Increasing the precision of canopy closure estimates from hemispherical photography: Blue channel analysis and under-exposure

Brusa, Anthony; Bunker, Daniel E.

doi:10.1016/j.agrformet.2014.05.001

Cited by 35 publications

(22 citation statements)

References 36 publications

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“…Images were recorded in 2048 × 1536 pixels, the highest resolution setting possible on the camera. Maximum resolution was used because image analysis is performed based on pixel-by-pixel methods, and image resolution is a major factor reflecting the quality of hemispherical photographs (Jelaska et al 2006;Brusa and Bunker 2014). We took the hemispherical photographs on uniformly overcast days between July and August from 2005 to 2011.…”

Section: Gap Monitoringmentioning

confidence: 99%

Gap closure process by lateral extension growth of canopy trees and its effect on woody species regeneration in a temperate secondary forest, Northeast China

Lu¹,

Zhu²,

Sun³

et al. 2015

Silva Fenn.

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G. (2015). Gap closure process by lateral extension growth of canopy trees and its effect on woody species regeneration in a temperate secondary forest, Northeast China. Silva Fennica vol. 49 no. 5 article id 1310. 17 p. Highlights• Gap closure process by lateral extension growth can be described by quadratic functions.• Large gaps (514-621 m 2 ) had higher closure rates but lower closure percentages compared with middle (174-321 m 2 ) and small gaps (68-125 m 2 ).• Gaps promoted woody species regeneration in early stage.• Large and middle gaps would provide opportunities for filling regeneration, but regeneration in small gaps may eventually fail. AbstractGap formation and its effects on regeneration have been reported as being important in forest development, but seldom studies concentrated on the gap closure process by lateral extension growth of canopy trees surrounding gaps. We monitored the closure process of 12 artificial gaps for 7 years with three size classes: small (from 68 m 2 to 125 m 2 ), middle (from 174 m 2 to 321 m 2 ), and large (from 514 m 2 to 621 m 2 ); and investigated the regeneration twice in a temperate secondary forest, Northeast China. The closure process can be described through quadratic functions, which showed the closure rates slowed down with gap ages. Large gaps had a higher closure rate (39 m 2 a -1 ) than middle gaps (25 m 2 a -1 ) and small gaps (11 m 2 a -1 ). According to the quadratic equations, the lateral growth could last 11, 13 and 16 years for small, middle and large gaps with a remaining size of 12, 69 and 223 m 2 , respectively. As expected, regeneration exhibited the highest seedling density and volume in large gaps. There was no significant difference in regeneration density between middle gaps, small gaps and forest understory in the final investigation; but the volume of regenerated woody species increased significantly from small gaps to large gaps compared with forest understory. These results may provide references on the choice of appropriate gap sizes to promote the regeneration in temperate secondary forests.

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Section: Gap Monitoringmentioning

confidence: 99%

Gap closure process by lateral extension growth of canopy trees and its effect on woody species regeneration in a temperate secondary forest, Northeast China

Lu¹,

Zhu²,

Sun³

et al. 2015

Silva Fenn.

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“…1b). We extracted the blue channel, because it is less influenced by exposure changes compared to the red and green channel (Brusa and Bunker, 2014) and has the best contrast between sky and canopy (Frazer et al, 2001;Jonckheere et al, 2005).…”

Section: Acquisition Of Raw Imagementioning

confidence: 99%

Correction for light scattering combined with sub-pixel classification improves estimation of gap fraction from digital cover photography

Hwang

Ryu

Kimm

et al. 2016

Agricultural and Forest Meteorology

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“…Each method has advantages and disadvantages for estimating the various components of light availability and canopy structure. Some of them are very costly (e.g., LIDAR, LAI2000), others although cheap (e.g., densitometers, photosensitive diazo paper) are strongly subjective (Brusa & Bunker 2014). Hemispherical photography is an option of intermediate cost that has several advantages such as a spatial discrimination, acquisition of foliage angular distribution, and gap fractions at different zenith and azimuthal angles.…”

Section: Hemispherical Photographsmentioning

confidence: 99%

“…The principle of this method is that a fish eye lens captures an image that spans a 180°a rc, and when pointed vertically can capture all possible angles of incoming light (Brusa & Bunker 2014). Other popular methods include the LAI-2000 ® (plant canopy analyzer -Li-cor, Lincoln, NE, USA), spherical densitometers, AccuPAR ® ceptometer (Decagon Devices, Pullman, WA, USA), LIDAR, TRAC (Tracing radiation and architecture of canopies), and photosensitive diazo paper (Jonckheere et al 2004, Chianucci & Cutini 2012, Brusa & Bunker 2014. There are several methods to determine light and canopy properties under a set of environmental conditions and ecosystems.…”

Section: Hemispherical Photographsmentioning

confidence: 99%

Distribution of juveniles of tree species along a canopy closure gradient in a tropical cloud forest of the Venezuelan Andes

Quevedo-Rojas¹,

Jerez-Rico²,

Kratzer³

et al. 2016

iForest

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Cloud forests represent a minor portion of the world forests, though outstanding in terms of biodiversity, endemisms, and environmental services provided. Understanding the factors that drive the regeneration and species composition of these forests, and in particular how light availability affects the patterns of juvenile tree distribution in the understory, is critical for conservation and restoration programs. In this study, we determined the range-size and overlap of the abundance distribution of juveniles for 20 tree species in an Andean tropical cloud forest in Venezuela along a gradient of percentage canopy openness (%CO) used as a surrogate of light availability. The observed distribution of %CO was then compared with a bounded null model of community structure in order to test light partitioning as a driver of tree species' coexistence. We measured %CO using hemispherical photography and the abundance and size of juvenile trees in 280 plots of 1-m radius spread over a 32 ha forest area. The distribution of sites was skewed towards the lower end of the %CO gradient (0.5 to 12.8%), while species abundance sharply diminished at both ends of the gradient. Nevertheless, 15 out of 20 species had a non-random distribution in relation to %CO, with many species concentrated near the lower side of the gradient. The observed pattern of species' overlap was within the 95% confidence limits for the average overlap expected under the bounded null model. These patterns indicate that low canopy openness is the rule in this forest, in spite of the scattered tree-fall gaps, and suggest that light partitioning does not determine the tree community structure at the juvenile stage. High redundancy in light requirements among juveniles of tree species may have a positive effect on species coexistence in cloud forests, thus maintaining a high species diversity. However, other factors such as recruitment limitation and differential growth/carbon-gain among species at the juvenile stage along the light gradient could contribute to the high diversity of these ecosystems.

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Increasing the precision of canopy closure estimates from hemispherical photography: Blue channel analysis and under-exposure

Cited by 35 publications

References 36 publications

Gap closure process by lateral extension growth of canopy trees and its effect on woody species regeneration in a temperate secondary forest, Northeast China

Gap closure process by lateral extension growth of canopy trees and its effect on woody species regeneration in a temperate secondary forest, Northeast China

Correction for light scattering combined with sub-pixel classification improves estimation of gap fraction from digital cover photography

Distribution of juveniles of tree species along a canopy closure gradient in a tropical cloud forest of the Venezuelan Andes

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