Transect

A transect is a sampling method in which a line or path is laid out through the study area, and observations or samples are collected along or across the line to examine how biological or environmental variables change across space or along gradients. It is used to assess distribution, abundance, or composition of communities, habitats, or physical properties.

The most common forms are line transects, where observers move along a straight line and record detections at specified points or intervals; distance sampling uses detections with measured perpendicular distance from the line to estimate density. Belt transects extend the line into a fixed-width belt, permitting measurement of continuous cover or abundance within that strip. Variants include systematic, stratified or repeated transects, and point transects where observations are made at fixed points rather than along the line.

Design requires planning the length, spacing, and number of transects, considering gradient, habitat heterogeneity, and logistics. Data collected may include species presence/absence, counts, cover, height, or environmental measurements. Analysis uses counts along the line, distance-to-line data, or cover estimates, with distance sampling to model detectability, or simply calculating density or percent cover for belts.

Used across ecology, botany, wildlife management, habitat assessment, and archaeology. Benefits include rapid coverage and gradient assessment; limitations include observer bias, detection probability biases, spatial autocorrelation, and the need for representative transects to avoid bias. Good balance between number and length of transects is important.

See also: sampling, quadrat, plot, distance sampling, ecological survey, vegetation survey.