Method: Canopy cover estimation using the line-intercept method

Canopy cover estimation using the line-intercept method

Puig-Gironès, R.^1,2

¹Institut de la Recerca de la Biodiversitat (IRBIO)

²Departament of Evolutive Biologu, Ecology and Environmental Sciences, University of Barcelona

Last updated: 24/09/2026

Recommended citation:

Puig-Gironès, R. 2026. Canopy cover estimation using the line-intercept method. In: Pere Casals, Davide Ascoli, Lena Vilà-Vilardell, Imma Oliveras, Madoka Krick (eds.) 2026. Methods handbook for characterizing fire use behavior, assessing fire effects, and monitoring soil and vegetation responses at the stand level. FIRE-ADAPT project (number 101086416), deliverable D1.1

Indicator

Fuel flammability: Fuel structure

Brief introduction

Canopy cover is a key control on fuel flammability and fire behaviour, influencing radiation, temperature, humidity, and understorey development. Reliable estimation of canopy cover is therefore essential for assessing fire risk and post-fire ecosystem dynamics.
This method provides a robust, repeatable, scalable, and standardised line-intercept approach to quantify canopy cover. Canopy cover is assessed from the vertical projection of vegetation elements onto a horizontal transect line. Vegetation elements are classified according to the plant layers and habitat elements described in Table 1, including arboreal and bushy vegetation, lianas, prostrated and herbaceous vegetation, and epiphytes. This classification allows canopy cover to be quantified while also providing information on the vertical structure and composition of the vegetation.
Canopy cover is quantified by recording the length of the horizontal transect line intercepted by the vertical projection of vegetation elements. The cumulative length of the intercepted sections is expressed as a percentage of the total transect length. The corresponding vegetation layer, sublayer, and, where applicable, plant category are recorded according to Table 1. Species identity may be optionally recorded. The method can be extended by incorporating systematic point sampling along the same transect to characterise surface vegetation layer and ground components.

Method specifications

Method type

Soft

Hard

Method timing

Before
fire

During
fire

After fire
(short-term)

After fire
(mid-term)

After fire
(long-term)

Field skills

Low

Medium

Hard

Lab skills

Low

Medium

Hard

Material cost

Low

Medium

Hard

Time cost

Low

Medium

Hard

Calculation expertise

Low

Medium

Hard

Equipment

Measuring tape (≥20 m recommended)
Compass (for transect orientation)
GPS device
Field data sheets or digital data logger
Marker flags or stakes
Clinometer (optional, for canopy structure interpretation)
Species identification guides
Diameter tape (optional, for woody debris)

Experimental design

Transect layout

Establish linear transects within each plot.
Recommended length: 10–50 m, depending on vegetation structure and heterogeneity. Longer transects are recommended for heterogeneous vegetation or multiple canopy layers.
Transects may be randomly oriented or systematically aligned (e.g. along contour lines). However, consistency across sampling campaigns is essential.

Replication

Minimum: 3–5 transects per plot
Increase replication in heterogeneous or patchy canopies

Units used

Percentage cover (%)
Coarse woody debris: m³
Intercept length: m

Special considerations

Observer consistency: Clear criteria for canopy inclusion must be defined and consistently applied.
Vertical overlap: In cases of overlapping vegetation layers, only the uppermost canopy layer should be considered to avoid double counting.
Edge effects: Ensure transects are fully within the sampling unit (avoid crossing plot boundaries).
Wind conditions: Movement of branches may affect measurements; avoid sampling under strong wind.
Post-fire conditions: Standing dead trees may contribute to canopy cover depending on study objectives; inclusion criteria must be clearly defined.
Sampling uncertainty: May arise from observer bias, canopy overlap, and heterogeneous vegetation structure. Adequate replication and observer calibration are recommended to minimise variability.

Methodology

Canopy cover (Line-intercept method)

Lay the measuring tape tightly along the ground
Record all segments where canopy vertically overlaps the line
Record start and end points (cm or m) along the tape for each intercept
Canopy cover is quantified by recording the length of a horizontal transect line intercepted by canopy elements¹
Include tree canopies and, if relevant to fuel structure, shrub canopies

Optional extension: Point-intercept and structural assessment

1. Point Sampling along Transect:

To complement canopy cover:

Record species identity and layer (see Table 1) at regular intervals (e.g. every 1 m) along the same transect. Record the height of vegetation layers and the thickness of ground components
This yields a series of equally spaced sampling points

2. Ground and non-vegetation components

Optionally record presence/cover of:

Bare soil
Mosses and lichens
Rocks (>0.5 m³)
Fine woody debris (FWD)
Coarse woody debris (CWD)

3. Coarse woody debris

For biodiversity purposes, coarse woody debris can be recorded separately from the canopy cover assessment. For intercepts involving woody debris (diameter > 7.5 cm; Table 1):

Measure diameter and intercepted length
Estimate volume
Aggregate to obtain plot-level averages

Variables recorded

Site and plot ID

GPS coordinates
Date and time
Fire history / burn severity (if available)
Transect length
Intercept start and end points
Total intercept length
Calculated canopy cover (%)

Optional:

Species identity
Canopy height class
Vegetation layer
Point intercept records
Ground cover types
Woody debris dimensions
Gap distribution

Table 1. Suggested classification for plant layers and other habitat elements that configure the habitat structure for each plot.

