Canopy Species Composition and Height - Line-point Intercept Method


In use from 2016-04-06


The composition and cover of canopy-forming plant species in grass, forb and perennial treatments of GLBRC Experiments is determined by the Line-Point Intercept (LPI) method. The LPI procedure consists of lowering a sampling pin or rod through the vegetation at regular intervals along a set of transects in each plot and recording the first plant species intercepted vertically in its path or the type of ground cover if not intercepted by plants. Percent cover for each plant species is calculated as the number of times that species is recorded (a “hit”) divided by the total number of sampling points along the transect. Height of the intercepted plant is also measured to provide information on community structure.

Sampling frequency: Once annually at or near maturity of the dominant plant species, typically August-September.

Sampling details:
Marginal Land Experiment: beginning 2017; Treatments G5-11; 4 transects/plot: 2 in the fertilized portion and 2 in the unfertilized. Method 2

Biofuel Cropping System Experiment: beginning 2018, Treatments G2-10; 3 NS transects per plot, main only. Each transect predetermined distance and direction from the station flags and numbered 1-3 based on the station number. Stop about every 1m to identify and measure first intercepted plant. Method 2

GLBRC Scale-up Experiment: beginning 2018; 4 NS transects stretching the full length of fields L2, L3, M2, M3, M4. Stop about every 5m to identify and measure first intercepted plant. Method 2



Metric measuring tape the length of the transect or slightly longer
Steel chaining pins for anchoring meter tape
Pointer – long pin flag preferably less than 1mm in dia.
Meter stick
3-4 meter aluminum grade rod
Clip board, data sheets and pencils
Small plastic bags and marker for samples to identify

Establish Transects:

Method 1:
• Set up a transect line between the designated start and end using chaining pins
• Pin the “0” end of the transect at the start point and walk with the tape reel out to the desired end point
• Transect line should be as straight, taut and as low to the ground as possible
• When you have reached the desired transect distance, pull tape taut and pin tape reel to the ground

Method 2:
• To be used in tall, thick vegetation when stretching a tape measure through the plot is too difficult and disruptive
• A transect line can be approximated by taking ~1 or 5 meter steps through the plot from a designated start to end point
• Try to stay on a straight path

Take Measurements:

1. For all LPI measurements, begin at the “0” end of the line and always stay on the same side of the line.
2. Start at the first sampling point (intervals of 1m or 5m) and stop to take measurements at every sampling point for the duration of the line.
3. For plots where the plants are all less than 1.5m tall, follow these steps. In plots where plants are taller than 1.5m tall, go to step 4.
a. Hold the pin and allow “to go” vertical – do not guide the pin.
b. Lower the pin to the intercept vegetation using the following rules:
i. Lower pin from a standard height each time.
ii. Pin should be vertical along the line.
iii. Do not guide the pin to the ground.
4. In plots with plants that are taller than 1.5m, it may not be possible to lower a pin from above the canopy. An aluminum grade rod can be used instead.
a. Stand the rod vertically for each measurement, resting on the ground.
b. In placing the rod each time, be careful not to shift the surrounding vegetation.
5. At each pin-drop or rod placement, record the first intercepted vegetation, litter, or bare ground.
a. Identify species and record species identification using the LTER plant code or the common name.
b. Record only first species intercepted vertically. This record constitutes a “hit”.
c. If vegetation is dead, record.
d. For unidentified species, bag, label and take to lab for identification.
6. Measure height of intercepted vegetation and record.


Percentage canopy cover by species = species hits/total sampling points per transect*100


Brady,W.W., Mitchell, J. E., Bonham, C. D., Cook, J.W. 1995. Assessing the power of the pointline transect to monitor changes in basal plant cover. Journal of Range Management 48: 187-190.
Bonham, C. D. 1989. Measurements for terrestrial vegetation. New York, NY: John Wiley and Sons.
Heady, H. F., Gibbens, R. P., Powell, R. W. 1959. A comparison of the charting, line intercept, and line point methods of sampling shrub types of vegetation. Journal of Range Management 12, 180-188.
Elzinga, Caryl L., Salzer, Daniel W., Willoughby, John W. 1998. Measuring and monitoring plant populations. BLM Technical Reference. 1730-1. 477 pp.

Date modified: Tuesday, May 14 2024



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