川西亚高山次生林恢复过程中土壤物理性质及水源涵养效应

Soil Physical Properties and Water Holding Capacity of Natural Secondary Forests in a Sub-alpine Region of Western Sichuan, China

川西亚高山原始针叶林遭受大规模采伐后自然恢复形成的次生林已成为该区域的主要森林类型之一,也是我国西南林区水源涵养林的重要组成部分。现有亚高山森林水源涵养功能研究主要集中在暗针叶林,对天然次生林关注较少。选择川西米亚罗林区亚高山次生林自然恢复演替序列上高山柳灌丛、次生桦木阔叶林、岷江冷杉桦木针阔混交林,以相邻岷江冷杉成熟林为对照,采用空间代替时间的方法,基于土壤容重、孔隙度、持水性能等测定,分析了次生林恢复过程中土壤物理性质变化及土壤水源涵养效应动态,结果表明:(1)次生林恢复过程中,土壤容重总体呈下降趋势,除灌丛与阔叶林、针阔混交林、暗针叶林间具有显著差异外,其余植被类型间无显著差异,随着土层的加深,土壤容重呈增加趋势;(2)不同恢复阶段土壤孔隙度具有显著差异,以针阔混交林0—30 cm土层总孔隙度(64.39%)和毛管孔隙度(50.49%)为最高,灌丛总孔隙度(41.25%)和毛管孔隙度(33.70%)为最低;而土壤非毛管孔隙度以暗针叶林(14.27%)为最高;随着土层的加深,土壤孔隙度大致呈现出递减的趋势;(3)随着林龄增加,次生林土壤0—30 cm土层最大持水量呈波动性增加趋势,在针阔叶混交林阶段达到最大(1 815.02 t/hm^2),到暗针叶林阶段有所下降(1 659.88 t/hm^2);土壤毛管持水量以针阔混交林(1 369.72 t/hm^2)为最高,而非毛管持水量以暗针叶林(534.95 t/hm^2)为最高,暗示针阔混交林树木生长所需有效水贮存量较大,亚高山暗针叶林具有较强的土壤水分调节能力和土壤渗透能力。从水源涵养功能角度,川西亚高山森林植被恢复应注重构建针阔叶混交林结构。

The secondary forest formed by natural restoration after the large-scale logging of primary conifer forests has become one of the dominant forest types in a subalpine region of western Sichuan, and plays an important role in water conservation in the forests of southwestern China. However, less attention was paid to the water conservation function of subalpine natural secondary forest. Therefore, by using the method of replacing space with time, four typical vegetation types of shrub (dominated by Salix cupularis), broad-leavedforest (dominated by Betula spp.), mixed coniferous and broad-leaved forest (dominated by Abies faxoniana and Betula spp.), and old-growth conifer forest (dominated by A.faxoniana) along natural restoration with different stand ages in Miyaluo of western Sichuan were selected to measure soil bulk density, porosity and water holding capacity. The aim of this study was to quantify the changes of soil physical properties and water-holding capacity. The results indicated as follows: (1) The soil bulk density decreased with the vegetation restoration and increased with the depth, and the trend was subalpine conifer mature forest<mixed coniferous and broad-leaved forest<broad-leaved forest<shrub. (2) There were significant differences in soil porosity along natural restoration. The mixed coniferous and broad-leaved forest had the maximum total porosity (64.39%) and capillary porosity (50.49%) in the 0—30 cm soil layer, and shrub had the minimum total porosity (41.25%) and capillary porosity (33.70%). However, the soil non-capillary porosity was the highest in conifer forest (14.27%), and the soil porosity showed a decreasing trend with the soil depth. (3) The soil maximum water-holding capacity along the natural restoration varied nonlinearly with the increasing stand age, from 1 172.07 t/hm^2 for the shrub stage to 1 815.02 t/hm^2 for the mixed coniferous and broad-leaved forest, and to 1 659.88 t/hm^2 for the conifer forest. The mixed conifer and broad-leaved forest has the maximum soil capillary water holding capacity (1 369.72 t/hm^2), while conifer forest has the maximum non-capillary water holding capacity (534.95 t/hm^2), which indicated that the former needs more available water storage capacity for vegetation growth, and the latter has strong soil water regulation ability and permeability ability. It is concluded from this study that attention should be paid to the construction of conifer and broad-leaf mixed forest structure in the alpine forest restoration in western Sichuan for the improvement of water conservation function.