Accumulation of above-ground biomass and nutrients in swidden fallows: A comparison between planted alder fallows and unmanaged grassy fallows in Yunnan
云南省自然休闲地与桤木休闲地地上部分生物量与养分蓄积量的研究

Planting alder (Alnus nepalensis D.Don) in swidden fields has long been a traditional fallow management practice in Yunnan province of southwestern China. Farmers may harvest the trees for firewood after about six years or, in the case of longer fallow periods, they may be harvested for timber. To compare the above-ground biomass and nutrient accumulation in planted alder fallows with those of unmanaged grassy fallows, plot measurements were taken in sample fallows in Ximeng county, Yunnan province. The results confirm a higher above-ground biomass in the alder fallows than compared grass fallows of similar ages. Nutrient accumulation in alder fallows exceeds that of grass fallows after two or three years. By six years, the above-ground biomass in alder stands reaches about 69,640kg/hm~2,roughly four times greater than grass fallows. This alder biomass contains 557 kg/hm~2 of N,which is three times that of grass fallows, 41 kg/hm~2 of P and 265 kg/hm~2 of K,both about double the levels found in compared grass fallows. These findings highlight alder's role as an efficient fallow species that both accelerates soil rejuvenation and provides harvestable products.