Analysis of the streamside vegetation within the Hubbell Trading Post Historic Site, Apache County, Arizona: Final Report

Baker, Marc

Foliage-height density (FHD) of perennial vascular plants and percent cover of annual vascular plants were estimated for the riparian vegetation along Pueblo Colorado Wash within the boundaries of the Hubbell Trading Post National Historic Site, Apache County, Arizona. Data were recorded for four years; 1998, 2001, 2002, and 2003, in a continuing assessment of changes in vegetation over time, especially with respect to areas treated for the eradication of exotic invasive shrub and tree species. Transects were measured in early summer, before monsoon rains, and, except for 2001, again in early fall, after monsoon rains. There were few apparent differences in perennial vegetation between the summer of 1998 and the summer of 2001, except where additional eradication treatments were made. Within the streamside legs of the transects, two perennials, Eleocharis parishii (Parish spikerush) and Equisetum arvensis (common horsetail) were present in 1998 and were absent in 2001. Conversely, within the floodplain legs of the transects, three native species of Sporobo/us, S. airoides (alkali sacaton), S. contractus (spike dropseed), and S. cryptandrus (sand dropseed) were present in 2001, although not in 1998. In both 1998 and 2001, the native graminoid Scirpus pungens (common three-square) was the dominant herbaceous perennial and Xanthium strumarium (cocklebur) was the dominant annual. The percent cover of S. pungens, however, was much greater in 2001 than in 1998. Between 2001 and 2003, the native shrub Chrysothamnus nauseosus (rabbitbrush) and the native grass Pascopyrum smithii (western wheatgrass) increased in FHD along the floodplain. Along the streambed there was an increase in the FHD for Scirpus pungens, and shrubs, such as Salix exigua (coyote willow) and S. Iucida var. lasiandra (pacific willow). AN OVA indicated an overall significant increase in the FHD among years for transects within treated areas.