Contributors: Jason Karl
Description and Uses
The Extensive Browse method estimates browse from tallies the number of annual growth leaders that have and have not been browsed for plants along a paced-off transect. Along each transect, plants are selected for sampling according to a set “pace interval.” The species, age class and form class (see cole_browse_method for list of form classes) of the plant are recorded. From the selected plant, a section of the plant is selected at random (or pseudo-random like using the seconds-hand on a watch) and 10 annual-growth leaders identified. The status of the leaders (i.e., browsed or not) is tallied, and the observer then moves on to the next pace interval and the procedure repeated.
Once 50 plants have been sampled, the average browse for each species is calculated. Species averaging 50% utilization or more are highlighted. For the remaining plants to be sampled, if the plant at the “pace interval” is one of the highlighted species, then the data are recorded as above. If the selected plant is not one of the highlighted species, then the nearest plant of any of the highlighted species is also selected and sampled as above with the exception that age and form class are not recorded for these additional observations.
The following information can be calculated from the plants sampled:
- Average utilization by browse species,
- Percent composition of browse species by age class,
- Percent composition by form class, and
- Percent composition by species.
Confidence intervals can be constructed around median or average leader use, and statistical tests (e.g., Chi Square analysis) can be used to determine if age or form class proportions are different than expected.
Advantages and Limitations
The biggest advantages to this method are that it is fast to implement and all browse species can be sampled along the same transect. The speed of this method comes from the fact that, in addition to form class and age class of the plants being sampled, tallies of the number of annual growth leaders that have and have not been browsed are all that is recorded – i.e., no measurements are made on the plants being sampled.
The fact that no measurements are being taken, only tallies, is one of the factors limiting the accuracy of this method. Because there are many opportunities for bias to enter into this method, attention must be paid to following the protocols listed in the Utilization Studies manual (see reference below) and to training observers to minimize the possibility of bias between observers and ensure consistency of measurements.
Utilization Studies and Residual Measurement: Interagency Technical Reference (BLM 1999). This manual includes field forms for the Cole Browse Method (see below).
Technical and Application References
- Hooper, Jack F. and Harold F. Heady. 1970. An economic analysis of optimum rates of grazing in the California annual-type grassland. Journal of Range Management 23:307-311.
- U.S. Department of Interior Bureau of Land Management. 1984. Rangeland Monitoring – Utilization Studies, TR4400-3.
Other browse removal methods include:
Related utilization and residue measurement methods include: