A Comparison of the Line Interception, Vertical Point Quadrat, and Loop Methods as Used in Measuring Basal Area of Grassland Vegetation

Abstract

A study was designed to determine the most efficient sample size and number of samples when any one of the line-interception, vertical point quadrat, or loop methods of vegetation survey is used, on different range types in southern Alberta. The procedure has involved obtaining basal area measurements by all methods on ten transects, 100 feet long, within each range type.Sampling intensities sufficient to sample the dominant and minor species to within ± 10 per cent of their true mean basal area, and the precision obtained when minor species were sampled at intensities found adequate for the dominant species, were calculated. Measurement of minor species at the latter intensities was highly variable. The loop method was the most rapid in the field, detected least species, and gave the most variable data. Data collected by this method were especially variable when the dominant plant species were of the single stemmed type. The line interception method was the most time-consuming, detected more species than either the loop or point methods and gave data which were slightly more variable than the point method. The point method gave the least variable data and, in general, seemed the most satisfactory of the three methods in the vegetative types studied.

Interpretation of Loop‐Frequency Data as a Measure of Plant Cover

“…However, the relation between percent plant area obtained by the line-intercept method is not always linear with loop-density index. Johnston ( 1957) compared the line-intercept, vertical-pointquadrat, and loop-frequency techniques. Data from the line-intercept and vertical-point-quadrat methods were approximately the same; but the loop-frequency method overrated vegetal cover for all species and all sites.…”

“…To avoid confusion we have adopted ''percent plant area'' to designate the proportion of ground surface covered by vegetation, and "number of plants per unit area" for density in its other sense. Parker (1950Parker ( , 1951, Johnston (1957), Sharp ( 1954), and Short ( 1953) have evaluated various features of the loop-index method, its variability in sampling plant area, its sensitivity in detecting changes in percent plant area, and sampling intensity requirements for statistical control. Also, some of these writers have suggested modifications to improve the measuring technique.…”

O método de pontos

“…Este, entretanto, foi melhor para a amostra de espé-cies de ocorrência rara. Johnston (1957) efetuou uma análise para indicar o tamanho, o número de amostras e o método mais eficiente entre a intercepção por linha, o método de pontos verticais e o método de linha de base, para estudos de campos em Alberta, Canadá. Obteve os seguintes resultados: o método de linha de base foi mais rápido, tendo detectado um número menor de espécies e fornecido dados mais variáveis; a intercepção linear tomou mais tempo, indicou o maior número de espécies e apresentou dados próximos aos do método de pontos que, por sua vez, apresentou a menor variação de dados.…”

Vegetation Surveys: A 12 Year History, Navajo Mine

“…" Brun aud Box (1963) reported, "It is generally accepted as one of the more rapid aud accurate methods of estimating attributes of desert shrubs." Johnston (1957) found this method to be more time consuming but detected more species by its use than by the point method. Savage (1940) found the line-interception method suitable for use in dune vegetation of the Southern Great Plains.…”

“…According to Cook aud Stubbendieck (1986), "The line intercept method is often considered one of the most reliable methods for determining cover aud is often used for comparing other methods (Hormay 1949, Whitrnen aud Sigersson 1954, Johnston 1957, aud Hauley 1978. " Brun aud Box (1963) reported, "It is generally accepted as one of the more rapid aud accurate methods of estimating attributes of desert shrubs."…”