晋西黄土区退耕还林20年后典型林地的持水能力

为探究晋西黄土区退耕20年后典型林地间持水能力的差异,选取山西省吉县蔡家川流域退耕20年的次生林和油松人工林、刺槐人工林、油松×刺槐人工混交林4种典型林分为研究对象,同时以耕地作为对照,通过外业调查和室内测定,比较分析了该地区退耕林分间林地(枯落物层和土壤层)的最大持水量和有效持水量。结果表明:1)次生林枯落物层的最大持水量和有效持水量为201.20和154.32 t/hm2,分别是人工林的1.35~2.14倍和1.33~2.06倍,人工林之间表现为油松×刺槐人工混交林刺槐人工林油松人工林;2)退耕林地土壤层的最大和有效持水量分别介于5 102~5 563 t/hm2和1 007~1 251 t/hm2之间,均显著高于耕地的4 695和812 t/hm2;典型退耕林地间土壤有效持水量表现为次生林油松×刺槐人工混交林油松人工林刺槐人工林,最大持水量为次生林油松×刺槐人工混交林刺槐人工林油松人工林;3)与退耕引起土壤非毛管孔隙度增加相一致,林地的最大持水量和有效持水量较耕地分别增加了10.7%~22.8%和32.9%~73.1%,表明退耕对林地持水能力的影响在有效持水量方面更突出;4)退耕林分间林地持水能力表现为次生林油松×刺槐人工混交林刺槐人工林油松人工林。林地最大持水量和有效持水量显著高于耕地,这主要源于土壤性质改善引起的土壤层持水能力增强,同时枯落物层的持水功能也发挥了一定作用。总之,退耕20年后林地持水能力显著增强,不同林分间次生林持水能力较好,表明次生林宜作为该地区退耕后植被恢复的主要参考。 

Water-holding capacity of different forestlands 20 years after converted from farmland in loess region,western Shanxi Province

To compare the water conservation capacity of four typical forest stands converted from farmland 20 years ago in loess region, western Shanxi Province, the maximum water-holding capacity ( WCm ) and effective water-holding capacity ( WCe ) of litter and soil layers in secondary forest ( SF ) , Pinus tabuliformis plantation( P) ,Robinia pseudoacacia plantation ( R) and P. tabuliformis × R. pseudoacacia plantation (P × R) were examined based on field investigations and laboratory analyses in July 2013,with the farmland as a control (CK). The results were as follows: 1) WCm and WCe of litter layer in secondary forest were 201. 20 and 154. 32 t/ha, respectively, which were 1. 35--2. 14 times and 1. 33--2. 06 times of those in the plantations. Both WCm and WCe showed the trend as P × R > R > P. 2) The WCe of the soil layer in four forest stands ranged between 5 102--5 563 t/ha, and the WCe was 1 007--1 251 t/ha, which were significantly higher than 4 695 and 812 t/ha of the farmland ( CK) , respectively. The WCe showed the trend as SF > P × R > P > R, while WCm as SF > P × R > R > P. 3) The WC e of the forestlands increased about 32. 9%--73. 1% and much higher than the WC m increment about 10. 7%--22. 8%, which was consistent with the changes of non-capillary porosity. This implied more significant effects of the conversion of farmland to forest (CFF) on WCethan WCm. 4) The water-holding capacity of the converted forestlands showed the trend as SF > P × R > R > P with significantly higher WCm and WCe than the farmland. This was mainly resulted from the improvement of soil characteristics and then the increase of water-holding capacity in the soil, and also certain water-holding effect of litter layers. In general, the water-holding ability has been significantly improved through the CFF in loess area of western Shanxi Province. The water-holding capacity of the secondary forest was better than the other three plantations, indicating that the secondary forest should be the main type of vegetation restoration in CFF program in the loess region.