The inner chain islands are mostly below 1000 meters elevation, with the exception of the conical stratovolcano Kolombangara which reaches 1,770 metres.

[6] The ecoregion is part of the Australasian realm, which also includes the neighbouring Bismarck Archipelago and New Guinea, as well as New Caledonia, Australia and New Zealand.

Guadalcanal's relatively high east-west running mountains create a rain shadow effect in the island's northeastern lowlands, with lower rainfall during the southwest trade wind season than elsewhere in the archipelago.

The highlands experience cloud cover during the southeast trade wind season, and windward slopes have higher rainfall than the lowlands.

[6] The natural vegetation of the Solomon archipelago consists mostly of lowland and montane tropical rain forests.

[7] Lowland forests are made up of trees up to 35 meters high forming a closed canopy, with Vitex cofassus and Pometia pinnata as common canopy trees along with species of Ficus, Alstonia, Celtis, Elaeocarpus, Canarium, Syzygium, Calophyllum, Didymocheton, Dysoxylum, Terminalia, and Sterculia.

Understorey plants include the palms Licuala, Caryota, and Areca, bamboos, tree ferns (Cyathea sp.

Characteristic submontane plants include Neonauclea, Sloanea, Cryptocarya, Palaquium, Canarium, and Ficus.

[6] Above 1500 metres elevation on Bougainville the forests transition to montane scrub of Pandanus and the palm Hydriastele macrospadix, or tree fern (Cyathea sp.)

and bamboo scrub on more recent volcanic deposits, with pockets of submontane forest in sheltered areas with deeper soils.

[6] In northern Guadalcanal, where the rain shadow of the mountains creates drier conditions from June to October, there are areas of mixed-deciduous forest and grassland.

The mixed-deciduous forest has an open, fragmented canopy with Pometia pinnata, Vitex cofassus, and Kleinhovia hospita common.

They are dominated by Themeda triandra growing 1 meter or taller, along with Phragmites karka and various introduced grasses including Imperata cylindrica and Setaria parviflora.

[6] Hydriastele hombronii is a palm endemic to outcrops of ultrabasic soil on Choiseul, Santa Isabel, and several other islands.

[8] The first evidence of human inhabitation of the archipelago is at Kilu Cave on Buka, dating back 29,000 years ago to the Pleistocene.

Lapita settlers, the ancestors of today's Oceanic Austronesian peoples, arrived by 3400 B.P., and introduced the marsupial gray cuscus (Phalanger orientalis) to the islands.

[6] Most of the mountain forests are relatively intact, while areas of the lowlands have been cleared for farms and gardens and plantations of coconut (Cocos nucifera) and other food, fiber, timber-producing trees.

Clear-cut logging began in the 1960s, and by 2012 less than 10% of the island's primary forest remained, restricted to inaccessible ridgetops, ravines, and within the central crater.