ENHANCING NUTRIENT RETENTION IN TROPICAL TREE PLANTATIONS: NO SHORT CUTS

Authors

  • Seth W. Bigelow,

    1. Institute of Ecosystem Studies, Box AB, Millbrook, New York 12545 USA
    2. Department of Botany, University of Florida, Gainesville, Florida 32611-8526 USA
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    • Present address: USDA-FS Sierra Nevada Research Center, Pacific Southwest Research Station, 2121 2nd Street, Suite A101, Davis, California 95616 USA. E-mail: sbigelow@fs.fed.us

  • John J. Ewel,

    1. Department of Botany, University of Florida, Gainesville, Florida 32611-8526 USA
    2. USDA-FS Institute of Pacific Islands Forestry, Pacific Southwest Research Station, 1151 Punchbowl Street, Suite 323, Honolulu, Hawaii 96813 USA
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  • Jeremy P. Haggar

    1. Department of Botany, University of Florida, Gainesville, Florida 32611-8526 USA
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    • Present address: CATIE, Apartado P-116, Managua, Nicaragua


  • Corresponding Editor: A. R. Townsend

Abstract

In the humid tropics large quantities of nutrients can be rapidly leached when the soil is unprotected by actively growing vegetation. We established experimental plantations of three indigenous tree species on a fertile Andisol in Costa Rica and managed them under 1- or 4-year cutting cycles with uncut stands as controls. Our goals were to test whether nutrient leaching was greatest under a regime of frequent disturbances that returned modest amounts of biomass to the soil surface (cutting and replanting on a 1-yr cycle) or less frequent disturbances that returned significantly greater amounts of plant tissues to the soil (cutting and replanting on a 4-yr cycle), and to compare those cutting cycles with nutrient leaching from uncut stands. Leaching of NO3 (over 9 yr), Ca2+, Mg2+, and K+ (over 4 yr) from upper soil horizons was monitored. Water balance was determined by linking Penman-Monteith evaporation with changes in soil water storage modeled from soil physical parameters. Drainage water for solute measurement was sampled from porous ceramic cups at 1.1 m depth in the soil.

Disturbance frequency proved to be an important determinant of NO3 leaching. Average long-term NO3 leaching losses from stands on a 1-yr cutting cycle were extraordinarily large: 442 mmolc·m−2·yr−1 (62 kg·ha−1·yr−1 of N), compared to 187 mmolc·m−2·yr−1 under a 4-yr cutting cycle and 71 mmolc·m−2·yr−1 from uncut stands. Elevated NO3 leaching was primarily due to increased concentration in the soil solution (rather than increased water drainage), because cutting usually resulted in a reduction of <10% in evapotranspiration. Resilience of stands decreased with continued disturbance; under a 4-yr cutting cycle, stands tended to take longer to return to the low levels of NO3 leaching characteristic of undisturbed stands with each episode of cutting and replanting, while NO3 losses from annually cut stands became increasingly variable over time. Due to high concentrations of soil Ca at the site, the stands proved resistant to treatment-induced losses of base cations: no increases in Ca2+ or Mg2+ leaching accompanied elevated NO3 leaching, although K+ leaching did increase under the 1-yr cutting cycle. Because of the potential for massive, sustained NO3 losses, development of land use systems for these soils should focus on minimizing frequency of disturbance.

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