Luke Gibson et al. argue that tropical conservation efforts should focus on primary and selectively logged forests, because these are the most diverse (Nature 478, 378–381; 2011). However, working in degraded habitats can also provide important conservation opportunities.

Worldwide, around 500,000 hectares of logged and secondary forests are converted every year to plantations such as oil palm, rubber, Acacia and Eucalyptus, reducing both their current biodiversity value and their capacity for regeneration. Because of the revenue they generate, conserving such forests may be more economically viable than the total protection of pristine forests.

Disturbed forests include important 'matrix habitats' between areas of intact forest that can buffer against the impact of habitat fragmentation on reserves. Species occupancy of protected areas is more strongly associated with the condition of the matrix than with either reserve size or isolation (L. R. Prugh et al. Proc. Natl Acad. Sci. USA 105, 20770–20775; 2008). Such forests also provide crucial habitat for wide-ranging species.

In many parts of the tropics, primary forests are confined to upland areas or to poor soils, and are biogeographically restricted. It may be more productive to focus on restoring degraded, but endangered, lowland habitats than on protecting yet more upland forest.

Another consideration is that hunting in tropical reserves significantly threatens their long-term viability. Protection of wildlife may be better achieved through working with timber or oil concessions, or in buffer-zone tourist reserves, than with cash-strapped (or otherwise compromised) nature-reserve agencies.

Tropical reserves cover roughly 11% of the tropical-forest biome, whereas 40% is deforested, 20% is logged and an unknown but significant proportion of the remainder is severely degraded (S. J. Wright Annals New York Acad. Sci. 1195, 1–27; 2010). Such figures alone make it necessary to consider the protection of biodiversity in degraded tropical habitats.