Canopy dynamics and growth of Pinusradiata.: I. Effects of irrigation and fertilization during a drought

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Abstract
A field experiment was commenced in 1983 in a 10-year-old plantation of Pinusradiata (D. Don) in the Australian Capital Territory to study the effects of varying levels of nutrition and water availability on the physiological processes controlling tree growth. The effects of treatments were accentuated by marked differences in precipitation during the first 2 years of the study. Tree canopies grew rapidly during the wet summer of 1983–1984, particularly with the addition of fertilizer. During the following dry summer transpiration by the large canopies rapidly depleted soil water, leading to severe water stress on nonirrigated plots. This stress restricted the expansion of new foliage, induced heavy shedding of foliage older than 1 year, and prevented stem growth during most of the summer. The stems of nonirrigated trees decreased in diameter for 4 months, and in the fertilized stand several trees died, while others suffered crown dieback. In the dry year, stem volume increments varied between 17 and 45 m3 ha−1 with the different treatments.