What is the relevance of smallholders’ agroforestry systems for conserving tropical tree species and genetic diversity in circa situm, in situ and ex situ settings? A review

Abstract

Smallholders’ agroforests may be valuable for conserving tropical trees through three main mechanisms. First, trees planted and/or retained by farmers in agricultural landscapes where wild stands were once found may be circa situm reservoirs of biodiversity. Second, farmland trees may support conservation in situ by providing an alternative source of product to reduce extraction from forest, and by acting as ‘corridors’ or ‘stepping stones’ that connect fragmented wild stands. Third, the additional value that planting assigns to trees may result in greater interest in including them in seed collections, field trials and field ‘genebanks’ that support ex situ conservation. Here, we critically review the evidence for these mechanisms, and highlight areas for research and for intervention so that agroforestry practices can better support conservation in each setting, with an emphasis on often neglected genetic-level considerations. Based on current global challenges to diversity, conservation will need to rely increasingly on a smallholder-farm circa situm approach, but concerns on long-term effectiveness need to be properly quantified and addressed. Connectivity between widely dispersed, low density trees in agricultural landscapes is an important factor determining the success of the circa situm approach, while improving farmers’ access to a diversity of tree germplasm that they are interested in planting is required. The circumstances in which agroforestry plantings can support in situ conservation need to be better defined, and research on the stability of active tree seed collections (how long are species and populations retained in them?) as ex situ reservoirs of biodiversity is needed.

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Fig. 1

Notes

  1. 1.

    Also referred to in the literature as circa situ conservation; circa situm is formally the more correct term (Heywood and Dulloo 2005) and is applied in the current paper.

  2. 2.

    The TSSD, the only major global effort to catalogue tree seed suppliers, is available at www.worldagroforestry.org/Sites-old/TreeDBS/tssd/treessd.htm.

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Acknowledgments

We contacted over 60 scientists working on agroforestry and related disciplines to ask for their views on the topics covered in this essay, and to provide relevant case studies. Many responded, including Manuel Bertomeu, Charles Clement, Sammy Carsan, Delia Catacutan, Steve Cobb, Ric Coe, Steve Franzel, Dennis Garrity, Anja Gassner, Lars Graudal, Chris Harwood, Verina Ingram, Hannah Jaenicke, Katja Kehlenbeck, Roger Leakey, Jens-Peter Lillesø, Seline Meijer, Edward Millard, Simon Mngomba, Mathew Mpanda, Jonathan Muriuki, Lucy Mwaura, Frank Place, Roberto Porro, Jim Roshetko, Cuauhtémoc Sáenz-Romero, Kate Schreckenberg, Tony Simons, Pal Singh, Marcos Tito, Julio Ugarte, Patrick van Damme, Meine van Noordwijk and Maarten van Zonneveld. Charles Clement also reviewed an earlier version of this manuscript. Several of the authors involved in this paper are part of the CGIAR Research Programme ‘Forests, trees and agroforestry: livelihoods, landscapes and governance’. This Programme aims to enhance management and use of forests, agroforestry and tree genetic resources across the landscape, from forests to farms. This Programme involves the Center for International Forestry Research, Bioversity International, the International Center for Tropical Agriculture, the World Agroforestry Centre, and others.

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Dawson, I.K., Guariguata, M.R., Loo, J. et al. What is the relevance of smallholders’ agroforestry systems for conserving tropical tree species and genetic diversity in circa situm, in situ and ex situ settings? A review. Biodivers Conserv 22, 301–324 (2013). https://doi.org/10.1007/s10531-012-0429-5

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Keywords

  • Agroforestry
  • Circa situm conservation
  • Ex situ conservation
  • In situ conservation
  • Effective population size
  • Genetic variation