Water utilization sources of Alnus nepalensis in the water source area of Yuanyang terrace AN EFFECTIVE WAY TO IMPROVE SOIL FERTILITY IN TRADITIONAL AGROFORESTRY: PLANTING ALNUS NEPALENSIS A STUDY ON THE WOOD POLYMER COMPOSITES WITHIN ALNUS NEPALEENSIS D.DON Accumulation of above-ground biomass and nutrients in swidden fallows: A comparison between planted alder fallows and unmanaged grassy fallows in Yunnan