Factors Affecting Growth of Wildlings in the Forest and Nurturing Methods in Nursery

ABSTRACT: Forest restoration by planting nursery-raised seedling stock is relatively expensive. There are many technical problems involved in seedling production from seeds. Transplanting tree seedlings from forests into nurseries may reduce these problems. The objectives of this research were to determine which factors affect the growth of wildlings in the forest and to develop techniques to nurture wildlings transplanted from the forest in the nursery. This research was conducted in Doi Suthep-Pui National Park at the Forest Restoration Research Unit (FORRU). The species tested were: Sarcosperma arboreum Bth. (Sapotaceae), Castanopsis tribuloides (Sm.) A. DC. (Fagaceae), Podocarpus neriifolius D. Don (Podocarpaceae) and Eugenia albiflora Duth. ex Kurz (Myrtaceae).

This research was divided into 2 parts: i) wildlings of these 4 species were monitored in the forest, to determine which factors affect their growth, including distance from parent tree, ground flora competition, canopy cover and soil moisture and ii) in the nursery, various treatments were tested on wildlings grown in plastic bags. Three size classes of wildlings were each subjected to two pruning methods.

For all species, most of the wildlings measured in the forest grew very slowly, on average approximately 4-5 cm in height, over 12 months. Most mortality occurred at the beginning of the rainy season (June-July, 10.17%). P. neriifolius wildlings had the highest mean mortality during 1 year, viz. 19.4%, followed by C. tribuloides 13.2%, S. arboreum 12.5% and E. albiflora 11.1%. Distance from the parent tree showed a negative and significant correlation with the mortality rates of P. neriifolius and C. tribuloides wildlings (r = 0.892, p = 0.024 and r = -0.903, p = 0.036). Canopy cover was positively and significantly correlated with the mortality rates of E. albiflora and C. tribuloides (r = 0.892, p = 0.042 and r = 0.976, p = 0.005). Analysis of the effects of soil moisture revealed a significantly positive correlation with mortality rates of P. neriifolius, E. albiflora, and C. tribuloides wildlings (r = 0.921, p = 0.009, r = 0.816, p = 0.047 and r = 0.935, p = 0.006). Correlation analysis failed to detect a significant linear relationship between these factors and relative growth rate of wildlings for all species (p > 0.05).

The optimum height of wildings for transfer was not more than 20 cm, since they could be dug up without injuring the roots, which reduced the transplantation shock. Pruning before potting significantly reduced mortality and promoted high relative growth rate. Optimum time of transfer was at the beginning of the rainy season.