Reducing Uncertainty In Current And Projected Carbon Sequestration In Southeastern US
Sponsored by: Southern Global Change Program
, US Forest Service, Department of Agriculture, and
Environmental Sciences Division, Office of Biological & Environmental Research, Department of Energy
This project is the longest-running forest experiment using Free Air CO2 Enrichment technology, the Duke Forest (FACE) prototype.
The focus of this project, is the need to incorporate the effect of projected
concentration of CO2 in our predictions of future
yields, forest productivity, and C sequestration.
Unlike the formal FACE experiment (FACE-FACTS 1), the FACE prototype (FACEP)
allows us to evaluate whether future forest growth and C sequestration is
dependent on site fertility. In FACE settings, however, net ecosystem exchange
(NEE) cannot be measured, and net ecosystem productivity (NEP) must be estimated
from biomass and heterotrophic respiration (RH) measurements.
FACEP (550 ppmv constant daytime CO2 concentration,
growing season enrichment) is a unique field facility for CO2
exposure of a forest ecosystem, and has been operating since 1994 in a
Pinus taeda L. (loblolly pine) plantation on a nutrient-poor ultic Alfisol.
Because it is the longest running elevated CO2
experiment on forest trees, it permits evaluation of longer-term responses
of an intact forest ecosystem to elevated CO2,
without artifacts characteristic of earlier short-term chamber studies on
artificial soils. We capitalize on the long-term CO2
exposure and data record for this facility along with enhanced fertility
of a portion of the plot to examine CO2–soil
nutrition interaction effects on growth and ecosystem processes of the loblolly
pine.
The interaction between CO2 and nutrients may affect
NEP and NEE in more ways than just by enhancing growth. For example, a higher
N content in the organic matter may cause higher decomposition rate, thereby
reducing the gain in C sequestration attained through fertilization. Conversely,
where higher nutrient availability increases aboveground growth, less carbohydrates
will be exuded belowground, perhaps reducing heterotrophic respiration. Thus,
it is possible that the benefit from fertilization under higher atmospheric
CO2 may include both enhanced biomass production,
and reduced heterotrophic respiration, both resulting in an increased NEE.
The study is designed to test the hypothesis that, under otherwise undisturbed
conditions, nutrient availability will limit forest response to elevated
atmospheric CO2. Therefore, stands on better
sites will respond more to elevated atmospheric CO2
, as will be evaluated based on the response of a fertilized stand.
Data
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