A Comparison of the Line-Interception, Variable-Plot and Loop Methods as Used to Measure Shrub-Crown Cover

Abstract

Determining the percentage of ground covered by shrubby vegetation is an integral part of range inventory and of range condition and trend studies. Measurement of plant cover is used in making site descriptions and in studying brush control, seeding, and grazing management. A change in plant cover often reflects a change in management practices. No accurate method of measuring plant cover has been devised. In most instances only an estimation of plant cover is made. However, Smith (1944) showed that cover estimates vary significantly among individuals on different days and even on the same day. Many range technicians, land managers, and ecologists have recognized the need for a rapid, accurate, and easyto-use method of measuring plant cover. The loop procedure of the Parker 3-Step Method is used widely in condition and trend studies. Ash-inch loop is utilized to obtain the plant density index, a frequency measurement. Recently, Johnston (1957) employed the loop procedure to

Image Analysis of Leafy Spurge (Euphorbia esula) Cover

“…Image analysis may estimate cover to be lower at high cover values compared to the ocular method, because image analysis may better account for foliar openings than the observers. The observers might see cover more as the gross crown spread without accounting for any foliar openings (Daubenmire 1959;Kinsinger et al 1960).…”

An Evaluation of Variable Plot Sampling in Shrub and Herbaceous Vegetation

“…K Dividing equation ( 11) by (12) and simplifying gives the relative amount by which variable plot sampling overestimates the ground cover of elliptical shrubs : E = 1 + b2 (13 2b ) To compute the actual ground cover on the plots used in their comparison of methods, Kinsinger et al ( 1960) measured the long and short axis of every shrub and calculated its area from the ellipse formula. From field data supplied by Kinsinger (personal communication) I have computed the ratio of minor to major axes of the shrubs on each of three plots (Table II).…”

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In the incessant search for new and simpler techniques of vegetation analysis, truly original ideas are rare. It seems appropriate to designate it the cm.>er percentage fa.ctor, analogous to the basal area factor used in plotless timber cruising.Tr:STS OF VARIABLE PLOT SAMPLING Comparison of line intercept, variable plot, and loop estimates with true coverage in the open desert shrub vegetation of Nevada showed that line intercept came closest to the value obtained from measurements of every shrub (Kinsinger, Eckert, and Currie 1960). Proposed for estimating tree basal area, it has been adapted to determination of timber volume, and is now widely used in routine forest inventory.

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“…One such idea, the Bitterlich variable plot (or plotless) method, has continued to grow in usefulness for a dozen years. Kinsinger et al (1960) concluded that the variable plot method is faster and more reproducible than the other techniques tested, but that it cannot be used to study minute vegetational changes.Crossarm length significantly affected variable plot estimates in three shrub types in Wyoming ( Fisser 1961). Modification of Bitterlich's geometry permits the variable plot technique to be used for direct estimation of shrub cover in open shrub communities.…”

“…Kinsinger et al (1960) concluded that the variable plot method is faster and more reproducible than the other techniques tested, but that it cannot be used to study minute vegetational changes. Depending on the nature of the vegetation, from 20 to more than 100 separate 100-foot lines, were needed to estimate cover to within 20o/o of the mean with 95o/o confidence.…”