Field Measurement of Effective Leaf Area Index using Optical Device in Vegetation Canopy

This protocol introduces the recently developed device LaiPen LP 110 for leaf area index estimation by indirect optical method, and compares it with the standard LAI-2200 Plant Canopy Analyzer. The new device takes both above and below canopy readings easily, due to its greater sense of sensitivity, in-built digital inclinometer, and automatic logging of readings at the correct position. Also operating control is intuitive.

The manual is necessary. For measurement design preparation, a brief planned canopy structure survey before its measurement is recommended to the operator. Begin by turning on both the instruments by holding the Set key for at least one second.

Find Settings in the main menu by repeatedly pressing the Menu button and set the current date and time of both instruments by pressing Set, Time, Set. Then, choose Return and hold the Set key to return to the main menu. Then, set both the instruments at a single angle measurement mode.

Select Settings holding the Set key, and press Angles, Set, Single, and confirm with the Menu key. Choose Return and hold the Set key to return to the main menu. After calibrating both the LAI sensor and the inbuilt inclinometer, calibrate both LP 110 devices, instrument one and instrument two with each other.

Select Settings in the main menu by pressing the Set key, choose LAI calibration, and press the Set button. Next, hold both the devices in a horizontal plane in the vertical position, and adjust the constant value marked as C on the display by repeatedly pressing the Set key on instrument one, to achieve the same values as depicted on the device's screen on instrument two. Then, press the Menu button and return to the main menu.

Attach instrument one vertically to a tripod placed in an open area or above the studied canopy. Obtain both above and below canopy readings under constant light conditions with standard overcast before sunrise or after sunset, to avoid obtaining incorrect irradiance values. First, select Settings in the main menu, and then choose Auto Interval pressing the Set key.

Next, repeatedly pressed the Set key and then hold the Menu button to select the required interval for automatically logging reference values from 10 up to 600 seconds. Set a shorter time interval if light conditions change rapidly. Press the Menu key, select Return, and hold the Set button to return to the main menu.

Subsequently press the Menu button repeatedly, holding the Set key to reselect measurement in the main menu. Then, choose Auto LAI Ref pressing the Set key to search for the correct LAI sensor position. Check the display, tilt the instrument both to the left and to the right, and forward and backward.

After reaching the zenith angle defined by X and Z axes with zero or less than the value of five, fix the device firmly at the required position mentioned above, and then press the Set key. To start measuring the transmitted irradiance below the vegetation canopy using instrument two, choose Measurement in the main menu. Press the Set key and select LAI.

Keep the orientation of the instrument two as that of instrument one. Press the Set key to activate the mode for our transmitted irradiance measurement below the canopy. Press the Set key again to obtain the value of transmitted irradiance below the canopy, and trigger both the inbuilt inclinometer and sound indicator serving to find the correct LAI sensor position.

Then, keep the device perpendicularly to the ground service to be the LAI sensor pointed up to the zenith. Check the display, tilt the instrument both to the left and to the right, and forward and backward. All below canopy readings are automatically acquired and stored immediately once the zenith angle defined by both the X and Z axes reach zero or less than five.

The beeping tone stops. Proceed with taking further measurements of transmitted irradiance that is below canopy readings, following steps for previous below canopy readings mentioned above. After taking the below canopy measurements using instrument two, press the Menu button and the Menu key repeatedly until Return is selected to return to the main menu, and then press the Set button.

The data is saved in the instrument's memory after each reading. Hold the Menu button for at least one second to turn off the device safely without erasing any data. For the Plant Canopy Analyzer, significantly higher LAI values were observed in the control plot, with no silvicultural intervention in the thin ones.

For the LP 110, the leaf area index did not significantly differ in the C and B treatments. For LP 110, a significant difference in leaf area index values between the C and A plots was found. Generally, the leaf area index significantly decreased after applied thinning treatments in the studied stance.

The leaf area index values recording using LP 110 and Plant Canopy Analyzer for each thinning treatment in pure Norway spruce pole stands exhibited spatial variability. Linear regression was performed for all leaf area index data measured at a particular point level using the LP 110 and the Plant Canopy Analyzer. Ensure measuring under suitable synoptic conditions, use sufficiently sizeable open area for a reference readings, and reflect stand heterogeneity and measurement design for below canopy readings.

Since transmitters can be recorded in different sensor view inclination angles, canopy elements angle orientation can be calculated. If canopy layer width is known, then the leaf area density can be deduced as well.