USE OF HEMISPHERICAL PHOTOGRAPHS IN FOREST ECOLOGY - MEASUREMENT OF GAP SIZE AND RADIATION TOTALS IN A BORNEAN TROPICAL RAIN-FOREST

Study of forest dynamics commonly requires measurement of canopy gap s ize. Hemispherical photographs can be analysed to provide various meas ures whereby gaps can be ranked in order of size. For ten artificial g aps in a Bornean tropical rain forest these measures were better corre lated with gap microclimate than gap area measured physically on the g round. All these measures are however relative. For detailed (e.g. eco physiological) studies the greater detail provided by absolute measure s 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 essent ial. Computed and measured PAR are compared for the test gaps. Both ha ve inherent limits which means that below c. 15% canopy openness, diff erences in PAR between gaps cannot be assessed accurately.