Layer	Sublayer	Description
Arboreal	High	Ligneous plants and lianas above 10 m height.
Arboreal	Low	Ligneous plants and lianas between 5 m and 10 m height.
Bushy	High	Ligneous plants and lianas between 3 m and 5 m height.
	Mid-High	Ligneous plants and lianas between 1.5 m and 3 m height.
	Mid-Low	Ligneous plants between 0.5 m and 1.5 m height.
	Low	Ligneous plants between the ground (0.05m) and 0.5 m height.
	Lianas	Lianas and climber plants, independently of the height.
	Prostrated	Ligneous plants which develop horizontally and with a height below 0.5 m.
Herbaceous	Megaphorb	Herbaceous plants above 1.5 m height.
	Graminoid	Plants with a grass-like morphology (grasses, sedges and rushes) below 1 m height.
	Leguminous	Plants from the family Fabaceae below 1 m height.
	Fern	Ferns below 1 m height.
	Others	Herbaceous plants of any type below 1 m height.
Epiphyte		Plants that grow on another living plants.
Mucilage		Mosses or lichenes covering soil, rocks or trunks (lives or dead).
Thick Necromass	Coarse Woody Debris; CWD: Woody debris with a diameter >7.5 cm
	Standing	Volume (m3) of dead standing trees with diameter above 7.5cm diameter.
	On ground	Volume (m3) of downed dead trees on the ground with diameter above 7.5cm diameter.
	Stumps	Volume (m3) of dead wood stumps with a diameter above 7.5cm.
	Branches	Volume (m3) of branches on the ground with a diameter above 7.5 cm.
Thin Necromass	Fine Woody Debris; FWD: Woody debris with a diameter ≤7.5 cm
	Litter fall	Dead leaves or little branches with a diameter below 2.5cm.
	Thin Branches	Branches on the ground with a diameters between 2.5 and 7.5cm.
Bare soil		Bare soil, without litterfall, branches or little rocks (below 0.5m3) coverage.
Rocks		Rocks above 0.5m3 size.

¹Canopy cover is defined as the vertical projection of tree and shrub crowns onto the ground surface. Inclusion criteria (e.g. live vs dead canopy elements, minimum height threshold) must be defined prior to sampling and applied consistently. Tree and shrub canopy cover should be recorded separately, using predefined criteria for distinguishing trees, shrubs, and regeneration, as shown in Table 1.

Calculations

$\mathrm{CC}(\%)= \frac{∑L_i}{L_{\mathrm{total}}}\times100$

\begin{array}{l} \textbf{Where:} \\[0.5em] \mathrm{CC} = \text{Canopy cover} \\ L_i = \text{Length of each canopy intercept segment along the transect} \\ L_{\mathrm{total}} = \text{Total transect length} \\ \end{array}

\mathrm{C_i}(\%)= \frac{\sum_{i=1}^{n} d_i}{n}

\begin{array}{l} \textbf{Where:} \\[0.5em] \mathrm{C_i} = \text{Cover of layer i} \\ d_i = \text{For line-intercept data, cumulative intercepted length} \\ \quad\quad\text{For point-intercept data, proportion of points where the layer is present} \\  n = \text{Number of sampling points} \end{array}

Relation with other methods

Leaf Area Index (LAI) measurements
Understorey vegetation cover assessments
Fuel moisture and microclimate monitoring
Remote sensing-based canopy cover estimation
Fuel load (FWD and CWD)
Lichen and moss cover
Soil exposure and erosion

Data templates

Link to template (or NA)

Further information

Bonham, C.D. (2013). Measurements for Terrestrial Vegetation. Wiley-Blackwell, Chichester, West Sussex, Hoboken, NJ.

Canfield, R. H. (1941). Application of the line interception method in sampling range vegetation. Journal of forestry, 39(4), 388-394.

Jennings, S. B., Brown, N. D., & Sheil, D. (1999). Assessing forest canopies and understorey illumination: canopy closure, canopy cover and other measures. Forestry, 72(1), 59-74.

Puig-Gironès, R., Muriana, M., Real, J., Sabaté, S. (2023). Unravelling the influence of annual weather conditions and Mediterranean habitat types on acorn production, availability and predation. Forest Ecology and Management, 543, 121149.