2.7 Forest regions in São Tomé and Príncipe
Scheme 4: Forest regions in S. Tomé and Príncipe
From Exell’s categories, the following can also be differentiated:
Low altitude forest, 0-800m;
Shade forest for cocoa and coffee;
Shrublands and grasslands;
Primary altitude mountain forest, comprised of mist forest, medium altitude forest >1000 and <800m and altitude forest >1800 and <2000m.
2.7.1 Low altitude forest, 0-800m
Equivalent to the equatorial forest in the African mainland.
On S. Tomé island, its typical species are: Rinorea chevalieri, Zanthoxylum thomensi, Drypetes glabra, Anisophyllea cabole e Sorindeia grandifolea; on Príncipe the following species are most frequent: Rinorea insularis, Ouratea nutans, Casearia mannii Croton stelluliferus e Erythrococca columnaris. (Source: J. LeJoly)
According to Chevalier, primary low altitude forests have disappeared due to sugarcane, cocoa and coffee plantations. A few species have been protected and/or have benefited from man’s action: Milicia excelsa, Ficus sp., Pycnanthus angolensis, Ceiba pentandra, (Chevalier, 1938).
Presents slow transition in species and greater variety than lower altitude formations. Trees are tall (30 to 40m) with dense canopies and the high humidity favors the epiphytes, lianas and ferns that cover the trunks of trees. Arboreal ferns are varied and plentiful. Rubiaceae and Euphorbiaceae are the most common families. Arboreal species typical of these formations are: Trichilia grandifolia, Pauridiantha insularis, Pavetta montícola, Erytrococca molleri, and Tabernaemontana stenosiphon. These formations have been changed little by men, mostly due to their altitude.
2.7.2 Mist forest, 1400-2024m
The forest reaches the summit of the Pico and in áreas of greater altitude trees are smaller; upper layers present more clearings. Luminosity is low due to constant mist and temperatures are relatively low. Rainfall is abundant. Epiphytes become much more abundant. Samambaias are an important element of flora up to the top. Mountain grasses are not found. Access is difficult and the slopes are steep, so this habitat has not been changed by human action and remains intact.
The elements above have caused the trees to grow smaller. Araliaceae can now be found such as Schefflera manii, rarely growing taller than 10 meters. Epiphytes, especially orchids, and ferns of the genus Asplenium are quite important to these formations.
Typical trees are: Podocarpus manii, (Pinheiro de S.Tomé) the only endemic gymnsoperm, Baltasaria mannii, Ilex mitis, Olea capensis (Pau Impé), Craterispermum montanum (Macambrará), Trichilia grandifolia (Cola macaco).
Typical shrubs are Erica thomensis, Psychotria guerkeana and P. nubicola, Lobelia barnsii (giant lobelia), endemic to S. Tomé. In the underbrush there are poaceae of the genus panicum and one endemic species of urticacea, the Elatostema thomense.
Lianas, or creeping vines, are frequent: Sabicea spp., Thunbergianthus quintasii, Tetracera alnifolia and Jasmin spp.
Due to climate and steep slopes, these formations were only sporadically modified by man and have not been the subject of any kind of intensive exploitation. They are currently well preserved. There are a few invading species, like Chinchona spp., which have expanded their distribution to these heights.
2.7.4 Medium altitude forest > 1000 and < 1800m
Found around Pico Cacumbé and the Lagoon. According to a 1990’s survey by the ECOFAC, whose herbaria are at the center of Bom Sucesso, on the Amélia Lagoon, an extinct volcano crater, there is a unique formation to be found.
The vegetation is evergreen, composed of Panicum hochstetteri and Panicum brevifolium poaceae. Other than the poaceans, there are also the following: Cyperus articulatus, Poligomum salicifoluium and Tristemma mauritianum, as well as a large quantity of ferns of the family Polypodiaceae and Hymenofoliaceae. Also remarkable is the predominance of rare orchids, such as Bulbophyllum cocleatum var. ternuicaule, Solenangis clavata and Diklangella liberica as well as small associated shrubs, Heteradelphia paulowilhelmia, Rapanea melonophoeos and Schefflera manni.
In the underbrush of this altitude forest are the following endemic species: Palisota pedicellata, Cyperus sylvicola, Mapania ferruginea, Begonia baccata, Impatiens buccinalis, Impatiens thomensis, Calvoa crassinoda, Sabicea ingrata, Sabicea exellii.
It is also comprised of the following endemic arboreal species: Trichilia grandifolia, Pavetta monticola, Craterispermum montanum, Tabernaemontana stenosiphon, Erythrococca molleri and Discoclaoxyllum occidentale.
2.7.4 Altitude forest between 1800 and 2000m.
This forest, located around regions like Mesa do Pico (1850m) and girts the Pico de São Tomé and Pico Pequeno, presents high rainfall and nearly constant mist, temperatures always low but still above freezing point. Trees do not grow tall and epiphytes are numerous. At this altitude, endemic species are Podocarpus mannii (Pinheiro-de-São Tomé), Psychotria guerkeana, Psychotria nubicola, the tchapo-tchapo d’obô (Peddiea thomensis), Calvoa crassinoda, Pilea manniana, Erica thomensis and Lobelia barnsii. Orchids, ferns, mosses and lichens are also frequent.
According to Tolen (1995), the most abundant trees in S. Tomé’s mist forest are the Tabernaemontana stenosiphon (Cata d’Ôbô), (Pseudogrostistachys africana Cacau d’Ôbô), Homalium henriquensii (Quebra machado), Rothmannia urcelliformis (Teia-teia), Trichilia grandifolia (Cola macaco), Pauridiantha floribunda (Pau formiga) and the Allophyllus africanus (Pau três).
Typical endemic plant species in this mountain ecosystem are: Peddiea thomensis (Tchapo tchapo d’ôbô), Balthasaria mannii, Psychotria guerkeana and P. nubicola.
On Príncipe island, according to a publication on preservation of forest ecosystems in the Democratic Republic of São Tomé and Príncipe ("Conservação dos Ecossistemas Florestais na República Democrática de São Tomé e Príncipe"), by P.J. Jones, J.P. Burlison and A. Tye, all of the northern primary forest and on the center of the island has been replaced with cocoa, coffee, coconut and banana plantations. According to the same publication, most of the primary humid forest on the island was destroyed during a campaign to eradicate sleeping sickness (African tripanosomiasis) in 1906, but recent research has shown that the efforts to this end were beyond the capabilities of control teams and most of the southern half of the island remains intact.