Branch development in the lower part of stem is critical to both early stem growth and wood quality of the most valuable section of tree, and its regulation through planting density has always been greatly concerned. Here the effect of planting density on branch development was examined in a five-year-old plantation of Betula alnoides with six planting densities (625, 833, 1111, 1250, 1667, and 2500 stems per hectare (sph)) in Guangdong Province, South China. Branch quantity (number, proportion, and density), morphology (diameter, length, and angle), position (height and orientation), and branch status (dead or alive) were investigated for 54 dominant or co-dominant trees under six treatments of planting density after the growth of each tree was measured. Factors influencing branch development were also explored by mixed modelling. The results showed that the mean tree heights of 1250 and 1667 sph treatments were higher than those of other planting density treatments. The quantity of live branches decreased with increasing planting density. However, planting density had no significant effect on the number of all branches, and there existed no remarkable difference in branch number and proportion among four orientations. As for branch morphology, only the largest branch diameter had a significantly negative correlation with planting density. In addition, high planting density significantly increased the height of the largest branch within the crown. Mixed effects models indicated that branch diameter, length, and angle were closely correlated with each other, and they were all in positively significant correlation to the branch height at the stem section below six meters. It was concluded that properly increasing planting density will promote natural pruning, improve early branch control, and be beneficial for wood production from the most valuable section of the stem.

Betula alnoides is a valuable timber species with wide ecological adaptability in Southeast Asia and southern China. There are more than 150,000 ha of B. alnoides plantations in China until now. However, heavy differentiation in growth and quality traits with low productivity are usually seen in the practice. Elite germplasm are thus urgently needed for this species. Here growth and quality traits for 199 families of 25 provenances were assessed at four sites when 10–15 years old to estimate genetic parameters and reveal genotype by environment (G × E) interaction, and screen out superior provenances and families for plantation forestry of B. alnoides. The growth and quality performances of provenances varied with sites. Significant site, provenance, family and provenance-site effects were revealed for most growth and quality traits, while significant family-site effects were only observed in crown width (CW) and crown shape (CS), inferring that there existed significant G × E interaction. The provenance repeatability ( $h_p^2$ ) and family heritability ( $h_f^2$ ) of all tested traits ranged from 0.026 to 0.636 and 0.148 to 0.578, respectively. Stem volume showed the highest genetic and phenotypic coefficients of variation (GCV, PCV) among all traits at each site. The diameter at breast height (DBH), tree height (H), height to live crown base (HCB) and CW were strongly correlated with other traits, and were also under relatively higher genetic control and had stronger discriminating ability on genotype differences. Through biplot analyses of main genotypic effect and G × E interaction (GGE) for these traits, five provenances and 20 families were screened out with selection ratio of 20 % and 10% at provenance and family level, respectively. The genetic and realized gains at provenance level ranged from 0.25% to 2.01% and 2.43% to 14.84%, and those at family level ranged from 0.85% to 21.22% and 5.76% to 36.71%, respectively. The findings lay a foundation for subsequent study on genetic improvement and breeding of this species, and application of the superior provenances and families will greatly increase the productivity of its plantations in practice.

Premise of the study: Microsatellite markers were developed for Vatica mangachapoi (Dipterocarpaceae), an endangered species indigenous to Southeast Asia and southern China.Methods and Results: Twenty microsatellite markers, including 12 polymorphic markers, were identified from V. mangachapoi using high‐throughput sequencing. Polymorphism at each marker was evaluated using 87 individuals from three natural populations. The number of alleles per polymorphic locus ranged from six to 15, and the observed and expected heterozygosity varied from 0.000 to 0.926 and from 0.177 to 0.864, respectively. These markers were transferred successfully to the endangered species V. guangxiensis.Conclusions: These markers may be used to investigate the genetic diversity and gene flow of V. mangachapoi and V. guangxiensis.

Erythrophleum fordii Oliv. is a valuable rosewood species indigenous to the tropical and warm sub-tropical zones of Vietnam, Laos, and South China. The natural forests have been heavily fragmented mostly due to over-exploitation and over-utilization, and alteration to croplands and fast-growing plantations. Therefore, it has been included in the IUCN Red List of Endangered Species as an endangered species. In the present study, genetic diversity and population genetic structure of 11 populations were estimated by SSR makers in South China. Five high polymorphic loci were studied with a total of 34 alleles, among which, seven were private alleles. The mean number of alleles per locus (A), the mean number of efficient alleles per locus (Ae), the observed (Ho) and expected (He) heterozygosity, and Shannon’s index (I) of the 11 populations were 3.40, 2.31, 0.52, 0.56, and 0.90, respectively. Correlation analysis between genetic parameters and geographical factors showed that He and I were in significant negative correlation with longitude, indicating that genetic diversity of E. fordii reduced gradually from West to East in south China. F_IS of eight populations with above five samples was on average 0.01, most loci conformed to Hardy-Weinberg equilibrium in these populations; their genetic differentiation coefficient (F_ST) was 0.18, indicating that genetic differentiation among populations was relatively low and there existed 18% genetic variation among populations. Gene flow (Nm) between these populations was 1.28. The Mantel test showed that genetic distance was not significantly correlated with geographical distance (p > 0.05). It was concluded that populations with high genetic diversity or private alleles, especially Longmen, Wuming and Pingxiang populations should be a priority for in situ conservations, meanwhile more populations and as many families as possible in each population should be collected for ex situ conservations of germplasm resources of this species in the future.