Methods
The sample agro-forestry system we studied here is poplar-button mushroom inter-plantations in
Shandong province, where poplar is a major and popular tree species (Fang et al., 2005) due to its fast
growing character. To make full use of growth space above the ground, many people choose to plant
button mushroom under wood. The main reasons for choosing button mushroom as the underwood
crop are (1) it has good market price so as to enhance the income for manager, (2) poplar can provide
shade environment for its growth, and (3) it can accelerate the annual volume growth of poplar (Sha