Significance: People are fascinated by the amazing diversity of tropical forests and will be surprised to learn that robust estimates of the number of tropical tree species are lacking. We show that there are at least 40,000, but possibly more than 53,000, tree species in the tropics, in contrast to only 124 across temperate Europe. Almost all tropical tree species are restricted to their respective continents, and the Indo-Pacific region appears to be as species-rich as tropical America, with each of these two regions being almost five times as rich in tree species as African tropical forests. Our study shows that most tree species are extremely rare, meaning that they may be under serious risk of extinction at current deforestation rates.

O MODELO da ocupação demográfica da Amazônia legalnos últimos cinqueta anos tem levado a níveis significativos de desmatamento, resultante de múltiplos fatores, tais como a abertura de estradas pioneiras, o crescimento das cidades, a ampliação de pecuária extensiva, a acelerada exploração madeireira e a crescente agricultura intensiva de monoculturas. A área cumulativa desmatada na Amazônia legal brasileira chegou a cerca de 653.000 km² em 2003, correspondendo a 16,3% da região. Este estudo visou a determinar o desmatamento dentro e fora dos atuais Unidades de Conservação (UC) e Terras Indígenas (TI) na Amazônia legal, nos estados de Mato Grosso, Rondônia e Pará, que, juntos, corresponderam por mais de 90% do desmatamento observado entre 2001 e 2003. Os resultados mostraram que o desmatamento foi cerca de dez a vinte vezes menor dentro das Unidades de Conservação e Terras Indígenas do que em áreas contíguas fora delas. Isto demonstra a importância dessas áreas protegidas para diminuir o processo do desmatamento nos três estados. Isto refuta a hipótese generalizada de que estas áreas não cumprissem a sua função principal na conservação e uso racional dos recursos na Amazônia legal.

Understanding how chronic anthropogenic disturbances are distributed in space leads to more effective conservation and management practices. This study provides a large‐scale overview of how the Caatinga dry forest is potentially altered by chronic anthropogenic disturbance. In particular, we investigate how the intensity of the potential disturbance varies (a) among geographic regions, (b) among fragment sizes, and (c) as a function of distance to the fragment edge. A chronic anthropogenic disturbance index (CDI) was derived to represent five anthropogenic disturbance vectors: human population, infrastructure, grazing, logging and fire. CDI was spatialized for the whole Caatinga landscape (826,411 km²) and posteriorly averaged for c. 47,100 remaining fragments. Chronic anthropogenic disturbance was unevenly distributed across the Caatinga landscape, with more conserved sites on the western and southern regions. Larger fragments were, on average, as disturbed as smaller ones. However, smaller fragments varied from highly disturbed to very well preserved depending on the regional context. Strong edge effects were recognized for the CDI and its five vectors. Policy implications. Although half of the original Caatinga vegetation remains, most remaining fragments probably suffer with chronic anthropogenic disturbances. This suggests that a large portion of the Caatinga can be currently threatened, and its biodiversity and natural resources eroded by processes that are less evident than habitat loss. Proper management practices and expansion of the existing protected area network are needed to halt the Caatinga biodiversity decline. Conservation and management actions in tropical ecosystems seem to be more urgent than previously assumed.