川中丘陵区人工柏木防护林适宜林分结构及水文效应

The suitable stand structure and hydrological effects of the cypress protection forests in the central Sichuan hilly region

川中丘陵区是长江上游水土流失最严重地区之一,该区大面积柏木防护林林分结构不合理、天然更新不良、林分稳定性差、产品产量和水土保持功能低,急需进行结构调整。通过48个典型柏木纯林样地林分郁闭度与灌木、草本及枯落物盖度和生物量分析,提出了该区人工柏木防护林适宜林分郁闭度为0.6—0.7。根据林分结构,将柏木纯林林分结构划分为5种类型。对比分析结果表明:(1)5种林分类型枯落物最大持水量取决于林分枯落物存贮量,适宜结构型林分与其它4种林分类型枯落物最大持水量存在显著差异,排序结果为适宜结构型(4.038±0.497)t/hm2>中低密度型(3.583±0.521)t/hm2>中高密度型(3.243±0.455)t/hm2>低密度型(2.841±0.656)t/hm2>过密型(2.272±0.580)t/hm2。(2)土壤饱和贮水量排序为适宜结构型(180.59±14.83)mm>中低密度型(173.84±18.06)mm>中高密度型(169.27±13.20)mm>低密度型(162.57±8.79)mm>过密型(150.77±5.08)mm,适宜结构型林分与其余4种林分之间均存在显著差异。(3)6次典型降雨产沙量排序为适宜结构型(360.07 kg/hm2)<中低密度型(577.08 kg/hm2)<中高密度型(625.98 kg/hm2)<低密度型(878.51 kg/hm2)<过密型(1026.74 kg/hm2),5种柏木林分类型产沙量之间均存在显著或极显著差异。

The study area is situated in the central Sichuan hilly region.Due to the long-term deforestation of natural ever-green broad-leaf vegetation,this area had been suffered from soil erosion over time and was regarded as one of the most serious eroded region in the upper reach of the Yangtze River.In order to mitigate soil erosion,a large area of cypress（Cuppressus funebris）protection forests was established starting early 1970s.However,the current cypress forests were in a quite poor state in terms of stand structure,natural regeneration,stand stability,product supply and ecological functions.The objective of the study was to identify optimum stand structure aiming to improve soil conservation functions of the cypress monoculture.Through the survey of 48 sample plots and analysis of the relationship between canopy closure and the coverage and biomass of shrubs,grasses and litter,the canopy closures of 0.6—0.7 was regarded as the most suitable one,and 5 stand types of cypress monoculture was categorized,that is,low density type,medium-low density type,suitable density type,medium-high density type and over-dense type.The following results were found through a comparative study of the hydrological effects of the 5 stand types.（1） The maximal water-holding capacity of the litter in the 5 stand types depended on the total litter storage,and it ranked from higher to lower as： suitable density type（4.038 ± 0.497） t/hm2 medium-low density type（3.583 ± 0.521） t/hm2 medium-high density type（3.243 ± 0.455） t/hm2 low density type（2.841 ± 0.656） t/hm2 over-dense type（2.272 ± 0.580） t/hm2.（2） The maximal water-holding capacity of soil was in the order of suitable density type（180.59 ± 14.83） mm medium-low density type（173.84 ± 18.06） mm medium-high density type（169.27 ± 13.20） mm low density type（162.57 ± 8.79） mm over-dense type（150.77 ± 5.08） mm;and the suitable density type had significant difference with other four types.（3） The data from runoff plot observation for six times of rainfall has indicated that the sediment yield of the 5 stand types ranked from lower to higher as suitable type（360.07 kg/ hm2） medium-low density type（577.08 kg/ hm2） medium-high density type（625.98 kg/ hm2） low density type（878.51 kg/ hm2） over-dense type（1026.74 kg/ hm2）,and significant difference existed among the 5 stand types.