Farmers' willingness to grow trees depends on many factors, and if governments or other organizations want farmers to grow more trees, these factors need to be understood. This article describes the expansion of the tree component in farming systems in recent decades in the Gunung Kidul district of Java. This trend is then explained with elements of the induced innovation model of agricultural development, viz. resource endowment, demand for products and institutional aspects. An increase in the productivity of staple crops seems to have been an important factor permitting farmers to plant trees. Another factor related to resource endowment that induced farmers to grow trees is the response to declining soil productivity as a result of erosion. The Indonesian government's trade and pricing policy for certain tree products has supported the favourable market trend for these products, and has induced farmers to plant fruit and fodder trees in particular. Improvement of the (physical) infrastructure has demonstrably encouraged tree growing. Examples are given of technological change in tree growing that result from farmers' own innovation as well as from research done by various organizations.