Poorly functioning equipment can jeopardize sample accuracy and sample precision. All measuring equipment, such as scales used to weigh samples for herbage biomass, should be regularly checked to confirm their accuracy. Other sources of measurement error include plastic tapes stretching with use and variations in pace-length among observers.
The dry-weight rank method is specifically designed to determine species composition by providing a measure of the relative contribution of various species to the total biomass (based on dry matter content) for a site.
Sampling distributions describe general patterns in the spread and frequency of the values in the sample data. The type of sampling distribution generated during sampling depends on the vegetation attribute, spatial patterns of the vegetation, the sampling method, and characteristics of sample unit.
Distance methods to determine density that involve plotless sampling regimes are based on determining the mean area associated with each plant by measuring the spacing between them. This approach builds on the pattern that when plants are crowded together in dense vegetation there is a small distance between individuals.
The variable plot method to determine cover was originally developed by European foresters, before being introduced to the USA by Cooper in the late 1950's as a technique for rangeland sampling. It is also referred to as the Bitterlich method (after the original German inventor), or the angle-gauge method (describing the instrument used to collect data).