of soil that magnifies the effects of drought. This series of maps emphasizes the value of long-term research and the deep perspective it affords. If maps had been made only in 1928 and 1936, no change would be evident, and the conclusion would be that desert vegetation is inordinately stable.
1906 |
1928 |
1959 |
1968 |
1975 |
1986 |
| Photographs of plot 16 from 1906 to 1986. You can click on any of these images to see a larger version (images are approximately 50 KB each), or you can view the larger versions together on one page (approximately 311 KB). | ||