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Large areas of the tropics are subject to long dry seasons, and the forests and woodlands which grow in these areas are quite different from the rain forests which attract much greater attention from both scientists and conservationists. Such seasonal areas are more suitable for agriculture and human settlement, and consequently deforestation there has been much greater than in the rain forests. Few areas are protected and more floristic information is necessary to identify priority conservation areas.
In 2003, RBGE hosted a major conference, "Tropical savannas and seasonally dry forests: ecology, environment and conservation", which highlighted the biodiversity, ecology and conservation of these biomes. It was attended by 150 delegates from 25 countries.
The RBGE is studying two types of seasonal vegetation in South and Central America, seasonally dry tropical forest and savanna, in projects co-ordinated by Dr Jim Ratter and Dr Toby Pennington. The 2003 conference resulted in a major synthesis of the floristic diversity and geographic patterns of the savanna and seasonally dry forest floras of the Neotropics:
Pennington, R.T., Lewis, G. & Ratter, J.A. (eds.) (2006). Neotropical savannas and dry forests: plant diversity, biogeography and conservation. CRC Press, Florida. 484 pp
Seasonally dry forests
These occur on fertile soils, and are found in many disjunct areas throughout South and Central America. The largest single area of this forest is the Caatingas region which extends over 850,000 km2 of north-east Brazil, but similar vegetation is also found on many other areas where the soils are suitable, ranging in size from a few hectares to 40,000 km2.
We have been carrying out floristic inventories in the poorly characterised dry InterAndean valleys of northern (the Jaén-Bagua, Tarapoto and Marañon areas) and southern (Mantaro and Apurimac valleys) Peru. The principal aim of this work is to assess the phytogeographic affinities and conservation status of these areas. Our collections have uncovered new species in the genera Celtis (Ulmaceae), Caesalpinia (Leguminosae), and Cedrela (Meliaceae). They also demonstrate that Peruvian inter-Andean dry forests are rich in endemic species and should be priorities for conservation.
A
Darwin initiative Scholarship awarded to Reynaldo Linares-Palomino allowed him to produce a checklist of the woody plants of Peruvian dry forests, while based at RBGE in 2004-05. This demonstrates that the Marañon dry forests are substantially more species-rich that those of the southern valleys.
Colin Pendry published a substantial monograph of the important dry forest genus Ruprechtia (Polygonaceae) in 2004.
Recent publications
Pennington, R.T., Lavin, M., Oliviera-Filho, A.T. (2009). Woody plant diversity, evolution and ecology in the tropics: perspectives from seaconally dry tropical forests. Annual Review of Ecology and Systematics 40: 437-457.
Pendry, C.A. (2004). A monograph of Ruprechtia (Polygonaceae). Systematic Botany Monographs 67: 1-113.
Bridgewater, S., Pennington, R.T., Reynel, C., Daza, A. & Pennington, T.D. (2003). A preliminary floristic and phytogeographic analysis of the woody flora of seasonally dry forests in northern Peru. Candollea, 58: 129-148.
Cerrado
Cerrado, Chapada dos Veiadeiros, Goiás, Brazil
This savanna woodland is the natural vegetation of about two million km2 of central Brazil where it occurs on well-drained, infertile soils. The cerrado is of enormous ecological importance, containing over 5000 species of higher plants, many of which
only occur in Central Brazil. Isolated areas of cerrado-like savanna vegetation also occur within the Amazonian rain forest, in Venezuela, and in Guyana, and also in Central American countries such as Belize.
Despite the fact that it covers an area equal to that of Western Europe (2 million km²), the cerrado's importance has been overshadowed by its more emotive neighbour, the Amazon rainforest. 
Since the late 1960s, there has been a drive to open up the cerrado territory for agriculture, and vast areas have been cleared. In addition to agricultural development, much of the charcoal used in the Brazilian steel industry is derived from native cerrado trees, putting further pressure on this vegetation. It is estimated that an area of about 70% of the cerrado has been destroyed to date. The urgent need for conservation is now being recognised by the Brazilian authorities and the wider scientific community.
RBGE's role in this project
A team from the RBGE and Brazilian scientists are currently collaborating on a project to:
- provide essential information on the flora. A comprehensive survey programme of the vegetation of the poorer known cerrado areas has been set up. Since 1992 over 200 new floristic surveys have been conducted covering a wide range of the cerrado biome.
- evaluate conservation areas. The biogeographical patterns of the cerrado flora are being analysed to provide information for the establishment of protected areas.
Recent publications
Ratter, J.A., Bridgewater, S. and Ribeiro J.F. 2006. Biodiversity patterns of the woody vegetation of the Brazilian Cerrado. In Pennington, R.T., Lewis, G.P. and Ratter, J.A. (eds) Neotropical savannas and seasonally dry forests: plant diversity, biogeography and conservation. CRC Press, Florida.
Bridgewater, S., Ratter, J.A. & Ribeiro, J.F. 2004. Biogeographic pattern, beta-diversity and dominance in the cerrado biome of Brazil. Biodiversity and Conservation, 13. pp. 2295-2318.
Ratter, J.A., Bridgewater S, Atkinson R.& Felipe J.F. 2003. Analysis of the Brazilian cerrado vegetation III: comparison of the woody vegetation of 376 acres. Edinburgh Journal of Botany, 60. pp. 57-109.
Oliveira-Filho, A.T. & Ratter, J.A. 2002. Vegetation physiognomies and woody flora of the cerrado biome. In Oliveira, P.S. & Marquis, R.J. (eds.). The Cerrado of Brazil: Ecology and Natural History of a Neotropical Savanna. Columbia University Press, New York. Chapter 6, pp. 91-120.