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ND-02 Abstract

Dynamics of Biogeochemical Cycles in Secondary Vegetation of Amazonia

Claudio José Reis de Carvalho — Embrapa Amazônia Oriental (SA-PI)
Eric A. Davidson — WHRC - Woods Hole Research Center (US-PI)
Ricardo Figueiredo — Embrapa Meio Ambiente (SA-PI)
Daniel Markewitz — University of Georgia (US-PI)
Paulo Moutinho — IPAM - Instituto de Pesquisa Ambiental da Amazônia (SA-PI)
Tatiana Deane De Abreu Sa — EMBRAPA (SA-PI)
Thomas A. Stone — Woods Hole Research Center (US-PI)
Ima Vieira — MPEG - Museu Paraense Emilio Goeldi (SA-PI)

Most deforested land in the Amazon Basin has passed

through stages of secondary forest succession following agricultural

abandonment.  Nutrients lost through logging, fire, and runoff have

immediate effects on air and water quality, and then have longer lasting effects

on plant productivity and stream quality during ecosystem recovery. 

Inadequate understanding of nutrient cycles during tropical forest secondary

succession, however, precludes confidence in predictions of spatial and temporal

variation of carbon sequestration, trace gas production, and nutrient losses to

stream water and ground water in the secondary vegetation of the Amazon Basin. 

Hence, this proposal is motivated by three questions concerning secondary

vegetation:





1.     

Do nutrients limit rates of forest regrowth in deforested lands of Amazonia?






We propose to continue

addressing this question experimentally in a long-term, replicated, and

controlled forest fertilization study in eastern Pará.  In addition, a

forest chronosequence study that we completed on sandy soils will be repeated in

a nearby area dominated by clayey soils, thus providing estimates of rates of

recuperation of biogeochemical cycles during succession. These results will be

integrated into a modeling framework designed to be generally applicable to the

successional dynamics of aboveground and belowground pools of plant-available

nutrients that affect C sequestration and trace gas emissions in disturbed

Amazonian forest ecosystems.





2.     

How well can stages of secondary forest succession be detected in satellite

imagery?






Confidence in spatial

extrapolation of C and nutrient stocks and fluxes in secondary forests depend

largely on identification of these ecosystems in remotely sensed imagery. Three

or four stages of forest succession usually can be distinguished in Landsat

imagery, but the stand ages represented by each stage vary by region, soil type,

and land use history.  Advanced regeneration can require 30-70 years,

depending on these factors.  Rather than forest age, we propose that stages

of succession (early, intermediate, advanced, and mature) identified from stand

characteristics and spectral properties will offer the most regionally

consistent approach for characterizing successional processes and attendant

changes in biomass and trace gas fluxes.  We will evaluate the feasibility

and accuracy of supervised classification at several scales by nesting

ground-based measurements within high-resolution IKONOS images of our study

sites, which will then be nested within Landsat imagery, which will finally be

nested within MODIS imagery.  In addition, we will collaborate with studies

of AVIRIS to estimate canopy N and LVIS to estimate stand height and structure

to aid identification of successional forest stages. 





3.     

How does land-use affect the exchange of nutrients between terrestrial and

aquatic habitats?






Forest cutting and subsequent

regeneration alter both the hydrology and biogeochemistry of the landscape. 

In both mature forests and altered landscapes the source of many elements to

stream waters is not well understood because links between stream chemistry and

upland nutrient status are unclear and because riparian zone and in-stream

processes are also important. We propose to measure changes in stream chemistry

along three first-order streams from their headwaters in remnant mature forests,

through pastures, secondary forests, and large fertilized fields of rice and

corn in a region of highly weathered deep Oxisols of the eastern Amazon Basin. 

Soils and groundwater in riparian zones will be studied in each land use. 

Collaborations with studies in other regions will provide an opportunity to

address interactions among soil substrates and land-use patterns as they affect

stream chemistry across the basin.

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