Shamsudin Ibrahim, director of FRIM's Forestry and Environment Division, says that they have planted a limited number of tree species in the hope that nature will do the rest of the work itself. He says the experiment here has been a valuable lesson in what to plant and when, in how to space out the seedlings, and in what kinds of plants and animals will readily return by themselves.
In 1926 one area in the former mining site was planted with nurse trees that would provide shade and improve the soil before the planting of dipterocarp species (large, hardwood rainforest trees valuable as timber). The nurse tree species introduced included Pterocarpus peltocarpum and camphor (Dryobalanops aromatica), locally known as kapur, and heavy hardwood species (such as Neobalanocarpus heimii). "The same technique of introducing nurse trees prior to planting with valuable timber species was repeated at all degraded sites in FRIM in early 1927, and today the site is fully covered with many tree species, which to untrained eyes of many visitors appears to be a multilayer vegetation, with no distinct differentiation between planted and natural species," Ibrahim says.
Initially around 15 tree species were planted, including fast-, medium- and slow-growing timbers, but now the area has more than 70 species of trees, says FRIM's director general Abdul Latif Mohmod. "The timber species that were initially planted acted as nurse trees to provide a microenvironment conducive for other timber species to establish and grow with minimal maintenance." The forest today looks very similar to mature rainforest—it has much of the structure of established forest, but what it lacks is the enormous ecological diversity.
The researchers are confident that will come with time, although it could take up to 1,000 years to get the majority of the diversity of plant species back. "What is being demonstrated at FRIM is an excellent testimony that restoration of tropical forests is feasible, but the process of returning them to their primary condition will definitely go beyond 90 years," Mohmod says. "The ecosystem is recovering but has not reached its original state, because in undisturbed tropical lowland forests the species richness is estimated at more than 200 species per hectare. The trees may reach their maturity at 60 to 80 years, but the maturity of the ecosystem may extend to hundreds of years or longer."
And getting the tools and know-how we need to help rainforests return is an urgent task, Laurance says: "In many parts of the world—such as the Philippines, Madagascar and the Brazilian Atlantic forests—there's hardly any old-growth forest left. We need to learn how to help these imperiled forests recover faster and better."