Diagnostic phytoliths for a ponderosa pine-bunchgrass community near Flagstaff, Arizona.

Phytolith analysis could play an important role in understanding vegetation dynamics in southwestern ponderosa pine (Pinus ponderosa) forests, which have been dramatically altered by fire suppression and other factors. My objectives were to develop a phytolith reference collection and classification system for a ponderosa pine-bunchgrass community found near Flagstaff Arizona. I examined 27 species of grasses found in and around the study area and ponderosa pine for diagnostic phytoliths. Twenty other species common to the area were examined for redundant phytolith forms. Eight phytolith forms were identified, including a diagnostic phytolith for ponderosa pine, the spiny body. The general Poaceae subfamily system validated by numerous researchers is applicable to this community. Examination of phytolith shape frequencies show that for 7 species in the subfamily Pooideae, and 1 species in the Panicoideae, very few (0 to 5%) nondiagnostic phytolith forms were present. Nondiagnostic phytoliths, particularly rondels, were more common (7 to 22%) for the 3 species from the Chloridoideae subfamily. This result is consistent with the observation by other authors that all grasses produce rondel forms and indicates that rondels will be over-represented in phytolith assemblages in comparison to actual vegetation. The ponderosa pixie spiny body appears to be a useful diagnostic for this area and vegetation reconstructions using soil phytolith assemblages based on the system developed in this study could be used to understand grass-tree and grass vegetation dynamics.