1. IntroductionForest restoration,

1. Introduction
Forest restoration, defined as the process of assisting the recovery
of a forest ecosystem that has been degraded, damaged, or destroyed,
is an intentional activity that initiates or accelerates the
recovery of a forest ecosystem with respect to its health, integrity,
and sustainability (Mansourian, 2005). In the restoration of abandoned
land, natural succession processes should be effectively utilized,
although the information required is not always adequate
(Donahue and Lee, 2008).
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.