What is Line Intercept Sampling?
In line-intercept sampling (also known as line transect sampling*), an element is included in a sample from a particular region if a certain line segment (called a transect) intersects the element. One way to choose the transect is to select a baseline, then run the transect perpendicular to the baseline (Muttlak & Sadooghi-Alvandi, 1993). The technique is used in ecology to estimate percent vegetation coverage, coarse woody debris (CWD) coverage, and plant abundance.
Lines can be single, multiple, L-Shaped, or unequal Length.
*Planet ecologists use line intercept sampling and line transect sampling to refer to the same sampling technique. While some authors (e.g. Pielou, 1985) insist on subtle differences between the two terms, the two terms are generally used synonymously (George & Valentine, 2002).
- Take two measurements for each item of interest: intercept length and maximum width of the item perpendicular to the transect.
- Measure the bare ground in the same way (Cox, 1990).
- Repeat steps 1 & 2 if there are multiple items of interest (e.g. two plant species).
- Calculate the density for each item of interest: multiply the total reciprocals of maximum plant/vegetation/CWD by the unit area/total length of the transect (Cox, 1990).
Advantages / Disadvantages
LIS takes less time than the quadrat method (which uses standard sized plots), but it’s just as accurate (Fidelibus & Mac Aller, 1993)
One major disadvantage is that some of the LIS literature is “…misleading, or worse, incorrect”; misconceptions appear “distressingly often” (George & Valentine, 2002, p.263). Therefore, caution must be used when interpreting or replicating LIS statistical techniques from published papers. Kaiser (1983) is one noted exception.
It is usually hard to replicate the transect line more than twice, for financial, time or practical reasons. This results in difficulty estimating any parameter’s variances (Muttlak & Sadooghi-Alvandi, 1993).
Cox, G. Laboratory manual. of general ecology 6th Ed. Dubuque, Iowa: WIlliam C. Brown; 1990.
Fidelibus, M. & Mac Aller, R. (1993) Methods for Plant Sampling. Retrieved December 11, 2017 from: http://www.sci.sdsu.edu/SERG/techniques/mfps.html
George, T. & Valentine, H. (2003). LIS: Ell-shaped transects and multiple intersections. Environmental and Ecological Statistics 10. 263-279.
Kaiser, L. (1983) Unbiased estimation in line-interception sampling. Biometrics, 39, 965-76.
Muttlak, H. & Sadooghi-Alvandi, S. (1993). A Note on the Line Intercept Sampling Method. Biometrics. Vol. 49, No. 4 (Dec), pp. 1209-1215.
Pielou, E. (1975). Line intersect sampling. In Encyclopedia of Statistical Sciences. S. Kotz & N.L. Johnson (eds.). 5. Wiley, New York, pp. 70-74.