The Ecology of Forest Biodiversity

Forests are home to a diverse range of organisms, from microorganisms in the soil to plants and mammals on the forest floor and insects and birds in the forest canopy, and their interactions with each other form a complex network of interactions. It is said that about 80% of all terrestrial species depend on forests. Therefore, understanding forest biodiversity and interactions between organisms will help us to conserve the diversity of life on Earth and to understand their ecosystem functions. In this laboratory, we are studying forest biodiversity and interactions using multifaceted approaches such as field surveys, field experiments, genome analysis, and statistical modeling, mainly in the Okuchichibu Mountains, where the pristine natural environment still remains, and in mountainous regions of eastern Japan. Our research targets all populations of organisms that grow in forests. In particular, we focus on major environmental change events to understand how forest biodiversity and ecosystem functioning are changed in general. And we hope to use the knowledge gained to help conserve forest flora and fauna and ecosystem services.

Current Projects

  1. Impacts of vegetation degradation by sika deer on forest biodiversity
  2. The function of soil microorganisms in forest plants-soil feedback
  3. The role of local adaptation in shaping elevational gradients in biodiversity
  4. Evaluation of ecosystem services in abandoned plantation forests
  5. Habitat management for mitigating human-wildlife conflicts


Impacts of vegetation degradation by sika deer on forest biodiversity

In recent years, the population density of Japanese deer has increased in many parts of Japan, causing major changes in forests. In the background, there are social issues such as the decrease in hunting, and it is not easy to solve these problems. In the Okuchichibu Mountains, deer density increased more than tenfold in the 2000s, which resulted in the decline of the understory vegetation and the death of the upper trees, due to the feeding of the deer. There is a growing concern that this decline in vegetation may lead to the loss of various ecosystem services that benefit forests. For example, forest biodiversity and inter-specific interactions may be altered by the decline of invertebrates, which use plants and humus as resources, and then the loss of habitat for higher-order predators that use invertebrates as food resources. In addition, only plants with low nitrogen content, which are not preferred by deer, remain, which reduces litter decomposition and nitrogen mineralization and slows down the biogeochemical cycle, which may affect the generational change of the forest. Since the effects of deer on vegetation decline are multifaceted, it is necessary to study the changes in various processes in forest ecosystems over the long term. Therefore, we are installing a large number of deer exclusion fences over a wide area to understand the diversity of plants, animals, and microorganisms, changes in their interactions, and their effects on ecosystem function.


The function of soil microorganisms in forest plants-soil feedback

The importance of plant-soil relationships for plant growth has long been known in agriculture. In recent years, it has been shown that this plant-soil relationship plays a universal role in determining the dynamics of terrestrial ecosystems. For example, plants may supply litter and root exudates to the soil, and decomposers who use these materials may mineralize nutrients, thereby promoting plant growth. On the other hand, as the plant grows, herbivores and pathogens may collect in nearby soils, limiting plant growth. Thus, plant-soil interactions can be both facilitative and restrictive, but the relationship between plants and soil is not simple because there are many unknown factors that intervene. One of these factors is the diversity and function of soil microorganisms. Identifying the role of functional core microbiome, especially those characteristics that are related to plant fitness, is expected to lead to a better understanding of plant-soil feedback. We are currently working to elucidate the mechanisms of plant-soil feedback in forest ecosystems through transplantation experiments of tree seedling and soil and hologenomic analysis of the functional core microbiota. Our goal is to apply this knowledge to the recovery of vegetation under deer-feeding and to guide natural forests in abandoned plantations.


The role of local adaptation in shaping elevational gradients in biodiversity

In order to understand the origins of natural ecosystems, it is necessary to examine the response of organisms to environmental change. For this reason, changes in ecosystems along with altitude have been focused on as a “natural experiment” for investigating the responses of organisms to environmental changes. Not only temperature and precipitation, but also sunshine, wind flow, seasonal length, geology, and human activities change with altitude, making it possible to simulate the changes in ecosystems in response to various environmental changes. The Okuchichibu Mountains are steep and have an elevation difference of more than 1500 m, making them ideal for studying the evolutionary response of organisms along the elevational gradient in terms of local adaptation. For example, in the Okuchichichibu Mountains, a wide variety of maple species grows, and their distribution areas are clearly demarcated along the elevation, and the elevational gradient is related to the diversification of maple species. In addition, in the Okuchichibu Mountains, the limestone is exposed at the ridge, and plants adapted to the limestone are distributed and a unique vegetation landscape is formed. This elevational gradient of biodiversity is a challenge that is closely related to climate change impact assessment and conservation of endangered species. We are currently combining field manipulation experiments and genomic analysis to understand the mechanisms that drive the elevational gradients in biodiversity.


Evaluation of ecosystem services in abandoned plantation forests

In addition to deer-feeding damage, abandoned planted forests are an important issue in forest management today. Japan’s forests cover about 70% of its total land area, of which about 40% are planted forests of cedar, cypress, larch and other trees. Most of these planted forests were established through the so-called “expansion afforestation policy,” in which natural broad-leaved forests were cut down and replaced with plantations of high economic value. However, with the subsequent increase in demand for foreign timber, the price of domestic timber slumped, and the number of planted forests that could not be thinned out and other nursery operations increased. It is thought that there are many abandoned planted forests in the area now. Because the Okuchichibu Mountains are difficult to access, there are also many abandoned forests that have never been cared for. In recent years, it has been pointed out that such abandoned plantation forests impair not only the economic aspect of timber production, but also forest ecosystem services. These range from reduced carbon fixation capacity and nitrogen cycling to reduced biodiversity and habitat. Therefore, we are working to quantitatively assess the ecosystem services of abandoned planted forests compared to natural forests and managed forests, and to propose guidelines for the conversion to mixed forest and natural forest to restore ecosystem services.


Habitat management for mitigating human-wildlife conflicts

The conflicts between wild animals and human society, such as damage to agriculture and their approach to residential areas, have been recognized as a social problem. Agricultural damage caused by wild animals has been evident since around 1990, but it has been characterized by the simultaneous increase in damage caused by many wild animals, not only deer. This suggests that the wildlife problem is not simply due to a decrease in hunting, but also to structural changes in the natural environment. One of these is that the expansion afforestation has replaced natural hardwood forests with coniferous plantations, creating large areas of resource-poor habitat for wildlife in the backcountry. On the other hand, due to the lack of demand for firewood, the sparse forests that used to spread around the human settlements have been replaced by broadleaf forests, and habitats rich in resources for wild animals have been created around the human settlements. It is thought that such environmental changes are also occurring in the Okuchichibu region, and it is necessary to clarify the relationship with the dynamics of wild animals. In addition, there are many wild animals, such as medium-sized carnivores, whose ecology and roles in the forest are not well understood. Currently, we are using camera traps and environmental DNA analyses to elucidate the regional habitat use of wildlife from rural villages to forests, and to propose guidelines for habitat management.