written by Karen Colson and Jason Karl
Description and Uses
The Ocular Estimate Method measures utilization along a transect by visually estimating the percentage by weight of forage removed for individual plants of the key species or from all plants of the key species within small quadrats.
This method is very versatile and is suited for use with both grasses and forbs.
Advantages and Limitations
The main advantage of the Ocular Estimate Method over other utilization methods is that it is very rapid. Another advantage is that, unlike harvesting techniques, vegetation is not disturbed using this method.
This method does involve estimation, which is not as direct as clipping and weighing and therefore involves personal judgment. It can be reasonably accurate however, assuming the observers are experienced and well trained. However, training can be intensive since observers must learn how to estimate weight by comparing ocular estimates against actual weight values obtained by clipping and weighing. In addition exclosures, cages, or fenced areas may be needed for training purposes. Without proper training and experience, this method can be very subjective. This training should be continuous and ideally should include a reference area that can be checked periodically to make sure observers are maintaining accuracy. And in situations where there is an unusual amount of herbaceous growth, the estimates of utilization will be inaccurate without some kind of reference.
Howver, by limiting observations to individual plants or small areas (quadrats) the reliability of estimates is increased. Errors in personal judgment on individual plants or quadrats tend to be somewhat compensating.
Manuals
Reid, E.H. and G.D. Pickford. 1941. A comparison of the ocular-estimate by plot and the stubble-height methods for determining percentage utilization of range grasses. Journal of Forestry 39:935-941.
Similar Approaches
Related utilization and residue measurement methods include: