Carbon cycling in a mid-latitude deciduous forest: Spatial and temporal dynamics.

摘要

To assess the role of various ecosystems in sequestering carbon, long-term flux networks (e.g., AmeriFlux, Euroflux, LBA) measuring surface-atmosphere carbon dioxide exchanges have been established utilizing micrometeorological techniques. However, these methods are plagued by the extreme variability of terrestrial ecosystems at a multitude of scales, distinct inter-annual variability, and uncertainty in some aspects of long-term flux measurements. As a complement to flux tower estimates, biometry (measuring changes in carbon stocks to produce annual estimates of carbon sequestration) has been undertaken at some of the flux tower sites, including Morgan-Monroe State Forest, the study-site in this dissertation. This method has been supplemented over the years with complementary studies of the major fluxes, principally the use of soil CO2 efflux auto-chambers. The aim of this project is to determine the consistency of spatially and temporally integrated estimates of net C sequestration for six years (1998-2003). It is shown here that both methods provide remarkably similar annual estimates of net ecosystem productivity (NEP). Additionally, both methods' contributions, when used conjunctively, are key to understanding carbon cycling in terrestrial ecosystems. This is particularly true when identifying factors driving inter-annual variability in carbon uptake. Also, bottom-up scaling of tower-based ecosystem fluxes to a large region involves several steps that must populate the space between a set of observational sites (i.e., the flux towers) with an estimate of the exchange that is matched to measured values at these sites.