Leaf area index estimates obtained for clumped canopies using hemispherical photography

Gardingen, P.R. van; Jackson, Gail; Hernandez-Daumas, S; Russell, G.; Sharp, Linda

doi:10.1016/s0168-1923(99)00018-0

Cited by 147 publications

(87 citation statements)

References 39 publications

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“…Five hemispherical images were taken in each site in June 2017 to estimate the leaf area index (LAI) with a Sony NEX-7 24M DSLR camera (Regent Instruments, Québec, QC, Canada). The images were processed with the WinSCANOPY software (Regent Instruments, Québec, QC, Canada) using the average of the available logarithmic LAI methods that compensate for clumping [43]. For the seasonal LAI, a 20% increase during summer was considered due to new needle development [44].…”

Section: Water Balance Model Calculationsmentioning

confidence: 99%

Recent Drought-Induced Vitality Decline of Black Pine (Pinus nigra Arn.) in South-West Hungary—Is This Drought-Resistant Species under Threat by Climate Change?

Móricz

Garamszegi

Rasztovits

et al. 2018

Forests

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This paper analyses the recent recurring dieback and growth decline of Black pine (P. nigra Arn. var austriaca) in the Keszthely mountains of south-west Hungary, and their relations to water deficits due to droughts. These relations were studied in five stands with low soil water storage capacity for the period 1981-2016. The vitality was assessed using 60 tree-ring samples and changes in remotely sensed vegetation activity indices, i.e., the normalized difference vegetation index (NDVI) and the normalized difference infrared index (NDII). Water deficit was estimated by using meteorological drought indices such the standardized precipitation-evapotranspiration index (SPEI) and the forestry aridity index (FAI), as well as the relative extractable water (REW), calculated by the Brook90 hydrological model. Results revealed a strong dependency of annual tree ring width on the amount of water deficit as measured by all the above estimators, with the highest correlation shown by the summer REW. Droughts also showed a long-term superimposed effect on tree growth. NDII seemed to be more sensitive to drought conditions than NDVI. The robust dependency of tree growth on the summer water availability combined with the projected increasing aridity might lead to decreasing growth of Black pine in Hungary towards the end of the century. We thus argue that the suggestion by several papers that Black pine can be a possible substitute species in the Alpine and Mediterranean region in the future should be revisited.

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Section: Water Balance Model Calculationsmentioning

confidence: 99%

Recent Drought-Induced Vitality Decline of Black Pine (Pinus nigra Arn.) in South-West Hungary—Is This Drought-Resistant Species under Threat by Climate Change?

Móricz

Garamszegi

Rasztovits

et al. 2018

Forests

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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%

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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“…Some ceptometers measure transmittance at the zenith (0°), LAI-2000 used 5 rings (0-74°), and these authors maintain that the most satisfactory measurement of LAI using this LAI-2000 is obtained when the field view is restricted to the upper three rings (0-43°). Van Gardingen et al (1999) stated that alternative methods applying a uniform correction factor to conventional analysis may produce erroneous results when the scale of clumping is not uniform throughout the canopy. Basically, there are two ways (and possibly a third) to correct for clumping: (i) using the log averaging procedures proposed by Lang & Yuequin (1986) derived from gap fraction distribution (LX), which was also applied to hemispherical photography by Van Gardingen et al (1999); (ii) to remove large gaps from total gaps, the Chen & Cihlar's (CC -Chen & Cihlar 1995) method, which is a gap size distribution correction; (iii) to combine the two above approaches.…”

Section: Introductionmentioning

confidence: 99%

A simplified methodology for the correction of Leaf Area Index (LAI) measurements obtained by ceptometer with reference to Pinus Portuguese forests

Lopes¹,

Nunes²,

Walford³

et al. 2014

iForest

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Leaf area index estimates obtained for clumped canopies using hemispherical photography

Cited by 147 publications

References 39 publications

Recent Drought-Induced Vitality Decline of Black Pine (Pinus nigra Arn.) in South-West Hungary—Is This Drought-Resistant Species under Threat by Climate Change?

Recent Drought-Induced Vitality Decline of Black Pine (Pinus nigra Arn.) in South-West Hungary—Is This Drought-Resistant Species under Threat by Climate Change?

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

A simplified methodology for the correction of Leaf Area Index (LAI) measurements obtained by ceptometer with reference to Pinus Portuguese forests

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