, 2012). Rural communities in parts of the tropics have planted trees within their farming systems for millennia. In the process, tree germplasm was sometimes widely exchanged, especially of food trees, as best exemplified by the ancient transfers of tree crops such as Theobroma cacao and Bactris gasipaes in South and Central America ( Lentz, 2000, Clement et al., 2010 and Powis et al., 2011). Throughout the colonial period, many other transfers of tree

commodity crop germplasm took place, including of T. cacao and Coffea arabica, both important species in the RG7204 in vivo past and still in the present (see Dawson et al., 2014, this special issue). In the case of C. arabica, modern cultivars are derived from two base populations known as Typica and Bourbon that were transported from East Africa throughout the tropics in the early 1700s. Theobroma cacao was introduced into Indonesia by the Dutch

from Venezuelan sources in 1560 and by the Spanish into the Philippines in around 1600. The French introduced T. cacao to multiple locations from the middle of the 17th century onwards, and the patterns of transfer and introduction thereafter were complex. Forastero T. cacao trees were apparently established from Brazilian sources on islands off the coast of continental West Africa from the 1820s onwards, before being transported to the mainland (see Mohan Jain and Priyadarshan (2009) for references to both coffee and cacao germplasm transfers in the colonial

period). The steps involved in the past global Enzalutamide distribution of other important agroforestry trees for small-scale farmers are generally less well understood, until documentation improved in the last few decades. Transfers prior to then were often clearly extensive, however, as evinced by the exotic nature of many of the tree species currently grown by smallholders. This was illustrated by Koskela et al. (2010), who undertook a review of the known indigenous and exotic distributions of 120 tree species important for smallholder agroforestry planting using the Agroforestree Database (AFTD, 2014). On average, the 120 tree species surveyed had been distributed to 21 countries beyond their native ranges (Koskela BCKDHA et al., 2010). Casuarina equisetifolia, mainly used for timber, is believed to be the most widely distributed agroforestry tree species, introduced to 110 countries outside its native range ( Table 1). Other widely distributed agroforestry tree species include Azadirachta indica, Mangifera indica and Leucaena diversifolia, providing medicine, fruit and fodder, respectively ( Koskela et al., 2010). Although in more recent times the documentation of germplasm transfers of agroforestry trees to support tropical agricultural practices has improved, much information, especially on the origin of provenances and if any selection was undertaken, frequently still remains unknown.