Influence of crown thinning on radial growth pattern of Pinus taeda in southern Brazil

Abstract

Loblolly pine is widely planted in southern Brazil. Despite its major relevance for the forestry sector, knowledge about its radial growth at different height levels is scarce—it is unprecedented for trees subjected to crown thinning. The following questions were answered: (1) how many competitors should be removed to favour the radial growth of potential crop trees? and (2) how long does it take to detect enhanced growth rates along the stem and how long do the effects last? The research design included four thinning treatments where competitor trees were removed in different intensities starting at age 5 years. At age 30 years, 20 trees from each thinning treatment were selected, of which cross-sectional discs were taken at 1.3 m, 25, 50 and 75% of commercial height. The removal of one competitor tree per potential crop tree is not sufficient to increase radial growth immediately after thinning—two competitors need to be removed. Growth responses were detected immediately at the tree base (1.3 m), but took ~ 3 and ~ 8 years to be detectable at 25% (~ 8 m) and 50% (~ 15 m) of commercial height. Positive influences on growth rate following thinning take longer to be detectable upwards in the stem than at the trees base. However, once present, enhanced growth rates last longer at higher levels than at the tree base.