Relationships between functional traits and the ability of forest tree species to reestablish in secondary forest and enrichment plantations in the uplands of northern Thailand

Many attempts to restore tropical forests at deforested lands have failed, mostly because the traits of planted species were inappropriate without information on their regeneration. Thus, a new approach for determining the ability of tree species to reestablish in degraded forest land is necessary for restoration practices. We investigated plant functional traits and the factors affecting restoration success in forest communities that had been restored both by natural regeneration and enrichment plantations, in abandoned shifting-cultivation areas within the tropical montane forests of Suthep-Pui National Park Chiang Mai, northern Thailand. Five 1-ha permanent plots (100. m. ×. 100. m) were established in three different forest management areas: primary forest, secondary forest, and enrichment plantations. The species composition of canopy trees, regenerated seedlings, and saplings were analyzed to determine tree functional traits and the factors governing forest composition, such as the physical environment and recruitment limitation. We found that trees within primary forest tended to have relatively heavier wood and larger seeds than secondary forest species. The dominance of certain species in primary forests was significantly correlated with wood density and seed size, although the correlations in secondary forests and enriched plantations varied among stands. The seedlings of the species with high leaf toughness, large leaf mass area, and wood density tended to be more sensitive to environmental conditions. Species with larger seeds tended to have a more limited recruitment, suggesting that enrichment plantations were more suitable for the establishment of these species. Our results suggest that the restoration of primary forest by natural regeneration is difficult because it is prevented by both environmental conditions and recruitment limitation. The contribution of these factors was species-dependent, which could be partly predicted by their functional traits.