ND-02 Abstract

Dynamics of Biogeochemical Cycles in Secondary Vegetation of Amazonia

Claudio Jose Reis de Carvalho, EMBRAPA/CPATU (SA-PI)
Eric A. Davidson, WHRC (US-PI)
Ricardo de Oliveira Figueiredo, Embrapa Amazônia Oriental (SA-PI)
Paulo Roberto de Souza Moutinho, IPAM - Instituto de Pesquisa Ambiental da Amazonia (SA-PI)
Tatiana Deane De Abreu Sa, EMBRAPA/CPATU (SA-PI)
Ima Celia G. Vieira, 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.