Silviculture

Natural Forest
The Silviculture Unit carries out the following systematic silvicultural activities in the logged-over forests in permanent forest estate:

• A silvicultural treatment (known as G1) carried out one year after logging in peat swamp forests was implemented from early 50's until 1995. The aim was to release the advance growth of better marketable species and to eliminate the lesser valued species.
• Ten to fifteen years after the first silvicultural treatment (G1), diagnostic sampling (DS) is carried out. The aim is to determine the condition of the residual stand, identify the areas which need further silvicultural treatment and the type of silvicultural treatment needed. The result of this DS will decide the nature of the second (known as G10) silvicultural treatment.
• Liberation Thinning, a type of silvicultural treatment, introduced by Food and Agricultural Organisation (FAO) in 1976 in Sarawak, was adopted as a tool to treat the logged-over mixed dipterocarp forests until 1995.
• Further information concerning recruitment, growth rates and silvicultural activities of regeneration would be obtained from the establishment of yield plots and research plots in these silviculturally treated forests. Data collected from these plots include not only the growth increment, mortality, ingrowth, species composition, but also the quality of the stands and the development of natural regeneration. These plots are regularly remeasured.

Wherever natural regeneration are poor as in the case of Shorea albida in the peat swamp forests, and Rhizophora apiculata and Rhizophora mucronata in mangrove forests, enrichment planting is done. Natural seeding was also practised by leaving mother trees for every certain number of trees cut.

Plantation
Planting of local species Shorea macrophylla and Eusideroxylon zwageri started in 1936 during the British era. The performance is promising. Plantation of exotic species (e.g. Gmelina arborea, few pine species, Eucalyptus species, Paraserianthes falcataria, Tectona grandis) and local species such as Shorea albida, Eusideroxylon zwageri, Shorea macrophylla, Shorea splendida, Shorea hemsleyana, Neolambarckia cadamba, Rhizophora mucronata and Rhizophora apiculata were planted on experimental and trial basis in hill, swamp and mangrove forests. In the early eighties, plantation activities became a big scale operation, planting Acacia mangium as the preferred species in the abandoned shifting cultivated areas. The species list now includes more species such as Durio zibethinus, Dryobalanops and Shorea species. Growth, mortality and vigour are monitored regularly.