Do market opportunities threaten tree species diversity in rural homegardens of Central Sulawesi, Indonesia?

Shifting from subsistence towards market-oriented production is generally said to threaten agrobiodiversity. Homegardens are regarded as a sustainable agroforestry system, based on their high plant diversity. Commercialization of homegardens is mostly related to increasing dominance of annual cash crops at the expense of trees. Integrating commercial trees may offer a more sustainable intensification of homegardens. However, little is known about the dynamics of tree diversity during such a transformation process. This study aimed to answer the following questions: (i) does the integration of commercial tree species negatively affect overall tree species diversity in homegardens; and (ii) which type of homegarden harbours high tree species diversity In 30 homegardens randomly selected from three villages in Central Sulawesi, diversity parameters of all woody plants (including trees, shrubs and vines) were assessed in 2001, 2004 and 2007; and in 20 homegardens from two additional villages in 2004 and 2007. Socioeconomic farm and household data were gathered through individual interviews of the gardeners. From 2001 to 2007, the abundance of the commercial crops cacao and vanilla markedly increased in the homegardens, but decreased for arabica coffee, reflecting the world market price fluctuations of the same commodities during this time. Although the overall number of woody individuals per garden decreased from 2001 to 2007, significant increase was found for average woody species richness (15 19), Shannon diversity (1.71 2.12) and evenness indices (0.65 0.73). Homegardens rated as commercial harboured higher numbers of woody individuals per garden, similar species richness, but lower Shannon diversity and evenness as compared to subsistence gardens. Highest species richness was found in large gardens of non-migrant farmers, who were less dependent on their gardens for income generation than migrant farmers. In conclusion, a modest tree crop-based commercialization of homegardens did not threaten the overall tree species richness, but reduced the evenness of species abundances

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