Feedbacks Between Tropical Forests, Climate, and Earth’s Carbon

Budget

Jacob Eisenberg

Advised by David Medvigy, Geosciences

Background Information

• Tropical Forests are essential to Earth’s climate, and specifically the carbon cycle

• Very substantial carbon sink (40% of Carbon in terrestrial biosphere)

• Important to maintain this to mitigate Carbon Dioxide in atmosphere

• Unique relationship with climate change, as they both exert influence on each other.

• Coupling Effect

• Need to better understand this relationship to predict what will happen

How can we do this?

• One popular approach is computer models.

• Ecosystem Demography Model (ED2).

• Can work on a smaller scale

• Uses data about the ecosystem on the plot of land (weather, tree size, tree species, soil, etc.) to model growth and carbon sequestration of the forest.

• Difficult to know all parameters, relationships between variables.

• To obtain a more accurate method of looking forward, we have to look backwards.

Checking the Model

• One way to check the accuracy of the model is to compare the model results with known data.

• If the results are similar, it suggests the model is on the right track.

• If not, it suggests that some parameters or relationships present in the model are not representative of the real world dynamics

• This process is what I spent the majority of my internship doing

• Initialization, how to run it, how to interpret results

Running the Model

Figure of Trees in a plot in Brazil, grouping trees by diameter, and computing the total basal area of all trees in a given diameter class. Colors represent different wood densities. This is necessary to initialize model.

Step 1: Initialization

Continued

Step 2: Running/Processing Results

•Pss/css files

•Remote access to computer

•Results Files

•Data Analysis in MATLAB

Results

• At first, results were very different than observed data.

• Mistakes, changing some parameters, results improved

• Main results of interest were Above Ground Biomass, Leaf Are Index, and Basal Area.

• Three decade-long runs, isolating meteorological data

• Supposed discrete jump in AGB in late 80s

• Also did runs from scratch (just seedlings)

Figures

Shows the LAI in a run started from scratch in three different decades. Results were similar, and also reasonable.

Shows the AGB in a run started from scratch. AGB was noticeably higher in the 90s than the 80s, supporting the discrete jump

FiguresBasal Area in a run started from scratch. Clearly increase until it reaches an equilibrium. (Ignore late drop) This plot of forest had a recorded basal area of 26 m^2, which is nearly identical to the results of the model.

Conclusions

• When run from scratch, the model is accurate.

• The results suggest that AGB did increase from the 80s to 90s

• However, when the model was run with the current ecosystem in a given plot as the starting point, the results were not as promising.

• Could be a problem with data (first person to use this database with this model)

• Still many interactions/relationships in tropical forests scientists do not understand

Reflection

• Importance of Computer models

• Original Research

• Lab Group Environment

• Future Plans

Thank you to PEI, Professor Medvigy, and his research group!