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Geophysical Monograph Series

 

Keywords

  • Rain forest ecology—Amazon River Region
  • Biosphere—Research—Amazon River Region
  • Climatic changes—Amazon River Region
  • Amazon River Region—Climate

Article

GEOPHYSICAL MONOGRAPH SERIES, VOL. 186, PP. 299-309, 2009

Nutrient limitations to secondary forest regrowth

Eric A. Davidson

Woods Hole Research Center, Falmouth, Massachusetts, USA


Luiz A. Martinelli

CENA, University of São Paulo, Piracicaba, Brazil


The old, highly weathered soils of the lowland forest within the Amazon Basin generally exhibit conservative P cycles and leaky N cycles. This generalization applies to mature forests, but accelerating land use change is altering Amazonian landscapes. About 16% of the original forest area has been cleared, and about 160,000 km2 is in secondary forest cover. Secondary forests are common in agricultural regions, but few persist in one place for much more than 5 years. The nutrients within ephemeral forests are important for smallholder traditional slash-and-burn agriculture and in alternatives developed to conserve nutrients. Forest clearing causes an initial loss of nutrients through timber harvesting, fire, erosion, soil gaseous emissions, and hydrologic leaching, with N losses exceeding P losses. In contrast, the Ca, Mg, and K present in woody biomass are largely conserved as ash following fire, redistributing these nutrients to the soil. After the initial postclearing pulse of nutrient availability, rates of N cycling and loss consistently decline as cattle pastures age. Fertilization experiments have demonstrated that growth of young forests in abandoned agricultural land is nutrient limited. Several N cycling indicators in a secondary forest chronosequence study also demonstrated a conservative N cycle in young forests. Variable N limitation in young forests helps explain a negative relationship observed between the burn frequency during previous agricultural phases and the rate of forest regrowth. Recuperation of the N cycle gradually occurs during decades of secondary forest succession, such that mature lowland forests eventually recover abundant N relative to a conservative P cycle.

Citation: Davidson, E. A., and L. A. Martinelli (2009), Nutrient limitations to secondary forest regrowth, in Amazonia and Global Change, Geophys. Monogr. Ser., vol. 186, edited by M. Keller et al., pp. 299–309, AGU, Washington, D. C., doi:10.1029/2008GM000732.

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