Vital Role of Fog Precipitation in Nutrient Input to Hyrcanian Forests

According to the Public Relations Office of the University of Tehran, the study, published in the internationally  journal of Ecohydrology, indicates that fog-derived moisture at high elevations supplies the equivalent of 6.5 percent of total water input to these forests—a finding that can serve as a basis for sustainable natural resource management in northern Iran.

Continuing studies by researchers from the Department of Forestry and Forest Economics, Faculty of Natural Resources, College of Agriculture and Natural Resources, University of Tehran, on the phenomenon of fog precipitation have shown that this atmospheric phenomenon is not only a source of moisture but also, by capturing and transferring nutrients, plays an effective role in the nutrient cycle of highland Hyrcanian beech stands.

This achievement was carried out as part of research by Kimia Mostafanejad, under the supervision and guidance of Dr. Pedram Attarod and with the advisory support of Dr. Vahid Etemad and Dr. Atefeh Dezhban, and in collaboration with Mohammad Sadegh Kavianpour, a doctoral student in forestry. The present study follows basic research previously conducted with precise field monitoring and measurement by Eng. Mohammad Sadegh Kavianpour and the research team over two years (1401 and 1402; 2022–2024), the results of which were published in 1404 (2025–2026) in the internationally reputable journal Ecohydrology, published by Wiley. The research documented, for the first time, the quantitative aspects of fog precipitation and showed that this phenomenon adds, on average, the equivalent of 6.5 percent of total water input through precipitation to the forest over two growing seasons. The potential for fog capture by beech stands is about 100 cubic meters per hectare per growing season (equivalent to about 500 liters per individual beech tree), which, at the regional scale annually, adds more than 120 million cubic meters to the water balance of the mountain forests of northern Iran through the canopy of beech trees.

Now, moving beyond purely quantitative studies, this research group has documented the chemical composition and nutritional value of fog precipitation for the forest.

Dr. Pedram Attarod, a faculty member of the University of Tehran and head of the group, referring to the importance of implementing this project in the mountain beech stands of Pespares village in Nur County (at an altitude of 2,000 meters above sea level), said: “Although fog precipitation had previously been recognized as a hidden source of water input in the forests of northern Iran, the new findings proved that fog droplets, as they pass through the branches and leaves of trees, become a nutrient source for forest soil. Based on data from this research during one growing season, the passage of fog precipitation through the dense beech canopy leads to a significant increase in electrical conductivity compared with rain, reflecting the considerable enrichment of water droplets with solutes and biological ions during contact with the tree canopy.”

He added: “Among the elements studied, potassium—one of the most vital nutrients for metabolism, stomatal opening and closing, and tree resilience—showed a significant and notable increase compared with rain in all measured events in fog precipitation beneath the canopy, with its concentration reaching more than five times that of rain. This indicates that the canopy of beech trees, through leaching, provides this essential element to the soil and roots of forest trees. Likewise, changes in sodium, calcium, and magnesium cations indicate the complex effects of cation exchange and the transport of suspended particles from the Caspian Sea through fog masses.”

He emphasized: “This study is part of the long-term program of this research group in the forests of northern Iran to comprehensively examine fog precipitation from ecohydrological, chemical, physiological, ecological, and silvicultural perspectives, and complementary studies are being planned.”

Dr. Attarod noted: “Given the vital role of Hyrcanian forests in biological security, water, and livelihood support for downstream areas, a more precise understanding of fog precipitation can greatly contribute to the sustainable management of these valuable ecosystems. The allocation of special and appropriate research funding to expand automatic measurement and data-recording stations, financial support for further field research, and the development of international collaborations will be a fundamental and necessary step toward examining the biological status of the mountain forests of northern Iran and achieving sustainable land management.”

It is worth noting that the Hyrcanian forests in northern Iran, with an age of more than 25 to 40 million years and inscription on the UNESCO World Heritage List, are considered one of the world’s most valuable biological treasures. Meanwhile, Iran’s beech stands have expanded at elevations of 700 to 2,200 meters in the humid and fog-prone areas of the northern slopes of the Alborz mountain range and constitute about 30 percent of the total area of Hyrcanian forests. This mountain belt is continuously affected by a natural phenomenon called “fog precipitation,” in which fine fog droplets are intercepted by plant surfaces, especially tree canopies, are converted into larger droplets, and ultimately fall to the forest floor as canopy drip. This vital phenomenon plays a decisive role in moderating and reducing water stress in soil and vegetation during dry seasons.