Methods for estimating understory light conditions using crown projection maps and topographic data

Abstract

Four types of indices of canopy characteristics were compared to estimate understory light conditions using crown projection maps and topographic data. Crown area (CA) was formulated from the crowns in a focal sub-block (20 m·20 m). Canopy shade index (CSI) was formulated from the crowns in a focal sub-block and the surrounding sub-blocks with topographic effect. Site shade index (SSI) incorporated the shade of the slopes into CSI and represented the total physical closure of the site. Site light index (SLI) incorporated the azimuth of the site into SSI and evaluated the light condition of the understory. We tested the methods using the data on steep old-growth Cryptomeria japonica forests on Yakushima Island and the three-dimensional canopy structures of the forests were digitized on a geographic information system. The results were validated by the basic indices obtained by hemispherical photographs: canopy openness (CO) and gap light index (GLI). The three-dimensional structure of the surrounding canopies and topography had significant effects on the understory light conditions. CA had no significant correlation with CO, whereas CSI and SSI had significant negative correlations with CO. Although SLI had the highest negative correlation with GLI (R 2 =0.69), CSI had practical utility in the estimation of GLI (R 2 = 0.65). Our method is applicable to past crown projection maps that have been recorded at many forest research sites, thus making it possible to reconstruct past understory light conditions and to compare them with present conditions.

Protective capacity of mangroves during tropical storms: a case study from ‘Wilma’ and ‘Gamma’ in Belize

“…Hale 2003, Takashima et al 2006 and survivorship of equipment, we found a negative, but non-significant, relationship. A negative relationship suggests that increasing stand density, quantified in this case by the inverse of light penetration, may further mediate the degree of coastal protection that mangroves confer.…”

“…Differences in light penetration among intact areas have been used as a proxy for stand density and stand structure in a number of forest types (e.g. Hale 2003, Takashima et al 2006 and references therein), which allows us to examine the effects of stand structure on the loss rate of experimental equipment in the intact areas.…”

Response of recruitment to light availability across a tropical lowland rain forest community

“…The consistency of the derived light response between the two census intervals indicates that our light index contains information relevant to the species' performance. Interestingly, our light estimation procedure is similar to the index that best described gap light index obtained by hemispherical photographs in a temperate forest in Japan (Takashima, Kume & Yoshida 2006). The latter estimates also accounted for shading from topography, but we ignored this at BCI due to the relatively flat topography.…”

Methodology comparison for slope correction in canopy leaf area index estimation using hemispherical photography

“…Currently, digital hemispherical or fish-eye photography is becoming a common means for measuring LAI as well as studying canopy architecture and solar radiation in forests (Galhidy et al, 2006;Gendron et al, 2006;Jelaska et al, 2006;Jonckheere et al, 2006;Morsdorf et al, 2006;Wagner and Hagemeier, 2006;Domke et al, 2007). Hemispherical photographs have been widely used to measure canopy biophysical parameters (Rich, 1990;Chen and Black, 1991;Pellikka, 2001;Pellikka et al, 2000;Lovell et al, 2003), and to characterize daily and seasonal vegetation light environment (Capers and Chazdon, 2004;Gersonde et al, 2004;Tomita and Seiwa, 2004;Takashima et al, 2006). The recent advancement in digital cameras and image processing (WinSCANOPY, Regent Instruments, Ste-Foy, Quebec; Hemiview, Rich, 1990;Hemiphot, ter Steege, 1994;GLA, Frazer et al, 1997; CAN_EYE, http:// www.avignon.inra.fr/can_eye; DHP, Leblanc et al, 2005;CIMES, Walter, 2007) may have brought us a needed tool at an affordable rate to estimate biophysical parameters.…”