Oceanic islands provide unique ecosystems with high levels of endemism. The Ogasawara Islands of Japan are typical oceanic islands and were inscribed on UNESCO’s World Heritage List in June 2011. The Ogasawara Islands exhibit the World Heritage values of ongoing ecological and evolutionary processes and high levels of endemism, especially in plants and land snails.

Oceanic island ecosystems often have limited adaptive capacity and are therefore fragile under disturbance caused by invasive alien species. In the Ogasawara Islands, like other oceanic islands, invasive species represent the most serious threat to the value of their unique natural inheritance. The management plan for the protection and management of nature in the Ogasawaras is being implemented effectively by Japan’s Ministry of the Environment, Forestry Agency, Tokyo Metropolitan Government and Ogasawara Village with the participation of local communities and scientists. The control of invasive alien species, however, has experienced both successes and setbacks. The principal conservation strategy for island ecosystems is adaptive management. In the process of implementing countermeasures to alien species, it is essentially important to consider direct and indirect effects on multiple species, including both native and alien organisms.

This special feature aims to introduce adaptive management and wise use of nature in the Ogasawaras from the viewpoint of natural science as well as humanities. I hope that the experiences gained in our on-going efforts toward achieving sustainability of nature and the culture of the Ogasawaras will provide useful ideas that can contribute to the conservation and sustainable use of nature on other oceanic islands with unique and outstanding values.

March 2020

Executive Editor

Naoki KACHI (Tokyo Metropolitan University, Japan)

The Ogasawara Islands were inscribed in the World Heritage List in 2011, recognized for their Outstanding Universal Value of the on-going process of biological evolution in remote oceanic islands. In a comparative study with other island World Heritage sites, the Ogasawara Islands showed characteristics of both island World Heritage sites with human settlements and island World Heritage sites without human settlements. To address the invasive alien species issue that threatens the Outstanding Universal Values of the Ogasawara Islands, strict biosafety measures are essential to safeguard the endemic species. To address the issue of infrastructure development, vigorous prior environmental impact assessments are required.

The Bonin Islands are oceanic islands of Japan that have never been connected to the continent, and include abundant endemic species and ecosystems. These islands were registered as a UNESCO Natural World Heritage Site in 2011, along with other islands of the Ogasawaras. The environment of the Bonin Islands has been disturbed by development and livestock since human settlement began, and many native organisms remain at risk of extinction due to alien species introduced by humans. To conserve and restore the native ecosystems, alien animals (cats, goats, pigs, bullfrogs, and rodents) have been eradicated on several islands through alien species control projects conducted with the cooperation of administrative organs, the private sector, and residents. The outcomes of these projects highlight the importance of understanding the interactions among multiple alien species and considering the indirect effects of alien species control. However, in recent years, further alien species countermeasures have been required for the big-headed ant and land nemerteans, which have been identified as posing an ecological risk, and for a predatory snail that has recently invaded. Control strategies for alien animals are associated with many issues, including legal restrictions, environmental and human impacts, and technical aspects. In particular, it is difficult to eradicate small-sized species that have high fecundity and invade easily. Therefore, for future protection of the Bonin Islands as a Natural World Heritage Site, it is essential to strengthen the quarantine system to prevent alien species from dispersing on other islands, and to prevent new alien species from invading.

In the Ogasawara Islands much effort has been invested in the management of alien invasive species. There are still many challenges to overcome to achieve management goals such as eradication and containment. In all cases, after determining the target alien invasive species for management, effective, low cost management strategies are needed. Essentially there is a need to establish such management strategies against alien invasive species, that both 1) specify what kind of management interventions to take and 2) provide a spatially explicit management plan. In this paper I focus on three problematic alien invasive plants, Bischofia javanica, Leucaena leucocephala and Casuarina equisetifolia. Aggressive management efforts have been made against these, but in some cases no strategic management plan was established so they still cause problems in the Ogasawaras. For two of the three species, there is a lack one or both of 1) effective management interventions and 2) a spatially explicit management plan. First, I explain what an effective management plan consists of, with one specific case in Japan. Then, I overview the current status and future challenges toward managing these three alien invasive species. Finally I discuss what further steps are needed for realizing effective management of alien invasive species in the Ogasawaras.

