Carbon and nutrient storage in primary and secondary forests in eastern Amazonia

We compared carbon and nutrient concentrations and stocks in aboveground ve getation and soils between secondary forests (10-, 20-, and 40-year-old sta nds subject to repeated cycles of slash-and-burn agriculture) and a primary forest fragment in the Bragantina region of Para, Brazil. We hypothesized that repeated agricultural use would result in lower nutrient concentration s and/or stocks in the plant tissue and soils of the secondary forest stand s relative to the primary forest fragment. Yet there were no significant di fferences in median foliar tissue concentrations of C, N, P, K, Ca, or Mg b etween the secondary forests and the primary forest. In woody tissue, the p rimary forest had a lower median Mg concentration (205 mug g(-1)) than all secondary forest plots (356-620 mug g(-1)) and a higher median N concentrat ion (0.3%) than the 40-year-old secondary forest (0.2%). Foliar nutrient st ocks were higher in the secondary forests than in the primary forest due to higher foliar biomass estimates for those plots. Aboveground woody nutrien t stocks were greatest in the primary forest with the exception of Mg. Soil concentrations of exchangeable Ca decreased with increasing stand age; soi l concentrations of exchangeable Mg were higher in all secondary plot soils than in the primary plot soil, Labile P stocks were greater in the primary forest soil than in all secondary forest soils. Soil labile P stocks were larger than aboveground P stocks in the 10- and 20-year-old secondary plots and the primary plot and approximately equal to aboveground stocks in the 40-year-old plot. Relative to other tropical and temperate locations, nutri ent capital at these sites is low in both the vegetation and the soil, but a century of shifting cultivation does not yet appear to have introduced so il nutrient limitations to forest regrowth. (C) 2001 Elsevier Science B.V. All rights reserved.