Bismarckian Ecosystems

Bismarckian Lowland Rain Forest

On the Solomon Islands these forests reach heights of between 30 and 45 m, but the canopy is occasionally exceeded in height by a few emergent species such as the strangling and banyan figs (Ficus benjamina, F. glandulosa, F. obliqua, F. subcordata, F. virgata and F. xylosycia) and Terminalia calamasanai. Altogether in these relatively species poor forests there are some 20 common canopy trees including Calophyllum kajewskii, Calophyllum vitiense, Campnosperma brevipetiolum, Elaeocarpus sphaericus, Endospermum medullosum, Gmelina molluccana, Maranthes corymbosa, Pometia pinnata, Schizomeria serrata, and the endemic Dillenia salomonensis (Dilleniaceae) and Parinari salomonensis (Chrysobalanaceae). Other less common endemic trees are Callophyllum confusum, C. obscurum (Hypericaceae), Elaeocarpus polyandrus (Elaeocarpaceae), Fagraea obtusifolia (Loganiaceae), Myristica kajewskii (Myristicaceae), Terminalia rerei and T. whitmorei (Combretaceae). In lowland rain forest of the Bismarck Archipelago other endemic trees have been found including Chisocheton novobritannicus (Meliaceae) and Elaeocarpus neobritannicus (Elaeocarpaceae) on New Briton, and Elaeocarpus rubescens (Elaeocarpaceae), Helicia peekelii (Proteaceae) and Osmoxylon lanceolata (Araliaceae) on New Ireland, while Helicia neglecta and Osmoxylon pfeilii occur on both New Briton and New Ireland.

The undergrowth of Solomon’s lowland forests is characterized by an abundance of pachycaul treelets (thick stemmed trees with few branches). These possibly primitive life forms appear have now been swamped by the more competitive leptocaul trees (trees with abundant branches) in the jungles of central Malesia. Solomons’ pachycaul species include Barringtonia papeh, Leea indica, Piper wichmannii and Taperinosperma pachycauloum. Other lower story species include the small endemic tree Elaeocarpus coodei (Elaeocarpaceae), and endemic shrubs such as Geniostoma rupestre var. solomonense (Loganiaceae) and Osmoxylon confertiflorum (Araliaceae). In contrast with other ecological groups within these forests, climbers and epiphytes are much more abundant than in the forests of West Malesia. Tree trunks are often completely obscured by bole climbers and epiphytes. Aroids are particularly abundant and include the endemic or near endemic Scindapsus salomonensis and Spathiphyllum solomonensis (Araceae). Higher up, various semi-parasitic aerial shrubs occur including the endemic Dactyliophora solomonia and Sogerianthe versicolor (of the Loranthaceae).

Bismarckian Valley Forests

On the Solomons certain large tree species like Planchonella thyrsoides and the endemic Albizia salomonensis (Fabaceae) and Archidendron oblongum (Fabaceae) are confined to the rich alluvial valleys. This is also the main habitat of palms, with the principal species being Areca macrocalyx and the endemic Rhopaloblaste elegans (Arecaceae), and other giant monocotyledonous plants like Heliconia indica, the gingers Catimbium novae-pommeraniae, Costus speciosus and Guillainia purpurata and members of the Marantaceae such as Cominsia gigantea and Donax cannaeformis.

Bismarckian Swamp and Riverine Forests

On the Solomons these have developed near the coast in small areas of impeded drainage, in often less than about one square kilometer. They are characterized by the dominance of the endemic tree Terminalia brassii (Combretaceae), which can grow to heights of 40 m. It also occurs in the riverine communities where it may be associated with the small endemic tree Osmoxylon chrysanthum (Araliaceae).

Bismarckian Montane Forest

No mountains in the Solomons reach above the tree line. The highest uplands zones are the Emperor Range on Bougainville and the Kavo Range on Guadalcanol and both are forested to their summits. Unlike the montane rain forests of New Guinea these forests are not characterized by an abundance of Nothofagus, Castanopsis or Araucaria species, and in fact mid-montane fagaceous and Araucaria forests are absent. Instead members of the Myrtaceae including genera such as Acmena, Eugenia, Mearnsia, Metrosideros and Rhodamnia dominate. The epiphyte flora includes four endemic rhododendrons, which is of interest because apart from these, species of Ericaceae are absent from the Solomons. Other endemic species include the two small trees Myristica petiolata (Myristicaceae) and Osmoxylon arrhenicum (Araliaceae). These formations are extremely rich in bryophytes and often the forest floor and tree trunks have a ‘mossy’ layer up to 30 cm thick.

Bismarckian Ultrabasic Forest

Ultrabasic rocks have their main outcrops on southern Santa Isabel, San Jorge and southern Choiseul, with smaller areas on Guadalcanol, San Cristobal and Floida. The forests here tend to be poor in species and usually dominated by Casuarine papuana and the endemic Dillenia crenata (Dilleniaceae). Other less common species include the myrtaceous shrub Myrtella beccarii and the endemic palms Gulubia hombronii and Pandanus lamprocephalus (Arecaceae). The latter is confined to San Cristobal.

Further information required.

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