鼎湖山不同演替阶段森林土壤水分时空变异研究

土壤水分作为森林生态系统水分蓄库的主体，森林土壤水分储量及其时空动态与变异对揭示区域植被恢复与气候变化背景下的森林生态系统水文过程响应与服务功能变化机制具有重要意义。本研究以南亚热带地区典型森林植被演替序列马尾松人工林（Pinus massoniana coniferous forest，PF）-马尾松针阔叶混交林（mixed Pinus massoniana/broad-leaved forest，MF）-季风常绿阔叶林（monsoon evergreen broad-leaved forest，MEBF）为研究对象，依托中国生态系统研究网络森林样地建设与监测统一规范对鼎湖山森林生态系统定位站站区内分布的上述森林类型土壤水分的长期定位观测（2005-2015年），通过分析各演替阶段森林土壤不同土层（0-15、15-30、30-45、45-60、60-75和75-90 cm）土壤体积含水量观测数据，探究该区域森林植被恢复过程中的土壤水分变化及其时空变异。结果表明：在雨热同期且干湿季明显的南亚热带地区，鼎湖山森林土壤储水量及其时间动态受降雨量的影响显著，森林土壤层对降雨具有强烈的调蓄和稳定作用，伴随PF→MF→MEBF自然演替进程，调蓄水分能力逐步增强。林型间，由初期阶段PF到顶级群落MEBF，森林土壤水分储量逐渐提高，且演替后期林型相对于早期林型，土壤储水量均呈现为较小的年际与年内变幅。干、湿季而言，干季时林型间的土壤储水量差异大于湿季，干季时MEBF和MF土壤含水量分别是PF的1.33倍和1.11倍。从土壤含水量的干、湿季期间变异来看，不同林型各土层土壤含水量的变异系数大小均表现为干季大于湿季；垂直剖面方向上，突出表现为无论干湿季MEBF各层土壤含水量变异均比其他两种林型较为缓和，充分体现了MEBF优越的土壤水分时空调配能力。整体上，伴随PF→MF→MEBF自然演替进程，土壤水分储量及其稳定性逐步提升。

Temporal and spatial variability of soil moisture in a forest succession series in Dinghushan

Soil moisture is the main component of water storage in forest ecosystems. The soil water reserve of forests and its spatiotemporal dynamics and variations are of great significance for revealing the response of hydrological processes and the change mechanism of service functions in forest ecosystems under the background of regional vegetation restoration and climate change. In this study, we focused on the typical forests in lower subtropical China: a Pinus massoniana forest (PF), mixed Pinus massoniana/broad-leaved forest (MF), and monsoon evergreen broad-leaved forest (MEBF), which formed a natural successional sequence in this region. Based on the unified standards for the construction and monitoring of forest plots by the Chinese Ecosystem Research Network, long-term positioning observation of soil moisture in the above forest types of the Dinghushan Forest Ecosystem Research Station was conducted during the 2005-2015 period. Through analysis of the measured soil volumetric water content in different soil layers (0-15, 15-30, 30-45, 45-60, 60-75 and 75-90 cm) of the above mentioned forests at each stage of succession, the change in soil water storage and its spatiotemporal variation in the process of forest vegetation restoration in this region were explored. The data showed that in the southern subtropical regions with simultaneous rain and heat and distinct dry and wet seasons, soil water storage and its seasonal dynamics in Dinghushan were significantly affected by rainfall, and the soil layer had a strong regulatory and stabilizing effect on rainfall. With natural succession from the planted (PF) to the climax (MEBF) stage, the ability to regulate and store water gradually increased. Among forest types, from the initial stage (PF) to the top community (MEBF), the soil water storage of the forest ecosystem gradually increased, and compared with the early forest types, the soil water storage of late succession forest types showed small interannual and intra-annual variation. At a seasonal scale, the difference in soil water storage between forest types in the dry season was greater than that in the wet season. The soil water content of MEBF and MF in the dry season was 1.33 times and 1.11 times that of PF, respectively. According to the variation in the soil water content in dry and wet seasons, the coefficient of variation of the soil water content in each soil layer of the different forest types was greater in the dry season than in the wet season. In the vertical direction, this coefficient of variation highlighted that the variation in the soil water content in each layer of MEBF was more moderate than that in the other two forest types in both the dry and wet seasons, which reflected the superior water regulation ability of MEBF. On the whole, with natural succession from the planted (PF) to the climax (MEBF) forest, the soil water storage and its stability improved.