科尔沁沙地人工杨树林生态服务效能评价

采用定位观测法，系统评价了杨树(Populus simonii)林的防风、抗蚀和滞尘等生态服务效能及其间接价值，同时定量探讨了风速减弱系数与实测林地叶面积指数的关系。结果表明，在研究区主害风(西北风)天气下，林地迎风区6H(H为平均树高)、3H、林地中央、林地背风区林缘、6和8H处2m高度的日平均风速与对照点(流动沙丘)相比均有不同程度减弱，风速减弱系数在18．3％～66．2％之间。林地背风区6H处0．25、0．5、1和2 m 4个高度的月平均风速减弱系数与林地叶面积指数呈显著非线性相关，其间存在良好的三次曲线关系(P<0．0001，R²=0．43～0．94，n=80)。在主害风天气下，林地各观测点的地表日风蚀量与对照点相比大幅度降低，平均降幅85．2％～99．9％。在观测期内，林地中央的日平均降尘量为13.2 kg·hm^-2，而林地迎风区6H处的日平均降尘量为9．9 kg·hm^-2，林地的日滞尘能力约为3．3kg·hm^-2。 

Evaluation of ecological services of Populus simonii forest on Heerqin sandy land

The main ecological services of the sand-fixed forest are windbreak, soil erosion control, and atmospheric dust retention. In this paper, the ecological services of Populus simonii forest were assessed by simultaneous measurements of wind speeds, daily amount of soil surface wind erosion, and amount of atmospheric dust deposition at different observation sites located within and outside the forestland. The results showed that compared with the control site (mobile sand dune), the daily mean wind velocity at 2 m height was reduced by 18.3, 31.6, 66.1, 66.0, 62.3 and 45.2% for the observation sites over the distances of 6 and 3 H (H meant average tree height) from forest edge of the windward side, forest center, and observation sites over the distances of 0, 6 and 8 H from forest edge of the leeward side, respectively. The greatest reduction in daily mean wind velocity was occurred in both forest center and forest edge of the leeward side. There was a significant positive relationship between leaf area index of the forest and monthly declining index of mean wind speed. The monthly declining index of mean wind speed increased with increasing the forest leaf area index by a cubic function. The daily wind erosion rates of soil surface in observation sites at 6 and 3 H from forest edge of the windward side, forest center, and at 0, 6 and 8 H from forest edge of the leeward side were reduced by as much as 85.2%-99.9%, in comparison with the control site. The greatest reduction in daily wind erosion rate of soil surface occurred in forest edge of the leeward side, followed in decreasing order by forest center, 6 and 8 H from forest edge of the leeward side, 3 and 6 H from forest edge of the windward side. During the observation period, the daily mean dust deposition within the forestland was 13.2 kg.hm-2, compared with 9.9 kg.hm-2 outside the forestland, with a 33% increase. All these results suggested that the poplar forest played an important role in reducing damaging winds, controlling wind erosion, and improving the local environment through increasing atmospheric dust deposition.