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Residual biomass estimation
The Stubble Height method is a technique for measuring the height of vegetation that is left ungrazed at a site. This method should typically be used in an area for which stubble height standards for different plant communities have been developed. The Stubble Height method has mostly been applied in riparian plant communities.
The Stubble Height method is implemented as follows (Note: the technical references below contain much more detailed instructions on how to implement this method). Stubble height is measured at specified intervals along fixed-length transects. The number and length of transects as well as the observation interval along each transect should be determined beforehand - ideally from pilot study data. At each observation interval, the stubble height of the key species nearest to the observation point is recorded. Measurements are recorded as inches (or cm) of leaf length left on the plant. The site average stubble height by species is calculated and compared to the stubble height guidelines.
The Stubble Height method is very quick and easy to implement, and accordingly can be used to assess or monitor large areas with less time and effort than other methods of measuring utilization. Also, minimal training is required beyond plant identification to accurately implement this method.
One limitation of the Stubble Height method is that it has been applied mostly to riparian communities and more research into its utility in upland environments needs to be conducted and stubble height guidelines developed. Also, problems can arise from attempting to infer grazing impact from stubble height data in an area where no stubble-height guidelines exist. Stubble height guidelines are based on an observed statistical relationship between the stubble height and the amount of biomass removed. Application of stubble height without these guidelines is tantamount to trying to estimate the portion of plants that are no longer there by looking at what's left while not knowing how much was there to begin with.
Image from Utilization Studies and Residual\\Measurements Interagency Technical Reference
Example of a filled-out Stubble Height form (front and back) from the Utilization Studies and Residual Measurements Manual.
Related utilization and residue measurement methods include:
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