مروری بر شاخص‌های ارزیابی کیفیت خاک‌های جنگلی

Background and Objectives:
Forests, often referred to as the "lungs of the Earth," play a fundamental role in regulating biogeochemical cycles and maintaining biodiversity. The health of these ecosystems is directly dependent on soil quality. However, in recent decades, factors such as land-use change, industrial pollution, climate change, and unsustainable exploitation have increasingly degraded forest soils. This degradation not only negatively impacts vegetation growth but also threatens critical soil functions, including carbon sequestration, nutrient cycling, and groundwater regulation. Addressing these challenges is essential for preserving forest ecosystems and their global ecological services. Soil, as one of the essential components of ecosystems, plays a vital role in supporting various functions of forest ecosystems. The concept of "soil quality" has emerged to assess the soil's ability to perform these essential functions and maintain ecosystem sustainability. Therefore, the development of accurate and practical indicators for assessing the quality of forest soils has become one of the research priorities in soil science and ecology. Given the clear gap in the development of integrated and practical indicators for monitoring the health of forest soils, this research has been conducted with the main objective of developing a novel set of soil quality indicators. For this purpose, the present study, through a systematic review of previous research, analyzes and integrates key physical, chemical, and biological parameters to provide a robust scientific framework for extracting and proposing comprehensive and effective indicators.
Materials and Methods:
The present study examines the relationship between soil health and human health and attempts to analyze and review previous research in this field by utilizing reputable scientific databases and search engines, including Google Scholar, Science Direct, Scopus, and the ResearchGate website. This study pays special attention to the evolution and development of the concept of soil quality from the past to the present and attempts to show how changes in soil quality can have profound effects on human health and other living organisms. In the following, by reviewing domestic and foreign sources, the latest and most important physical, chemical, and biological soil indicators for assessing soil quality, especially for forest soils, are introduced. This study emphasizes the importance of examining key indicators such as organic matter and its layering, and also addresses biological soil indicators including earthworms, Acari, Collembola, nematodes, protozoa, bacteria, and fungi. Soil microbial and enzymatic activities (urease, phosphatase, invertase and arylsulfatase) are also examined as important indicators for assessing soil quality and their relationship with soil functions is described in detail. Also, new and potential soil biological indicators such as abundance and diversity of individual soil organisms, microbial and fungal biomass and fungal to bacterial ratio, indicators based on fungal or nematode communities, soil biological community composition, community composition with PLFA, genetic methods (such as DGGE, T-RFLP, ARISA, etc.), sequencing, community physiological profiling, soil respiration, nitrification, denitrification, mineralizable nitrogen, metabolic rate, DNA and protein synthesis, enzymatic activities, genes and transcripts, metabolomics and proteomics, and stable isotope tracking were discussed. This study systematically reviews and analyzes previous research with the aim of developing a comprehensive and integrated framework of soil quality indicators suitable for the accurate assessment of forest soils.
Results:
The findings of this research demonstrate that soil health and quality serve as fundamental components in maintaining both human health and the sustainability of forest ecosystems. The review of previous studies reveals that the concept of soil quality is continuously evolving, highlighting an urgent need for more accurate criteria to assess its intricate relationship with forest ecosystem sustainability and human wellbeing.The results of this research demonstrated that soil biological indicators - particularly the activity of urease and dehydrogenase enzymes, soil microbial respiration, and labile organic carbon - possess significantly higher sensitivity and accuracy in monitoring forest soil quality compared to physical and chemical indicators. Measuring their changes in response to management practices or natural and anthropogenic disturbances can provide comprehensive information about alterations in soil functions. Based on the systematic literature review, an integrated framework incorporating the fungal-to-bacterial ratio, metabolic quotient, and ecological stoichiometric indices is proposed as a novel set for soil quality assessment. This framework demonstrates applicability across various management levels and can effectively reveal changes resulting from human activities and natural disturbances with high precision.
Conclusion:
This paper addresses the development of the soil quality concept and its pivotal role in sustainable forest management. As an outcome of this systematic review, it can be emphasized that future approaches to assessing forest soil quality must focus on transitioning from traditional physical and chemical indicators toward an integrated framework centered on sensitive biological indicators. This framework, derived from a synthesis of previous studies, introduces metrics such as the fungal-to-bacterial ratio, metabolic quotient, key enzyme activities (e.g., urease and dehydrogenase), and stoichiometric indices (e.g., microbial carbon-to-nitrogen ratio) as the core components for monitoring soil quality. The application of this framework by forest managers will not only enable early detection of degradation and evaluation of the effectiveness of conservation management practices but also facilitate dynamic and functional monitoring of forest ecosystem health. A key research priority for the future will be the localization and validation of these integrated indicators in Iranian forest ecosystems, such as the Hyrcanian and Zagros forests.