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 Research Projects
- Impacts of vegetation decline by sika deer on forest biodiversity
- Roles of soil microorganisms in forest plants-soil feedback
- Climate change adaptation for the conservation of flora and fauna endemic to mountainous regions
- Habitat management for mitigating human-wildlife conflicts
- Solutions for carbon neutrality through forest ecosystem functions
In recent years, the population density of sika deer has increased in many parts of Japan, causing major changes in forests. In the background, there are social issues such as the decline of hunting and forestry, which are not easy to solve. In the Okuchichibu Mountains, deer density increased more than tenfold in the 2000s, which resulted in the decline of understory vegetation and the death of canopy trees, due to deer herbivory. There is a growing concern that this decline in vegetation may lead to the loss of various ecosystem services that benefit forests. For example, the decline of invertebrates that use plants and humus as resources, and then the loss of habitat for higher-order predators that use invertebrates as food resources may alter forest biodiversity and biological interactions. In addition, only plants with low nitrogen content, which are not preferred by deer, remain, reducing litter decomposition and nitrogen mineralization and slowing down the biogeochemical cycle, which may affect the regeneration 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 install a large number of deer exclusion fences over a wide area to understand changes in the diversity of plants, animals, and microorganisms and their interactions, and to clarify the effects on ecosystem functions.
The importance of plant-soil relationships for plant growth has long been known in agriculture. In recent years, it has become clear that this plant-soil relationship plays a universal role in determining the dynamics of terrestrial ecosystems. For example, plants supply litter and root exudates to the soil, and decomposers that use these materials mineralize nutrients, which may promote plant growth. On the other hand, as the plant grows, nearby soils attract herbivores and pathogens that may limit 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. In particular, identifying the role of functional core microbiome, whose characteristics are related to plant fitness, is expected to lead to a better understanding of plant-soil feedback. We currently work on elucidating the mechanisms of plant-soil feedback in forest ecosystems through transplantation experiments of tree seedlings and soil, and hologenomic analyses of the functional core microbiota. Our goal is to apply this knowledge to the restoration of vegetation under deer herbivory and the conversion of unmanaged plantations into natural forests.
Recently, extreme weather events, such as localized torrential rains and rising temperatures, have been frequently reported in various regions. These phenomena are considered to be associated with climate change, and there are concerns that they may cause changes in the phenology and distribution areas of organisms, affecting biodiversity and ecosystem services. In particular, flora and fauna endemic to mountainous regions are considered to be vulnerable to climate change. For example, in the Okuchichibu Mountains, there are many plant species that are adapted to limestone habitats. However, the population of limestone plants is very small and can be easily lost due to changes in climatic conditions and the resulting expansion of the distribution areas of other plants and animals, so conservation approaches are needed. One approach to counteracting the effects of such climate change is to increase the adaptability of organisms to climate change by reducing other stressors. There is also a need to assess the effects of climate change and identify high-risk areas and organisms. By considering adaptation to climate change, we expect to contribute to the conservation of biodiversity and ecosystem services in mountainous regions. We currently combine of field surveys and genome analyses to elucidate the distribution and adaptability of plants and animals endemic to mountainous regions, and to develop climate change adaptation for their conservation.
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 apparent 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 such change is the replacement of natural broad-leaved forests by coniferous plantations through expanded afforestation, which has created large areas of resource-poor habitat for wildlife in the backcountry. On the other hand, as the demand for firewood and charcoal disappeared, the sparse forests that used to spread around human settlements shifted to broad-leaved forests, creating resource-rich habitats for wildlife around human settlements. Therefore, it is necessary to clarify the relationship between such environmental changes and the dynamics of wildlife. It has also been pointed out that wild animals are no longer afraid of humans due to the decrease in human activities in forests. We currently use camera traps and environmental DNA analyses to elucidate the regional habitat use of wildlife from rural areas to forests, and to propose approaches to mitigate conflicts between human society and wildlife.
As addressing climate change becomes a common global issue, the goal of carbon neutrality by 2050 has been set. In order to achieve this goal, we need to take a new approach that not only addresses energy issues, but also proposes nature-based solutions that utilize ecosystem functions and implement them in society. One of the main pillars is to improve the carbon storage function of forests. The forest area in Japan covers about 70% of the land area, of which about 40% is plantations such as cedar, cypress, and larch. Most of these plantations were established through the so-called “expanded afforestation” policy, in which natural broad-leaved forests were cut down and replaced with economically valuable plantations. However, with the subsequent increase in demand for foreign lumber, the price of domestic lumber has slumped, and as a result, it is considered that there are many plantations that are no longer able to be thinned or nurtured. It has been pointed out that these unmanaged forests have a low timber volume, which not only affects the economic aspect of timber production, but also impairs the carbon storage function. Therefore, we quantitatively evaluate the carbon sequestration function of unmanaged plantations, including not only the above-ground parts but also the below-ground parts, and experimentally verify the results by actually inducing the plantations to natural forests, in order to examine effective management approaches for improving the carbon sequestration function.