The peat swamp forests have a major role in the economic development of the State since 1947. They were the first forests to be logged commercially due to their easy access and the occurrence of the highly valuable timber, Ramin (Gonystylus bancanus). Peat swamp forests are located immediately behind the coastline and extend inland along the lower reaches of the main river systems.

Five peat swamp forest types are recognised:-

1. Mixed Swamp Forest
   Occurring on the peripheral zone of the swamp, the mixed swamp forests cover extensive areas of mainly shallow peat near the coast. This is the most valuable forest type consisting of species such as Ramin (Gonystylus bancanus), Jongkong (Dactylocladus stenostachys), Geronggang Padang (Cratoxylum glaucum) and Swamp Meranti (Shorea spp.).
2. Alan Batu Forest
   This forest, in its primary condition, is similar to that of the mixed swamp forest except that it is dominated by large trees of Alan (Shorea albida). The total number of species in this forest type is only slightly less than that in mixed swamp forest.
3. Alan Bunga Forest
   The primary stands of Alan Bunga forest are dominated by an even canopy of Alan (Shorea albida) which may reach a high volume. This forest type, generally, does not have any middle storey. The lower storey, although moderately dense, is composed of very few species.
4. Padang Batu Forest
   The mature stands of this forest type are usually dense, pole-like with small crowns, and have a stunted appearance. They consist of almost pure stands of Alan (Shorea albida).
5. Padang Paya Forests
   This is actually a group of several minor types which, for practical convenience, are grouped as one forest type. They are small in area, fragmentary in occurrence and of little commercial importance.
   One major type of the Padang Paya forest is similar to the Padang Alan Forest but is not dominated by Alan. It is characterised by dense stands of pole-size trees which may reach rather high volume. The stands may be dominated by Medang (Litsea spp.), Geronggong Padang (Cratoxylum glaucum), Bintangor (Calophyllum spp.), Keruntum (Combretocarpus rotundatus) and/or other minor species.