Pure and mixed plantations of Persian walnut (Juglans regia L.) for high quality timber production in Chile, South America

Abstract

Aims Persian walnut (Juglans regia L.), an interesting forest species for the veneering industry, requires adequate management to produce valuable high-quality logs. Since species associations and management level can improve stand productivity, the novelty of this work was to assess Persian walnut performance in different planting mixtures and in pure plantations conditioned to management intensity. Methods Growth, straightness and survival measurements were taken annually for 7 years after planting pure and mixed plantations under two contrasting management scenarios. Diseases were recorded at Age 7 in all plantations. Under each management intensity, besides the monoculture, three mixtures were tested: a mixture of only main forest species, main forest species plus one arboreal companion species, Black alder (Alnus glutinosa L.) and main species plus the shrub Russian olive (Elaeagnus angustifolia L.) as nurse species. A test of interaction between plantation type and management scenario was conducted using repeated growth data. Important Findings The interaction was significant, indicating the presence of different mechanisms underlying plantation effects under high and low management level. Compared with pure plantations, Persian walnut associated with the nurse shrub exhibited 78% higher height and 53% higher diameter growth in plantations under low management. Health benefits (lower presence of walnut blight than in the monoculture) and better straightness were also found in the association including the shrub when the management intensity was not high. These beneficial effects in the presence of Russian olive were not present under high management intensity (irrigation, fertilization, tutoring and frequent pruning). Site-specific designs for Persian walnut plantations would depend on the foreseen management intensity.