The vegetation and flora of the Cabo Frio Region

Dorothy Sue Dunn de Araujo
Associate Professor
Biology Institute - UFRJ
e-mail: dotaraujo@globo.com

The Cabo Frio region is very special in climate as well as vegetation and flora in the in the context of southeastern Brazil. That is why it was chosen by WWF/IUCN (World Wildlife Fund/International Union for Conservation of Nature) as one of the 12 Centers of Plant Diversity in Brazil (Araujo, 1997). This region has the lowest annual rainfall (around 900 mm) in the state of Rio de Janeiro, due in part to the upwelling phenomenon.

There is great habitat diversity in Cabo Frio, from extensive restingas and high dunes to sizeable lagoons and alluvial deposits, from peninsular mountains of the Armação dos Búzios and Cabo Frio to more rugged ranges like Sapiatiba. The long Massambaba beach ridge separates Araruama lagoon from the sea. Here, a twofold system of sandy ridges is covered in some spots by dunes that lie in a northeast/southwest direction, often exceeding 20 meters in height. The most extensive alluvial plains of the region are located in the Una and São João river basins, while near the Emerencias mountain range, the plains consist of colluvial/alluvial deposits.

The vegetation of the Cabo Frio region reflects this great geomorphologic diversity, and also the paleo-evolutionary history and current climate. It is a relic of vegetation that existed during colder, drier glacial periods of the Pleistocene (Ab'Saber 1974).

The Cabo Frio Center of Plant Diversity embraces mainly restinga formations, Atlantic Rain Forest and low xenomorphic scrub that covers the coastal mountains between Cabo Frio and Armação dos Búzios. There are also mangroves and flooded habitats (swamps and lagoon borders). The rich flora has several endemic species and others with interesting phytogeographic links.

Near the ocean, the low shrubby vegetation (averaging 3 meters tall) grows on slopes exposed to salt spray and sea breezes. The shrubs are densely packed with thin trunks. In more protected spots, humid ravines or on the mountains farther from the sea (e.g., Sapiatiba), the vegetation is much more robust, similar to lowland Atlantic forest (Rizzini, 1979).

An interesting species from the coastal mountains is the endemic cactus Pilosocereus ulei, found only in the Cabo Frio region. It is characteristic of this xenomorphic vegetation. Other species have unconnected distributions between Cabo Frio and the northeastern caatinga, suggesting ancient links between these two areas during drier Pleistocene periods. These are the Leguminosae Bauhinia albicans e Machaerium leucopterum (Lima, 2000) and the beautiful creeper with yellow flowers, Skytanthus hancorniaefolius (Apocynaceae).

On the colluvial/alluvial deposits, the forest is more exuberant than on the hillsides. The trees average 10 meters in height with some of up to 17 meters. However, there is a dry period from June to August when many trees lose their leaves. The Brazilian rosewood, Caesalpinia echinata, the most well-known species of the region, is an integral part of these forests, as are other tree species that occur in the seasonal forests of semi-arid Brazil (e.g., Parapitadenia pterosperma, Lonchocarpus virgilioides - Lima 2000). Faramea brachyloba an endemic Rubiaceae of this region, is found in these forests.

The restinga and dune plant formations from this area vary from the herbaceous strand vegetation to the forests on the older beach ridges, and include the open shrubby formation of Massambaba, Dama Branca and Peró dunes. The only relatively well-preserved dry restinga forests left in the region are found in Jacarepiá, at the western end of the Massambaba restinga and, on land belonging to the Navy near the Una river. The former is habitat for the golden lion tamarin, and also shelters many species of the endemic restinga flora in Rio de Janeiro state (e.g., Algernonia obovata, Calathea dorothyae, Neoregelia eltoniana, Serjania fluminensis).

On the dunes, rare species can be found in the middle of the thickets, as well as species of great phytogeographic interest. An example of this is Lithraea brasiliensis, a species of Anacardiaceae which is very common in the southern state of Rio Grande do Sul, but which is only found in the Cabo Frio region of Rio de Janeiro. Between the dunes, in lower, wetter habitats, smaller forests grow creating a shady environment; populations of the showy endemic bromeliad Vrieseae sucrei are found here, as well as another endemic shrub of the Melastomataceae (Mouriri arenicola). Other endemic species of Rio de Janeiro state have a wider range of tolerance and are found in the restingas as well as on the slopes of the coastal mountains in Cabo Frio (e.g., Cryptanthus acaulis, Capparidastrum brasilianum, Swartzia glazioviana, Erythroxylum glazioui, Inga maritima, Ouratea luschnathiana, Passiflora farneyi).

Although the survey of the coastal range and sandy plain vascular flora in the Cabo Frio region is still preliminary, over 600 species have been recorded in the restingas (Araújo 2000) and around 300 on the slopes and other types of habitat (Araujo et al. 1998). This number will certainly increase substantially due to studies being carried out in the area by UFRJ (Federal University of Rio de Janeiro) and the Rio de Janeiro Botanical Garden. But one distressing question remains: will we come to know the true floristic wealth of this Center of Plant Diversity before man's activities cause yet unknown species that may be essential to the ecosystems to become extinct?