Spatial Variability of Stem Wood and Soil Respiration in Tropical Forests

It is commonly accepted that stem wood respiration and soil surface/atmosphere trace gases fluxes are spatially highly variable. However there are few studies that attempt to quantify this variability. Manual measurements of soil and stem wood CO2 fluxes can be useful in determining spatial heterogeneity. During the periods of March 14 to 16 and June 7 to 13 we measured stem wood respiration from a wet tropical forest in La Selva, Costa Rica; and between July 16 and 27, 2002 we measured soil CO₂ exchanges in a tropical forest located near Santarem, Para, Brazil. Measurements were obtained using manual chamber systems. Fluxes were measured in chamber headspace air using a pump and an open \- path infrared gas analyzer. Generally, fluxes ranged between 2 and 6 μmol m^-2 s^-1 for soil and 0.13 and 6.4 æmol m^-2 s^-1 for stem wood during the sampling periods. The average flux of all points was 4.6 +/-1.7 μmol m^-2s^-1 for soil and 1.8 +/-1.14μmol m^-2s^-1 for stem wood. Existent automated systems installed at these sites have showed a range of soil CO₂ flux values between 1.5 and 6 \mumol m^{-2} s^{-1} in Santarem site, and 0.001 and 8.95 μ mol m^-2 s^-1 for stem wood respiration in La Selva site for the same period of year.