| Changes in vegetation structure and species composition were analyzed in secondary forests, following swidden agriculture, in a semi-deciduous forest of Bolivian lowlands. Twenty-eight fallows, stratified by four successional stages (early = 1--5 yr, intermediate = 6--10 yr, advanced = 12--20 yr and older = 22--36 yr), and ten stands of mature forests were sampled. The overstory (plants ≥ 5 cm dbh) was sampled using a plot 20 x 50 m and the understory (plant < 5 cm) in three nested subplots 2 x 5 m. Semi-structured interviews provided information on fallow management. Canopy height, basal area and liana density of the overstory increased with stand age. Fifty-percent of stems occurred in the smallest size category. Herbs and tree saplings were abundant in the early stage. A total of 280 plant species, 226 in the understory and 157 in the overstory, belonging to 75 families were recorded. Early stage had the lowest species richness and diversity for the overstory, but the highest diversity for the understory. Species composition and abundance differentiated mature forests and early successional stage from other stages according to the Bray-Curtis ordination. Species had individualistic responses within the temporal gradient. A total of 123 species were useful species. Edible, medicinal and construction plants were most abundant for both over- and understory. Most Gwarayo preferred mature forests for making new swidden whereas a minority preferred older fallows; they considered fallow valuable for growing some crops, preparing new swidden, providing useful species and regenerating timber species. |
