Light Transmittance


 Light (400-700 nm) transmitted through the canopy to 50 cm above the forest
 floor was measured at five points within the lm2 quadrat and averaged to determine the
 mean for the quadrat. A LiCor 185b quantum/radiometer/photometer with a quantum
 sensor was used to determine available photosynthetically active radiation at 50 cm. A
 measurement was also taken in full sun immediately prior to those taken on the forest
 floor. Shrubs were removed to determine the light being intercepted by the canopy and
 subcanopy only.

 % transmittance = radiation @ 50 cm / radiation in full sun [7.1]


 Soil

 At the center of each 1m2 quadrat (Figure 7.3c), a 20 cm soil core was collected
 using 3.7 cm diameter coring tube. Cores were placed in a plastic bag, stored on ice, and
 wet weight of the core was recorded within 24 hours of collection. Each core was
 thoroughly homogenized by thoroughly hand mixing, and a 25g subsample was placed in
 a drying oven at 700 C until constant weight was achieved. A dry/wet conversion (dry
 weight/wet weight) factor was established from each subsample and multiplied by the
 wet weight of the entire core to estimate the dry weight of the entire core. The following
 formula was used to calculate percent moisture.

 (Core wet weight Core dry weight) / Core wet weight = % moisture [7.2]

 Bulk density for each core was determined by dividing the core dry weight by the
 total volume of soil contained in each sample. Soil sample volume was estimated by
 calculating the volume of the coring device (1.85 cm 1.85 cm 3.14 20 cm = 214.9
 cm3). Dried samples were then ground with a mortar and pestle and stored in an airtight
 container.

 One gram of dried soil from each core was ashed in a muffle furnace for 6 hours
 at 5000 C. This relatively low temperature was used to drive off the organic matter while
 leaving inorganic carbon (CaCO3), which volatizes at approximately 5400 C. The loss
 from ignition was reported as a rough estimate of organic matter. This method can over
 estimate organic carbon because inorganics can lose mass after heating. Specifically,
 clays can lose water bound within their chemical structure.

 Available nutrients were estimated using the Mehlich I extractant (Mehlich 1978)
for Ca, Mg, K, P, and Fe. Twenty ml of Mehlich I extractant (0.05 M HCI in 0.025 N
H2SO4) was added to 5 g of dried soil. The soil and extractant were shaken for five
minutes using a reciprocating shaker and then filtered. Elements were analyzed by
Inductively Coupled Argon Plasma (ICAP) Spectroscopy at the IFAS Analytical
Research Laboratory at the University of Florida. Results are presented as mg nutrient
kg'- soil and g nutrient m-2 to a depth of 20 cm.


7-22