BIOMASS OF PRIMARY AND SECONDARY VEGETATION IN RONDONIA, WESTERN BRAZILIAN AMAZON

Biomass estimates of primary and different ages of secondary vegetatio n are reported for a tropical forest region in Rondonia, Western Brazi lian Amazon. The estimates are based on published allometric equations , and on vegetation composition and allometric data collected in areas of primary forest and secondary vegetation of ages 2, 3, 5, 9, 11, 16 and 18 years. Primary forest biomass estimates varied from 290 to 495 t ha(-1). Secondary vegetation biomass estimates accounted for 40-60% of the primary forest biomass after 18 years of abandonment. Secondar y growth rates in lightly used areas are estimated to have varied from 6.6 to 8.7 t ha(-1) y(-1) between the third and the eighteenth years after abandonment. CO2 sequestration by regrowing vegetation is discus sed for two scenarios of land abandonment.