亚高山森林自然与人工恢复对土壤涵水能力的影响

西南亚高山原始针叶林被大规模采伐后,在皆伐迹地上营造了大量云杉林进行人工恢复。但关于这些人工林的土壤涵水能力如何,一直没有系统深入的研究与评价。选择川西米亚罗林区系列不同林龄云杉人工林(20 a、30 a、40 a、70 a)为对象,以相邻同龄自然更新恢复的针阔混交林为对照,比较人工林土壤涵水能力随着演替进程的动态及其与自然恢复次生林之间的差异,结合人工与自然恢复后的林地特征(如细根生物量、凋落物储量和土壤有机碳等)和土壤物理结构参数等差异,阐释自然与人工恢复后土壤涵水能力差异的影响因素。结果显示:随着人工林演替,土壤0—40 cm层最大持水量随林龄的增加而降低,但变化不显著,从20年的2200 t/hm~2下降到70年的2138 t/hm~2,年平均下降速率为1.24 t/hm~2;然而在自然次生林中,土壤最大持水量随着林龄的增加呈现出波动式变化,从20年的2142 t/hm~2增加到40年的2565 t/hm~2,到70年又下降为2302 t/hm~2。通过土壤持水特性与林地凋落物贮量、细根生物量和土壤物理结构参数的相关分析表明,由不同恢复途径导致的林地土壤有机碳含量、凋落物特性及细根差异,进而改变土壤物理结构是影响土壤持水性能差异的主要因素。这些结果说明,从土壤持水量角度考虑,在对采伐迹地进行造林恢复时,应尽量避免营造结构单一、高密度的人工纯林,应选择营造针阔混交林的模式进行恢复。

Effects of natural and artificial restoration approaches on soil water-holding capacity in subalpine coniferous forests

Thousands of hectares of spruce plantations were established in the eastern Tibetan Plateau of China after the deforestation of primary conifer forests. However, the water-holding capacity of soils in these plantations remains unclear. Here, we investigated how soil water-holding capacity varied across a chronosequence of spruce plantations (20 a, 30 a, 40 a, 70 a) in the western region of Sichuan Province and determined the differences between artificial forests (spruce plantations) and mixed broadleaf-conifer forests, which naturally developed on the cutovers. We further analyzed how the fine root biomass, litter stock, soil organic carbon, and soil physical structure affected soil water-holding capacity. Our results showed that across spruce plantations, the maximum water-holding capacity of 0-40 cm soil depth linearly, but not significantly, decreased with increasing stand age, from 2200 t/hm² in the 20-year-old spruce plantations to 2138 t/hm² in the 70-year-old spruce plantations, and the average annual rate of decline was 1.24 t/hm². In contrast, soil maximum water-holding capacity in the natural secondary forest varied nonlinearly with the increasing stand age, from 2142 t/hm² for 20 a to 2565 t/hm² for 40 a and 2302 t/hm² for 70 a. The correlation analysis revealed that differences in soil organic carbon, litter stock, and fine root biomass, which would affect soil physical structure, were the main factors leading to differences in soil water-holding capacity between spruce plantations and natural secondary forests. Overall, our results indicated that we should avoid establishing dense monoculture plantations on cutover land for restoration. Instead, afforestation of mixed broadleaf-conifer forests would be better for the improvement of soil structure and water-holding capacity.