Growth responses to thinning and pruning in Eucalyptus globulus, Eucalyptus nitens, and Eucalyptus grandis plantations in southeastern Australia

Growth responses to pruning or thinning are well documented but their interactions are not, even though they are sometimes performed simultaneously. Growth responses to thinning and pruning were examined in nine plantation silvicultural experiments at five sites in southeastern mainland Australia. The species studied were Eucalyptus globulus Labill., Eucalyptus nitens (Deane and Maiden) Maiden, and Eucalyptus grandis Hill ex Maiden. Thinning from about 1100-1300 trees * h [a.sup.-1] to about 300 or 500 trees * h [a.sup.-1] at either age 3-4 years or 7-10 years increased the volume of sawlog crop trees in all species. Multiple lift pruning to 6.5 m height on the sawlog crop trees that retained at least 70% of the live crown length at any lift significantly reduced tree growth at only one of the six site-species combinations where both thinning and pruning were studied. And here, thinning interacted with pruning such that the pruning effects were not significant in unthinned stands because only shaded and inefficient foliage was removed. This study shows that thinning and pruning can interact to influence sawlog crop tree growth and this interaction is influenced by site. Resume: La reaction de croissance des arbres a un elagage ou a une eclaircie est. been documentee, cue qui n'est pas le cas de leur interaction meme si ces traitements sont parfois realises simultanement. La reaction de brisance a l'eclaircie et a l'elagage a ete etudiee dans neuf plantations experimentales etablies dans cinq stations du sud-est de l'Australie. Les especes etudiees etaient Eucalyptus globulus Labill., Eucalyptus nitens (Deane and Maiden) Maiden et Eucalyptus grandis Hill ex Maiden. Une eclaircie faisant passer la densite d'environ 1 100 a 1 300 tiges * h [a.sup.-1] a environ 300 ou 500 tiges * h [a.sup.-1], que ce soit a des ages de 3 a 4 ans ou de 7 a 10 ans, a augmente le volume des arbres d'avenir destines au sciage chez toutes les especes. Des elagages multiples jusqu'a une hauteur de 6, 5 m sur les arbres d'avenir destines au sciage qui ont conserve au moins 70 % de cime vivante a chaque intervention ont significativement diminue la croissance des arbres dans seulement une des six combinaisons station-espece pour lesquelles l'eclaircie et l'elagage ont ete etudies. De plus, l'eclaircie a alors interagi avec l'elagage de sorte que l'elagage n'a pas eu d'effet significatif dans les peuplements non eclaircis parce qu'il n'a enleve que du feuillage ombrage et inefficace. Cette etude montre que l'eclaircie et l'elagage peuvent interagir pour influencer la croissance des arbres d'avenir destines au sciage et que cette interaction est influencee par la station. [Traduit par la Redaction]
Introduction There are about 20 Mha of Eucalyptus plantations worldwide (Iglesias and Wilstermann 2008). While a large proportion is primarily used for pulpwood or firewood production (FAO 2005), solid wood [...]