Togging changed the canopy structure and altered the composition of the stand, reducing the number of shade
tolerant species and stimulating light demanding species. There was a net increase in stem number and stand basal
area during the 11 year observation period, and this trend also holds for most of the individual species. The stand
basal area 13 years after logging was about 75% of that in a comparable unlogged forest. Logging stimulated growth,
but this effect was short-lived, lasting only about 3 years, and current growth rates are similar to those in the
unlogged forest.
Between the first and second remeasures, average diameter increment decreased from 0.4 to 0.2 cm year-‘,
mortality remained relatively constant at 2.5Oh year-‘, while recruitment (at 5 cm diameter at breast height)
decreased from 5 to 2W. Total volume production declined from approximately 6 to 4 m3 ha-’ year-‘, while
commercial production remained about 0.8 m3 ha-’ year-‘. New commercial species increased the commercial
volume in 1992 from 18 to 54 m3 ha-‘, and the increment to 1.8 m3 ha-’ year-‘.
Results from this experiment provide the first quantitative information for management planning in the Tapajb
Forest, and may guide the choice of cutting cycle and annual allowable cut. Silvicultural treatment to stimulate
growth rates in forest areas zoned for timber production should be considered as a viable management option.
Extrapolations of these results to an anticipated 30-35 year cutting cycle must be interpreted with caution. Ongoing
remeasurement and analysis of these and other plots over the next 30 years or more are necessary to provide
a stronger basis for management inferences.