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Associate Professor Ayumi Katayama and her research team reveal that the impacts of sika deer-driven understory vegetation loss on soil animals depend on climate conditions
Severe impacts are observed in regions with high rainfall and low snowfall, where soil erosion is more likely to occur
Points
- Deer population increases have been known to cause the loss of understory vegetation*1, leading to declines in soil-dwelling organisms; however, regional differences in these impacts have not yet been fully understood.
- Under climate conditions where soil erosion―an important driver of soil degradation―is more likely to occur, the research group demonstrated that the loss of understory vegetation has more severe impacts on soil animal communities.
- This study is the first to demonstrate that the effects of understory vegetation loss on soil environments and soil biota in Japan are climate dependent, and the findings are expected to provide valuable insights for developing future conservation strategies for understory vegetation.
Abstract
In recent years, in natural forests across Japan, understory vegetation such as dwarf bamboo has declined as a result of increased browsing by the sika deer (hereafter referred to as deer), whose populations have expanded. The loss of dwarf bamboo promotes soil erosion and degrades soil-dwelling organisms (soil animals) that support essential ecosystem functions, including nutrient cycling in forest ecosystems. The extent to which soil erosion occurs is also influenced by climatic conditions. However, it has remained unclear how differences in climate―such as precipitation and snowfall―affect soil erosion, soil environments, and soil animals following the loss of dwarf bamboo.
A research group consisting of Ms. Erika Kawakami, a doctoral student in the Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University; Associate Professor Ayumi Katayama of the Faculty of Agriculture, Kyushu University; and Professor Takuo Hishi of the Faculty of Science, Fukuoka University, investigated these relationships in six beech forests located in the Kyushu mountainous region and the San'in mountainous region, which experience contrasting climatic conditions. Using soils from sites where dwarf bamboo had been lost due to deer browsing and from sites where it remained, the team examined the relationships among soil erosion, soil environmental properties, and soil animals, including microarthropods*2 such as springtails and mites.
The results showed that soil erosion was driven by both the loss of dwarf bamboo and differences in climatic conditions, and that erosion was more pronounced in the Kyushu region. In addition, the occurrence of soil erosion increased soil bulk density*3, an indicator of soil hardness, thereby reducing pore spaces available for soil animals. This process led to declines in both the abundance of soil animals and the number of taxonomic groups*4, a measure of biodiversity. Such deterioration in the abundance and diversity of soil animals is likely to affect forest ecosystem functions, including nutrient cycling.
These findings indicate that conserving understory vegetation is critically important for maintaining soil biodiversity, particularly in forests located under climatic conditions where soil erosion is more likely to occur. This study was published online in the international scientific journal European Journal of Soil Biology on January 7, 2026.
Researcher's Comment
Research on the impacts of deer-driven understory vegetation loss on forest ecosystems has accumulated regionally with respect to aboveground organisms, including trees themselves as well as birds and insects. However, the effects on less visible organisms in the soil, and regional differences in those effects, have not been examined to date. This study shows that the degradation of soil biodiversity is of particular concern under climatic conditions where soil erosion is more likely to occur. At the same time, future climate change may lead to increased precipitation and reduced snowfall, raising the possibility that irreversible changes could occur even in regions that are currently considered to experience relatively minor impacts. Soil animals play an indispensable role in forest nutrient cycling. Our research team will continue to investigate the relationships between deer browsing and soil ecosystems in order to provide scientific knowledge that can inform conservation guidelines.
(Erika Kawakami, second-year doctoral student)
Glossary
*1 Understory Vegetation
A collective term for plants that cover the lower layer of forests, including tree seedlings, herbaceous plants, and shrubs with relatively low stature.
*2 Microarthropods
A group of animals characterized by a hard exoskeleton and jointed appendages, including insects, arachnids, and myriapods. In this study, the target organisms were soil microarthropods extracted using a Tullgren apparatus, such as springtails, mites, and pseudoscorpions, all of which are 2 mm or less in body length.
*3 Soil Bulk Density
The mass of the solid phase of soil per unit volume. It is expressed as the dry weight (g) per 1 m³ of dry soil.
*4 Number of Taxonomic Groups
Soil animals were grouped into single taxonomic units based on the order level (and, in some cases, the class or suborder level). This term refers to the number of such taxonomic groups present in 100 cc of soil.
Publication Information
Journal: European Journal of Soil Biology
Title: Effects of understory degradation induced by sika deer on soil microarthropods in beech forests: comparison between two different climatic conditions
Authors: Erika KAWAKAMI *, Takuo HISHI, Ayumi KATAYAMA
DOI：10.1016/j.ejsobi.2026.103803
- For more details on this research, click here.
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