陕西黄土高原土壤干层对植树造林的影响

根据野外考察和陕北、关中土壤含水量测定,讨论了陕西黄土高原土壤干层的分布范围及其对恢复植被的影响。资料表明,黄土高原土壤干层分布普遍,向南分布已达关中平原地区。不同植被带土壤干层发生原因有一定差别,干层发育程度有明显不同。在生态环境建设中,应根据不同地区土壤干层发育强度差别恢复不同类型的植被。在以往划分的延安以南的落叶阔叶林带,土壤干层发育较轻,可采取草、灌、乔木相结合的措施逐步恢复森林植被。在延安到长城之间的森林草原带,土壤干层发育严重,应当先发展草灌植被,后恢复森林草原植被。在长城以北的草原带应自然恢复草原植被。在土壤干层发育严重的地区,造林一般不能带来环境效益与经济效益,反而会导致深部土壤水分的过量消耗等不良后果,是不适于造林的地区。在黄土高原退耕还林还草的生态建设中,不论是发展人工林还是发展草灌为主的植被,都不宜选择耗水多、生长快的植物种,而应当发展生长适中偏慢的乔、灌、草种。

Effects of Soil-drying Layer on Afforestation in the Loess Plateau of Shaanxi

According to the investigation and the determination of soil moisture content in Guanzhong area and the North of Shaanxi, the scope of soil-drying layer and effects on afforestation are discussed. The results indicate that the soil-drying layer is widely distributed and has extended to the Guanzhong Plain. There are different origins and levels of soil-drying layer development in different vegetation zones. In ecological and environmental construction, the recovery of different kinds of vegetation should accord to the different levels of drying layer's development. In the deciduous broad leaf forest areas of less drying layer in south beyond Yan an, measures of combining grasses, shrubbery with trees should be taken to recover forest vegetation. In the forest-steppe areas of serious drying layer between Yan an and the Great Wall, grasses and shrubbery vegetation should be developed first and then forest-steppe vegetation should be developed. In the steppe areas of serious drying layer in the north beyond Yan an, steppe should be restored naturally. Tree planting is unsuitable in the areas of serious drying layer because it cannot improve the ecological environment and will lead to bad results to soil moisture. In ecological and environmental construction of tree planting and grass planting, we should choose growing slowly or moderately grass and shrubbery instead of plants which grow fast and consume a lot of water.