汉江上游不同林龄麻栎林枯落物的水文功能评价

麻栎林普遍存在于汉江上游,其涵养水源能力的发挥对维持汉江上游流域生态平衡具有重要的作用。于2020年12月对汉江上游天柱山3个不同林龄(15 a、25 a、33 a)的麻栎林样地进行了枯落物厚度和蓄积量调查,利用浸泡法测定了枯落物各水文功能指标,运用熵权法对3个林龄麻栎林枯落物的水源涵养能力进行了综合评价。结果表明:麻栎林枯落物总厚度在3.0—4.8 cm,蓄积量介于13.76—14.39 t·hm^?2,二者在林龄之间差异不显著(P=0.591;P=0.993);不同林龄麻栎林内半分解层枯落物的瞬时持水量和吸水速率略大于未分解层的;二者的枯落物瞬时持水量均在10 min内快速增加,20 min后缓慢增加,其与浸泡时间呈对数关系,R²为0.7646—0.9606;未分解层枯落物的瞬时持水量表现为15 a>33 a>25 a,而半分解层的则表现6 h之前25 a的略大于15 a的,之后二者的持水量几乎相等,但二者均大于33 a的;相应的不同林龄内未分解层和半分解的枯落物吸水速率均在20 min内很快降低,2 h之后吸水速率以接近0的趋势变小,其与浸泡时间呈幂函数关系,R2为0.9933—0.9943;未分解层的枯落物瞬时吸水速率表现为15 a>33 a>25 a,而半分解层的表现为25 a>15 a>33 a;不同林龄的枯落物自然持水率差异显著(P=0.017),总枯落物层、未分解层和半分解层的自然含水率的大小依次均为15 a>33 a>25 a,而自然持水量、最大持水量和最大持水率在林龄之间差异均不显著(P=0.508;P=0.428;P=0.997);不同林龄内枯落物最大拦蓄量介于21.22—26.03 t·hm^?2,有效拦蓄量介于6.45—14.52 t·hm^?2,二者在不同林龄之间差异不显著(P=0.331),主要受枯落物自然持水率影响;水源涵养能力综合评价大小依次为33 a(35.45)>25 a(34.10)>15 a(30.35)。

Evaluation of Hydrological Function of Litter of Quercus Acuvarius at Different Ages in the Upper Reaches of Han River

Quercus acutissima, as a ubiquitous forest type in the upper reaches of the Han River, plays an important role in maintaining the ecological balance in the capacity of water conservation. In December 2020, the thicknesses and volumes of litters were investigated in three forest plots in the Tianzhu Mountain of the upper reaches of the Han River, whose stand ages were 15 years, 25 years and 33 years, respectively. The hydrological function indexes of the litters were measured by the soaking method. In addition, water conservation capacity of litters at the three forest ages was comprehensively evaluated using the entropy weight method. The results showed that the total thicknesses of litter of the Quercus acutissa forest were between 3.0 cm and 4.8 cm and the volumes of litters between 13.76 t· hm^?2 and 14.39 t· hm^?2. However, there were no significant differences among forest types at three stand ages(P>0.05). The instantaneous water holding capacity and water absorption rate of litters in the semi-decomposed layer were slightly higher than those in the undecomposed layer. The instantaneous water holding capacity of the litters increased rapidly in the first 10 minutes and then increased slowly in the next 20 minutes for different stand ages of the Quercus acutissa forest. The instantaneous water holding capacity and the soaking time exhibited a logarithmic relationship, whose coefficients were between 0.766 and 0.966. The instantaneous water holding capacity of litters in the undecomposed layer of 15 years was the largest, followed by those in 33-year and 25-year age classes. Whereas in the semi-decomposed layer, the water holding capacity of litters that were 25 years old was slightly larger than that of 15-year-old littles in the first 6 hours. The water holding capacity of 15-year and 25-year-old litters were almost equal and were larger than those 33 years old. Correspondingly, the water absorption rate of litters at different stand ages decreased rapidly in the first 20 minutes and decreased after 2 hours. A power function relationship was found between water absorption rates and soaking times(R2= 0.993 3–0.994 3). In terms of the instantaneous water absorption rate of the undecomposed littler layer, results showed the following pattern among stand ages: 15 years > 33 years > 25 years. For the rate of the semi-decomposed litter layer of different stand ages, 25 years > 15 years > 33 years. There were significant differences in the natural water holding rate of stand litters among different stand ages(P<0.05). For the natural water holding rates among the total litter layer, undecomposed layer, and semi-decomposed layer in different age groups, 15 years > 33 years > 25 years. However, there were no significant differences between the natural water holdup rate, maximum water holding rate, and maximum water capacity among different stand ages(P>0.05). The maximum storages and effective storages of litters ranged from 21.22 to 26.03 t·hm^?2 and from 6.45 to 14.52 t·hm^?2, respectively. There were no significant differences among different stand ages, which were mainly affected by the natural water holding rate of litters(P=0.331). Overall, the comprehensive evaluation of water conservation capacity of 33-year-old Quercus acutissima was 35.45 and was the largest, followed by that of 25 years(34.10) and 15 years(30.35).