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Clicker Question 1:

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- Jose has just clearcut his lodgepole pine forest to minimize fire risk. He learns that there are things he can do to make money from forestry practices related to carbon credits, but he doesn’t know whether he will make money from doing this.
- For carbon credits, Jose should be focusing on
- 1. Net primary production
- 2. Net ecosystem production

- The first 30 years probably takes the following trend following his cutting:

2.

2

1.

Biomass (kg/m2)

Biomass (kg/m2)

300000

30000

0

0

time

time

Time of cutting

Time of cutting

3.

4.

30000

30000

Biomass (g/m2)

0

Biomass (kg/m2)

0

-30000

-30000

time

time

Time of cutting

Time of cutting

- Biomass (when we say this, we mean all live and dead biological material, so all plants + animals + detritus + detritivores!) must decrease with the clearcutting,and for some time afterwards, as the dead material will decompose faster than new plants can get established and photosynthesize. After plants get established, they will build up their production until it exceeds ecosystem respiration…
- Thus, the answer is 2.

NPP (g/m2/y)

1000

0

time

Time of cutting

2.

3

1.

NPP (g/m2/y)

1000

0

time

Time of cutting

4.

1000

3.

1000

NPP (g/m2/y)

0

NPP (g/m2/y)

0

-1000

-1000

time

time

Time of cutting

Time of cutting

- REMEMBER that NPP is the total gross photosynthesis minus only plant respiration, and that it is always positive on an annual basis if plants are alive and receiving light. Plants, if alive and photosynthesizing at all will accumulate plant biomass.
- It is a RATE, then, that can be between 0 and a positive number.
- After Jose cuts his forest, NPP decreases because he killed all the trees. As they re-establish and begin as seedlings to photosynthesize, they continue to grow, and be able to produce more each year, as their leaf area expands.
- So…the answer is 2.

NEP (g/m2/y)

1000

0

time

Time of cutting

1.

2.

4

NEP (g/m2/y)

1000

0

time

Time of cutting

4.

1000

3.

1000

NEP (g/m2/y)

0

NEP (g/m2/y)

0

-1000

-1000

time

time

Time of cutting

Time of cutting

- Recall that net ecosystem is:
- Total gross photosynthesis minus ECOSYSTEM respiration (plant PLUS heterotrophic respiration).
- It is the same thing as biomass accumulation, or the RATE OF BIOMASS CHANGE
- So, the NEP is equal to the slope, or the derivative, of the Biomass curve.

- Because plants are killed, and dead biomass is being respired away for some time, more rapidly than recovering plants are photosynthesizing, biomass decreases initially, and NEP is NEGATIVE. After some time, photosynthesis begins to exceed ecosystem respiration, and biomass begins to accumulate. The biomass accumulation diagram shows a positive slope, so NEP is Positive. As the biomass curve begins to level off, NEP is STILL POSITIVE, but less so, it peaks and begins downward. After some time NPP = ecosystem respiration, and biomass is at steady state…so NEP goes back to 0.