Study of ants suggests a need for better biodiversity conservation across agricultural land in the tropics

A new study, led by CABI scientist Dr Elizabeth Finch, is the first to investigate the impacts of swidden agriculture on ant communities across the full degradation gradient, highlighting the utmost importance of the conservation of existing closed canopy forests.

Swidden agriculture, known more commonly as slash and burn agriculture, is a widespread subsistence farming method in the tropics which is being intensified and expanded to meet the demands of a growing human population. In Madagascar, for example, fallow times have decreased from 8-15 years to 3-5 years over three decades, resulting in faster land degradation.

The research, conducted while Dr Finch was completing her PhD at the School of Biological Sciences, Queen’s University Belfast and now published in the journal Biological Conservation, reveals that degradation due to swidden agriculture leads to a reduction in native ant species diversity and an increase in introduced ant species diversity. There were also correlated community compositional changes in both native and introduced species.

Introduced ant species are often favoured in disturbed habitats and can reduce the diversity and distributions of native ant species. They, therefore, represent a confounding factor when looking at the effects of habitat degradation. The results of the study, however, found little statistical evidence that introduced ant species were negatively impacting native ant species. This suggests that the patterns in the native ant communities were driven solely by habitat degradation caused by swidden agriculture.

Dr Finch said, “Ants, in soil structuring, seed dispersal, decomposition, pollination and nutrient recycling, play important ecological roles in tropical ecosystems and as such, understanding how they are impacted by land use change is important for assessing sustainability.”

The scientists, including those from the Madagascar Biodiversity Centre, Bangor University, Wales, University College Dublin and the California Academy of Sciences, found that in general, predatory species were the most likely to be negatively affected by swidden, whilst omnivorous species were the most likely to benefit from this form of agriculture.

Dr Finch added, “We found that closed canopy forests had the highest ant species diversity and were compositionally unique. This underlines the importance of their conservation.

“However, we also found that the less degraded swidden habitats harboured unique and native ant species. We recommend that if these habitats are used sustainably, with long fallows to avoid the degradation spiral, these could still play an important role in biodiversity conservation in swidden landscapes across the tropics.

“We need to find a way to increase in crop yields to relieve pressure sufficiently so that longer, sustainable, fallows may be achieved. Swidden systems have demonstrated capacity to maintain and even enhance carbon stocks. REDD+, a United Nations-backed framework that aims to curb climate change by stopping deforestation, could, therefore, potentially bridge the economic gap that is critical to ensure the sustainable implementation of such measures.”

Additional information

Main image: Ant communities in forests were ‘species rich and compositionally unique’ according to the CABI-led research (Credit: Pixabay).

Full paper reference

Elizabeth A. Finch, Eric T. Rajoelison, Matthew T. Hamer, Tancredi Caruso, Keith D. Farnsworth, Brian L. Fisher, Alison Cameron, ‘The effect of swidden agriculture on ant communities in Madagascar,’ Biological Conservation, Volume 265, 2022, DOI: 10.1016/j.biocon.2021.109400.

You can read the paper open access here: https://www.sciencedirect.com/science/article/pii/S0006320721004523

Funding acknowledgement

E.A.F was funded by a Department of Employment and Learning scholarship and by start-up funding from Queen's University Belfast to AC. This research was conducted in close collaboration with the ESPA project (NE/K010085/1 and NE/K010085/2): Can capturing global ecosystem service values reduce poverty? (ww.p4ges.org), awarded to A.C. and was supported in part by the National Science Foundation grant number DEB-1655076 to B.L.F.

CABI is an international intergovernmental organisation, and we gratefully acknowledge the core financial support from our member countries (and lead agencies) including the United Kingdom (Foreign, Commonwealth & Development Office), China (Chinese Ministry of Agriculture), Australia (Australian Centre for International Agricultural Research), Canada (Agriculture and Agri-Food Canada)), Netherlands (Directorate-General for International Cooperation), and Switzerland (Swiss Agency for Development and Cooperation). See https://www.cabi.org/about-cabi/who-we-work-with/key-donors/ for full details.

Redd+

REDD+ is a United Nations-backed framework that aims to curb climate change by stopping the destruction of forests. REDD stands for ‘Reducing Emissions from Deforestation and forest Degradation’; the ‘+’ signifies the role of conservation, sustainable management of forests and enhancement of forest carbon stocks.