保留密度对飞播油松林下植被发育影响的研究

Effect of Reserve Density on Undergrowth Development of Aerial Seeding Pinus tabulaeformis Stands

在北京市延庆县王家堡飞播造林基地,对9 a生飞播油松林设置4种间伐强度5 600(Ⅰ)、4100(Ⅱ)、3 700(Ⅲ)、1 830(Ⅳ)株.hm-2的林分密度调整及对照8 000(CK)5个处理。5 a后,通过比较林下植被组成、外貌、多样性及生物量的差异,研究不同保留密度对飞播油松林植被恢复的效果。结果表明:间伐改变了林下植物的生活型谱。保留密度不同,林下植被的优势种各异,灌木层优势种由中旱生物种向中生生物种更替。随林分保留密度的减小,林下植物种替代速率加快,生物量增大。运用林下植被多样性指标评价间伐效果较生物量理想。飞播油松林林下植物多样性峰值出现在郁闭度0.8～0.9,郁闭度过高或过低均不利于林下植被的发育。及时对郁闭林分进行适宜强度的间伐是实现飞播油松林可持续经营的有效途径,地位级Ⅳ、初植密度8 000株.hm-2的9 a生飞播油松幼林,密度选择4 100株.hm-2左右林下植被发育最优。

Four thinning intensities with the reserved densities of 5 600,4 100, 3 700 and 1 830 tree/hm^2, and a concontrol ,with reserve density of 8 000 tree/hm^2 were established in the 9-year-old air-seeded Pinus tabulaeformis stands in of Yanqing Country, Bejing. In 2005, 5 years after thinning, the composition, abundance, diversity, and biomass of the undergrowth in the four plots were investigated and compared. The results showed that the life-form spectrum could be affected by thinning intensity as well as latitude and altitude. Meanwhile, the composition of the dominant species varied and the meso-xerophytes tended to the mesophytes of shrub layers with the decline of the reserved density. Compared with control, both the rate of substituted species and biomass among undergrowth were accelerated by the drop of reserved density. However, too high or too low shade density was negative to the development of the undergrowth, the peak values of diversity indices appeared when the shade density was between 0. 8 and 0. 9. Based on the results, it was concluded that reasonable thinning intensity was benefitial to the development of the undergrowth and it could be an effective way for the sustainable use of stands. Generally, when the stand with both site class IV and high density of 8 000 trees · hm^-2 grows up to 9 years old, the reasonable density should be 4 100 trees/hm^2 or so by thinning.