Forest restoration and hydrological parameters effects on soil water conditions: a structural equation modelling approach

ABSTRACT Although the effects of land use changes on hydrological functioning are widely addressed, issues such as which components of the hydrological system are affected, how and on what time scales are still poorly understood. In this context, we evaluated whether forest restoration improves soil water conditions in a Cerrado area, and whether the combined effects of forest structure and hydrological variables influence soil attributes. For this, we monitored three areas in different stages of natural succession over seven months, and evaluated vegetation structure indicators, hydrological indicators and soil indicators. Vegetation structure variables were analyzed with Principal Components Analysis, and to evaluate the direct and indirect effects among the variables we used structural equations modelling. Each successional stage differed in relation to forest structure, affecting the hydrological processes and causing the improvement of soil attributes with forest development. In the initial stage, throughfall was higher due to the more open vegetation, and the soil was more resistant to penetration. With the development of the vegetation, stemflow and interception also increased. As a result of the structural and hydrological changes, the model indicated that soil moisture was influenced directly by throughfall and stemflow, as well as by soil resistance to penetration and infiltration rates, and indirectly by forest structure, which influenced these variables, except infiltration rates. These results suggest that hydrological variables can be good indicators of forest restoration monitoring, providing a direct link to changes in soil conditions.

摘要 尽管土地利用变化对水文功能的影响已得到广泛研究，但诸如水文系统的哪些组分受到影响、影响方式以及作用时间尺度等问题，仍未得到充分阐释。在此背景下，本研究评估了森林恢复是否能改善塞拉多（Cerrado）地区的土壤水分状况，以及森林结构与水文变量的联合效应是否会对土壤属性产生影响。为此，我们对处于不同自然演替阶段的3个区域开展了为期7个月的监测，并对植被结构指标、水文指标与土壤指标进行了评估。采用主成分分析（Principal Components Analysis）对植被结构变量进行分析，并通过结构方程模型（structural equations modelling）评估变量间的直接与间接效应。各演替阶段的森林结构均存在差异，进而影响水文过程，并随森林发育程度提升带来土壤属性的改善。在演替初期，由于植被更为稀疏开阔，林冠穿透雨（throughfall）更高，且土壤穿透阻力更大。随着植被发育，树干茎流（stemflow）与冠层截留（interception）也随之增加。基于结构与水文变化的分析结果显示，模型表明土壤含水量直接受到林冠穿透雨、树干茎流、土壤穿透阻力以及入渗速率的影响，同时间接受到森林结构的调控——森林结构会影响除入渗速率外的上述各项变量。本研究结果表明，水文变量可作为森林恢复监测的良好指标，为土壤条件变化提供直接关联依据。