Tree biodiversity: research in development

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The conservation and sustainable use of tree biodiversity — the range of variation found within and between tree species — to support livelihoods and the environment is central to the Tree Productivity and Diversity research theme at World Agroforestry (ICRAF).  

Supporting biodiversity-based livelihoods initially requires characterising patterns of biodiversity in agricultural and forest mosaiced landscapes and how these are changing as farming systems and climates alter.

To do this, the Tree Productivity and Diversity theme conducts inventories of the diversity of tree species in farmlands across the tropics, taking into consideration whether the trees are of local origin or introduced from elsewhere, and how common individual species are in farm landscapes.

‘Inventories look at how particular tree species are valued,’ said Roeland Kindt, senior ecologist of ICRAF with the Tree Productivity and Diversity theme, ‘and the positions on farms in which they are found and — when trees are planted rather than naturally established — the source of the planting material. The patterns of diversity we have found vary by location but inventories often show that while farms contain high tree species’ richness, a few exotic species dominate, limiting these farms’ ability to conserve indigenous trees.’

In a typical survey, for example, explained Kindt, of 265 farm plots assessed around Mount Kenya, over 400 woody plant species, of which approximately three-quarters were indigenous, were found. However, only two of the 10 most common species were of indigenous origin, thereby limiting farms’ conservation value.

Inventories also often show that certain tree species dominate particular human uses of trees (for example, only one or two species are used for fuelwood or fodder in a given location). This indicates that diversification would be useful for supporting the resilience of human use. So, too, would the widening of sources of planting material because the theme’s surveys show that tree planting often relies on seed that is likely to be of inferior quality. This is because seed is collected from only a few trees, potentially leading to inbreeding. Where regeneration is occurring naturally from forest remnants on farmland, only a few trees also appear to be involved and the same limitation applies.

To address national governments’ commitments to the Bonn Challenge on restoration and to harness the benefits of planting trees of good quality, the Tree Productivity and Diversity theme characterises tree genetic diversity through field and laboratory research.

In the Provision of Adequate Tree Seed Portfolios (PATSPO) initiative in Ethiopia, for example, field trials are conducted on a range of sources (known as ‘provenances’) of tree species prioritised by farmers to indicate productive planting material matched to different restoration sites. The trials are then converted into seed sources for farm tree-planting. PATSPO supports biodiversity in Ethiopia’s restoration programmes because it is developing seed sources for a range of indigenous as well as exotic trees. Similar field work has been conducted in Peru, where suitable seed sources for a range of locations were determined for farmer-prioritised indigenous timber-tree species.

Crucially, the Tree Productivity and Diversity theme also designs functional tree-planting material delivery systems for restoration programmes implemented by smallholders. The lack of functional delivery systems to date helps explain why restoration efforts have generally failed to embrace species’ diversity but instead have focused on a few, often exotic, species. Making delivery systems more functional requires ensuring the right mix of public and private-sector agencies are involved and that each agency is assigned an appropriate responsibility.

The Tree Productivity and Diversity theme emphasises the role of small-scale entrepreneurial suppliers in the delivery of tree-planting material, moving away from more centralised delivery systems that have been tried in the past but have generally failed to reach smallholders

‘In Indonesia, for example,’ said Jens-Peter Lillesø, a senior fellow of ICRAF from the University of Copenhagen associated with the Tree Productivity and Diversity theme, ‘we have placed emphasis on developing appropriate models of smallholder and community tree-nursery enterprises to sustainably supply restoration projects. The role of NGOs and national tree seed programmes is then to provide back-up in business and technical training and in the provision of “foundation” germplasm.’

To support the productivity of agroforestry trees and their appropriate integration into diverse farm landscapes, the Tree Productivity and Diversity theme also engages in active tree domestication work. The theme’s recent emphasis, informed by the preferences of farming communities, has been on improving food trees that support farmers’ nutritional status and improve their incomes. The approaches we have developed to carry out domestication include participatory methods that combine scientific advances in selection, propagation, processing and market development with local communities’ tree management expertise,’ said Alain Tsobeng, tree domestication expert with ICRAF Cameroon. ‘When designed properly, these participatory approaches support the conservation of tree crop genetic diversity in farm landscapes, thereby helping to allay the biodiversity threats associated with tree cultivation where single cultivars could dominate. Once learnt, participatory approaches are applicable to a wide range of trees, supporting species’ diversity.’

Another approach the theme uses to ‘mobilise’ tree genetic diversity is genomics-based improvement. In Nairobi, the theme hosts the genomics laboratory of the African Orphan Crops Consortium that seeks to genetically improve Africa’s ‘orphan’ crops — ‘minor crops’, ‘underutilized plant species’ or ‘neglected crops’ — as part of a biodiversity-based initiative to address hidden hunger on the continent. The initiative works on 101 orphan crops identified through the African Union’s New Partnership for Africa's Development in a participatory manner with growers and consumers. Prasad Hendre, the scientific manager of the Consortium highlights that half of the crops on the Consortium’s list are trees that together provide a wide range of nutritious foods — including edible leaves, seeds and fruit — and are part of Africa’s historically neglected bounty of biodiversity.

‘These species form a unique biological resource for crop development, but the window of opportunity to realise their value is closing as their genetic diversity is threatened by the relentless simplification of Africa’s landscapes,’ said Alice Muchugi, manager of the recently combined genebank of ICRAF and the Center for International Forestry Research.

The vital pathway to impact for the Consortium is through the African Plant Breeding Academy, led by the University of California Davis. This is an intensive training and mentoring programme that empowers the continent’s plant breeders to apply advanced genetic approaches to tailor orphan crops to producers, processors and consumers’ needs.

For more information on the Trees for Productivity and Diversity theme’s work on this topic, contact Ramni Jamnadass (r.jamnadass@cgiar.org), Lars Graudal (l.graudal@cgiar.org), or Ian Dawson (Ian.Dawson@sruc.ac.uk).The work is done with national and international partners and supported by bilateral funding partners and theCGIAR Research Program on Forests, Trees and Agroforestry.