Biomass and dry matter production in planted forests and an adjacent secondary forest in the grassland area of Sakaerat, northeastern Thailand

Biomass and dry matter production in 12-to 14-year-old planted forests (including three exotic and three indigenous species) and secondary forest, and the biomass of grasslands were studied in Sakaerat to quantify the capability of plantations to rehabilitate degraded tropical lands. The reforestation of Imperata cylindrica grasslands enhanced the aboveground biomass growth by 5 to 37 times 12 years after planting. Exotic species, especially two Acacia species, accumulated greater biomass in their aboveground and belowground parts than did indigenous species and secondary vegetation at a similar age, and reached or surpassed the biomass in secondary or natural forests within the same area. Indigenous species also accumulated biomass at rates higher than those of secondary vegetation. Aboveground net primary production (ANPP) was greater in plantations of exotic species than in plantations of indigenous species, which had ANPP similar to those in secondary forest. The high ANPP in plantations of exotic species, including one Acacia and Eucalyptus plantation, was associated with higher annual leaf production and shorter leaf lifetime, combined with a small leaf biomass. The rate at which photosynthates were allocated to biomass was similar for plantations of exotic and indigenous species, but was lower in secondary forest than in plantations. The results showed the superiority of artificial plantations over natural regeneration for the rapid restoration of grassland in Sakaerat.