Abstract
In 1963, several canals were constructed in the vicinity of the Florida Panther National Wildlife Refuge (FPNWR) altering natural processes such as water flow and fire regime. These ecosystem alterations have allowed the spread of both native and exotic species, increased the competition for limited resources such as water and nutrients, and allowed successional changes from systems that were previously open pine flatwoods to pine systems with diverse herbaceous understories. Of particular concern to FPNWR management is the increase in density of the native cabbage palm (Sabal palmetto) in the pine flatwoods ecosystems. It is hypothesized by FPNWR management that the cabbage palm's increased presence in these communities depletes water resources, competes with forage species for light resources and that removal of the cabbage palm will increase water and light availability for forage species of importance to whitetailed deer. The focus of this study is in the water use of the slash pine (Pinus elliottii) and cabbage palm (the canopy dominant) species in the FPNWR, and to investigate differences in water use resulting from efforts to reduce the number of cabbage palm plants on the landscape. Water use was quantified using leaf-level transpiration measurements, scaling leaf-level to ecosystem level transpiration, and by quantifying ecosystem evapotranspiration (ET) through analysis of the diurnal changes in water level in a series of wells located on the refuge. Observations reveal that at the leaf-level, cabbage palm plants transpired at a rate 20.1% higher in sites where older and larger cabbage palm plants had been removed. Leaf area was determined by developing allometric equations which use measurements of physical traits to estimate leaf area of cabbage palm and slash pine trees, and performing population and physical trait surveys. Scaling to the ecosystem level reveals that FPNWR management removal efforts removed enough leaf area to result in a net ecosystem reduction in water loss due to transpiration of the cabbage palm and slash pine trees of 9.3%, with 74.4% of that amount attributable to a reduction in cabbage palm transpiration. Well water level studies suggest that (ET) increases with density of cabbage palm and slash pine trees, with results not inconsistent with FPNWR management hypothesis that removal of cabbage palm plants will increase available water. Population surveys revealed that cabbage palm plants are prolific on the landscape at the FPNWR. Comparison of surveys with studies performed on the establishment phase of the cabbage palm suggest that increased aboveground stems and leaf area may be prodigious in the next ten to fifteen years unless removal efforts are continued and expanded to include smaller plants.