Scrub oak and pine flatwoods are two contrasting ecosystems common to the humid
subtropical climate of Florida. Scrub oak forests are short in stature (<2 m) and occur on
well-drained sandy soils, and pine flatwoods are much taller and occur in areas with
poorly drained soils. Eddy covariance measurements were made from January 2001 to
February 2003 over a scrub oak forest and from January 2002 to February 2003 over an
adjacent pine flatwoods located on in central Florida, USA, and exposed to similar
atmospheric conditions to evaluate how the dynamics of latent heat (lE) and sensible heat
(H) exchanges are affected by environmental and biological variables. Annual
evapotranspiration (Et) for the scrub oak was 737 and 713 mm in 2001 and 2002,
respectively. Et was comparatively higher, 812 mm, in 2002 at the pine flatwoods due to
higher soil moisture and leaf area. In both ecosystems, springtime increases in lE
coincided with increasing leaf area and evaporative demand. However, H was the main
energy-dissipating component in the spring due to the seasonal decrease in soil water
content in the upper soil profile. In the spring, mean weekly Bowen ratio (b, i.e. H/lE)
values reached 1.6 and 1.2 in the scrub oak and pine flatwoods, respectively. With the
onset of the summertime rainy season, lE became the dominant energy flux and b fells to
< 0.4. In both ecosystems, b was strongly controlled by the interaction between leaf area
and soil moisture. The lowest values of the decoupling coefficient (W, 0.2 and 0.25 scrub
oak and pine flatwoods, respectively) also occurred during the dry springtime period
indicating that surface conductance (gs) was the mechanism controlling energy
partitioning causing high b in both ecosystems. Et increases in the spring, when water in
the upper soil profile was scarce and strongly retained by soil particles, indicated that
plants in both ecosystems obtained water from deeper sources. The results from this
research elucidate how energy partitioning differs and is regulated in contrasting
ecosystems within the Florida landscape, which is important for refining regional
hydrological and climate models.
