Poor tree form ofPinus radiataD. Don on former pasture sites in New South Wales

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Abstract
The merchantable timber yield from Pinus radiata plantations established on former pastures is reduced compared with stands on ex-native forest sites in comparable areas because the trees develop numerous defects including sinuous stems, multiple leaders and heavy branches. The causative factors have not been identified, but deformation is most severe on highly improved sites where the soils have a high nitrification potential. In NSW, other site-specific nutritional factors including boron and sulphur deficiencies also appear to be involved in the development of “poor form” on ex-pastures. The availability to trees of several elements including phosphorus, boron, sulphur, aluminium and manganese is affected by previous land use. Most plantations on previous pastures in NSW are of pre-commercial age so the major impact on timber yields has yet to be realized. Over the past decade there has been a steady increase in the area and proportion of plantations established each year on pasture country. Of the 4000 ha planted in 1987, 58% were on ex-pasture sites. The proportion was much higher in Bathurst Region (80%) where land purchased for plantations is almost entirely cleared agricultural and pasture country. There are possible alternatives for forest management in order to ameliorate the effects of pasture sites on tree form. In the short term these include mass plantings of vegetatively propagated cuttings from families already shown to be less susceptible to deformation, closer initial spacing, early form pruning, and site-specific fertilization carried out with effective weed control. In the longer term, specific form characteristics can be selected through tree breeding programmes and progeny tests.