Testing framework species for restoring biodiversity on degraded forestland in Northern Thailand

ABSTRACT: The framework species method of forest restoration is designed to restore diverse forest ecosystems on degraded forestland for biodiversity conservation of environmental protection. It involves planting 20-30 tree species, to rapidly re-establish basic forest structure and ecological functioning, whilst accelerating natural forest regeneration. Framework tree species are those with high growth and survival rates when planted out in degraded areas. They should have dense spreading canopies, to shade out herbaceous weeds, and they should provide resources that attract seed-dispersing animals. Tree-planting restores basic ecosystem structure and function, whilst seed-dispersing animals re-establish biodiversity and the original tree species composition of the forest.

This paper presents results from experimental plots established, to test this technique in a watershed at 1,207-1,310 elevation, in Doi Suthep-Pui National Park, northern Thailand. The area had formerly been covered with evergreen forest, which had been cleared and the deforested land cultivated by Hmong hill-tribe people. Saplings, 50-60 cm tall of 39 tree species, were planted 1.6-1.8 m apart, over 6 rai in 1998 and 1999, to test their potential to act as framework tree species. The planted trees were monitored for survival, growth, canopy width, flowering and fruiting and use by birds.

In the 1998 plots, five species maintained a 75% survival rate through to the end of the third growing season: Bischofia javanica, Castanopsis calathiformis, Ficus altissima, Melia toosendan and Spondias axillaris. In 1999, a short period without rain immediately after planting enabled identification of drought-tolerant species. Such species (with higher than 75% survival after the first growing season) were Ficus benjamina, Ficus glaberrima, Ficus hispida, Ficus racemosa, Heynea trijuga, Hovenia dulcis and Rhus rhetsoides. Fourteen species achieved a mean height of 1.5 m by the end of the second growing season: Acrocarpus fraxinifolius, Balakata baccata, Castanopsis calathiformis, Erythrina subumbrans, Ficus hispida, Gmelina arborea, Hovenia dulcis, Macaranga denticulata, Melia toosendan, Michelia baillonii, Nyssa javanica, Prunus cerasoides, Rhus rhetsoides and Spondias axillaris. Nine achieved a canopy width of 1.8 m or more by the end of the second growing season, enabling them to close canopy with neighbours: Acrocarpus fraxinifolius, Balakata baccata, Castanopsis calathiformis, Erythrina subumbrans, Ficus subulata, Macaranga denticulata, Melia toosendan, Prunus cerasoides and Spondias axillaris. Four species (Prunus cerasoides, Quercus semiserrata, Erythrina subumbrans and Ficus subulata) produced flowers or fruits, likely to attract seed-dispersing animals, within 3 years. Trees species most commonly used as perches by birds were Melia toosendan, Spondias axillaris, Prunus cerasoides, Balakata baccata, Gmelina arborea and Rhus rhetsoides.

Considering all criteria combined, 16 species were classified as the most suitable framework tree species: Balakata baccata, Castanopsis calathiformis, Erythrina subumbrans, Eugenia albiflora, Ficus hispida, Ficus racemosa, Gmelina arborea, Hovenia dulcis, Macaranga denticulata, Melia toosendan, Michelia baillonii, Nyssa javanica, Prunus cerasoides, Rhus rhetsoides, Sarcosperma arboreum and Spondias axillaris.