The Duke Forest FACE Experiment
Forest-Atmosphere Carbon Transfer And Storage (FACTS-1)
Sponsored by: Environmental Sciences Division, Office of Biological & Environmental Research, Department of Energy
In 1996 we began a Free-Air CO2 Enrichment (FACE)
experiment in replicated 30-m diameter plots of a 15-year-old loblolly pine
(Pinus taeda L) forest, using an experimental addition of +200 ppmv
CO2, 24 hrs/day, 365 days/year. This level
was chosen to simulate the atmospheric environment globally for the year
2050.
During the subsequent four seasons of growth, we found an increase in canopy
leaf photosynthesis (50%), net primary production (25%), and carbon storage
in the ecosystem (38%); however, incipient evidence for nutrient deficiencies
suggests that this growth response will not be sustained in future years.
The integrated program of studies in this experimental forest examines the
processes that determine its net ecosystem production (NEP), nutrient cycling,
and the potential for long-term accumulations of carbon in woody vegetation
and soils. The project examines the mechanisms responsible for increasing
NEP under future levels of atmospheric CO2.
The mechanisms considered are changes in forest physiology, structure, and
species diversity. The project also attempts to reconcile estimates
of NEP obtained independently from harvest measurements and from measurements
of net ecosystem exchange using eddy-covariance techniques under ambient
conditions. The results will show how coniferous forests may contribute to
the carbon "sink" in eastern North America.
The project includes studies of the potential "downregulation" of tree growth due to nutrient deficiency. This work is motivated
by observations in the FACE Prototype plot, as well as measurements of nitrogen
cycling under ambient and elevated CO2 in the
replicated experiment. We will test for nutrient limitations, without
disruption of site fertility, using an 15N-tracer addition in conjunction
with on-going measurements and models that couple carbon and nitrogen dynamics.
These studies gain additional relevance from the enhanced rates of nitrogen
deposition that are currently experienced in eastern North America. The
project seeks to improve our understanding of the processes that control
respiration in plants and soil heterotrophs, as these processes determine
the fate of carbon stored in the forest. Our recent effort to balance
a soil carbon budget suggests that a mechanism not previously considered
(e.g., root exudation) may cause accumulations of soil carbon when forests
are grown at high CO2.
Ultimately, this project provides unique scientific knowledge guiding the
quantification at multiple time scales of biosphere-atmosphere exchange
processes relevant to the present and future global carbon cycle.
Data
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