Assessing rooting depths of an Austrian pine stand by inverse modeling soil water content maps

Rooting depths in a forested stand (0.11 ha) were estimated indirectly by i nverse modeling maps of soil water contents from time domain reflectometry (TDR) measurements at 150 points. These maps were described with a calibrat ed one-dimensional soil water flow model, with specific values for the root ing depth, van Genuchten's [1980] alpha parameter, and throughfall fraction at each point. At about one third of the 150 points, modeled rooting depth s did not fall within the a priori likely range of rooting depths; these va lues were discarded when kriging the point estimates to a map of rooting de pths. The resulting rooting depths range from 0.8 m to 3.5 m within the sta nd in good agreement with root observations (R-2 = 0.85). Several factors c ontributed positively to this good match, such as the fairly uniform soil h ydraulic properties and the high sensitivity of soil water dynamics to root water uptake. Overall, the results demonstrate the suitability of soil wat er content maps based on TDR measurements to quantify spatial variability i n soil water dynamics.