Soil Water Repellency Dynamics in Pine and Eucalypt Plantations in Portugal – A High-resolution Time Series

During the 20th century, afforestation resulted in plantations of Pine and Eucalypt becoming the main crops in north-central Portugal with associated and well-known soil water repellency (SWR). The aim of this study was to improve the insights in the temporal dynamics and abrupt transitions in water repellency of the topsoil and the mechanism that determine the behaviour of SWR. Topsoil water repellency was monitored in the Caramulo Mountains (north-central Portugal) between July 2011 and June 2012. The intensity of SWR was measured in situ at soil depths of 0, 2.5 and 7.5 cm using the ‘molarity of an ethanol droplet’ test. Volumetric soil moisture content was monitored in situ using a Decagon ECH2O EC-5 probe. SWR behaviour broadly followed five alternating dry and wet periods during the 12-month period, with more pronounced differences in the Pine site than in the Eucalypt site. SWR under Eucalypt was substantially more temporally dynamic than under Pine, with double the number of moderate and large SWR changes at the 7.5 cm depth. Soil moisture content and antecedent rainfall were better correlated to SWR under Pine than under Eucalypt, although in both cases insufficient to predict the temporal variations