Effects of Mature Trees on Seedling Establishment on Deforested Sites

In Thailand, accelerated natural regeneration (ANR) of forest on degraded land has not been successful due to lack of knowledge about the natural processes of forest regeneration. The role of remnant trees in disturbed areas has been widely assumed to help to increase seedling recruitment by attracting seed dispersers. This study was carried out to determine the effects of mature isolated trees on tree seedling recruitment in deforested areas and to find out which tree species should be planted to attract seed-dispersing birds. Naturally established tree seedlings were surveyed beneath fifty-one remnant trees (7 species) compared with open areas at deforested areas, south and above of Mae Sa Mai village in Doi Suthep-Pui National Park. Observations of birds visiting trees were done on the remnant trees studied and on fruiting trees in intact forest. A total of seventy-eight tree seedling species (1,156 individuals) had become established in the study plots. Animals dispersed fifty-seven of the tree species (64.2% of individuals), while wind disperse twenty-one (35.9% of individuals). Most mature remnant trees did not increase seedling recruitment beneath their crowns, except for Schima wallichii (DC.) Korth. (Theaceae) (p > 0.05). The density and species richness of animal-dispersed seedlings beneath mature remnant trees did not depend on the species of the mature trees (p > 0.05). Species with fleshy fruits (e.g. Callicarpa arboreae Roxb. var. arborea, Verbenaceae) were not necessarily more attractive than those with dry fruits (e.g. Schima wallichii (DC.) Korth.). There was no relationship between tree size and seedling density established beneath their crowns (p > 0.05). Bigger crowns tended to support a lower species richness of natural seedlings. Growth rates of natural seedlings beneath tree crowns and in open areas were similar (p > 0.05). Trema orientalis (L.) Bl. (Ulmaceae) was the fastest growing species of natural seedling. Bird observations showed that Schima wallachii (DC.) Korth. (Theaceae) was the remnant tree species that attracted most birds. Three bulbuls species, Pycnonotus aurigaster (Sooty-headed Bulbul), P. flavescens (Flavescent Bulbul), and P. jocosus (red-whiskered Bulbul) were the most important frugivorous birds that dispersed seeds from intact forests into the deforested site.