Abstract:

Objective: The stand characteristics of 13-year-old Cyclobalanopsis glauca natural forest which was converted from Eucalyptus grandis plantations were reported, aiming to provide scientific basis for revealing the basic conditions for the conversion of plantations into natural broad-leaved forests in central-subtropical zone, the vegetation control of plantation, the protection of natural broad-leaved forest and the development of native hardwood trees. Method: 3 sample plots in size of 20 m×20 m were set in the C. glauca natural forest which was converted from E. grandis plantations in Yong'an, Fujian Province, and each plot was divided into 4 quadrats of 10 m×10 m. 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, the structure and growth of the stand were analyzed by using importance values, commonly used diversity indices and main stand description factors. Result: The mean DBH, mean height, density, and volume of the 13-year-old C. glauca natural forest were 6.2 cm, 9.5 m, 6 308 stems·hm^-2, and 94.43 m³·hm^-2, respectively. The ratio of height to diameter was between 41 and 380, and the average was 155. Both the diameter and tree height structure showed the characteristics of uneven-aged forest. 36.99% of the trees in the stand were from sprouts, among which the largest number of trees was C. glauca, accounting for 57.86% and 66.12% of the total number of trees from sprouts and the total number of C. glauca trees in the stand, respectively. E. grandis was in the form of dead standing tree or dead fallen tree, and the density of dead standing tree was 966 stems·hm^-2. There were 45 species in the arbor layer, and the Shannon-Wiener index, evenness index and dominance index were 3.74, 0.68, and 0.14 respectively. The number of arbor and shrub species in the arbor layer were 34 and 11, and the importance values were 88.65% and 11.35%, respectively. There were 30 evergreen and 15 deciduous tree species in the arbor layer, with the importance values were 67.38% and 32.62%; the number of trees, tree species, and the importance value of broad-leaved evergreen were obviously more than that of deciduous broadleaf trees. Broad-leaved evergreen was the main part of the arbor layer and C. glauca was the dominant species with its relative abundance (32.36%), relative frequency (7.69%), relative dominance (16.75%) and importance value (18.94%) being the largest in the arbor layer. There were 27 tree species in the shrub layer. The Shannon-Wiener index, evenness index and dominance index were 3.69, 0.78, and 0.13, respectively. The tree species of arbor and shrub species were 15 and 12, respectively, but the proportion (69.85%) and importance value (60.87%) of shrub species were higher than that of arbor species (the percentage and importance value were 30.15% and 39.13%, respectively). The number of trees, tree species, and the importance value of evergreen tree species were much higher than deciduous tree species. The majority of shrub layer was evergreen shrub and Camellia sinensis was the dominant species in the layer. Compared with the natural C. glauca forests of similar age, there were no differences in characteristics of the 13-year-old C. glauca natural forest, appearing to be a typical subtropical natural broad-leaved forest at young age. In both arbor and shrub layer, there were many precious or high value timber tree species. Conclusion: The E. grandis plantation has been successfully converted into a 13-year-old C. glauca natural forest that has a high crown density, high density of trees, high height-diameter ratio, rich tree species diversity and distinct characteristics of uneven-aged stands. There was no essential difference between the stand characteristics of this 13-year-old C. glauca natural forest with those natural C. glauca forests at similar age. It was a 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.

Key words: Eucalyptus grandis plantation, conversion, Cyclobalanopsis glauca natural forest, stand characteristics, natural regeneration