岷江干旱河谷典型地段整地造林效果评估

长期以来通过整地造林去恢复重建植被已在横断山区干旱河谷广为采用,然而这样的实践是否能有效提高植被覆盖率并改善土壤水源涵养能力仍不清楚.选择岷江干旱河谷3个典型地段,调查了多年(7～16 a)后整地造林地上植被覆盖、土壤物理性质以及目的造林树种岷江柏(Cupressus chengiana S.Y. Hu)的保存、生长与结实状况,以评价干旱河谷乡土树种造林成效及造林后的生态效果.结果表明:(1)岷江柏在栽植多年后仍有大量死亡,保存率明显下降,造林16 a后仅为38%;(2)不同年代栽植的岷江柏在造林后2～6 a即开始旱现直径年生长量下降趋势;(3)造林带内乡土植被总盖度、灌木盖度、草本盖度、地衣苔藓盖度均低于保留带,因此等高线水平沟整地造林措施未能有效促进乡土植被发育;(4)造林带土壤水分物理性质也不如保留带,整地造林也没有有效改善土壤水源涵养能力.综合分析发现,整地造林多年后岷汀柏造林不仅没有达到岷江干旱河谷预期的生态恢复重建效果,甚至有加剧生态退化的趋势.因此认为:(1)规模化整地造林并不是有效的干旱河谷生态恢复和保护措施;(2)尽管岷江柏是乡土树种,但并不是干旱河谷植被恢复的适宜种.图3表3参29

Assessment on Ecological Restoration Effect of Afforestation with Cupressus chengiana seedlings in the Dry Minjiang River Valley, Southwestern China

Afforestation has long been used as an important measure to restore vegetation in the dry valley of the Hengduan Mountains with low vegetation coverage and serious soil and water loss. But due to lack of ecological assessment on long-term afforestation aftereffects, it has not been fully understood that under the condition of harsh climate and pool soil of the dry valley, whether afforestation is a promising measure in promoting ecological restoration and increasing ecological services. The present study was conducted at fifteen plots with different planting years (7～16 a) in three afforestation demonstration areas of the dry Minjiang River valley in Maoxian County, Sichuan, China, aiming at assessing the ecological results of the afforestation using native trees (Cupressus chengiana S. Y. Hu)by preparing the plots with contour trenches. The survival and growth of C. Chengiana trees (including conservation rate, tree height, diameter and diameter increment process, canopy coverage, and fecundity), vegetation coverage (trees, shrubs, herbs, moss, litter and the whole), and soil physical properties (soil bulk density, water content, total porosity and water holding capability) were investigated, and then their differences across 7～16 years after afforestation were compared and analyzed. It was found that: (1) There was still a high mortality of C. Chengiana during the 7～16 years after afforestation. The percentage of all the survived trees gradually decreased with time, and only 38% trees were alive in the 16~(th) year after afforestation; (2) In the period of 2～6 years after afforestation the cypress trees presented the significant decline in annual diameter increment across the fifteen plots in all the three afforestation demonstration areas. (3) Compared with those in preserved belts, total vegetation cover, shrub cover, herb cover, and lichen/ moss cover in sylvicultural belts were significantly lower; (4) The water-physical properties of soil in sylvicultural belts were worse than those in preserved belts. Those all displayed that C. Chengiana plantation by preparing the plots with contour trenches could not effectively accelerate vegetation development and improve water and soil conservation, and would fail to achieve the expectant result for ecological restoration, even inducing ecological degradation in the dry Minjiang River valley ecosystem. Therefore, it is concluded that the afforestation by preparing the plots with contour trenches is not a promising measure and C. Chengiana, a native plant endemic to this dry valley, is not suitable for ecological restoration in the dry valley region. Fig 3, Tab 3, Ref 29