Use of hemispherical photographs in forest ecology: measurement of gap size and radiation totals in a Bornean tropical rain forest

Abstract

Study of forest dynamics commonly requires measurement of canopy gap size. Hemispherical photographs can be analysed to provide various measures whereby gaps can be ranked in order of size. For ten artificial gaps in a Bornean tropical rain forest these measures were better correlated with gap microclimate than gap area measured physically on the ground. All these measures are however relative. For detailed (e.g. ecophysiological) studies the greater detail provided by absolute measures of photosynthetically active radiation (PAR) are required. Long term PAR values can be computed from hemiphots so long as measurements in the open nearby are available. Correction for cloudy weather is essential. Computed and measured PAR are compared for the test gaps. Both have inherent limits which means that below c. 15% canopy openness, differences in PAR between gaps cannot be assessed accurately.

Influence of environmental variables on the shrub and tree species distribution in two Semideciduous Forest sites in Viçosa, Minas Gerais, Brazil

“…Compared to other studies that have also used hemispheric photographs, the canopy openness values in the mature forest were similar to those obtained in other well preserved tropical forests with closed canopy, while the values of the initial forest were similar to those reported in natural gaps (Brown 1993, Whitmore et al 1993, Valverde and Silvertown 1997, Trichon et al 1998, Martins and Rodrigues 2002.…”

“…As canopy openness is considered a good indicator of light conditions in the forest (Brown 1993, Whitmore et al 1993, Trichon et al 1998, Martins and Rodrigues 2002, these differences between the two forest sites must determine the division of this resource by species of the different ecological groups (Silva Júnior et al 2004), contributing to the establishment of light requiring and shade tolerant species in the initial and mature forests, respectively.…”

Light environment under Rhododendron maximum thickets and estimated carbon gain of regenerating forest tree seedlings

“…Quantum sensors and hemispherical photographs allow comparisons of daily light patterns in multiple sites and dates (Rich 1990;Mitchell and Whitmore 1993;Jennings et al 1999). Light factors derived from hemispherical photographs are correlated with seedling and sapling growth in the tropical (e.g., Turner 1990;Clark et al 1993;Oberbauer et al 1993;Whitmore et al 1993), temperate and boreal (e.g., Easter and Spies 1994;Constabel and Lieffers 1996) forests. And in some cases, differences in height and diameter growth of plants among sites were associated with light factors derived from hemispherical photographs (i.e., direct, diffuse or total; Anderson 1964;Clark et al 1993).…”

Gap Area and Tree Community Regeneration in a Tropical Semideciduous Forest

“…The function "gap area" is available as a tool of this software (Steege 1997). This kind of canopy gap area estimation had already been disseminated by other authors (Whitmore, www.intechopen.com 1990; Whitmore et al, 1993;van der Meer & Bongers, 1996;Eysenrode et al, 1998;Martins et al, 2002) and provides an accurate estimation of canopy opening as well as the occupied area by gaps in different vegetation types.…”

“…The camera was mounted on a leveled tripod 1.3 m above ground (Nascimento et al, 2007), with the fish eye focus setting into infinity, as previously described by Mitchell & Whitmore (1993). The photographs were taken in full-color tones, always between 8-10 a.m., and 2-6 p.m., as recommended by Whitmore et al, (1993). Afterwards, we turned all the pictures taken into images in grey tones (8 bits) and reduced the resolution to 968 x 648 pixels.…”