Performance of Quercus rubra and Quercus robur in pure and mixed-species plantations

Abstract

Context: Quercus robur L. and Q. rubra L. (pedunculate and Northern red oak, respectively) produce high-value timber. Mixed plantations are attracting attention because they provide several benefits; however, they have been included in few trials in non-native habitats. Aims: This study assessed growth, health, and timber quality of Quercur robur and Q. rubra trees growing in pure and mixed plantations including companion tree species. Methods: Growth was measured periodically in Q. robur and Q. rubra pure and mixed plantations established in southern Chile for 23 years. Mixed plantations consisted of a main forest species association (Castanea sativa Mill., Quercus rubra, Q. robur and Prunus avium L.) and three mixed plantations including the four main forest species plus one companion tree species (Alnus glutinosa L., Gevuina avellana Mol. or Embothrium coccineum J.R. Forst. & G.Forst.). Timber quality variables and health status were measured at age 23. Growth variables were analyzed using linear mixed models and quality timber variables, using a χ2 test. Results: Both species exhibited a positive performance in tree growth, vigor, and phytosanitary status. Across treatments, Q. rubra presented bigger trees than Q. robur at age 23. In the pure plantation, Q. robur initially showed higher growth rates than Q. rubra, but from age 15, the latter outperformed the former. Q. robur tree volume was higher in the main species association and the one including E. coccineum than in the pure plantation. Q. rubra tree size showed no differences between plantation types. The association with A. glutinosa reduced both oak species growth, and the one with Gevuina avellana had a neutral effect on Q. rubra and a negative effect on Q. robur (reduced height and volume). Finally, the main species association showed higher volume per hectare than the pure Q. robur plantation. Conclusion: Both species showed productive potential in pure and mixed plantations. Mixed plantations can be recommended as an alternative to pure plantations to produce quality timber. Adequately selecting the main and companion species based on site-specific conditions is crucial for the success of productive plantations.