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
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.
How well can stages of secondary forest succession be detected in satellite
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.
How does land-use affect the exchange of nutrients between terrestrial and
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.