Converting rainforest to plantation impacts food webs and biodiversity

The researchers set out to study both biodiversity -- plants, insects, vertebrates -- and changes in how food webs function -- biomass, trophic structure, energy fluxes. To do this, they estimated the abundance and biomass of the following: arthropods (such as spiders, insects, mites and centipedes) in the tree canopies using a technique known as "fogging"; birds using audio recorders and observation at specific points; and soil arthropods and earthworms from soil cores. This information was collected across 32 sites representing rainforest or plantations. They analysed their findings using existing models on traits and feeding preferences to reconstruct food webs at each site and across all animal groups. The results were used as measures of the distribution of energy and consumption of different resources (living plants, litter, bacteria, fungi, soil organic matter, other animals) in food webs above and below the ground. This method takes into account decomposition and quantifies the actions of predators (such as certain spiders or birds) in food webs.

The scientists identified that most energy in rainforest animal communities flows to arthropods in soil food webs. Plantations, by contrast, had a very different energy distribution: food webs in canopies were less rich and less complex, and food webs in the soil were also changed. Instead of diverse arthropod communities, virtually all energy was allocated to invasive species of earthworms. Because of these changes, there was generally little predation and relatively high numbers of plant feeding insects (such as caterpillars and beetles) in plantations.

"It is fascinating to see how all these different organisms are connected, from minute arthropods to birds, from soils to canopies. Scientists clearly need to investigate such connections in different parts of the ecosystem, particularly endangered areas of biodiversity -- such as the one beneath our feet!" said first author Anton Potapov, who was employed at the University of Göttingen during the data collection and then at the German Center for Integrative Biodiversity Research (iDiv).

"The ongoing conversion of rainforest into plantations is not just causing a massive decline in biodiversity, but it is also changing the way these ecosystems function," explains Professor Stefan Scheu, senior author and head of Animal Ecology, University of Göttingen. "For sustainable management of converted ecosystems, we need to understand how all these linked elements and connections are impacted. A more holistic approach can then be developed to promote the functioning of ecosystems both above and below ground."

This research benefited from the German Research Foundation (DFG) funding for the Collaborative Research Centre (990) "Ecological and Socioeconomic Functions of Tropical Lowland Rainforest Transformation Systems EFForTS." Researchers from the Universities of Hohenheim, Bern and Cambridge were also involved in the study.