四川盆地四种柏木林分类型的水文效应

A comparative analysis of the hydrological effects of the four cypress stand types in Sichuan Basin

四川盆地丘陵区是长江上游水土流失最严重地区之一,该区大面积柏木纯林林分结构不合理、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。通过群落样地调查和坡面径流场观测,对比分析了四川盆地4种柏木林分类型的水文效应。结果表明:(1)4种林分类型林冠截留量与降水量呈幂函数关系;林冠截留率随雨量级的增大而减小,对次降雨的最大截留量为栎柏混交林(9.5 mm)>桤柏混交林(9.2 mm)>松柏混交林(8.8 mm)>柏木纯林(8.5 mm)。(2)4种林分类型之间未分解层和半分解层枯落物持水量随浸泡时间的变化存在极显著差异;枯落物总存储量变化范围为4.06—7.62 t/hm2,枯落物总持水量排序为栎柏混交林(17.07 t/hm2)>桤柏混交林(13.26 t/hm2)>松柏混交林(8.89 t/hm2)>柏木纯林(7.57 t/hm2)。(3)4种林分0—40 cm土层非毛管孔隙度变化范围为4.21%—6.94%,土壤最大持水量排序为栎柏混交林(1820.83±124.80)t/hm2>松柏混交林(1686.85±76.15)t/hm2>桤柏混交林(1644.45±119.84)t/hm2>柏木纯林(1574.14±119.89)t/hm2;4种林分类型雨季产沙量变化范围在534.2—1467.9 kg/hm2之间。综合分析表明,栎柏混交林是4种柏木林分类型中水土保持效果最优的;因此,该区柏木纯林的结构调整应以促进栎柏混交林的演替为目标。

The study area,situated in the eastern Sichuan province,is characterized by hilly landscape.Due to 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 Yangtze River.In order to mitigate soil erosion,a large area of cypress（Cuppressus funebris） monoculture was established starting early 1970s.However,the current monoculture was in a quite poor state in terms of stand structure,natural regeneration,stand stability,product supply and ecological protection.The objective of the study is to identify optimum technical approach for stand restructure aiming to improve multiple functions of the cypress monoculture.Through the survey of sample plots and observation of hillslope runoff grounds designed for cypress monoculture,pine-cypress stand,alder-cypress stand and oak-cypress stand,the hydrological effects of the four cypress stand types were analyzed.It was found that：（1） highly significant relationship existed between canopy interception and atmospheric precipitation.Canopy interception ratio decreased with the increase of rainfall intensity.The maximal interception for single rainfall ranked from higher to lower as： oak- cypress stand（9.5 mm） alder-cypress stand（9.2 mm） pine-cypress stand（8.8 mm） cypress monoculture（8.5 mm）.The canopy interception of cypress monoculture in each rainfall intensity class was significantly lower than that of other three stand types.（2） Among the four cypress stands,there were highly significant differences in water-holding capacity and its changes with length of soaked time for either non-decomposed litter or semi-decomposed litter.With a total litter storage ranging from 4.06 t/hm2 to 7.62 t/hm2;the total maximal water-holding capacity of the litter ranked was in the order of： oak-cypress stand（17.07 t/hm2） alder-cypress stand（13.26 t/hm2） pine- cypress stand（8.89 t/hm2） cypress monoculture（7.57 t/hm2）.For both total storage and total maximal water-holding capacity,oak-cypress is significantly higher than other three stand types.（3） The non-capillary porosity and total porosity for 0-40 cm soil depth varied between 4.21%-6.94% and 39.35%-45.52%respectively.The non-capillary porosity and total porosity of oak-cypress were 6.94% and 45.52%,which were significantly higher than that of other three stand types.The maximal water-holding capacity of 0-40 cm soil depth ranked in the order of： oak-cypress stand（1820.83±124.80） t/hm2 pine- cypress stand（1686.85±76.15） t/hm2 alder- cypress stand（1644.45±119.84） t/hm2 cypress monoculture（1574.14±119.89） t/hm2.For the four stands,the surface runoff and sediment yield in rainy season（May to October in 2007） varied between 77.8-139.0 mm and 534.2-1467.9 kg/hm2 respectively.In conclusion,the oak-cypress stand is the optimal among the four cypress stand types in terms of water and soil conservation.This suggests that restructure of cypress monoculture should aim to the succession of oak-cypress stand.