Biodiversity and ecosystem services in a tropical smallholder landscape in Madagascar

Abstract

The overarching theme of this thesis is how biodiversity and ecosystem services respond to land-use change by smallholder farming in north-eastern Madagascar. The region is a global biodiversity hotspot and a major vanilla production area, where shifting cultivation and cash cropping are driving forest-agriculture frontiers. However, little is known about the value of shifting cultivation and vanilla agroforestry for biodiversity and ecosystem services. In addition, knowledge on sustainable land management to aid biodiversity conservation and livelihoods is urgently needed. My dissertation closes this research gap by investigating ecosystem services and the (endemic) diversity of herbaceous plants, ants, and butterflies in prevalent land-use types (forest fragment, vanilla agroforest, woody fallow, herbaceous fallow, and rice paddy), with old-growth forest as a baseline. To do so, we applied the framework of land-use history and differentiated land-use types depending on the method of land clearance into forest-and fallow-derived or burned and unburned. Furthermore, we categorized species depending on their origin into endemic, native, and exotic.Overall, we found biodiversity to show mixed responses to land-use change depending on taxa, land-use history, and species origin (Chapter 2-4). Endemic herbaceous plants and ants decreased while exotics increased with increasing land-use intensification. In addition, endemic herbaceous plant and ant richness were higher on unburned than on burned land-use types and their composition was similar among unburned land-use types. We recommend increasing canopy closure and maintaining landscape forest cover to increase endemic ants while containing both exotic ants and herbaceous plants. For butterflies, we found that, in particular, land-use types with woody vegetation harbor diverse forest and endemic species, whereas herbaceous fallow and rice paddy are rich in open-land species. We show that the establishment of vanilla agroforests on fallow land increases endemic species of both butterflies and ants. For all three taxa (ants, butterflies, and herbaceous plants), we highlight that old-growth forest remains a key habitat for conservation, as it harbors a unique species community of ants, butterflies, and herbaceous plants.The alteration of predation can indicate changes in biological pest control, an important ecosystem service in the context of agricultural production. Using caterpillar dummies, we found predation rates to be higher on unburned than on formerly burned land-use types (Chapter 5). In addition, old-growth forest and forest fragment harbored one unique predator community and showed the highest predation rates. To increase predation rates in vanilla agroforests, we recommend preserving or promote trees and dense understory vegetation. natürlichen Bestäubung bieten kann, wie zum Beispiel die Kontrolle über Pollenherkunft undmenge, Bestäubungszeitpunkt und -häufigkeit sowie die Unabhängigkeit von Umweltschwankungen. Die Hauptnachteile der Handbestäubung sind jed...