Evaluation of hemispherical photography for determining plant area index and geometry of a forest stand

Chen, J.M.; Black, T. Andrew; Adams, Russell

doi:10.1016/0168-1923(91)90108-3

Cited by 271 publications

(140 citation statements)

References 8 publications

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“…Dans le cas très fréquent d'une distribution planophile du feuillage, l'erreur commise par l'omission arbitraire d'un ou plusieurs anneaux est globalement compensée par la sous-estimation d'indice foliaire due à l'utilisation du modèle aléa-toire. Nous discutons des conséquences du mode d'exploitation des données, et [8,18,20].…”

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Validity of leaf areas and angles estimated in a beech forest from analysis of gap frequencies, using hemispherical photographs and a plant canopy analyzer

Planchais

Pontailler

1999

Ann. For. Sci.

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-Using both a Li-Cor Plant Canopy Analyzer (PCA) and the hemispherical photographs technique, we measured the gap fraction in two young beech pole stands of known leaf tip angle distribution. The average contact number at various zenith angles (K(&thetas;) function) was determined and leaf area index was calculated using the method proposed previously. The following cases were examined: 1) data from PCA using five, four or three rings, 2) data from hemispherical photographs, arranged in rings, and divided into azimuth sectors (90, 45 and 22.5°) or averaged over azimuth (360°). These results were compared with a semi-direct estimation of the leaf area index derived from allometric relationships established at tree level. We also compared the G(&thetas;) functions calculated using direct measurements of the leaf tip angle distribution with those deduced from transmittance data. The two indirect techniques gave the same estimation of the gap fraction at all zenith angles. When data were processed using the random model (averaged over azimuth), the PCA and photographs provided the same values of leaf area index, these values being considerably lower than those from allometric relationships (-25 %). When data from hemispherical photographs were divided into narrow azimuth sectors (22.5°), assuming a quasi-random model, the estimate of leaf area index was improved, but remained about 10 % below the allometric estimates. Leaf area index estimated using the random model was found to be 75 % of that estimated using allometric relationships. It is shown that the underestimation of the leaf area index observed considering all five rings on the PCA is due to an inappropriate use of the random model. It is also shown that the increase in leaf area index that was observed when neglecting one or two rings (PCA)

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Validity of leaf areas and angles estimated in a beech forest from analysis of gap frequencies, using hemispherical photographs and a plant canopy analyzer

Planchais

Pontailler

1999

Ann. For. Sci.

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“…Correct exposure maximized plant/sky contrast while retaining foliar resolution. Using software developed by Chen et al (1991), the digital scans were subjected to algorithms which derived effective leaf area index (Le) 1 and sky view factor (SVF) (Norman andCampbell 1989, Chen et al 1991) differences between the SVF and Le values of the underexposed and correctly exposed, and the overexposed and correctly exposed photos were averaged to establish Le and SVF correction factors. From each of the remaining sets of photos, the photo nearest the correct exposure (i.e.…”

Section: Operative Temperaturesmentioning

confidence: 99%

Forest cover selection and activity of cow moose in summer

Demarchi¹,

Bunnell²

1995

Acta Theriol.

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Mike W. Demarchi and Fred L. Bunnell 1995. Forest cover selection and activity of cow moose in summer. Acta Theriologica 40: 23-36.Although thermal cover receives attention from managers, variations in data regarding its use by ungulates hinders development of effective cover guidelines. We examined patterns of habitat selection and activity of radio-collared cow moose Alces alces Linnaeus, 1758 to determine if these 2 parameters were influenced by ambient thermal environment. Cow moose used sites with relatively denser forest canopies when conditions of heat stress existed in open areas. Use of open areas did not change with ambient temperature; some sites classed as open on forest cover maps, however, had willow canopies capable of providing thermal cover. An increase in the use of open sites from 11.00 to 24.00 hr corresponded to a simultaneous decrease in the likelihood of thermal stress in such areas; predator-avoidance was deemed unlikely to explain observed behaviour. Moose decreased activity and distance traveled between successive locations during hot periods. Summer thermal cover is a selected, manageable component of moose habitat in southern British

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“…The HPA Software program [31] was used to calculate the PAI by determining the amount of vegetation, wood presence and leaf angle position in each hemispherical photograph. Since PAI is affected by sunlight angle, hemispherical photos were taken early in the morning and late in the afternoon to avoid the direct sunlight effect at the solar zenith [32]. Lastly, canopy height (CH) was measured by taking the average of the three tallest trees' heights inside each radial plot using a hand-held Blueskysea 600 M waterproof laser rangefinder.…”

Section: Forest Biophysical Propertiesmentioning

confidence: 99%

Lianas Abundance is Positively Related with the Avian Acoustic Community in Tropical Dry Forests

Hilje

Stack

Sánchez‐Azofeifa

2017

Forests

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Dry forests are important sources of biodiversity where lianas are highly abundant given their ability to grow during times of drought and as a result of secondary growth processes. Lianas provide food and shelter for fauna such as birds, but there are no studies assessing the influence of liana abundance on birds in dry forests. Here we evaluate the influence of liana abundance on the avian acoustic community in the dry forests of Costa Rica at Santa Rosa National Park. We selected forest sites with different levels of liana abundance and set up automated sound recorders for data collection, analysis and estimation of the avian acoustic community. When the number of lianas increases, the avian acoustic community becomes more complex. Lianas could provide important direct and indirect resources for birds such as structure for shelter, protection, nesting and roosting, and food. The positive relationship that lianas have with birds is particularly important in dry forests where lianas are becoming highly abundant due to the level of forest disturbance and climate change, especially for some bird species that are restricted to this ecosystem. By validating the number of bird species detected in the recordings with the acoustic complexity index, we found that a higher acoustic complexity means higher species richness.

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Evaluation of hemispherical photography for determining plant area index and geometry of a forest stand

Cited by 271 publications

References 8 publications

Validity of leaf areas and angles estimated in a beech forest from analysis of gap frequencies, using hemispherical photographs and a plant canopy analyzer

Validity of leaf areas and angles estimated in a beech forest from analysis of gap frequencies, using hemispherical photographs and a plant canopy analyzer

Forest cover selection and activity of cow moose in summer

Lianas Abundance is Positively Related with the Avian Acoustic Community in Tropical Dry Forests

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