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Vegetation types & biomass

Dams usually flood land covered by some sort of vegetation. The vegetation cover varies in the amount of plant material, called biomass, present per hectare. Around half of plant biomass is made up of carbon atoms. When areas are flooded (or cleared in anticipation of flooding) the biomass is broken down and the carbon atoms join with oxygen to form carbon dioxide, the main greenhouse gas. Flooded vegetation also produces methane, a more potent greenhouse gas.

Larger reservoirs in areas of tropical forest release large amounts of greenhouse gases, while smaller reservoirs in areas of sparse vegetation release relatively small quantities of greenhouse gases. The net greenhouse effect of a new dam depends on whether its emissions per unit of energy generated are more or less than those from the other sources of energy that are likely to be used if the dam is not constructed.


Read a book titled "Tropical Deforestation and Climate Change" that more deeply explores the link between the destruction of biomass and greenhouse gas emissions.
Read an article about Amazonian deforestation.

Table source: http://cdiac.ornl.gov/epubs/ndp/global_carbon/tables.html#tables


Vegetation Types Selection Directions*

• Step 1) Find the continental region for which you are conducting a study.

• Step 2) Find the ecofloristic zone within the chosen region which best represents the area to be flooded.

• Step 3) Find the forest class within the chosen region and ecofloristic zone which best represents the area to be flooded.

• Step 4) Select “frontier” or “non-frontier” as a final vegetation characteristic to the previous three you have already selected. If carbon content is not dependent on frontier type, then neither “frontier” nor “non-frontier” will be available and you may ignore this step. Follow this link for an explanation of frontier and non-frontier forests.

*If the vegetation comprising the area consists mainly of grassland:

• Step 1) Between “grassland” or “sparse grassland and grassland mosaic”, select the description which
best represents the area to be flooded.

• Step 2) Find the ecofloristic zone within the chosen grassland classification which best represents the
area to be flooded.

*If the vegetation comprising the area consists mainly of shrub cover:

• Step 1) Find the continental region for which you are conducting a study.

• Step 2) Find the latitudinal classification (temperate, tropical, or subtropical) within the chosen region which best represents the area to be flooded.

*If the area consists predominantly of cultivated and managed land:

• Step 1) Select “cultivated and managed land”.

*If the area consists of no vegetation:

• Step 1) Select “bare areas".