Biología

Journal of Biogeography (J. Biogeogr.) (2006) 33, 491–505

SPECIAL ISSUE

A global overview of the conservation status of tropical dry forests
Lera Miles1*, Adrian C. Newton2, Ruth S. DeFries3, Corinna Ravilious1, Ian May1, Simon Blyth1, Valerie Kapos1 and James E. Gordon4 

UNEP World Conservation Monitoring Centre, Cambridge, UK, 2School of Conservation Sciences, Bournemouth University,Talbot Campus, Poole, Dorset, UK, 3 Department of Geography, University of Maryland, College Park, MD, USA, and Earth System Science Interdisciplinary Center, College Park, MD, USA and 4Department of Geography, University of Durham, Durham, UK

1

ABSTRACT

Aim To analyse the conservation status of tropical dry forests at the global scale, by combining a newly developed global distributionmap with spatial data describing different threats, and to identify the relative exposure of different forest areas to such threats. Location Global assessment. Methods We present a new global distribution map of tropical dry forest derived from the recently developed MODIS Vegetation Continuous Fields (VCF) product, which depicts percentage tree cover at a resolution of 500 m, combined withpreviously defined maps of biomes. This distribution map was overlaid with spatial data to estimate the exposure of tropical dry forests to a number of different threats: climate change, habitat fragmentation, fire, human population density and conversion to cropland. The extent of tropical dry forest currently protected was estimated by overlaying the forest map with a global data set of the distributionof protected areas. Results It is estimated that 1,048,700 km2 of tropical dry forest remains, distributed throughout the three tropical regions. More than half of the forest area (54.2%) is located within South America, the remaining area being almost equally divided between North and Central America, Africa and Eurasia, with a relatively small proportion (3.8%) occurring within Australasia andSoutheast Asia. Overall, c. 97% of the remaining area of tropical dry forest is at risk from one or more of the threats considered, with highest percentages recorded for Eurasia. The relative exposure to different threats differed between regions: while climate change is relatively significant in the Americas, habitat fragmentation and fire affect a higher proportion of African forests, whereasagricultural conversion and human population density are most influential in Eurasia. Evidence suggests that c. 300,000 km2 of tropical dry forest now coincide with some form of protected area, with 71.8% of this total being located within South America. Main conclusions Virtually all of the tropical dry forests that remain are currently exposed to a variety of different threats, largely resulting fromhuman activity. Taking their high biodiversity value into consideration, this indicates that tropical dry forests should be accorded high conservation priority. The results presented here could be used to identify which forest areas should be accorded highest priority for conservation action. In particular, the expansion of the global protected area network, particularly in Mesoamerica, should begiven urgent consideration. Keywords Biodiversity, climate change, deforestation, dry forests, fire, protected areas, threat, vulnerability.

*Correspondence: Lera Miles, UNEP World Conservation Monitoring Centre, 219 Huntingdon Road, Cambridge CB3 0DL, UK. E-mail: lera.miles@unep-wcmc.org  Current address: Center for Tropical Plant Conservation, Fairchild Tropical Botanic Garden, FL, USA

ª2006 Blackwell Publishing Ltd www.blackwellpublishing.com/jbi

doi:10.1111/j.1365-2699.2005.01424.x

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L. Miles et al. INTRODUCTION In 1988, Janzen (1988) stated that tropical dry forests are the most threatened of all major tropical forest types. This statement was largely based on the observation that less than 2% of the tropical dry forest (TDF) in the Mesoamerican region was...