Managing genetic variation in tropical trees: linking knowledge with action in agroforestry ecosystems for improved conservation and enhanced livelihoods

Abstract

Tree species in agroforestry ecosystems contribute to the livelihoods of rural communities and play an important role in the conservation of biodiversity. Unless agroforestry landscapes are productive, however, farmers will not maintain or enhance the range and quality of tree species in them, and both income opportunities and biodiversity will be lost. Productivity depends on both tree species diversity and genetic (intra-speciWc) variation, but research on the latter has until recently not received the recognition it deserves. Worse, when knowledge on tree genetic variation in agroforestry systems has become available, it has not generally been linked in any systematic way with management, indicating a disjunction between research and Weld-level practice. In this essay, we attempt to bridge this gap by considering three questions: why is genetic diversity important in tree species? What is our current state of knowledge about intra-speciWc variation in trees in agroforestry systems? And, Wnally, what practical interventions are possible to support the conservation of this diversity in agricultural landscapes, while enhancing farmers' livelihoods? A wide genetic base in agroforestry trees is essential to prevent inbreeding depression and allow adaptation to changing environmental conditions and to altering markets for tree products. Recent evidence shows, however, that many species are subject to poor germplasm collection practice, occur at low densities in farmland, and are found in highly aggregated distributions, all of which observations raise concerns about productivity and sustainability. A range of germplasmaccess based interventions is necessary to improve current management, including the enhancement of community seed-and seedling-exchange networks, and the development of locally based tree domestication activities. Equally necessary, but more diYcult to address, is Biodivers Conserv (2009) 18:969-986 1 C the development of markets that support genetic diversity in tropical tree species; we discuss approaches by which this may be undertaken.

Innovation in input supply systems in smallholder agroforestry: seed sources, supply chains and support systems

“…Support from NGOs should therefore come through greater focus on the establishment of good quality (rather than unknown quality) seed sources. It should extend to providing business training to entrepreneurial seed dealers and tree nurseries, and should support networks of producers and distributors of seed and seedlings (Dawson et al 2009;Kindt et al 2006). The role of NGOs is also to support the development of smallholder product value chains through better linkages with markets; this in turn will drive better input supply chains.…”

“…Thus, for the majority of potential tree crops, equivalent farmer-to-farmer production and distribution of seed is a less feasible configuration than for annuals. Furthermore, this approach carries particular risks for outbreeding tree species that are potentially subject to inbreeding depression in farmland, if genetic bottlenecks arise through narrow a As several species occur in more than one type of source, numbers for individual categories are different from the overall totals diffusion (Dawson et al 2009;Dhakal et al 2005). A commercial 'Decentralised Model' introducing new species and varieties therefore requires special attention to how tree seed sources are utilised as breeding, foundation, and commercial seed in the input supply chains.…”

Genetic differentiation and diversity of Adansonia digitata L (baobab) in Malawi using microsatellite markers

“…In addition, different anthropogenic factors and natural phenomenon such as death due to drought, fungal diseases and destruction by elephants have shaped genetic diversity within the populations (Guy (1971;Wilson 1988;Edkins et al 2007). Furthermore, differences in time of tree flowering within and between populations happening in Malawi may reduce the effective number of trees in baobab populations differently; setting in varying degrees of random drift impacting on genetic diversity (Dawson et al 2009). Mwase et al (2006) indicated that distribution range and population size have strong relationship within population genetic variation in tropical tree species with restricted populations displaying significantly less variation than those with wide distribution.…”

“…Wild trees are genetically structured through natural processes such as mutation, genetic drift, selection, reproductive isolation, and migration (Buiteveld et al 2007). Plant molecular studies have shown that fragmentation of habitats and small population sizes negatively affect population genetic diversity (Dawson et al 2009). For instance, the genetically less diverse populations have reduced chance to buffer the effects of poor environmental conditions or competitions (Pluess and Stöcklin 2004).…”

Relationships of stable carbon isotopes, plant water potential and growth: an approach to asses water use efficiency and growth strategies of dry land agroforestry species

“…Assessment of vegetation level vulnerability, climate change resilience and human adaptation options requires understanding of the diversity, among tree species in the current vegetation, of genetic and phenotypic growth strategies and response to fluctuating water availability (Dawson et al 2009). Human livelihoods in many parts of Africa depend on the use and management of trees in forms of dryland agroforestry (Poschen 1986).…”