Objective: It's the first time to report the characteristics of 7-year-old Castanopsis fargesii natural forest which was converted from Eucalyptus dunnii plantation that suffered from successive freezing damage in Yong'an, Fujian Province, aiming to provide a scientific basis for revealing the basic conditions for the conversion of plantations into natural broad-leaved forests in mid-subtropical zone, the vegetation control of plantation, the protection of natural broad-leaved forest and the development of native hardwood forest. Method: 3 sample plots in size of 20 m × 20 m were set in the natural forest of C. fargesii which was converted from E. dunning plantation in Yong'an, Fujian Province, and each plot was divided into four 10 m × 10 m quadrats. The arbor layer of each quadrat was investigated and one representative quadrat in each plot was selected for shrub layer investigation. At the same time, a small quadrat of 4 m × 4 m was set in the center of each plot for the investigation of the herb layer. The stand characteristics such as tree species composition, diversity of the arbor layer and shrub layer and stand growth were analyzed by using important values, commonly used diversity indices and main stand description factor. Results: The mean DBH, mean height, density and volume of the 7-year-old C. fargesii natural forest which was converted from E. dunnii plantation were 5.1 cm, 6.8 m, 6 350 stems•hm-2 and 47.70 m3•hm-2, respectively. The ratio of height to diameter was between 43 and 393, and the average was 146. Both the diameter and tree height structure showed the characteristics of heterogeneous forest. The proportions of regenerated seedlings and sprouts were 84.78% and 15.22%, respectively. E.dunnii was in the form of dead standing tree or down-timber, and the density of dead standing tree was 550 stems •hm-2. There were 51 tree species in the arbor layer, and the Shannon-Wiener index, evenness index and dominance index were 4.20, 0.74, and 0.11, respectively. The number of arbor and shrub species in the arbor layer were 38 and 13, and the importance values were 87.32% and 12.78%, respectively. There were 30 evergreen and 21 deciduous tree species in the arbor layer, with the importance values of 57.93% and 42.07%; and the number of trees and tree species of broad-leaved evergreen were more than that of deciduous broad-leaf trees. C. fargesii was the dominant species in the arbor layer, and its relative abundance, relative frequency, relative dominance and importance value were the largest. There were 21 tree species in the shrub layer. The Shannon-Wiener index, evenness index and dominance index were 3.68, 0.84, and 0.10, respectively. The number of arbor and shrub species were 15 and 6, respectively, and the proportion of arbor species (47.68%) was less than shrub species (52.32%), but its importance value (53.91%) was higher than that of shrub species (46.09%). In the shrub layer, not only the number of tree species but also the relative abundance, relative frequency, relative dominance and importance value of evergreen tree species were higher than that of deciduous tree species. Among all the tree species in the shrub layer, the relative abundance, relative frequency, relative dominance and importancevalue of the Eurya loquaiana were the largest. Compared with the C. fargesii forest by artificial measures promoting natural regeneration (AMPR) of similar ages, there were no differences in characteristics of the 7-year-old C. fargesii between the natural forest and those of similar ages. It belongs to a relatively typical subtropical natural broad-leaved forest in the young stage. Both in arbor and shrub layer, there were many precious or high value timber tree species. Conclusion: The E. dunnii plantation has been successfully converted into 7-year-old C. fargesii natural forest with rich tree species diversity and distinct characteristics of heterogeneous forest. This C. fargesii natural forest has a high canopy density, tree number density, ratio of height to diameter and stand volume. The stand characteristics of the 7-year-old C. fargesii natural forest were no longer essentially different from those of C. fargesii forest byartificial measures promoting natural regeneration atsimilar age. It was a relatively typical subtropical natural broad-leaved forest in the young period and a typical case of successful conversion of the subtropical plantation into a natural broad-leaved forest. © 2021, Editorial Department of Scientia Silvae Sinicae. All right reserved.
