Long-Term Chronosequence of Forest Succession in the Upper Rio Negro of Colombia and Venezuela

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Abstract
(1) In the upper Rio Negro region of Colombia and Venezuela, a chronosequence of twenty-three stands ranging from recently abandoned fallows to mature forests in a tierra firme (unflooded) area was examined for species composition, structure and biomass following slash-and-burn agriculture. (2) Number of species increased during the early stages of succession, with stands twenty to forty years old having a species richness similar to that found in mature forests. (3) Basal area varied from 11 m2 ha-1 in a ten-year-old stand to 37 m2 ha-1 in a mature forest. (4) Allometric relationships between tree dimensions and tree weight were used to estimate biomass harvested in the field. (5) Dry weights are given for leaves, twigs, branches, stems and roots in successional and mature tierra firme forests. The biomass for each component for ten-year-old and mature forest stands, respectively, was 6.sbd.11 t ha-1 for leaves, 11.sbd.23 t ha-1 for twigs, 9.sbd.76 t ha-1 for branches, 18.sbd.145 t ha-1 for stems and 7.sbd.65 t ha-1 for roots. (6) Above-ground living biomass ranged from 44 t ha-1 for ten-year-old stands to 326 t ha-1 for mature forests. Dead biomass varied from 1 t ha-1 for twenty-year-old stands to 53 t ha-1 for a mature forest. (7) Above-ground living biomass increases linearly during the first forty years. No significant changes occur for the next forty years, because biomass accumulation is offset by the death of long-lived successional species. Approximately 190 years was the estimated time taken by a previously-cultivated site to reach mature forest basal area and biomass values.