川西不同树种人工林对土壤涵水能力的影响

为评价青藏高原东缘不同树种造林对土壤涵水能力的影响,选择立地条件与营林方式相同的4种人工林(连香树(Cercidiphyllum japonicum)、油松(Pinus tabulaeformis)、落叶松(Larix kaempferi)和华山松(Pinus armandii))为研究对象,以落叶阔叶灌丛为对照,比较造林恢复28 a后不同人工林土壤孔隙度及持水性的变化,结合林地凋落物贮量及细根生物量等参数,试图揭示造成不同人工林地土壤涵水能力及潜力差异化的因素。结果显示:营造油松和华山松纯林不仅没能有效改善土壤孔隙状况,反而加剧了土壤涵水功能的退化。相反,连香树和落叶松在代替次生落叶灌丛造林后,土壤容重显著下降,孔隙度增加且小孔隙比例升高,持蓄水能力提高。凋落物及细根特性是不同林地土壤持水性能差异的重要因素。综合分析表明,在对退化生态系统进行造林恢复时,应尽量避免营造高密度针叶纯林,应结合种植有助于土壤结构改良的落叶或阔叶树种。

Effect of reforestation with different tree species on soil water-holding capacity in western Sichuan province

Reforestation of degraded ecosystems (e.g.,cut-clearing area or degraded secondary shrubland) is an important forest practice to restore the soil ecological function.However,there is scarce information about the effects of conversion from shrubland to plantations of different tree species on water-holding capacity of soils.To evaluate the effect of reforestation after conversion from coppice on soil water-holding capacity in the eastern Tibetan Plateau,four plantations stands were selected (each 28 years old,1987-2015),each with a different dominant tree species (namely Cercidiphyllum japonicum,Pinus tabulaeformis,Larix kaempferi,and Pinus armandii).A native broad-leaf coppice was used as the control.The four plantations were cultivated on similar site conditions,by using the same patterns of planting and management practices.We determined the soil bulk density,soil porosity,and soil water-holding capacity.Correlations between the soil physical index and the stock of litter in the forest floor and fine root biomass were used to elucidate the factors that influenced the changes in soil water-holding after replacing the native shrub by different tree species.Our results showed that compared with native broad-leaf coppice,either the deciduous or the broad-leaved plantations (C.japonicum and L.kaempferi) better improved the porosity and water-holding capacity of soils.In contrast,the evergreen pure coniferous plantations (P.armandii and P.tabulaeformis) decreased the porosity and water-holding capacity of the soils.Low rate of litter decomposition in the P.armandii and P.tabulaeformis plantations hindered the turnover of organic materials forming soil organic matter,and this may have indirectly contributed to the lower soil water-holding capacity,via influencing soil physical porosity.Additionally,the fine root biomass in different plantations may be an important factor,since it too can alter soil physical parameters,and thus,further affect the soil water-holding capacity.Our results highlighted that reforestation in a degraded ecosystem with the aim to restore soil water-holding capacity should avoid planting pure stands of coniferous tree species.Deciduous or broad-leaved tree species are appropriate tree species for improving the soil structure of monoculture plantations in the eastern Tibetan Plateau.