Extinction thresholds and negative responses of Afrotropical ant-following birds to forest cover loss in oil palm and agroforestry landscapes

Meta-analysis contrasting freshwater biodiversity in forests and oil palm plantations with and without riparian buffers

The expansion of oil palm plantations has led to land-use change and deforestation in the tropics, which has affected biodiversity. Although the impacts of the crop on terrestrial biodiversity have been extensively reviewed, its effects on freshwater biodiversity remain relatively unexplored. We reviewed the research assessing the impacts of forest-to-oil palm conversion on freshwater biota and the mitigating effect of riparian buffers on these impacts. We searched for studies comparing taxa richness, species abundance, and community composition of macroinvertebrates, amphibians, and fish in streams in forests (primary and disturbed) and oil palm plantations with and without riparian buffers. Then, we conducted a meta-analysis to quantify the overall effect of the land-use change on the 3 taxonomic groups. Twenty-nine studies fulfilled the inclusion criteria. On average, plantations lacking buffers hosted 44% and 19% fewer stream taxa than primary and disturbed forests, respectively. Stream taxa on plantations with buffers were 24% lower than in primary forest and did not differ significantly from disturbed forest. In contrast, stream community composition differed between forests and plantations regardless of the presence of riparian buffers. These differences were attributed to agrochemical use and altered environmental conditions in the plantations, including temperature changes, worsened water conditions, microhabitat loss, and food and shelter depletion. On aggregate, abundance did not differ significantly among land uses because increases in generalist species offset the population decline of vulnerable forest specialists in the plantation. Our results reveal significant impacts of forest-to-oil palm conversion on freshwater biota, particularly taxa richness and composition (but not aggregate abundance). Although preserving riparian buffers in the plantations can mitigate the loss of various aquatic species, it cannot conserve primary forest communities. Therefore, safeguarding primary forests from the oil palm expansion is crucial, and further research is needed to address riparian buffers as a promising mitigation strategy in agricultural areas.

Win-win opportunities combining high yields with high multi-taxa biodiversity in tropical agroforestry

Resolving ecological-economic trade-offs between biodiversity and yields is a key challenge when addressing the biodiversity crisis in tropical agricultural landscapes. Here, we focused on the relation between seven different taxa (trees, herbaceous plants, birds, amphibians, reptiles, butterflies, and ants) and yields in vanilla agroforests in Madagascar. Agroforests established in forests supported overall 23% fewer species and 47% fewer endemic species than old-growth forests, and 14% fewer endemic species than forest fragments. In contrast, agroforests established on fallows had overall 12% more species and 38% more endemic species than fallows. While yields increased with vanilla vine density and length, non-yield related variables largely determined biodiversity. Nonetheless, trade-offs existed between yields and butterflies as well as  reptiles. Vanilla yields were generally unrelated to richness of trees, herbaceous plants, birds, amphibians, reptiles, and ants, opening up possibilities for conservation outside of protected areas and restoring degraded land to benefit farmers and biodiversity alike.

Resolving ecological-economic trade-offs is a challenge in agriculture. Here, Wurz et al. find that in Malagasy vanilla agroforests, vanilla yield is generally not related to tree, herbaceous plant, bird, amphibian, reptile and ant biodiversity, creating opportunities for conservation outside protected areas.

Conservation value of vanilla agroecosystems for vertebrate diversity in north-east Madagascar

As a result of increasing global demand for food, large areas of natural habitat are being converted to agroecosystems to accommodate crop cultivation. This agricultural expansion is most prominent in the tropics, where many rural communities are dependent solely on farming income for their livelihoods. Such agricultural land conversion can have severe implications for local fauna. In this study, we compared vertebrate species diversity between natural forest habitat and three types of vanilla plantations maintained under varying management regimes in north-east Madagascar. We used diurnal and nocturnal transects to survey vertebrate diversity. Natural forest habitat contained the greatest vertebrate species diversity, and had proportionally more threatened and endemic species than all vanilla plantation types. However, we observed a greater number of species and a higher inverse Simpson index in minimally managed vanilla plantations located within or near natural forest compared to intensively managed vanilla plantations. These findings are important and encouraging for animal conservation and sustainable crop cultivation in Madagascar, and suggest that newly created vanilla plantations, and already existing plantations, should endeavour to follow the more traditional, minimalistic management approach to improve sustainability and promote higher faunal diversity.