Statement of Interest
Christopher Potter
Research Scientist
Ecosystem Science and Technology Branch
NASA Ames Research Center
Modeling Land Use Change and Ecosystem Processes in the Amazon Basin
I am a terrestrial ecologist by training. My main research interests are
global change, biogeochemistry, and land use. I've been at NASA's Ames
Research Center for the past six years developing simulation models that
couple these three areas of interest. The main tools of this trade are
super computers, remote sensing, GIS, field research, and (hopefully) some
creative thinking.
My main interest with respect to this Land Use Modeling workshop is on
coupling our ecosystem modeling knowledge to land use modeling at the
regional scale. Our current geographic focus area is the Amazon Basin. I
am considering a series of model-based questions that can best be addressed
through joint research among several disciplines:
Our regional geographic information system (GIS) for the Brazilian Amazon
serves as the data source of land cover, climate drivers, satellite
greenness images, and soil properties for input to the NASA-CASA
(Carnegie-Ames-Stanford Approach) model at a 8-km grid resolution.
Simulation results already reveal regional effects of forest conversion on
plant production potential and soil carbon content, especially in
seasonally dry areas. These results are being used to formulate a series
of research hypotheses for testing in the next phase of regional modeling,
which ideally will include linkage to land use simulations.
The background for our work is global change. Humans are causing
environmental alterations of planetary significance. One of the clearest
signals of human impact is the rapidly rising concentration of greenhouse
gases like carbon dioxide (CO2) in the atmosphere as a result of combustion
of fossil fuels and changes in land use. Other trace gases such as methane
(CH4) and nitrous oxide (N2O) can significantly influence the energy
balance of the Earth. Moreover, these compounds are linked to
atmosphere-biosphere feedbacks (CO2 fertilization effects on vegetation),
tropospheric chemistry (CH4 reactions with OH, O3 and NOx dynamics) and
stratospheric chemistry (N2O-mediated destruction of ozone).
By the use of recently assembled satellite images of the global land
surface, we have developed the simulation model called NASA-CASA to study
of the role of terrestrial plants and soils in the cycling of carbon to and
from the atmosphere. This research has produced a dynamic and detailed
picture of the contemporary balance between photosynthetic fixation and
microbial respiration of CO2. In the NASA-CASA Biosphere model, a
greenness index from satellite sensors is combined with modeled climate
stress to estimate plant production. Carbon and nitrogen fluxes from
decomposition of plant residues are simulated in the soil and at the
surfaces of forest and grassland soils.
The results of our latest multi-year simulation of global ecosystems
directly infer the presence of a net sink for carbon dioxide in the
terrestrial biosphere over the period 1985-1988. This is, to our
knowledge, an original research result that has not been demonstrated
before at the global scale using actual remote sensing observations and
land surface climate data. By combining medium-term (decade long) climate
data with ecosystem modeling, new answers emerge with respect to
biosphere-atmosphere exchange of trace gases resulting from climate
fluctuations. However, the results from this ecosystem modeling study,
along with others that have used satellite observations to infer plant
production, must be qualified to point out that conclusions cannot be
extrapolated directly to infer long-term (several decades) response of the
biosphere to global warming or land use change. The processes of
disturbance and land management must be included in additional modeling
analyses that include potential geographic shifts occurring over several
decades in plant functional types, physiological responses, and soil carbon
turnover rates.