While the designation "rain forest" applied to the vegetation of New Britain is correct in a broad, general sense, this term conveys no idea of the variations in this rain forest which occur in response to such local influences as soil, drainage, and differences in elevation.

Vegetation may affect military operations by limiting or preventing movement; by limiting or preventing observation; and by providing cover and concealment from both ground and air. Further, vegetation serves as an excellent index to the character of the terrain, since there are definite, consistent relationships between plants and the habitats in which they grow. In the Southwest and Western Pacific the relatively uniform natural conditions, which have been little disturbed by man, are reflected by a small number of broad, uniform vegetation types. In that part of New Britain where the 1st Marine Division operated, and with which this discussion deals specifically, the vegetation may be classified in only six types--in contrast to more than twenty types in current use in the western United States. These are recognized and described as follows: mangrove swamp, swamp forest, tropical rain forest, secondary growth, grassland, and plantations.

Mangrove Swamp.--Mangrove trees may range from twenty to sixty feet tall; those in one locality generally are of uniform height. The main trunk is raised above the ground, supported by a dense tangle of stout prop roots which develop at an angle to the trunk, often ten feet above the ground. Mangroves can begin growth only in brackish or salt water, hence are found only near coasts on tidal flats and estuaries subject to flooding. The terrain is always poorly drained, and usually flooded at high tide; deep, muddy, meandering streams are common.

Cover from air observation is complete: ground observation and visibility are restricted to 10 to 15 yards. Movement of troops is virtually impossible due to the tangle of trunks and roots, as well as the poorly-drained or flooded terrain.

A CAPE GLOUCESTER PATROL makes its way through a devastated swamp forest.

Swamp Forest.--Swamp forest is characterised by widely spaced trees of very irregular height, the tallest being upwards of 100 feet high. Quite commonly these trees have widely spreading buttress roots, which give a fluted appearance to the bottom of the trunk. Wide spacing and irregular height of the mature trees permit a moderately dense to very dense undergrowth of varying heights. Both undergrowth and mature trees are generally thickly matted with lianas, vines, and lawyer cane.

Swamp forest occurs near coasts or along lower courses of streams and similar inland areas; wherever it occurs much of the area is subject to periodic or occasional overflow by flood waters during the rainy season. The terrain under swamp forest always is of low relief and poorly drained. Some areas are comparatively dry during the dry season, but they are commonly flooded in the wet season by standing water or overflow from nearby streams. This vegetation type is the dank, steaming tropical jungle of the fiction writer.

Cover and concealment are complete in swamp forest. Ground observation usually is restricted to a few yards. Movement of troops or vehicles is very difficult. Flooded areas virtually preclude movement during the wet season. Large areas of swamp forest occur in the Cape Gloucester-Borgen Bay area: the vegetation behind the landing beaches was a strip of swamp forest which extended nearly to the airdrome area on the west, as well as eastward around Borgen Bay. In fact, a major part of the area where the 1st Marine Division operated was characterized by this type of cover.

Tropical Rain Forest.--Above the swamp forest is found the true rain forest of the tropics. Here the tallest trees are of fairly uniform height, set so closely together as to form virtually a complete canopy overhead. Usually there are only ten to twenty of these mature trees per acre, commonly 125 to 150 feet tall. There is a second "story" of smaller trees, their crowns reaching to just below the canopy formed by the tallest trees; frequently there is an understory of brush and young trees beneath these, ranging up to twenty or thirty feet tall. Sometimes there is a fairly complete ground cover of ferns and other herbs up to about two feet in height. The actual interior of such a forest is relatively open except for occasional small tangles of climbing bamboos, rattan palms, or lianas. Rain forest is characteristic of higher ground and well-drained terrain which may vary from gently rolling to rugged.

Complete cover and concealment from air observation are afforded. Ground observation is limited--a standing man can be observed at about 50 yards; a prone man usually will be concealed at 10 yards. Foot troops can move through rain forest with little difficulty and require practically no trail cutting. Physical character of the terrain--spur ridges, deep stream channels, or the like--may make travel difficult, but the vegetation itself offers little hindrance in true rain forest, which covers practically all of New Britain from an elevation of about 500 feet up to about 7,000 feet.

THIS IS THE JUNGLE found at the base of Hill 660.

LUSH VEGETATION and coconut plantations were found at Talasea.

Secondary Growth.--Secondary growth occurs in vicinity of native villages where clearings for gardens have been abandoned and are reverting to forest. It forms a dense tangle of young trees, brush and vines; height and density depend on age of growth.

Since garden clearings are made in rain forest, the terrain under secondary growth is the same--well-drained, and gently rolling to rugged in configuration. This type of vegetation provides complete concealment for vehicles in its early stages. Ground observation is limited to a few feet. It is practically impossible for troops or vehicles to move through secondary growth without extensive cutting. Due to native practices of abandoning a garden after three or four years of cultivation, this vegetation type is relatively extensive about large villages.

Grassland.--Two kinds of grassland occurs on New Britain. First, the Kangaroo grasses (Themeda spp.), blade grass (Imperata sp.) and a number of similar grasses form stands which resemble the taller pasture grasses. Second, wild sugar cane (Saccharum spontaneum) occurs in pure stands over considerable areas; the stems are thick and reedlike, frequently an inch or more in diameter, and up to 15 feet tall. Both of these types of grassland were commonly called "Kunai grass" by our troops. Strictly speaking, Kunai refers to a variety of blade grass, Imperata cylindrica var. koenigii--supposedly "kunai" is a corruption of koenigii, which has been loosely applied throughout Australasia to all species of Imperata.

On New Britain grassland is confined to a few small areas near the coast, mostly in

vicinity of Cape Gloucester, and on the west coast south of Aisega. It occurs only where the moisture supply is locally deficient. Configuration of the terrain varies from gently undulating to mountainous; the footing is firm. Foot troops frequently find complete concealment from ground observation; concealment from air observation is partial to complete, depending on height of the grass. In low grasslands visibility is excellent, but in taller grasses it is restricted to a few feet. Movement is easy for foot troops in the lower grasses, but entails considerable difficulty in old growth stands of wild cane. Grassland vegetation presents little problem to operation of vehicles.

Plantations and Cultivated Areas.--The cultivated areas here are planted mainly to coconuts; there are a few plantations of cocoa, coffee, and rubber. The coconut plantation is so familiar it needs no description. In most cases the trees are underplanted with grasses or legumes, which then are controlled by grazing cattle, to keep down weeds and shrubs. Usually plantations are located on the coast or navigable rivers.

Coconut plantations frequently are planted on swampy or poorly drained ground; other plantation crops are on well-drained ground. In a well-kept plantation there is little cover or concealment from aircraft. Ground observation and cover are poor. Movement of foot troops and mechanized equipment are relatively easy if swampy areas can be avoided. In plantations untended for a few years considerable young growth will be present, affording better cover and reducing visibility, but not appreciably affecting movement.

Footnote

1. This scholarly discussion was contributed by Capt Burcham, now Forestry Technician with California Division of Forestry, at the request of the authors of this monograph as a service to the Marine Corps. He served as Ass't D-2 through the Cape Gloucester phase of the operation, and as R-2, 5th Mar at Talasea.