contributed by Karen Colson and Jason Karl
Description and Uses
The Comparative Yield Method is used to estimate production or total standing crop at a study site remaining after a use period by assigning relative ranks to each quadrat. As with most production estimates, the Comparative Yield method can be used to compare relative production between different sites.
This method works well for herbaceous vegetation as well as for shrubs and half-shrubs; however it is not well suited for large-shrub communities.
In general this method, which is a modification on the clipped plot methods, involves comparing the total production in a sample quadrat to one of five reference quadrats. The five reference quadrats are set up to represent the range of weights likely to be encountered at the sample site ranging from quadrat 1, which represents the least amount of biomass present on the site to quadrat 5, which represents the largest amount of biomass on site. A similar plot to each of the standard plots is then clipped and weighed to ensure that the standard plots selected represent the proper amount of standing crop or residual dry matter. Using a transect line, additional quadrats are then sampled by comparing the total yield in the sample quadrats that in the reference quadrats.
Advantages and Limitations
The Comparative Yield Method is a rapid technique, allowing observers to obtain a large amount of samples more quickly than using traditional harvesting techniques. Samples can be obtained quickly because 1. total production is evaluated, so clipping calibration on a species basis is not needed, 2. identification of individual species is not required, and 3. the process of developing reference quadrats for ranking purposes reduces both sampling and training time. It does involve training however as observers must calibrate their estimates when sampling situations change, such as changing sites, sampling at different times of day, and for seasonal changes.
Monitoring California’s Annual Rangeland Vegetation, UC/DANR Leaflet 21486, Dec. 1990.
Related utilization and residue measurement methods include: