Synergy in mixed Nothofagus spp. plantations: the effect of deciduous/evergreen neighbourhood on tree growth in the Chilean Andes

Background: The genus Nothofagus is a key component of the Valdivian temperate rainforests of South America, and several of its species have shown promising growth in plantations. Plantations with these species are an opportunity to diversify the Chilean forest sector, ideally through mixed-species arrangements, but the existing literature in this regard is scarce. This work aimed to evaluate individual tree growth for three Nothofagus species in a mixed plantation, considering two types of neighbourhoods. Methods: In a mid-elevation site in the foothills of the Andes ranges we evaluated growth of Nothofagus alpina (Poepp. & Endl.) Oerst, Nothofagus dombeyi (Mirb.) Oerst and Nothofagus obliqua (Mirb.) Oerst according to their neighbourhood, comprised of evergreen or deciduous tree species. We conducted stem analyses for 30 trees (10 per species, one-half with each type of neighbourhood; 370 cross-sections in total) and compared growth in diameter (d), height (h), and volume (v) for each of the 30 trees with nine nonlinear mixed-effects models. Results: Nothofagus alpina showed significantly greater cumulative growth in all variables when growing in an evergreen neighbourhood (EN) compared with a deciduous neigbourhood (DN): average diameter (± 1SD) of 15.3 ± 1.4 vs. 10.8 ± 2.0 cm; average height (± 1SD) of 15.5 ± 1.8 vs. 13.2 ±1.0 m; average volume (± 1SD) of 0.15 ± 0.05 vs. 0.06 ± 0.02 m3. Nothofagus dombeyi showed similar cumulative growth in both conditions for all variables, but there was less variability and greater cumulative volume in the evergreen neighbourhood condition. Finally, Nothofagus obliqua showed similar cumulative growth in both conditions, for average diameter (± 1SD) (14.7 ± 2.0 cm) and average volume (± 1SD) (0.01 ± 0.03 m3), but the average height (± 1SD) was significantly greater in the EN compared to DN (13.8 ± 0.8 vs. 11.2 ± 0.9 m). Conclusions: A suitable arrangement of mixed Nothofagus species plantations may deliver greater growth and productivity than pure plantations, or at least greater timber value considering that one species (N. dombeyi) usually surpasses the others in growth, but its timber is less valuable and its silviculture more costly. In these mixtures both facilitation and complementarity mechanisms occur, which was mostly expressed in the mid-tolerant N. alpina surrounded by the evergreen neighbourhood dominated by the shade-intolerant N. dombeyi. Our results provide new information relevant for the establishment of mixed plantations for production or restoration purposes. Both in Chile and Argentina, these three Nothofagus species cover extensive areas within the Valdivian Temperate Rainforests, so there is a great potential for these plantations in this or other regions with similar site conditions.