Utilization Zones
Creating maps that describe utilization zones within the management unit is an important step in many rangeland inventory or monitoring programs to provide valuable background information for further management. Utilization maps assist in the identification of key areas for sampling and management, the recognition of problems in livestock distribution, and in decisions concerning the location of additional range improvements.
Methods adopted to identify utilization zones should be rapid and accurate in order to ensure that a complete description is obtained for the entire management unit. Most techniques are based on a reconnaissance approach, whereby the whole area is visited to obtain a general impression of utilization levels and patterns. These patterns are directly transcribed onto baseline maps or aerial photographs while in the field. Utilization need not be determined with a high degree of precision because the primary aim of the map is to identify general patterns across the management unit. For example, rather than directly assessing utilization, classes could be defined from descriptions that compare the appearance of better forage species and less preferred species (Table 1). At a later stage, actual utilization levels might be estimated with more vigorous techniques.
| Use Class | Description | Degree of Use |
|---|---|---|
| None | Very little or no use of key forage plants. | 0-15% |
| Light | Key forage plants lightly to moderately used. Practically no use on low value forage plants. | 16-35% |
| Safe | Key forage plants used to allowable intensity for the season the season of grazing and sites involved. Some use of low value forage plants. | 36-65% |
| Heavy | Key forage plants closely cropped. Low value forage plants generally being grazed. Some trampling damage may be evident. | 66-80% |
| Severe | Key forage plants destroyed. Low value forage plants carrying the grazing load and are closely cropped. Trampling damage may be evident. | >80% |
Source: Anderson and Currier (1978), p 88.
Mapping is easiest to conduct at the end of the grazing season, when utilization is greatest. In other cases, surveys earlier in the grazing season may indicate early grazing distribution problems. Patterns of wildlife use may also be described by mapping utilization before livestock are released into the management unit. Utilization zones are likely to remain relatively constant from year to year, so remapping is usually necessary only following changes in management such as stocking rates or season of grazing.
References and Further Reading
(Note: pdf files require Adobe Acrobat (free) to view)
Anderson, E.W., and W.F. Currier. 1973. Evaluating zones of utilization. Journal of Range Management 26:87-91. (pdf)
Bureau of Land Management. 1996. Utilization studies and residual measurements. Interagency Technical Reference, BLM/RS/ST-96/004+1730. pp. 23-24.
Nevada Range Studies Task Group. 1984. Nevada rangeland monitoring handbook. Soil Conservation Service, Forest Service, Bureau of Land Management, University of Nevada Reno, Agricultural Research Service and Range Consultants. September 1984. pp. 4-5,19-20.