Line-Intercept Sampling
Also known as: Line Intercept, LIS
Line-Intercept Sampling (LIS) is an ecological field method developed by Richard H. Canfield in 1941 for estimating vegetation cover, plant density, and structural characteristics in rangeland and forest surveys. By laying a linear transect across a study area and recording all plants intersecting the line, LIS provides efficient, unbiased estimates without requiring plots or quadrats.
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When to use it
Use LIS for rangeland vegetation surveys, forest understory assessment, riparian vegetation monitoring, invasive species detection, and post-fire recovery studies. It is particularly effective in heterogeneous or large landscapes where plot sampling is impractical. LIS works best when vegetation is clumped or sparse (not very dense and homogeneous, where it may underestimate small plants). It is cost-effective and produces reliable cover estimates without requiring predetermined plot sizes.
Strengths & limitations
- Efficient: covers large areas with relatively little effort compared to plot sampling
- Unbiased estimators of cover and density under proper design
- No need to predetermine plot locations or sizes; adapts to vegetation structure
- Repeatable: transects can be rewalked to detect temporal changes
- Low cost relative to plot-based methods, suitable for large survey areas
- Provides detailed spatial information about vegetation structure along the transect
- Requires careful marking and navigation along the transect line, especially in dense or rugged terrain
- May underestimate cover of small plants or very sparse vegetation
- Cover estimates depend on observer skill; consistency training is necessary
- Line orientation and placement can bias results if not randomized properly
- Cannot directly measure plant density for individuals that do not intersect the line
Frequently asked
How long should my transect be?
Transect length depends on vegetation density and heterogeneity. Sparse vegetation may require longer lines (50–100 m) to obtain reliable cover estimates. Dense vegetation may need only 25–50 m. Conduct a pilot study to ensure adequate sample sizes of plant contacts.
How many transects do I need?
The number of transects depends on desired precision and variation in the study area. Rule of thumb: at least 3–5 transects per stratum, replicated spatially or temporally. Power analysis and pilot data inform optimal replication.
How do I handle plants that only touch the line at a point?
Points are recorded as line contacts (e.g., counts) and contribute to density estimates. They may be treated as zero-length cover intersections if the focus is on cover; count-based density is more appropriate for point touches.
Does line-intercept cover sum to more than 100 percent if plants overlap?
No. Total cover from line-intercept is the sum of all intersection lengths divided by transect length. This reflects the vertical projection of cover along the line and is a measure of space occupation, not a count of distinct layers.
Can I compare line-intercept cover to quadrat cover estimates?
Directly comparing the two requires careful calibration, as they measure cover differently. Line-intercept is robust to observer bias but may miss small understory plants. Quadrat methods capture small plants but are labor-intensive. Running parallel transects and plots can establish conversion factors specific to your vegetation.
Sources
- Canfield, R. H. (1941). Application of the line interception method in sampling range vegetation. Journal of Forestry, 39(4), 388–394. DOI: 10.1093/jof/39.4.388 ↗
- Warren, S. D., Conquest, L. L., & Brenkert, A. L. (1971). Cost and precision of methods for sampling shrub cover in ecological surveys. Journal of Range Management, 24(2), 141–147. link ↗
- Krebs, C. J. (1998). Ecological Methodology (2nd ed.). Addison Wesley Longman. link ↗
How to cite this page
ScholarGate. (2026, June 3). Line-Intercept Sampling. ScholarGate. https://scholargate.app/en/sampling/line-intercept-sampling
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
- Systematic SamplingSurvey Methodology↔ compare