GROWTH AND YIELD OF A TROPICAL RAIN-FOREST IN THE BRAZILIAN AMAZON 13YEARS AFTER LOGGING

Successive inventories of a silvicultural experiment in terra firme ra in forest within the Tapajos National Forest in the Brazilian Amazon a re examined to provide guidelines for operational forest management on a sustainable basis. The experiment was logged in 1979 without additi onal silvicultural treatment, but included protection from further log ging and encroachment ('log and leave'). Thirty-six permanent plots es tablished in 1981 were remeasured in 1987 and 1992. Logging changed th e canopy structure and altered the composition of the stand, reducing the number of shade tolerant species and stimulating light demanding s pecies. There was a net increase in stem number and stand basal area d uring the 11 year observation period, and this trend also holds for mo st of the individual species. The stand basal area 13 years after logg ing was about 75% of that in a comparable unlogged forest. Logging sti mulated growth, but this effect was short-lived, lasting only about 3 years, and current growth rates are similar to those in the unlogged f orest. Between the first and second remeasures, average diameter incre ment decreased from 0.4 to 0.2 cm year-1, mortality remained relativel y constant at 2.5% year-1, while recruitment (at 5 cm diameter at brea st height) decreased from 5 to 2%. Total volume production declined fr om approximately 6 to 4 m3 ha-1 year-1, while commercial production re mained about 0.8 m3 ha-1 year-1. New commercial species increased the commercial volume in 1992 from 18 to 54 m3 ha-1, and the increment to 1.8 m3 ha-1 year-1. Results from this experiment provide the first qua ntitative information for management planning in the Tapajos Forest, a nd may guide the choice of cutting cycle and annual allowable cut. Sil vicultural treatment to stimulate growth rates in forest areas zoned f or timber production should be considered as a viable management optio n. Extrapolations of these results to an anticipated 30-35 year cuttin g cycle must be interpreted with caution. Ongoing remeasurement and an alysis of these and other plots over the next 30 years or more are nec essary to provide a stronger basis for management inferences.