晋西黄土区不同密度刺槐林枯落物层水文生态功能研究

为对比分析林分密度对枯落物层水文生态功能的影响,以晋西黄土区6种不同密度(475,900,1 200,1 575,1 825,2 350株/hm~2)刺槐(Robinia pseucdoacacia)人工林为对象,采用样地调查与室内试验相结合的方法,对其枯落物层总厚度、总蓄积量、最大持水量、有效拦蓄量、枯落物持水量与浸水时间的关系、枯落物吸水速率与浸水时间的关系等水文特征进行研究,以期从中提出该区刺槐林经营的合理密度,为充分发挥水土保持功能、实现功能导向型植被调控与优化配置提供理论依据。结果表明:(1)研究区6种密度刺槐人工林枯落物总厚度变化范围为28.67~54.33mm,总蓄积量为2.98~10.65t/hm~2,且在一定范围内,随林分密度增大,枯落物蓄积量出现先增加后减少的变化趋势,6种密度枯落物蓄积量由大到小依次为1 575株/hm~21 825株/hm~21 200株/hm~2900株/hm~22 350株/hm~2475株/hm~2;(2)枯落物最大持水率的变动范围为295.35%~427.84%,无明显的规律性;最大持水量为11.16~37.01t/hm~2,在一些林分间差异显著,表现为随密度的增加呈先增大后减小的趋势,密度为1 575株/hm~2的林分枯落物持水性能表现最好,达37.01t/hm~2;半分解层枯落物持水量均高于未分解层;不同密度刺槐林枯落物的吸水速率与密度关系不显著;(3)各林分枯落物有效拦蓄量为7.22~23.64t/hm~2,其中以1 575株/hm~2的有效拦蓄能力最强,为23.64t/hm~2;(4)枯落物持水量与浸水时间之间存在明显的对数函数关系:Q=aln t+b,R20.95;枯落物吸水速率与浸水时间之间存在明显的幂函数关系:V=ktn,R20.99。综上所述,在本研究范围内,林分密度在1 575株/hm~2时枯落物层表现出较好的水文生态功能,当密度低于1 200株/hm~2,枯落物层水文效应急剧下降;从枯落物水文功能角度,建议今后研究区刺槐林的经营密度以1 200~1 800株/hm~2为适宜调控范围。

Hydrological and Ecological Functions of Litter Layer Under Robinia pseucdoacacia Plantation with Different Densities in Loess Region of Western Shanxi Province

In order to compare and analyze the impacts of stand density on hydrological and ecological functions of litter layer, the Robinia pseucdoacacia plantations with 6 different densities (475, 900, 1 200, 1 575, 1 825 and 2 350 trees/hm²) in Loess region of Western Shanxi Province were chosen as the object. By the methods of field survey and laboratory experiment, the hydrological characteristics of litter layer, such as the litter total storage capacity, the maximum water holding capacity and modified interception capacity and their relationships with soaking time, were studied, aimed to propose the reasonable density of the Robinia pseucdoacacia management in this area and provide scientific basis for giving full play to soil and water conservation functions as well as achieving function-oriented vegetation regulation and optimal allocation. The results showed that:(1) The litter total thickness of Robinia pseucdoacacia plantations with 6 densities ranged from 28.67 mm to 54.33 mm in the studied area. The total volume was about 2.98~10.65 t/hm², and in a certain stand density, the litter total storage capacity increased first and then decreased with the increase of densities, showing an order of 1 575 trees/hm² > 1 825 trees/hm² > 1 200 trees/hm² > 900 trees/hm² > 2 350 trees/hm² > 475 trees/hm². (2) The maximum water holding rates varied from 295.35% to 427.84% with no obvious regularity. The maximum water holding capacity was 11.16~37.01 t/hm² and had significant differences among some plantations with different densities, which achieved the best (37.01 t/hm²) at 1 575 trees/hm². The water holding capacity in half-decomposed litter layers was higher than that in un-decomposed litter layers, but different stand densities had little effects on water absorption rates. (3)The modified interception capacity was about 7.22~23.64 t/hm² in different stands and the maximum was found in 1 575 trees/hm², reaching 23.64 t/hm². (4) Water holding capacity of litter had a logarithmic correlation with immersion time (Q=aln t+b, R²>0.95), and water absorption rates showed a power function with soaking time (V=ktⁿ, R²>0.99). In summary, within the scope of this study, the litter layer showed better hydrological and ecological function under plantation with around 1 575 trees/hm². When the density was lower than 1 200 trees/hm², it tended to drop sharply. From the perspective of litter hydrological function, it is recommended to maintain the rational stand density range of 1 200~1 800 trees/hm² in future Robinia pseucdoacacia plantation management of this area.