1. Lowland Dipterocarp Forests

The term 'Lowland Dipterocarp Forest' was used by Symington (1943) to comprise all the Malayan well-drained primary climatic climax forests (as opposed to edaphic climax forests) of the plains, undulating land and foothills up to an average elevation of about 1,000 feet above sea level, or in other words the forests that would be included in Burtt Davy's (1938) tropical lowland evergreen rain-forest formation. Symington excluded the beach and heath forests which he listed under his edaphic climax formations. These lowland dipterocarp forests comprise the bulk of the commercially important forests in the country.

The forests are usually dense, though comparative freedom of movement on the ground is possible. They are composed of many thousands of species of trees* (often up to one hundred different species to the acre.), as well as shrubs, herbs and woody climbers. The upper or emergent storey is usually about 100 to 150 feet high, though trees nearly two hundred feet in height are often present, often rather discontinuous. Trees with a girth of ten feet or more often occur to a number of one to two trees per acre. This upper or emergent storey is usually characterised by a high occurrence, about fifty percent., of the family Dipterocarpaceae (Anisoptera, Dipterocarpus, Dryobalanops, Hopea, Shorea, Parashorea) though in some forests they are rare or almost absent. Other common large trees of this storey are Dyera costulata, Glutta spp., Intsia palembanica, Koompassia malaccensis, Melanorrhoea spp., Palaquium spp., Sindora spp. and Tarrietia spp.

The Main storey or second tree layer, which occupies a region of about 70 to 100 feet from the ground, forms a continuous canopy except immediately below the large emergent storey trees. This storey consists of young trees of the normally upper storey species together, predominantly, with members of the families Burseraceae, Guttiferae, Myristicaceae, Myrtaceae (Eugenia spp.) and Sapotaceae. The understorey or third tree layer consists of saplings of the upper two storeys together mainly with members of such families as Annonaceae, Euphorbiaceae, Flacourtiaceae and Rubiaceae. The density of the shrub layer is very variable, from very thick and dense to particularly open. It contains young saplings of larger trees, shrub species of Annonaceae, Euphorbiaceae and Rubiaceae and palms of which Arenga westerhoutii is common on steepish wooded slopes, Licuala spp., Pinanga disticha and Teysmannia altifrons in undulating country and Eugeissona triste (mainly west Malaya) on low ridges. The herb layer consists mainly young seedlings of the other layers and lianes with some aroids and ferns near streams and in moist valleys. Epiphytes are usually very poorly represented. There is usually a comparatively poor layer of litter though fallen leaves often cover the forest floor.

Many of the trees are buttressed, the buttresses ranging from short to tall and from thin to thick; some tree have stilt roots; some trees have fluted stems; the bark ranges from smooth, scaly to fissured; and the form of the stems is excellent, with typically a long clear bole and little taper.

It has usually been considered impossible to subdivide these lowland dipterocarp forests into recognised associations. It has long been recognised, however, that species in each of the storeys may be segregated and grouped to form a number of plant communities but it has been thought probable with the exception of Dryobalanops aromatica that the main factors determining distribution of species within the forest were chance and opportunity. Symington (1943) found it convenient to apply the term association-segregate of Braun (1935) to these communities. On the other hand it has become increasingly evident during recent years that certain broad and rough divisions into definite types can be made on the basis of the larger economic trees, in fact must be made if progress in forest management is to be made and correct silvicultural treatment is to be given in regenerating the forest after exploitation. As explained at beginning this chapter these types may not necessarily have any ecological significance. These forest types are:

• Red Meranti (Light Hardwood Shorea) -keruing (Dipterocarpus) forests.