Productivity and dynamics of pure and mixed-species plantations of Populous deltoids Bartr. ex Marsh and Alnus subcordata C. A. Mey

Mixed-forest plantation with native species have gradually become the focus of forest research. The need to better understand their performance and productivity is, nowadays, a matter of particular relevance to forestry practice. The objective of this study was a long-term analysis of the effects of species-mixing of Populus deltoides Bartr. ex Marsh and Alnus subcordata C. A. Mey on aboveground biomass and net primary production, growth dynamics, and their relative yields total in pure and mixed stands. The experiment consisted of a replacement series that was established in 1996, using a randomized block design with five treatments (100P:0A, 67P:33A, 50P:50A, 33P:67A, 0P:100A) in four replicate blocks and two species were systematically mixed within rows. In the early stages, both species had a similar growth trend, while the differences were more pronounced at higher ages. The results show that inter- and intraspecific competition and nutrient cycling had the most pronounced effect on stand growth over time. Populus deltoides benefited from growing in mixture; canopy stratification reduces interspecific competition for light, and this species functioned best in mixed stands. In contrast, A. subcordata was sensitive to competition and had the highest growth in pure stands. In general, positive interactions between the two species led to the highest relative yield total and productivity in mixtures compared with pure stands. Within the framework of this experiment, it seems that the relative proportions of 50% Populus deltoides and 50% Alnus subcordata could provide economic and environmental benefits and increase the stability and productivity of the stands.