[Major features of decline of Pinus sylvestris var. mongolica plantation on sandy land].

In view of the decline of man-made sand-fixation forest of Pinus sylvestris var. mongolica in Zhanggutai sand land of Liaoning Province, this paper studied the major characteristics of the decline. The appearance of the declining man-made sand-fixation forest of Pinus sylvestris var. mongolica was grey green, its needle leaf was very thin, the blooming and fruiting rate was low, the average quantity of cones per tree was only 10.4-16.5, with only 6.96 g to 7.39 g per thousand seeds, and there were many empty and astringent seeds. The seasonal dynamics of nutrients in 2-year-old pine needle leaf was similar, i.e., the N and P contents decreased, while K content increased, showing that the nutrient cycle was imbalance. The chlorophyll content in 2-year-old needle leaf of declined forest was high, while that in 1-year-old healthy forest was also high but with a wide increasing range. The infected harm of shoot blight was the clearest mark to the decline of man-made sand-fixation forest of Pinus sylvestris var. mongolica. After the forest declined, the height and the DBH of the pine trees decreased evidently, and the structure of DBH distribution moved "left". The quantity of weak pine trees increased by 15.9%-27.2%, the roots decreased by 22.9%-28.9%, and the absorbing roots (diameter < 0.5 cm) decreased most seriously.