Mixed Castanea sativa plantations including arboreal companion species enhance chestnut growth and high-quality timber production

Context: Chestnut (Castanea sativa Mill.) is an important tree species for its timber, which is widely used for multiple purposes, including the veneer industry. The species has an interesting productive potential in Chile and requires specific management strategies to produce valuable, high-quality logs. Although mixed plantations including companion species usually enhance timber quality of several trees, the performance of chestnut under different associations is not well known. Aims: The objective of this study was to assess growth, survival, health, and timber quality of chestnut trees in several plantation types, including monoculture and mixtures with other companion trees and/or shrub. Methods: Growth and survival measurements were taken periodically in pure chestnut and mixed plantations established in southern Chile for a 20-year period after planting. The mixed plantations tested were: a main forest species mixture (Castanea sativa Mill., Quercus rubra L., Quercus robur L. and Prunus avium L.); three mixtures including main forest species plus one arboreal companion species (Alnus glutinosa L., Gevuina avellana Mol. or Embothrium coccineum J.R. Forst. & G. Forst.); one including main forest species plus one shrub nurse species (Fabiana imbricata Ruiz & Pav.); and three mixtures including one of the arboreal companion species and the shrub. Timber quality variables were assessed at age 20, and health status was recorded at ages 7 and 20 in all plantations. Growth variables were analyzed using linear mixed models to assess plantation effect over time. Kaplan-Meier survival analysis and Log Rank Test were used to compare chestnut tree survival among plantation types. Quality timber variables were analyzed with a chi 2 test. Results: Chestnut trees associated with arboreal main species (P. avium, Q. rubra, Q. robur) (Mix1) showed the best performance, with 10.1 % and 8.3 % higher height than average values of the other mixtures and the monoculture, respectively, and 19.1 % and 12.8 % higher diameter growth than across plantation types and monoculture average values, respectively. Mix1 had the highest average volume per tree (0.34 m(-3)), at least 30 % higher than the average volume of pure and other mixed plantations. This mixture including only main species also exhibited the highest percentage of trees with high trunk length values of all plantation types. No pest or diseases were recorded on chestnut trees, and survival was high in all plantation types. Conclusion: The impact of mixed plantations on growth and timber quality was evidenced at age 20. In particular, the association including arboreal companion species enhanced chestnut tree performance.

Automated summary

The study aimed to assess the impact of different plantation types on the growth, survival, health, and timber quality of chestnut trees. The results showed that the association between chestnut trees and arboreal companion species (P. avium, Q. rubra, Q. robur) had the best performance, with higher height and diameter growth compared to other mixed plantations and monoculture. This plantation type also exhibited the highest average volume per tree and percentage of trees with high trunk length values, and chestnut trees had high survival rates in all plantation types.