The measurement of leaf litter water content in a deciduous forest

The water content of leaf litter below deciduous forests is an important component of the energy, water, and carbon budgets of forest environments. While significant achievements have been attained with micrometeorological techniques in the measurement of vegetation environments, methods available at the soil surface beneath vegetation remain limited by the cost and the difficulty of accurately measuring the small magnitude and large spatial variability of fluxes prevailing below vegetation stands. The objective of this study was to examine the ability of a low-power, low-cost soil moisture probe to measure the water content of the leaf litter layer on the floor of a deciduous forest in Oak Ridge, Tennessee during the growing seasons of 2009 and 2010. Successful operation of the probe required site calibration factors that convert the millivolt response of the probe to the equivalent water content of the leaf litter cover. When the leaf litter water content measured in millivolts by the moisture probe was compared with gravimetric measurements by leaf litter samples inside wire mesh baskets positioned across the forest floor, the change in the magnitude of the millivolts described the water content of the leaf litter. This comparison was used to derive a regression equation to determine the litter water content as a linear function of the millivolt response from the moisture probe. Measurements of the litter water content reached a maximum of about 3 g (H2O) g-1 (litter dry weight), with hourly and daily values that showed a strong variability related to within-forest precipitation, radiation, and wind speed. The results of this study suggest that a careful adoption of the low-cost moisture probe may be a reasonable and direct way to obtain continuous measurements of litter water content.