Name: field measurement of effective leaf area index using optical device in vegetation canopy
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Description: Watch this Scientific Journal Video about Field Measurement of Effective Leaf Area Index using Optical Device in Vegetation Canopy at JoVE.com

The authors are indebted to the Journal of Forest Science editorial board for encouraging and authorizing us to use the representative results in this protocol from the article published there.
The research was financially supported by the Ministry of Agriculture of the Czech Republic, institutional support MZE-RO0118, National Agency of Agricultural Research (Project No. QK21020307), and the European Union&#39;s Horizon 2020 research and innovation program (grant agreement No. 952314).
The authors also kindly thank three anonymous reviewers for their constructive criticism, which improved the manuscript. In addition, thanks go to Dusan Bartos, Alena Hvezdova, and Tomas Petr for helping with field measurements and Photon Systems Instruments Ltd. company for their collaboration and providing device photos.

NOTE: Before beginning to take planned field measurements, sufficiently charge the battery of the LP 110 device. Connect the instrument (USB connector, see Figure 1) and the computer through the attached cable. Battery status is shown in the left-upper corner of the device display.
1. Calibration before measurement
NOTE: For the LP 110, perform a dark calibration of the LAI sensor and in-built inclinometer calibrations before beginning ea...

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What are the differences between the LP 110 as a newly presented device for estimating LAI (or taking PAR intensity measurements) and the LAI-2200 PCA as an improved version of the previous standard LAI-2000 PCA for estimating LAI via an indirect method? Beyond the price being about fourfold higher for the Plant Canopy Analyzer compared to the LP 110, the number of output parameters, measurement conditions, methodological approaches, and possibilities of estimating LAI for different canopies, accuracy of results, etc., c...

