Abstract A 3.7 m diameter by 1.2 m deep soil container was constructed around the root ball of a 28 m Douglas-fir tree in a naturally regenerated stand. The container, soil, and tree weighed 28,900 kg. The weighing mechanism, consisting of 165.6 m of 6.35 cm butyl rubber tubing filled with water connected to a stand pipe, was placed under the soil container. Weight changes are detected by measuring the differential pressure between the active standpipe and a dummy standpipe. The sensitivity of the system is 630 g, equivalent to 0.06 mm of H 2 O. Forest Sci. 19:256-261.