DEFINING CANOPY GAPS IN A TROPICAL RAIN-FOREST - EFFECTS ON GAP SIZE AND TURNOVER TIME

The effects of different gap definitions on gap size and concomitant c hanges in turnover time were investigated. In a tropical rain forest i n French Guiana, 18 canopy gaps were measured using 3 different gap de finitions. Gap size was significantly affected by gap definitions. Str ong positive correlations were found between gap sizes according to th e different definitions. Based on one of these linear relations, effec ts of gap definitions on turnover time calculations were evaluated. It was found that in the studied forest, the turnover time at the forest floor is much lower (some 4 to 8 times) than the turnover time at the forest canopy. It is concluded that it is doubtful whether it is vali d to compare gap- and turnover time studies which have been carried ou t so far. To be able to make valid comparisons between different studi es on forest dynamics in the future, it is important to reach a consen sus on the choice and application of one or more clearly defined gap d efinitions.