The effects of forestry and agroforestry plantations on bird diversity: a global synthesis.
The increasing expansion of productive lands around the world during the last decades constitutes a strong driver of biodiversity loss, as they are usually established near to high diversity areas. Despite many studies that have compared bird diversity between natural and productive systems, a global synthesis is still missing and important for understanding how biodiversity is being altered. We conducted a meta-analysis based on 144 case studies to assess the effects of four types of plantations (forestry, oil palm, coffee, and cacao) on bird species richness and abundance. We examined those effects in function of plantation type, latitudinal zone (temperate or tropical), geographical context (mainland or island), zoogeographic zone, and biodiversity hotspots. Plantations presented negative effects on both bird species richness and abundance. Oil palm plantations showed more negative effects followed by forestry plantations, whereas coffee and cacao agroforestry plantations had no significant effects. Those effects were geographically variable, being more pronounced in islands and temperate zones, as well as at the Oriental, Palearctic, and Neotropical zoogeograghic regions, and at the Sundaland and Mediterranean Basin biodiversity hotspots. Our results showed that productive systems reduce both species richness and abundance of bird species, being insular species particularly susceptible. Exotic monocultures with low structural heterogeneity (e.g., oil palm plantations) derive in highly impoverished bird communities dominated by generalist species. We identified South East Asia, tropical South America, and the Mediterranean Basin as the most threatened regions because of the sensitivity of their bird communities and the increasing rates of native forest replacement.