A theoretical analysis of the frequency of gaps in plant stands

Nilson, Tiit

doi:10.1016/0002-1571(71)90092-6

Cited by 834 publications

(411 citation statements)

References 6 publications

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“…As it is involved in the computation of T(θ), and where gap fraction is underestimated (e.g. Nilson, 1971;Ross, 1981;Oker-Blom and Kellomaki, 1983;Baldocchi et al, 1985;Andrieu and Sinoquet, 1993;Chen et al, 1994;van Gardingen et al, 1999). Such underestimation may be significant in the highly clumped canopies of shortgrass ecosystems.…”

Section: Daily Integrated Interception and Absorptionmentioning

confidence: 99%

“…Such underestimation may be significant in the highly clumped canopies of shortgrass ecosystems. For canopies with non-random leaf dispersion, Nilson (1971) has proposed a statistical model based on the theory of Markov processes. The model allows the computation of the extinction coefficient of the heterogeneous canopy by multiplying k(θ) by a coefficient 8.…”

Section: Daily Integrated Interception and Absorptionmentioning

confidence: 99%

“…However, this assumption does not hold for canopies with clumped leaf dispersions, which are known to have lower extinction coefficients than those with randomly dispersed leaves (e.g. Nilson, 1971;Lemeur and Blad, 1974;Baldocchi and Collineau, 1994). For such canopies, models based on negative binomial probability functions or on the theory of Markov processes have been proposed (Nilson, 1971).…”

Section: Introductionmentioning

confidence: 99%

“…Nilson, 1971;Lemeur and Blad, 1974;Baldocchi and Collineau, 1994). For such canopies, models based on negative binomial probability functions or on the theory of Markov processes have been proposed (Nilson, 1971). These models introduce a clumping factor that is unknown and must be determined.…”

Section: Introductionmentioning

confidence: 99%

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PAR extinction in shortgrass ecosystems: effects of clumping, sky conditions and soil albedo

Nouvellon

Bégué

Moran

et al. 2000

Agricultural and Forest Meteorology

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The amount of photosynthetically active radiation (PAR) absorbed by a canopy (APAR) is an important driving variable for vegetation processes such as photosynthesis. PAR extinction in clumped canopies of shortgrass ecosystems is the focus of this paper.Directional gap fractions estimated at peak biomass on several Mexican shortgrass ecosystems with a hemispherical radiation sensor (Li-Cor LAI-2000) were higher than those predicted by a Poisson model assuming a random leaf dispersion. LAI-2000-estimated gap fractions, together with independent estimations of plant area index (PAI), and leaf and stem angle distribution (LSAD) were used for estimating the angular course of a leaf dispersion parameter 8(2). Radiation extinction coefficients simulated for all solar zenith angles using Markov chain processes and estimated 8(2) were subsequently incorporated in a simple radiative transfer model for estimating the efficiencies of instantaneous and daily integrated PAR interception and absorption and for studying the effects of clumping, sky conditions and soil albedo on PAR absorption.For clear sky condition, instantaneous PAR absorption showed marked directional effects, therefore indicating that using a constant extinction coefficient in canopy photosynthesis models working at hourly time step would be inaccurate. The effects of clumping, sky conditions and soil albedo were all found to be significant for low PAI, and decreased with higher PAI. As shortgrass ecosystems are characterized by low PAI, neglecting these effects would give inaccurate estimations of PAR absorption.Daily PAR absorption was found to be significantly higher than PAR interception for low PAI, especially when soil albedo was high, and lower than PAR interception for high PAI.These results indicate that in canopy photosynthesis models where APAR is estimated 3 from simple exponential like relationships calibrated using PAR interception measurements, the PAR available for photosynthesis might be significantly underestimated in the first stages of the growth, and may be overestimated in the later stages of the growing season.

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Section: Daily Integrated Interception and Absorptionmentioning

confidence: 99%

Section: Daily Integrated Interception and Absorptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

PAR extinction in shortgrass ecosystems: effects of clumping, sky conditions and soil albedo

Nouvellon

Bégué

Moran

et al. 2000

Agricultural and Forest Meteorology

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“…This approach, using the annual shoot as the basic structural unit, has long been applied in light interception models (Cescatti, 1998;Nilson, Anniste, Lang, & Praks, 1999;Oker-Blom & Kellomäki, 1983;Stenberg, Smolander, & Kellomäki, 1993) and LAI measurement techniques (Chen, Rich, Gower, Norman, & Plummer, 1997;Stenberg, 1996). A key parameter entering these models is the shoot silhouette to total area ratio (STAR) (Oker-Blom & Smolander, 1988), which is conceptually analogous to the G-function, or the mean projection of unit foliage area, defined for flat leaves (Nilson, 1971). These models have been designed specifically for the estimation of photosynthesis, and the spectral properties of shoots have not been considered important because the scattering of photosynthetically active radiation (PAR) by conifer needles is known to be very small (Daughtry, Ranson, & Biehl, 1989).…”

Section: Introductionmentioning

confidence: 99%

A method to account for shoot scale clumping in coniferous canopy reflectance models

Smolander¹,

Stenberg²

2003

Remote Sensing of Environment

126

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The three-dimensional structure of a coniferous shoot gives rise to multiple scattering of light between the needles of the shoot, causing the shoot spectral reflectance to differ from that of a flat leaf. Forest reflectance models based on the radiative transfer equation handle shoot level clumping by correcting the radiation attenuation coefficient with a clumping index. The clumping index causes a reduction in the interception of radiation by the canopy at a fixed leaf area index (LAI). In this study, we show how within-shoot multiple scattering is related to shoot scale clumping and derive a similar, but wavelength dependent, correction to the scattering coefficient. The results provide a method for integrating shoot structure into current radiative transfer equation based forest reflectance models. The method was applied to explore the effect of shoot scale clumping on canopy spectral reflectance using simple model canopies with a homogeneous higher level structure. The clumping of needles into shoots caused a wavelength dependent reduction in canopy reflectance, as compared to that of a leaf canopy with similar interception. This is proposed to be one reason why coniferous and broad-leaved canopies occupy different regions in the spectral space and exhibit different dependency of spectral vegetation indices on LAI. D

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A model to consider the spatial variability of rainfall partitioning within deciduous canopy. I. Model description

Davie

Durocher

1997

Hydrol. Process.

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A theoretical analysis of the frequency of gaps in plant stands

Cited by 834 publications

References 6 publications

PAR extinction in shortgrass ecosystems: effects of clumping, sky conditions and soil albedo

PAR extinction in shortgrass ecosystems: effects of clumping, sky conditions and soil albedo

A method to account for shoot scale clumping in coniferous canopy reflectance models

A model to consider the spatial variability of rainfall partitioning within deciduous canopy. I. Model description

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