EFFECT OF FOREST LITTERS ON SOIL PHYSICAL AND CHEMICAL PROPERTIES IN SUBALPINE CONIFEROUS FORESTS OF WESTERN SICHUAN

Two stands of Picea plantations, a secondary forest and a primary forest, in western Sichuan, China were investigated to study the impact of forest litters on soil physical and chemical properties in artificial and natural subalpine coniferous forests. The results showed that in 30 a Picea plantation, 40 a Picea plantation, secondary forest and primitive forest, the annual litter were 2.67×10 3 kg hm -2 , 4.38×10 3 kg hm -2 , 4.27×10 3 kg hm -2 and 4.77×10 3 kg hm -2 ; the reserves of litters were 3.19×10 4 kg hm -2 , 3.64×10 4 kg hm -2 , 1.42×10 5 kg hm -2 and 1.45×10 5 kg hm -2 ; the total annual amounts of nutrient elements(namely N, P, K, Ca Mg)returning to soil from the litters were 82.01 kg hm -2 ,129.04 kg hm -2 , 130.57 kg hm -2 and 170.55 kg hm -2 ; and the annual mass loss rates of litters were 24.35%, 22.87%, 36.96% and 32.23%, respectively. For the litters to be half decomposed, it would take about 2.5 years in Picea plantations, while c. 1.6 years in natural forests. Moisture, porosity and nutrient contents in the forest soil approximately followed the order: secondary forests≈primary forests 30 a plantations40 a plantations. The soil factors of field water, contents of organic maters, N, P and K showed positive correlation with forest litter, reserve of litter, returned nutrieuts and mass loss, but the factor of soil apparent density showed negative correlation with those of forest litter. The ecological function restoration of Picea plantations was inferior to that of secondary forests. The relatively slow decomposition of litter was a key factor attecting soil moisture and nutrient status in the subalpine coniferous forest areas. When the artificial Picea forest started to grow rapidly, the litter increased, which resulted in the increase of nutrients returning to soils. At this time the ferest possessed high potential to replenish fertility to soil. However, owing to the slown decomposition of litters, most nutrients were held in the forest floor, causing poor physical and chemical properties of the soil under Picea plantations. Fig 1, Tab 6, Ref 18