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ND-02 Abstract

Biogeochemical Cycles in Degraded Lands

Claudio José Reis de Carvalho — Embrapa Amazônia Oriental (SA-PI)
Eric A. Davidson — WHRC - Woods Hole Research Center (US-PI)
Moacyr Bernardino Dias-Filho — Embrapa Amazonia Oriental (SA-PI)
Paulo Moutinho — IPAM - Instituto de Pesquisa Ambiental da Amazônia (SA-PI)
Tatiana Deane De Abreu Sa — EMBRAPA (SA-PI)
Ima Vieira — MPEG - Museu Paraense Emilio Goeldi (SA-PI)

Objectives





The objectives of the proposed research are to define and describe the types of

landscapes that fall under the broad category of "degraded lands," and to study

biogeochemical cycles across a range of degradation found in secondary forests and cattle

pastures of Amazonia. Half of the 10-20 million hectares of Amazonian forest converted to

cattle pasture are thought to be "in an advanced state of degradation," but

"degraded" means different things to different people. Degrees of degradation

are poorly defined and quantified, and yet are important with respect to future land-use

options and current rates of C sequestration, trace gas emissions, and water use. We

define degraded land as that which has lost part of its capacity to support plant

productivity, either in the context of agro-ecosystems or as communities of native

vegetation. We propose a suite of biogeochemical measurements that may be used as indices

of degradation. Organized according to the LBA themes, these include:







CARBON STORAGE AND EXCHANGE: We propose to measure productivity (as rates of above

ground biomass accumulation), soil respiration, radiocarbon content of soil CO2

and of soil organic matter (in collaboration with Susan Trumbore) in a range of degraded

lands. We will also measure associated diversity of species of plants and soil fauna.







NUTRIENT DYNAMICS: We will measure net N mineralization, net nitrification, stocks

of N, P, and cations in soils and vegetation, fluxes of nutrients in precipitation,

throughfall, soil solutions, and stream-water, and activity of soil fauna. We also have

proposed a fertilizer experiment in capoeiras to test whether nutrients limit rates of

growth of secondary vegetation.







TRACE GAS FLUXES: In addition to CO2, we will measure emissions of N2O,

NO, and CH4.







LAND USE/LAND COVER: We also proposed transects of videography using low flying

aircraft to improve classification of subclasses of degraded lands and to estimate their

relative aerial importance within Landsat TM scenes. Spectral properties of high

resolution images will be used to estimate the percentages of vegetation cover and visible

bare soils, vegetation index, brightness, greenness, and wetness/shadow components of the

land cover. These estimates will be compared to our field data to determine if indices of

degradation deduced from image analyses agree with field measurements of biogeochemical

processes.





Because the complexity of interactions among land-use histories, soils, and climate

makes extrapolation from a few secondary forest tower sites precarious, our proposed

studies at numerous secondary forest sites are necessary to capture the range of rates of

biogeochemical cycling processes found within the broad class of degraded lands. Our

results will be relevant to biogeochemical constraints of sustainable local land

management and will be necessary for regional scale models and budgets of carbon and trace

gases.





Research Team Responsibilities







  • Eric A. Davidson: nutrient cycling and trace gases


  • Thomas Stone: remote sensing


  • Tatiana Sá: secondary forest chronosequences


  • Moacyr B. Dias-Filho: fertilization experiment


  • Regina Moller: soil and water analyses


  • Claudio R. De Carvalho: fertilization experiment


  • Paulo Moutinho: soil fauna, nutrient cycling


  • Ima G. Vieira: biomass and species diversity in secondary forests


  • Daniel Markewitz, (WHRC/ University of Georgia): nutrient stocks and fluxes in soils and

    vegetation


  • Paul Lefebvre, (WHRC): research assistant, remote sensing


  • Elizabeth Belk, (WHRC): research assistant, trace gas fluxes






Study Sites





Study sites that were proposed include:







  1. the primary tower site cluster (e.g., primary, secondary, and logged forest and cattle

    pasture) of the LBA eastern Amazon transect (in collaboration with Keller's group and

    others)


  2. a broad survey of degraded lands in the vicinity of this tower site, and areas of

    ongoing studies in eastern Pará state, where chronosequences of secondary forest sites

    have been identified in Peixe Boi, Igarapé Açu, and Paragominas


  3. comparisons of eutrophic and dystrophic soils in Acre (in collaboration with Foster

    Brown's group)






Activities







  • Site selection, biomass studies and surveys of species diversity: 1998-1999


  • Nutrient stock measurements: 1998-1999


  • Trace gas measurements: 1998-2000


  • Fertilization experiment: 1999


  • Videography: 1999 and/or 2000


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