Contrasting ecological mechanisms mediate the impact of land conversion on ecosystem multifunctionality

Land use/cover (LULC) changes have unequivocally affected biodiversity and ecosystem functioning, with enormous repercussions for human well-being. However, the mechanistic ecological mechanisms underlying the impact of land conversion on ecosystem multifunctionality (EMF) remain insufficiently examined from the perspective of multiple biodiversity attributes in dryland regions with increasing deforestation rates. We investigated how the conversion of natural forests and savannas to agroforestry parklands alters the relationships between multiple biodiversity attributes (taxonomic, functional, phylogenetic and structural) and EMF, while accounting for the effects of environmental factors in the dryland landscapes in Benin. We used forest inventory data from 145 plots spanning forests, savannas and agroforestry parklands and assessed the implications of three land conversion scenarios. We quantified EMF using eight functions that are central to primary productivity and nutrient cycling. We found that EMF was positively related solely to structural diversity in forests. The conversion of forests and savannas to agroforestry parklands decreased EMF both directly and indirectly. The indirect effects were mediated by two contrasting biodiversity effects. When forests were converted to agroforestry parklands through savannas, indirect effects were driven by shifts in functional composition towards the dominance of species with acquisitive traits. In contrast, species diversity reduction explained the indirect effects when savannas were converted to agroforestry parklands. The aridity index and soil texture influenced biodiversity attributes, but not EMF. The present study provides evidence that the biodiversity–EMF relationship is dependent on the LULC type and was evident only in the natural ecosystem through the effects of structural diversity, thereby emphasizing the importance of enhancing structural diversity for promoting EMF in forests. Our findings also demonstrate that land conversion weakened natural EMF through biotic homogenization resulting from two contrasting biodiversity-related mechanisms, including loss of species diversity and dominance of species with acquisitive resource-use strategy. Read the free Plain Language Summary for this article on the Journal blog.