Canopies are loci of numerous biological, physical, chemical, and ecological processes. Most of them are affected by canopy structures1. Therefore, accurate, rapid, non-destructive, and reliable in situ&#160;vegetation canopy quantification is crucial for a wide range of studies involving hydrology, carbon and nutrient cycling, and global climate change2,3. Since leaves or needles represent an active interface between the atmosphere and vegetation4, one of the critical canopy structural characteristics is leaf area index (LAI)5, defined as one-half of the total green leaf surface area per unit of horizontal ground surface area or crown projection for individuals, expressed in m2 per m2 as a dimensionless variable6,7.
Various instruments and methodological approaches for estimating terrestrial LAI and their pros and cons in diverse ecosystems have already been presented8,9,10,11,12,13,14,15. There are two main categories of LAI estimation methods: direct and indirect (see comprehensive reviews8,9,10,11,12 for more details). Mainly used in forest stands, ground-based&#160;LAI estimates are routinely obtained using indirect optical methods due to the lack of direct LAI determination, but they usually represented a time-consuming, labor-intensive, and destructive method9,10,12,16. Moreover, indirect optical methods derive LAI from more easily measure related parameters (from the viewpoint of its time-demanding and labor-intense nature)17, such as the ratio between incident irradiation above and below the canopy and the quantification of canopy gaps14. It is evident that Plant Canopy Analyzers have also been widely used to validate satellite LAI retrievals18; therefore, it has been considered a standard for LP 110 comparison (see Table of Materials for more details about employed instruments).
The LP 110, as an updated version of initially self-made simple instrument ALAI-02D19 and later LP 10020, was developed as a close competitor for Plant Canopy Analyzers. As a representative of indirect optical methods, the device is hand-held, lightweight, battery-powered, without any need for a cable connection between the sensor and data-logger that uses a digital inclinometer instead of a bubble level and enables faster and more accurate positioning and value reading. In addition, the device was designed to note immediate readouts. Thus, the time estimate needed for collecting data in the field is shorter for the LP 110 than Plant Canopy Analyzer by approximately &#8531;. After the export of readouts to a computer, the data are available for subsequent processing. The device records irradiance within the blue light wavelengths (i.e., 380-490 nm)21,22 using an LAI sensor for making an LAI calculation. The LAI sensor is masked by an opaque restriction cap with 16&#176; (Z-axis) and 112&#176; (X-axis) fields of view (Figure 1). Thus, light transmittance can be noted using the device held either perpendicularly to the ground surface (i.e., zenith angle 0&#176;), or at five different angles of 0&#176;, 16&#176;, 32&#176;, 48&#176;, and 64&#176; to be able also to deduce canopy elements&#39; inclination.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62802/62802fig01.jpg" /> 
Figure 1: Physical features of the LP 110. The MENU key enables the user shift up and down throughout the display, and the SET button serves as the Enter key (A).The zenith view under different inclination angles (&#177;8 due to the side view) and the horizontal view is fixed for LP 110 to 112&#176; (B) similarly to the Plant Canopy Analyzer&#160;(modified by restrictors). <a href="https://www.jove.com/files/ftp_upload/62802/62802fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Due to the higher sensitivity of the LAI sensor, its restricted field of view, in-built digital inclinometer, automatic logging of reading values at the correct position indicated by sound without a button press, the new instrument is also suitable for above-canopy readings at narrow valleys or even on broader forest roads to measure a wide range of sky conditions. Besides that, it enables quantification of mature stand canopies above the relatively high regeneration, and it attains higher accuracy of irradiance values than Plant Canopy Analyzer. Moreover, the price of LP 110 equals about &#188; of the Plant Canopy Analyzer. Contrariwise, the utilization of LP 110 in dense (i.e.,&#160;LAIe at stand level over 7.88)23 or very low canopies as grassland is limited.
The LP 110 can work within two operating modes: (i) a single sensor mode taking both below-canopy and reference readings (above the studied canopy or in a sufficiently widespread clearing located within the vicinity of the analyzed vegetation) performed before, after, or during below-canopy measurements taken with the same instrument and (ii) a dual sensor mode using the first instrument for taking below-canopy readings, whereas the second one is employed for automatically logging reference readings within a regular predefined time interval (from 10 up to 600 s). The LP 110 can be matched with a compatible GPS device (see Table of Materials) to record each below-canopy measurement point&#39;s coordinates for both the modes mentioned above.
The effective leaf area index (LAIe)24 incorporates the clumping index effect and can be derived from measurements of solar beam irradiance taken above and below the studied vegetation canopy25. Thus, for the following LAIe calculation, transmittance (t) must be calculated from irradiation both transmitted below the canopy (I) and incident above the vegetation (Io) measured by the LP 110 device.
t = I / I0 (1)
Since the irradiation intensity exponentially decreases as it passes through a vegetation canopy, LAIe can be calculated according to the Beer-Lambert extinction law modified by Monsi and Saeki9,26
LAIe = - ln (I / I0) x k-1 (2),
Where, k is the extinction coefficient. The extinction coefficient reflects each element&#39;s shape, orientation, and position in the vegetation canopy with the known canopy element inclination and view direction9,12. The k coefficient (see equation 2) depends on the absorption of irradiance by foliage, and it differs among plant species based on the morphological parameters of canopy elements, their spatial arrangement, and optical properties. Since the extinction coefficient usually fluctuates around 0.59,27, equation 2 can be simplified as presented by Lang et al.28 in a slightly different way for heterogeneous and homogenous canopies:
In a heterogeneous canopy
LAIe = 2 x |<img alt="Equation 1" src="/files/ftp_upload/62802/62802eq01.jpg" />ln t| (3),
or
In a homogeneous canopy
LAIe = 2 x |ln T| (4),
Where, t: is transmittance at each below-canopy measurement point, and T: is the average transmittance of all t values per measured transect or stand.
In forest stands, LAIe must be further corrected due to a clumping effect of the assimilation apparatus within the shoots29,30,31,32,33,34 to obtain the actual LAI value.
The protocol is devoted to the practical utilization of the LP 110 optical device for estimating LAIe in a selected example of Central European conifer forest stands (see Table 2 and Table 3 for the site, structural, and dendrometric characteristics). LAIe estimation in a vegetation canopy using this device is based on a widely used optical method related to the transmittance of photosynthetically active radiation and canopy gap fraction. The paper aims to provide a comprehensive protocol for performing LAIe estimation using the new LP 110 optical device.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>AccuPAR</td>
			<td>METER Group, Inc., Pullman, WA, USA</td>
			<td>AccuPaR LP-80</td>
			<td>https://www.metergroup.com/environment/products/accupar-lp-80-leaf-area-index/</td>
		</tr>
		<tr>
			<td>DEMON</td>
			<td>CSIRO, Canberra, Australia</td>
			<td>DEMON</td>
			<td></td>
		</tr>
		<tr>
			<td>File Viewer</td>
			<td>LI-COR Biosciences Inc., NE, USA</td>
			<td>FV2200C Software</td>
			<td>https://www.licor.com/env/products/leaf_area/LAI-2200C/software.html</td>
		</tr>
		<tr>
			<td>FluorPen</td>
			<td>Photon System Instruments Ltd. (PSI), Czech Republic</td>
			<td>FluorPen 1.1.2.3 Sofware</td>
			<td>https://handheld.psi.cz/products/laipen/#download</td>
		</tr>
		<tr>
			<td>Hand-held GPS device</td>
			<td>Garmin Ltd., Czech Republic</td>
			<td>Garmin eTrex 32x Europe46</td>
			<td>https://www.garmin.cz/garmin-etrex-32x-europe46/80117</td>
		</tr>
		<tr>
			<td>Hand-held device for leaf area index estimation(LP 110)</td>
			<td>Photon System Instruments Ltd. (PSI) Czech Republic</td>
			<td>LaiPen LP 110</td>
			<td>https://handheld.psi.cz/products/laipen/#info</td>
		</tr>
		<tr>
			<td>Plant Canopy Analyser</td>
			<td>LI-COR Biosciences Inc., NE, USA</td>
			<td>LAI-2000 PCA</td>
			<td>LAI-2200 PCA or LAI-2200C as improved versions of LAI-2000 PCA can be used, see: https://www.licor.com/env/products/leaf_area/LAI-2200C/</td>
		</tr>
		<tr>
			<td>Statistical software</td>
			<td>Systat Software Inc., CA, USA</td>
			<td>SigmaPlot 13.0</td>
			<td>https://systatsoftware.com/products/sigmaplot/sigmaplot-version-13/?gclid=Cj0KCQjwzYGGBhCTARIs 
			AHdMTQzgfb42vv0mWmcbVcflNO 
			UvrLl802Lrhkfh23Qie2mIZfw4O8kp 
			7p0aAsoiEALw_wcB</td>
		</tr>
		<tr>
			<td>Statistical software</td>
			<td>StatSoft Inc., OK, USA</td>
			<td>STATISTICA 10.0</td>
			<td>For LAI visualization, wafer-plots in STATISTICA 10.0 were employed.</td>
		</tr>
		<tr>
			<td>SunScan</td>
			<td>Delta-T Devices, Ltd., Cambridge, UK</td>
			<td>SS1 SunScan</td>
			<td>https://www.delta-t.co.uk/product/sunscan</td>
		</tr>
		<tr>
			<td>TRAC</td>
			<td>3rd Wave Engineering, Ontarion Canada</td>
			<td>Tracing Radiation and Architecture of Canopies</td>
			<td>http://faculty.geog.utoronto.ca/Chen/Chen&#39;s%20homepage/res_trac.htm</td>
		</tr>
		<tr>
			<td>Tripod</td>
			<td>Any</td>
			<td>NA</td>
			<td>Tripod with standard nut</td>
		</tr>
		<tr>
			<td>Water level</td>
			<td>Any</td>
			<td>NA</td>
			<td></td>
		</tr>
	</tbody>
</table>

field measurement of effective leaf area index using optical device in vegetation canopy

Leaf area index (LAI) is an essential canopy variable describing the amount of foliage in an ecosystem. The parameter serves as the interface between green components of plants and the atmosphere, and many physiological processes occur there, primarily photosynthetic uptake, respiration, and transpiration. LAI is also an input parameter for many models involving carbon, water, and the energy cycle. Moreover, ground-based in situ measurements serve as the calibration method for LAI obtained from remote sensing products. Therefore, straightforward indirect optical methods are necessary for making precise and rapid LAI estimates. The methodological approach, advantages, controversies, and future perspectives of the newly developed LP 110 optical device based on the relation between radiation transmitted through the vegetation canopy and canopy gaps were discussed in the protocol. Furthermore, the instrument was compared to the world standard LAI-2200 Plant Canopy Analyzer. The LP 110 enables more rapid and more straightforward processing of data acquired in the field, and it is more affordable than the Plant Canopy Analyzer. The new instrument is characterized by its ease of use for both above- and below-canopy readings due to its greater sensor sensitivity, in-built digital inclinometer, and automatic logging of readings at the correct position. Therefore, the hand-held LP 110 device is a suitable gadget for performing LAI estimation in forestry, ecology, horticulture, and agriculture based on the representative results. Moreover, the same device also enables the user to take accurate measurements of incident photosynthetically active radiation (PAR) intensity.

The spatial structure obtained from both tested devices obviously differed in all studied plots, i.e., thinned from above (A), thinned from below (B) and a control without any silvicultural intervention (C; see Table 2 for more details). At the stand level, similar differences in LAI values obtained from the LP 110 and the Plant Canopy Analyzer were confirmed between thinned plots with various densities (A vs. B) using ANOVA and Tukey&#39;s test. For the Plant Canopy Analyzer, significantly higher LAI va...

Watch this Scientific Journal Video about Field Measurement of Effective Leaf Area Index using Optical Device in Vegetation Canopy at JoVE.com

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

Fast and precise leaf area index (LAI) estimation in terrestrial ecosystems is crucial for a wide range of ecological studies and calibrating remote sensing products. Presented here is the protocol for using the new LP 110 optical device for taking ground-based in situ LAI measurements.

Leaf area index (LAI) is an essential canopy variable describing the amount of foliage in an ecosystem. The parameter serves as the interface between ...

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.

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