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

Published online by Cambridge University Press:  10 July 2009

T. C. Whitmore
Affiliation:
Department of Plant Sciences, Oxford University, 0X1 3RB, UK
N. D. Brown
Affiliation:
Department of Plant Sciences, Oxford University, 0X1 3RB, UK
M. D. Swaine
Affiliation:
Department of Plant and Soil Science, Aberdeen University, AB9 2UD, UK
D. Kennedy
Affiliation:
Department of Plant and Soil Science, Aberdeen University, AB9 2UD, UK
C. I. Goodwin-Bailey
Affiliation:
Department of Plant Sciences, Oxford University, 0X1 3RB, UK
W.-K. Gong
Affiliation:
Department of Plant Sciences, Oxford University, 0X1 3RB, UK

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.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1993

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