WATER-USE BY PINUS-RADIATA TREES IN A PLANTATION

We used the heat-pulse velocity technique to estimate transpirational water use of trees in an experimental 16-year-old Pinus radiata D. Don plantation in South Australia during a 4-month period from November 1 993 to March 1994 (spring-summer). Fertilization and other silvicultur al treatments during the first 8 years of the plantation produced tree s ranging in diameter at a height of 1.3 m from 0.251 to 0.436 m, with leaf areas ranging from 83 to 337 m(2). Daily water use was greater f or large trees than for small trees, but transpiration per unit leaf a rea was nearly identical. Daily transpiration was highly correlated wi th available soil water in the upper 1 m of soil and weakly correlated with irradiance and air temperature. For the stand (0.4 ha), estimate d rates of transpiration ranged from 6.8 to 1.4 mm day(-1) in wet and dry soil conditions, respectively. Total water use by the plantation d uring the 4-month study period was 346 mm. Water transpired by the tre es was about three times that extracted from the upper 1 m of soil. La rge trees extracted water from the same soil volume as small trees and did not exhibit a greater potential to extract water from deeper soil when the upper horizons become dry.