PARENT SESSION
Oral Session #13: Success Criteria and Monitoring Restoration.
Presiding: D. Gluesenkamp
Monday, August 5. 1:00 PM to 3:45 PM. Mohave Meeting Room, TCC.

Stabilization of the Mean as a Demonstration of Sample Adequacy.

Clark, David^*,1, ¹ Mining and Minerals Division, Santa Fe, New Mexico

ABSTRACT- Adequate sampling of plant populations can be problematic. Commonly estimated population parameters are seldom normally distributed, and minimum sample sizes that are based on confidence intervals for normal populations may overestimate how many samples are required to accurately estimate production and density, and sometimes cover. Alternative procedures for determining sample adequacy based on the ideas underlying the species-area curve have been proposed, but few studies have evaluated the effectiveness of these procedures on field data. Running mean calculations from undisturbed and reclaimed vegetation communities in New Mexico indicate that a stable estimate of the mean is often obtained after 30 to 40 production and density samples. Mean cover estimates typically stabilize after 15 to 20 samples. For data where the mean fails to stabilize after 40 samples, quadrat size problems are indicated. A case is made for the adoption of a minimum sample size of 30 and a maximum sample size of 40, and calculation of sample adequacy using the standard deviation of the consecutive means, instead of the standard deviation of the individual samples. The merits of appropriately-sized quadrats when measuring plant production and density are also illustrated.

KEY WORDS: reclamation, mined land, vegetation inventory