Abstract

A plant canopy gap-size analyzer, the Tracing Radiation and Architecture of Canopies (TRAC), developed by Chen and Cihlar [Appl. Opt. 34, 6211 (1995)] and commercialized by 3rd Wave Engineering (Nepean, Canada), has been used around the world to quantify the fraction of photosynthetically active radiation absorbed by plant canopies, the leaf area index (LAI), and canopy architectural parameters. The TRAC is walked under a canopy along transects to measure sunflecks that are converted into a gap-size distribution. A numerical gap-removal technique is performed to remove gaps that are not theoretically possible in a random canopy. The resulting reduced gap-size distribution is used to quantify the heterogeneity of the canopy and to improve LAI measurements. It is explicitly shown here that the original derivation of the clumping index was missing a normalization factor. For a very clumped canopy with a large gap fraction, the resulting LAI can be more than 100% smaller than previously estimated. A test case is used to demonstrate that the new clumping index derivation allows a more accurate change of LAI to be measured.

© 2002 Optical Society of America

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References

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  1. J. M. Chen, J. Cihlar, “Plant canopy-gap size analysis theory for improving optical measurements of leaf-area index,” Appl. Opt. 34, 6211–6222 (1995).
    [CrossRef] [PubMed]
  2. T. Nilson, “A theoretical analysis of the frequency of gaps in plant stands,” Agri. Meteorol. 8, 25–38 (1971).
    [CrossRef]
  3. J. M. Chen, “Optically-based methods for measuring seasonal variation in leaf area index of boreal conifer forests,” Agri. For. Meteorol. 80, 135–163 (1996).
    [CrossRef]
  4. E. E. Miller, J. M. Norman, “A sunfleck theory for plant canopies. I. Length of sunlit segments along a transect,” Agron. J. 63, 735–738 (1971).
    [CrossRef]
  5. J. M. Chen, P. M. Rich, T. S. Gower, J. M. Norman, S. Plummer, “Leaf area index of boreal forests: theory, techniques and measurements.” J. Geophys. Res. 102, 29429–29444 (1997).
    [CrossRef]
  6. S. G. Leblanc, J. M. Chen, M. Kwong, TRAC Manual (Version 2.1) (Canada Centre for Remote Sensing, Natural Resources Canada, Ottawa, Canada, 2002).
  7. B. E. Law, S. Van Tuyl, A. Cescatti, D. D. Baldocchi, “Estimation of leaf area index in open-canopy ponderosa pine forests at different successional stages and management regimes in Oregon,” Agri. For. Meteorol. 108, 1–14 (2001).
    [CrossRef]

2001 (1)

B. E. Law, S. Van Tuyl, A. Cescatti, D. D. Baldocchi, “Estimation of leaf area index in open-canopy ponderosa pine forests at different successional stages and management regimes in Oregon,” Agri. For. Meteorol. 108, 1–14 (2001).
[CrossRef]

1997 (1)

J. M. Chen, P. M. Rich, T. S. Gower, J. M. Norman, S. Plummer, “Leaf area index of boreal forests: theory, techniques and measurements.” J. Geophys. Res. 102, 29429–29444 (1997).
[CrossRef]

1996 (1)

J. M. Chen, “Optically-based methods for measuring seasonal variation in leaf area index of boreal conifer forests,” Agri. For. Meteorol. 80, 135–163 (1996).
[CrossRef]

1995 (1)

1971 (2)

T. Nilson, “A theoretical analysis of the frequency of gaps in plant stands,” Agri. Meteorol. 8, 25–38 (1971).
[CrossRef]

E. E. Miller, J. M. Norman, “A sunfleck theory for plant canopies. I. Length of sunlit segments along a transect,” Agron. J. 63, 735–738 (1971).
[CrossRef]

Baldocchi, D. D.

B. E. Law, S. Van Tuyl, A. Cescatti, D. D. Baldocchi, “Estimation of leaf area index in open-canopy ponderosa pine forests at different successional stages and management regimes in Oregon,” Agri. For. Meteorol. 108, 1–14 (2001).
[CrossRef]

Cescatti, A.

B. E. Law, S. Van Tuyl, A. Cescatti, D. D. Baldocchi, “Estimation of leaf area index in open-canopy ponderosa pine forests at different successional stages and management regimes in Oregon,” Agri. For. Meteorol. 108, 1–14 (2001).
[CrossRef]

Chen, J. M.

J. M. Chen, P. M. Rich, T. S. Gower, J. M. Norman, S. Plummer, “Leaf area index of boreal forests: theory, techniques and measurements.” J. Geophys. Res. 102, 29429–29444 (1997).
[CrossRef]

J. M. Chen, “Optically-based methods for measuring seasonal variation in leaf area index of boreal conifer forests,” Agri. For. Meteorol. 80, 135–163 (1996).
[CrossRef]

J. M. Chen, J. Cihlar, “Plant canopy-gap size analysis theory for improving optical measurements of leaf-area index,” Appl. Opt. 34, 6211–6222 (1995).
[CrossRef] [PubMed]

S. G. Leblanc, J. M. Chen, M. Kwong, TRAC Manual (Version 2.1) (Canada Centre for Remote Sensing, Natural Resources Canada, Ottawa, Canada, 2002).

Cihlar, J.

Gower, T. S.

J. M. Chen, P. M. Rich, T. S. Gower, J. M. Norman, S. Plummer, “Leaf area index of boreal forests: theory, techniques and measurements.” J. Geophys. Res. 102, 29429–29444 (1997).
[CrossRef]

Kwong, M.

