Growth dynamics and productivity of pure and mixed Castanea sativa Mill. and Pseudotsuga menziesii (Mirb.) Franco plantations in northern Portugal

Abstract

Abstract: Since the late 1980’s the productivity of monocultures versus mixed-species forests has been the object of special interest and study by forest managers and ecologists. All over the world mixed plantations have been established in different proportions to analyse if mixtures can provide greater yields and more benefits than monocultures of the component species and also to understand if they can be an interesting economic option. An experimental design trial was set up in the north of Portugal in a replacement series with pure and mixed Castanea sativa Mill. and Pseudotsuga menziesii (Mirb.) Franco. The objective of this study was to assess growth dynamics and compare the aboveground biomass and net primary production of the two species in pure and mixed treatments in proportions 1:1 and 1:3. The growth was measured at 7, 11, 15, 17, 19, 27 and 28 years after planting and aboveground net primary production was estimated at age 28 years. As a component of the mixed treatments, P. menziesii exhibited greater height, diameter and aboveground biomass than C. sativa. Relative yield total indicated a higher productivity in the mixtures compared with the pure treatments. Early in the development the pure treatments had a similar aboveground biomass per hectare as the mixtures, but later the mixtures had more yield than the pure treatments. The mixture productivity increase trough time appears to be a result of both canopy stratification and better use of site resources. The aboveground net primary production was also higher in mixed than in the pure treatments. This study shows the importance of comparing mixed and pure stands.