Figure 6 & 7 - (Older image is on the left.) Creosotebush (Larrea tridentata) arrived at the Sevilleta Long-Term Ecological Research site south of Albuquerque ca. 2500 years ago, and expanded into what was once open grassland during the 20th century, as shown in photograhs by N. H. Darton in July 1915 and by R. M. Turner and J. L. Betancourt in August 1989. The site of the photograph was open grassland when the Spanish began grazing sheep and cattle in the 1700s, but this grassland was invaded by snakeweed (Gutierrezia sarothrae) and later by creosotebush (Larrea tridentata). Note lone creosotebush at right foreground, and beachball-sized snakeweed throughout the foreground of 1915 photograph. Darton took this photograph after one of the wettest years in New Mexico history. By the time of the 1989 photograph, creosotebush had expanded throughout this former grassland, with the invasion accelerated during an extended drought between 1942 and 1972 (Betancourt et al. 1993). Also note increase in one-seed juniper (Juniperus monosperma) on the slopes in the right background.
Figure 8 & 9 - Views from Acoma Pueblo to Enchanted Mesa, 100 km west of Albuquerque, taken by W. H. Jackson in 1899 and H.E. Malde in 1977 (Malde 1973; Rogers and others 1984). Note expansion of junipers (Juniperus monosperma) between 1899 and 1977. In many parts of the west, juniper expansion has been blamed on fire suppression and livestock grazing, justifying an aggressive program of chaining and burning pinyon-juniper woodlands in the 1960s and 1970s to improve forage and water yield. Several authors have suggested that pinyon-juniper expansion instead may represent recovery from prehistoric fuel harvesting, at least in those areas that were heavily populated within the last 1000 years (Samuels and Betancourt 1982; Kohler 1988). One such place could be Acoma Pueblo.