Height-Weight Method

Assessment of utilization by height-weight methods closely follows the approaches of indirect sampling to determine biomass. This technique involves initially establishing a regression relationship between the height and biomass of selected species. This relationship is developed by cutting ungrazed plants into equally spaced segments and weighing each portion. The regression relationship then allows utilization to be predicted by relating grazed plant height to the proportional reduction of plant biomass.

This approach is most successful to determine utilization of bunchgrasses, but has occasionally been applied to forbs and sedges. The regression relationship is rarely linear because a the greater proportion lies close to the ground. A major drawback of the method is that considerable effort must be devoted toward establishing the initial regression relationship and that relationship is likely to change between sites and from year to year. Furthermore, it is insensitive at low levels of utilization, particularly when livestock tend to take bites from only part of the plant rather than uniformly grazing the entire plant.

Similar indirect sampling methods based on dimension analysis are commonly used to determine utilization of browse species. Most approaches have focused on establishing relationships between the biomass of browse plants and their twig weight, twig length or twig diameter.

References and Further Reading

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Basile, J.V., and S.S. Hutchings. 1966. Twig diameter-length-weight relations of bittterbrush. Journal of Range Management 19:34-38. (pdf)

Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Sons, New York, NY. pp. 295-298, 302-305.

Bureau of Land Management. 1996. Utilization studies and residual measurements. Interagency Technical Reference, BLM/RS/ST-96/004+1730. pp. 89-102.

Cook, C.W., and J. Stubbendieck. (eds.). 1986. Range research: Basic problems and techniques. Society for Range Management, Denver, CO. pp. 123-125, 129.

Harshmann, E.P., and R. Forsman. 1978. Measuring fireweed utilization. Journal of Range Management 31:393-396. (pdf)

Heady, H.F. 1950. Studies on bluebunch wheatgrass in Montana and height-weight relationships of certain range grasses. Ecological Monographs 20:55-81.

Lommasson, T., and C. Jensen. 1943. Determining utilization of range grasses by height-weight tables. Journal of Forestry 41:589-593.

McDougald, N.K., and R.C. Platt. 1976. A method of determining utilization for wet mountain meadows on the summit allotment, Sequoia National Forest, California. Journal of Range Management 29:497-501. (pdf)

Mitchell, J.E., R. Elderkin, and J.K. Lewis. 1993. Seasonal height-weight dynamics of western wheatgrass. Journal of Range Management 46:147-151. (pdf)

Provenza, F.D.. and P.J. Urness. 1981. Diameter-length-weight relations for blackbrush (Coleogyne ramosissima) branches. Journal of Range Management 34:215-217. (pdf)