Long-term Dynamics of Carbon, Water and Energy Fluxes for Managed and Natural Pine Ecosystems in Florida

We used instrumental meteorological towers to measure the net movement of carbon, water and energy into and out of three pine

 ecosystems in northern Florida; a four year-old, regenerating slash pine plantation, a 123 year old, mid-rotation pine plantation,

and a ~ 70-year old, naturally-regenerated stand of slash and longleaf pine. This choice of sites enabled us to investigate how climate,

stand development (or stand age) and different types of management affect the ability of pine ecosystems to take up and store carbon.

Stand development had a strong impact on annual net ecosystem exchange (NEE) of carbon. The regenerating platform stand started

out as a net source of CO2 immediately following clear-cut harvest,  with an NEE of 1,269 g C m^-2 (positive values indicate losses to

the atmosphere) in the first year (1998). As tree leaf area developed on the site, progressively larger amounts of C were fixed each year,

until the stand was almost at a "null" C balance with an NEE OF 108 g C m^-2 in the fourth year after harvest (2001). The mid-rotation

stand remained a strong sink for C from 1998-2001, with annual NEE ranging from 543 to -603 g C m^-2 yr ^-1.The naturally-regenerated

pine stand was also a net sink for C from 1998-2001, with NEE of -178 and -193 g C m^-2 in 2001-02, respectively. The latter

measurements were made during a period of increasing drought. Additional physiological and structural measurements enabled us to

better understand the biological mechanisms that caused theses differences in diurnal, seasonal and annual NEE across sites.