Calculate NEP before the outbreak and identify the most appropriate conclusion about whether the forest was a carbon sink or a carbon source.

Before the outbreak, the forest was a carbon sink because NEP was greater than 0.

Explanation:

Net ecosystem production (NEP), defined as the difference between gross primary production and total ecosystem respiration, represents the total amount of organic carbon in an ecosystem available for storage, export as organic carbon, or non biological oxidation to carbon dioxide through fire or ultraviolet oxidation.

Total production vs total respiration of all organisms in an ecosystem

NEP = GPP - (Ra + Rh)

Ra = Respiration of autotrophs

Rh = Respiration of hetertrophs

NEP can be positive or negative.

NEP is useful to ecologists because its value determines whether

an ecosystem is gaining or losing carbon over time. A forest may

have a positive NPP but still lose carbon if heterotrophs release

it as CO2 more quickly than primary producers incorporate it

into organic compounds.

The most common way to estimate NEP is to measure the

net flux (flow) of CO2 or O2 entering or leaving the ecosystem.

If more CO2 enters than leaves, the system is storing carbon.

As before the outbreak, the forest is a carbon sink because its NEP is greater than zero as there will be some or more NEP. But after the outbreak, the forest system will be disturbed and NEP will be less than zero and forest will become a carbon source.