Multi-site comparison of clonal arrangements for tropical and subtropical hybrids of Eucalyptus

The definition of the ideal eucalyptus clonal arrangement directly affects the forest industrial chain, quality of products, and stand yield. The impact of eucalyptus in mono- versus multiclonal stands on plantation production and sustainability has been frequently discussed by primary stakeholders within the pulp industry, but few studies have examined this topic through direct comparison. In this study, we evaluated the differences in genotype ranking and yield of Eucalyptus spp. and clones displayed in mono- and multiclonal arrangements. In this context, the objectives addressed were: (i) to estimate genetic parameters in multi-environment and site-by-site analyses; (ii) to predict genotypic values of clones and the effects of species in mono- and multiclonal experiments, and (iii) to compare the similarity between the ranks of clones and species in the two types of clonal stands. The study was conducted in 2018 at four different sites of the CMPC Celulose Riograndense company, located in the state of Rio Grande do Sul, Brazil. Mono- and multiclonal arrangements were tested at each site, involving 33 eucalyptus clones belonging to 10 species and hybrids. Multiple-tree-plot (MTP) and single-tree-plot (STP) experiments were used to simulate monoclonal stands and multiclonal or composite stands, respectively. In each experiment, a randomized block design was set with three repetitions, 16 plants per plot for MTP, and 24 repetitions and one plant per plot for STP. Traits monitored were diameter at breast height (DBH), total height (H), tree volume (VOL), mean annual volume increment (MAI), and survival (SUV). Data were analyzed using mixed model approaches, considering a normal distribution for growth traits and a binomial family for survival. There was a strong genotype × site interaction for all traits, indicating that edaphoclimatic conditions must be considered for the successful establishment of clonal composites of differing genotypes. There was high similarity in the classification of clones in both mono- and multiclonal experiments, with genetic correlation values above 0.90. The performance of clones differed in mono- and multiclonal experiments, which correlated with their competition behavior toward each other (aggressive, suppressed, or homeostatic). Thus, clonal composites can be recommended based on clonal competition and genetic heterogeneity to maximize the yield of the stand and safeguard the plantations from biotic and abiotic disturbances. This study allowed us to identify the differences between the two types of commercial stands and provide direction for future research regarding the performance of Eucalyptus spp. in differing clonal arrangements. Novel information about competition categories for different eucalyptus tropical and subtropical species were provided.