ESTIMATES OF EVAPORATION IN PLANTATIONS OF <em>AGATHIS</em> <em>DAMMARA</em> WARB. IN SOUTH-CENTRAL JAVA, INDONESIA

Abstract

A water balance is presented for a 19-ha catchment covered with 11- to 35-y old plantation forest of Agathis dammara Warb. in central Java.

During the rainy season the ratio (f) between actual evapotranspiration (ET) and Penman open water evaporation (Eo) remained close to 0.79. The study period included an exceptionally severe dry season. Due to the deep nature of the soils, moisture stress did not limit transpiration (Et) until the last month of the drought (November, f = .69). It was inferred that during years with average rainfall ET would be close t o 1070 m l. Mme asureyments of throughfall rin 11- and 35-y old sta-nds of Agathis 1 and in Chromolina thicket indicated average rainfall interception (Ei) of 23,14 and 9% of incident rainfall. Subtracting Ei from ET yielded an average rate of Et of about 400 mm yr-l for the entire catchment, a rather low value.

The available information on ET and various tropical land-use types is reviewed.briefly. The presently obtained throughfall figures are discussed in the light of results from over twenty throughfall studies in Southeast Asian forests. The use of a roving gauge technique is stressed if reliable estimates are to be obtained.