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The average nighttime evaporation rate of water intercepted on an evergreen mixed forest canopy is estimated as 0.37 mm/h from a regression of interception loss on gross rainfall for 35 storms occurring between 1900 and 0700 LT. The mean wet canopy evaporation rate estimated by the same method for both daytime and nighttime rainfall in 1975-1976 was also 0.37 mm/h. The similarity of daytime and nighttime evaporation rates indicates that evaporation from the wet canopy is driven by advected energy not by radiation. The diurnal rainfall distribution and nighttime evaporation rate indicate that net interception loss was 81-84% of gross interception, considerably higher than net losses estimated in other studies where nighttime losses were not considered separately from daytime losses. Interception losses at night were 40-50% of total gross interception, 50-60% of the total net interception, and ,--30% of total evaporation.

Six small, steep, south-west facing catchments (1.63-4.62 ha) have been monitored in Westland, New Zealand since 1974. Two catchments were retained in native mixed evergreen forest and the rest were subjected to various harvesting and land preparation techniques before being planted with Pinus radiata between 1977 and 1980.The 1 1-year water balance for the native forest catchments was: rain = streamflow + interception loss + transpiration + seepage (2370mm = 1290mm + 620 mm + 360 mm + 100 mm). In the year after treatment streamflow generally increased by 200-250 mm, except for one treatment (clearfelling, herbicide application, no riparian reserve) where the increase was 550mm. The catchments were planted with Pinus radiata, but rapid colonization by bracken (Pteridium esculentum) and Himalayan honeysuckle (Leycesteria formosa) led to a rapid decline in streamflow, which returned to pre-treatment levels after an average of about five years. Streamflow yields then continued to decline for another two to three years before stabilizing at a level about 250mmyr-' lower than pre-treatment levels. At this time the catchments had a dense bracken/honeysuckle understorey beneath 5 m tall pine trees.

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