Terrestrial vegetation and soils monitoring in the Rincon Mountain District, Saguaro National Park, 2008–2009

Hubbard, J.; Studd, Sarah; McIntyre, Cheryl

This report summarizes provisional data collected by the Sonoran Desert Network during the first two seasons of terrestrial vegetation and soils monitoring in upland areas of the Rincon Mountain District of Saguaro National Park, in southern Arizona. Twenty-five permanent monitoring sites were sampled, with another 35 planned for 2010–2012, after which time a detailed status and trend report will be produced. This report summarizes effort to date, evaluates the sampling design in the context of our monitoring objectives, and suggests modifications to the design. Based on estimates from this initial data, the current sampling design does an excellent job of providing statistical power to detect trends in perennial species and soil stability. The design also provides good power for detecting changes in lifeform composition and soil surface cover, although our projected power for a few variables failed to meet our initial design criteria. Species detectability appears to be very reasonable based on species-accumulation curves. Although only about 20% of the known park flora has been detected to date, it is important to note that monitoring under this protocol does not differentiate among annuals (with the exception of exotic plants); nor does it sample aquatic, riparian, or xeroriparian systems. The elevation × soil texture stratification scheme appears to be effective, although vegetation-community similarity of the three strata that encompass lower-elevation sites (<4,500') did not differ significantly. This may be due to the small sample sizes of these more constrained areas of the park; we will investigate this question by adding three sites at lower elevations in 2010. Results will be analyzed in the 2010 data summary. Sampling efficiencies can be gained if the lack of differences is real. Overall, we conclude that the sampling and response designs are efficient and effective, and should provide data that meet our monitoring objectives. We will continue to evaluate and adjust our sampling strategy annually, culminating in the full analysis for the comprehensive status and trends reports after the 2012 season. Therefore, it is important that results in this and other annual data summaries not be directly interpreted for evaluating the condition of park resources.

Terrestrial vegetation and soils monitoring in the Rincon Mountain District, Saguaro National Park, 2008–2009

Series

Collections