S. G. Leblanc, J. M. Chen, M. Kwong, TRAC Manual (Version 2.1) (Canada Centre for Remote Sensing, Natural Resources Canada, Ottawa, Canada, 2002).

Law, B. E.

B. E. Law, S. Van Tuyl, A. Cescatti, D. D. Baldocchi, “Estimation of leaf area index in open-canopy ponderosa pine forests at different successional stages and management regimes in Oregon,” Agri. For. Meteorol. 108, 1–14 (2001).
[CrossRef]

Leblanc, S. G.

S. G. Leblanc, J. M. Chen, M. Kwong, TRAC Manual (Version 2.1) (Canada Centre for Remote Sensing, Natural Resources Canada, Ottawa, Canada, 2002).

Miller, E. E.

E. E. Miller, J. M. Norman, “A sunfleck theory for plant canopies. I. Length of sunlit segments along a transect,” Agron. J. 63, 735–738 (1971).
[CrossRef]

Nilson, T.

T. Nilson, “A theoretical analysis of the frequency of gaps in plant stands,” Agri. Meteorol. 8, 25–38 (1971).
[CrossRef]

Norman, J. M.

J. M. Chen, P. M. Rich, T. S. Gower, J. M. Norman, S. Plummer, “Leaf area index of boreal forests: theory, techniques and measurements.” J. Geophys. Res. 102, 29429–29444 (1997).
[CrossRef]

E. E. Miller, J. M. Norman, “A sunfleck theory for plant canopies. I. Length of sunlit segments along a transect,” Agron. J. 63, 735–738 (1971).
[CrossRef]

Plummer, S.

J. M. Chen, P. M. Rich, T. S. Gower, J. M. Norman, S. Plummer, “Leaf area index of boreal forests: theory, techniques and measurements.” J. Geophys. Res. 102, 29429–29444 (1997).
[CrossRef]

Rich, P. M.

J. M. Chen, P. M. Rich, T. S. Gower, J. M. Norman, S. Plummer, “Leaf area index of boreal forests: theory, techniques and measurements.” J. Geophys. Res. 102, 29429–29444 (1997).
[CrossRef]

Van Tuyl, S.

B. E. Law, S. Van Tuyl, A. Cescatti, D. D. Baldocchi, “Estimation of leaf area index in open-canopy ponderosa pine forests at different successional stages and management regimes in Oregon,” Agri. For. Meteorol. 108, 1–14 (2001).
[CrossRef]

Agri. For. Meteorol. (2)

J. M. Chen, “Optically-based methods for measuring seasonal variation in leaf area index of boreal conifer forests,” Agri. For. Meteorol. 80, 135–163 (1996).
[CrossRef]

B. E. Law, S. Van Tuyl, A. Cescatti, D. D. Baldocchi, “Estimation of leaf area index in open-canopy ponderosa pine forests at different successional stages and management regimes in Oregon,” Agri. For. Meteorol. 108, 1–14 (2001).
[CrossRef]

Agri. Meteorol. (1)

T. Nilson, “A theoretical analysis of the frequency of gaps in plant stands,” Agri. Meteorol. 8, 25–38 (1971).
[CrossRef]

Agron. J. (1)

E. E. Miller, J. M. Norman, “A sunfleck theory for plant canopies. I. Length of sunlit segments along a transect,” Agron. J. 63, 735–738 (1971).
[CrossRef]

Appl. Opt. (1)

J. Geophys. Res. (1)

J. M. Chen, P. M. Rich, T. S. Gower, J. M. Norman, S. Plummer, “Leaf area index of boreal forests: theory, techniques and measurements.” J. Geophys. Res. 102, 29429–29444 (1997).
[CrossRef]

Other (1)

S. G. Leblanc, J. M. Chen, M. Kwong, TRAC Manual (Version 2.1) (Canada Centre for Remote Sensing, Natural Resources Canada, Ottawa, Canada, 2002).

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Figures (3)

Fig. 1
Fig. 1

Representation of a forest stand in which a large gap is found in a forest canopy in which the foliage is otherwise randomly distributed.

Fig. 2
Fig. 2

Relative LAI decrease between the uncorrected and the corrected clumping index derivations as a function of the uncorrected clumping index for different gap fractions.

Fig. 3
Fig. 3

Accumulated gap fraction from two red pine plantations in which the second plantation has half the number of trees of the first plantation.

Tables (1)

Tables Icon

Table 1 Information about the Two Stands and the Parameters Used to Compare the Two Clumping Index Retrieval Methodsa

Equations (11)

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Pcθ=exp-GθΩEθL/cosθ,
ΩEθ=LeθL=lnPcθlnPRθ,
Fλ, θ=1+LpθλWpθ×exp-Lpθ1+λ/Wpθ,
ΩEθ=lnFm0, θlnFmr0, θ1+Fm0, θ-Fmr0, θ.
L=L1x1+L2x2x1+x2=L1x1x1+x2.
Fm0, θ=PCθ=P1θx1+x2x2+x1.
Leθ=-cosθGθlnFm0, θ.
L1=-cosθGθlnP1θ=-cosθGθlnFmr0, θ.
ΩEθ=LeθL=lnFm0, θlnFmr0, θ1+x2x1.
x2x1=Fm0, θ-Fmr0, θ1-Fm0, θ.
ΩEθ=lnFm0, θlnFmr0, θ1+Fm0, θ-Fmr0, θ1-Fm0, θ.

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