Studies on Nutrition Cycle of Abies georgei Forest Ecosystem of Mountain Segila in Tibet

The results on nutrition cycle of Abies georgei forest ecosystem of Mountain Segila in Tibet(94°25′～94°45′ E,29°35′～29°57′ N, 3 850 m 950 m) showed that the total preserving quantity in the ecosystem of the Abies georgei forests was 35.41 kg·hm-2·a-1, the total quantity of nutrient reversion was 54.89 kg·hm-2·a-1, and the total quantity of nutrient absorption was 90.3 kg·hm-2·a-1. Therefore, the total quantity of nutrient inputs per year was larger than that of nutrient outputs per year, and the net deficit per year of the soil (the litter layer is not included) in forest lands was not so significant. Nevertheless, the deficit of the element K was a little bid serious. The nutrient utilization efficiency of the Abies georgei forests and nutrient utilization index of the soil showed that the requirement for the element N of the forests was the largest, and that for the element Fe was the least. It was shown from the prediction of the nutrients in the ecosystem that the quantity of the nutrient elements would change very slowly within the next eighty years.