Selection of Attributes

Rangeland inventory and monitoring programs have usually focused on describing vegetation attributes, although soil characteristics are assuming greater importance in recent proposals for evaluating the status of rangeland resources. Vegetation attributes are generally regarded as easier to quantify compared to soil properties, which often rely on subjective assessments. Information on weather conditions, stocking rates, utilization patterns, wildlife, wildfires, and multiple use activities are useful to supplement measured vegetation responses, and to aid in interpreting the results. Photographs also provide a valuable visual record of the overall status of rangeland resources.

No single vegetation attribute is best suited to describe the existing status or to detect trends in rangeland vegetation. Instead, attributes should be selected in light of the objectives of each inventory or monitoring program, the type of vegetation, and the availability of skilled observers. Ideally, attributes should involve rapid and simple sampling methods, to ensure that accurate and precise data can be collected within the budgetary and time constraints associated with many rangeland evaluation plans.

Vegetation attributes commonly measured in rangeland inventory and monitoring programs include:

  • Biomass - is the primary objective of inventories conducted to determine carrying capacity, utilization patterns, or range condition. Despite its importance in management applications, few techniques are available to rapidly obtain accurate and precise biomass data for large areas, so that other attributes such as cover are usually recommended for large scale monitoring programs. It is also difficult to isolate fluctuations in biomass created by weather conditions and immediate grazing history from changes induced by active management.
  • Cover - is widely adopted for both inventory and monitoring purposes because it is an attribute that provides rapid and repeatable data that is relevant to many practical interpretations regarding land use (eg., forage availability, wildlife habitat) and resource status (eg., erosion potential). Basal cover is generally considered a more stable measure than canopy cover to identify herbaceous vegetation change, since it is less influenced by weather fluctuations, time of year, and immediate grazing history.
  • Density - may provide useful inventory information for large perennial species, particularly trees and shrubs. However, density is rarely measured in monitoring situations, because it can be very time consuming, and there are errors associated with the identification of individual plants.
  • Frequency - is regularly used in monitoring programs, because it is a rapid technique that provides precise results. Although a sensitive index of changes in a species over time, additional data must be collected to reveal which other attribute caused the change. Frequency has less relevance in inventory applications, because it does not provide an absolute measure of species abundance.
  • Species Composition - is commonly assessed to describe the character of vegetation during detailed inventory programs. However, accurate determination of species composition can be tedious, because all species must be sampled. Therefore, in long-term or broadscale monitoring situations, it can be more efficient to concentrate on a few key species or species groups, chosen to meet the objectives of the program.

In addition to deciding which vegetation attributes to measure, the planning of inventory or monitoring programs must also select which plant species to include in the sampling protocol.

References and Further Reading

Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Sons, New York, NY. pp 268-283.

Bureau of Land Management. 1996. Sampling vegetation attributes. Interagency Technical Reference, BLM/RS/ST-96/002+1730. pp 23-29.

Holechek, J.L., Pieper, R.D., and C.H. Herbel. 1995. Range management principles and practices. Prentice Hall, Englewood Cliffs, NJ. 2nd ed. pp 162-165.

McClaran, M.P., and D.N. Cole. 1993. Packstock in wilderness: Use, impacts, monitoring, and management. General Technical Report INT-301. Intermountain Research Station, United States Department of Agriculture, Forest Service. Ogden, UT. pp 11-13.

Pieper, R.D. 1984. A critique of "Methods for Inventory and Monitoring of Vegetation, Litter, and Soil Surface Condition". In: National Research Council/National Academy of Sciences. Developing strategies for rangeland management. Westview Press. pp 691-701.

Risser, P.G. 1984. Methods for inventory and monitoring of vegetation, litter, and soil surface condition. In: National Research Council/National Academy of Sciences. Developing strategies for rangeland management. Westview Press. pp 647-690.

Smith, E.L., and G.B. Ruyle. 1991. Considerations when monitoring rangeland vegetation. G.B. Ruyle. (ed). Some methods for monitoring rangelands and other natural area vegetation. University of Arizona, College of Agriculture, Extension Report 9043. pp 1-2.