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Background and Objectives: The stable stand structure of mixed plantations is the basis of giving full play to forest ecological function and benefit. However, the monocultural Eucalyptus plantations with large-scale and successive planting that caused ecological problems such as reduced species diversity and loss of soil nutrients have presented to be unstable and vulnerable, especially in typhoon-prone areas. The objective of this study was to evaluate the nonspatial structure difference and the stand stability of pure and mixed-Eucalyptus forests, to find out the best mixed pattern of Eucalyptus forests with the most stability in typhoon-prone areas. Materials and Methods: In this study, we randomly investigated eight plots of 30 m × 30 m in pure and mixed-Eucalyptus (Eucalyptus urophylla S. T. Blake × E. grandis W. Hill) plantations of different tree species (Neolamarckia cadamba (Roxb.) Bosser, Acacia mangium Willd., and Pinus elliottii var. Elliottii Engelm. × P. caribaea Morelet) on growth status, characterized and compared the distribution of nonspatial structure of the monoculture and mixtures, and evaluated the stand quality and stability from eight indexes of the nonspatial structure, including preservation rate, stand density, height, diameter, stem form, degree of stem inclination, tree-species composition, and age structure. Results: Eucalyptus surviving in the mixed plantation of Eucalyptus and A. mangium (EA) and in the mixed plantation of Eucalyptus and P. elliottii × P. caribaea (EP) were 5.0% and 7.6% greater than those in pure Eucalyptus plantation (EE), respectively, while only the stand preservation rate of EA was greater (+2.9%) than that of the pure Eucalyptus plantation. The proportions of all mixtures in the height class greater than 7 m were fewer than that of EE. The proportions of EA and mixed plantation of Eucalyptus and N. cadamba (EN) in the diameter class greater than 7 m were 10.6% and 7.8%, respectively, more than that of EE. EN had the highest ratio of branching visibly (41.0%), EA had the highest ratio of inclined stems (8.1%), and EP had the most straight and complete stem form (68.7%). The stand stability of the mixed plantation of Eucalyptus and A. mangium presented to be optimal, as its subordinate function value (0.76) and state value (ω = 0.61) of real stand were the largest. Conclusions: A. mangium is a superior tree species to mix with Eucalyptus for a more stable stand structure in the early growth stage to approach an evident and immense stability and resistance, which is of great significance for the forest restoration of Eucalyptus in response to extreme climate and forest management.

The superior provenance is a prerequisite for ecological restoration, and a better mastery on the growth rhythms of Ormosia species is fundamental to reforest effectively. For the selection of better provenance and the formulation of artificial cultivation methods, the height and the ground diameter of Ormosia hosiei Hemsl. et Wils., O. xylocarpa Chun ex L. Chen and O. henryi Prain seedlings of different provenances were monitored in the first year. The results showed that their dynamic growths presented a slow-fast-slow trend that fit a “S” growth curve by the logistic mathematical model, and the growth of Ormosia species seedlings of different provenances significantly differed. The accumulated growth increment of O. xylocarpa was the largest (averagely 45.50 cm) and the accumulated growth increment of O. henryi was the least (averagely 20.33 cm). Thus, O. hosiei of Jiujiang provenance, O. xylocarpa of Liping provenance and O. henryi of Longquan provenance have a stronger adaptability for future artificial cultivation in Jiangxi China. RESUMO A origem melhor é um pré-requisito para a restauração ecológica, e um melhor domínio dos ritmos de crescimento das espécies Ormosia é fundamental para reflorescimento com eficácia. Para a seleção de melhor origem e a formulação de métodos artificiais de cultivo, a altura e o diâmetro do solo de mudas Ormosia hosiei Hemsl. et Wils., O. xylocarpa Chun ex L. Chen e O. henryi Prain de diferentes origens foram monitoradas no primeiro ano. Os resultados mostraram que seus crescimentos dinâmicos tiveram uma tendência lenta-rápida-lenta que se correspondia a uma curva de crescimento “S” no modelo matemático logístico, e o crescimento de espécies de mudas Ormosia de diferentes origens diferiram significativamente. O incremento de crescimento acumulado de O. xylocarpa foi o maior (em média de 45,50 cm) e o incremento de crescimento acumulado de O. henryi foi o menor (em média de 20,33 cm). Assim, O. hosiei da origem de Jiujiang, O. xylocarpa da origem de Liping e O. henryi da origem de Longquan têm uma adaptabilidade mais forte para o futuro cultivo artificial em Jiangxi, China.

Genomic loci related with resistance to gall-inducing insects have not been identified in any plants. Here, association mapping was used to identify molecular markers for resistance to the gall wasp Leptocybe invasa in two Eucalyptus species. A total of 86 simple sequence repeats (SSR) markers were screened out from 839 SSRs and used for association mapping in E. grandis. By applying the mixed linear model, seven markers were identified to be associated significantly (P ≤ 0.05) with the gall wasp resistance in E. grandis, including two validated with a correction of permutation test (P ≤ 0.008). The proportion of the variance in resistance explained by a significant marker ranged from 3.3% to 37.8%. Four out of the seven significant associations in E. grandis were verified and also validated (P ≤ 0.073 in a permutation test) in E. tereticornis, with the variation explained ranging from 24.3% to 48.5%. Favourable alleles with positive effect were also mined from the significant markers in both species. These results provide insight into the genetic control of gall wasp resistance in plants and have great potential for marker-assisted selection for resistance to L. invasa in the important tree genus Eucalyptus.

Identification of loci or genes under natural selection is important for both understanding the genetic basis of local adaptation and practical applications, and genome scans provide a powerful means for such identification purposes. In this study, genome-wide simple sequence repeats markers (SSRs) were used to scan for molecular footprints of divergent selection in Eucalyptus grandis, a hardwood species occurring widely in costal areas from 32° S to 16° S in Australia. High population diversity levels and weak population structure were detected with putatively neutral genomic SSRs. Using three FST outlier detection methods, a total of 58 outlying SSRs were collectively identified as loci under divergent selection against three non-correlated climatic variables, namely, mean annual temperature, isothermality and annual precipitation. Using a spatial analysis method, nine significant associations were revealed between FST outlier allele frequencies and climatic variables, involving seven alleles from five SSR loci. Of the five significant SSRs, two (EUCeSSR1044 and Embra394) contained alleles of putative genes with known functional importance for response to climatic factors. Our study presents critical information on the population diversity and structure of the important woody species E. grandis and provides insight into the adaptive responses of perennial trees to climatic variations.