Exotic ponderosa pine plantations are being planted in the natural distribution area of cordilleran cypress (Austrocedrus chilensis (D.Don) Pic. Ser. et Bizzarri) in Argentinean Andean Patagonia. The productivity of exotic plantations is much greater than native forests (Schlichter and Laclau, 1998), which suggests greater utilization of water resources. We hypothesized that: 1- ponderosa pine plantations have higher total annual transpiration than native cordilleran cypress stands, due to higher transpiration rates and/or longer growing season; 2- they extract water from deeper soil layers and deplete water to lower levels of soil moisture; and 3- rainfall interception losses are similar between species but vary with tree density. Using continuous measurements of sap flow, soil water content and below- and above-canopy rainfall precipitation, we examined the water budget components of four forest stands: a high density ponderosa pine timber plantation (HDPP), a low density silvopastoril ponderosa pine plantation (Silvo), a low and a high density cordilleran cypress stands (LDCip and HDCip respectively). Measurements were carried out during two years with contrasting amounts of precipitation. HDPP had the highest use of water at the stand level. Water depletion was observed simultaneously at all depths for all the sites, even in the wet year. Differences between the soil water depletion and sap flow suggests a higher use of water below 1.8m by the HDPP stand than the rest of the stands. Rainfall interception losses were greater in the native stands, and partially compensated the increased evapotranspiration of the exotic plantations.