Soil profiles under natural forest vegetation on four islands of the Ogasawara Islands, Japan, were compiled and evaluated based on chemical analysis to learn about the natural habitats of the past and determine adequate management measures for conserving the respective ecosystems. The majority of the soils could be characterized as high acidity (high exchangeable acidity, low pH(H2 O) with low pH(KCl)), high cation exchange capacity (CEC) and high proportions of exchangeable Mg over exchangeable Ca and K, and those soils are in fairly early stages of weathering, differing from “laterite” and/or “laterite-like soils.” Available P for plants in the soils is bimodal: very low or very high. The very high level of soil-available P was caused by seabird activities in the past. The high proportion of exchangeable Mg would induce Ca and K deficiency in plants, and this situation would have prevailed in the Ogasawara Islands. Available N for plants in the surface horizons of the soils is generally high and does not limit the ecosystem productivity in many cases of natural forest. Soil erosion would cause fatal effects on the ecosystem by removing the surface horizons and exposing subsoil horizons with extremely high levels of soil acidity, high proportions of exchangeable Mg and low levels of available P and N, with inappropriate permeability and aeration ability for plant growth. Such subsoil horizons would provide very poor conditions for growing plants. Conserving soils is essential and important to the recovery and restoration of the natural vegetation and ecosystems.

Feral goats (Capra hircus), an invasive non-native ungulate, have naturalized on many of the world’s oceanic islands. Overgrazing and trampling by feral goats often cause vegetation degradation and soil erosion, resulting in loss of biodiversity and ecosystem functions on oceanic islands. For restoration and management of the disturbed ecosystems, eradication and control of feral goats have been conducted on many islands. Recovery of vegetation after goat eradication has occurred at some sites but not others. To explain reasons for the lack of vegetation recovery even after goat eradication, I describe processes of changes in ecosystem functions before and after eradication of feral goats on an island, Nakoudo-Jima, in a subtropical archipelago in the northwestern Pacific Ocean. I focus on the relationships between vegetation states and soil chemical properties with vegetation degradation and soil erosion. Loss of vegetation cover caused by overgrazing and trampling by feral goats causes loss of surface soil, which can expose deeper soil horizons. The exposed soils often have lower amounts of nutrients and extremely low pH on the island. Soil with fewer nutrients and lower pH often limits plant growth, and can prevent recovery of vegetation even after goat eradication. In addition, I explore the process of loss of ecosystem functions using a conceptual model based on the relationships between ecosystem states and functions. According to this model, loss of functions occurs in two steps. The first step is vegetation degradation and the second is soil erosion. Finally, I propose a new framework for more flexible and practical restoration of island ecosystems disturbed by invasive mammals, using the concept of a “novel ecosystem,” which should be one of the goals for disturbed ecosystems on islands.

Projects to restore ecosystems have been conducted in various regions. To assess the effects of these projects, studies have been launched to predict changes in ecosystems by constructing mathematical models to reproduce target ecosystems and performing computer simulations. When an entire ecosystem including many species is the target, models using differential equations are often used to calculate population dynamics of the species constituting the ecosystem. When interactions among species are reproduced, the types of interactions are determined based on previous studies and experts’ opinions. Since it often happens that the strength of interactions cannot be measured, multiple models with randomly determined strengths of interactions are prepared to perform simulations to select a model that satisfies the requirements. After that, simulations of eradication of invasive species are performed to predict the outcome. This is the general procedure. A plurality of simulations has predicted that if there are multiple invasive species, eradicating these species simultaneously will be effective for restoring the ecosystem efficiently. However, since simultaneous eradication has a larger impact on ecosystems, monitoring must continue even after eradication and appropriate measures taken. Furthermore, since the models are still in the course of development, a framework is required to feed data obtained from monitoring into the models to improve them further.

The Ogasawara Islands were registered as a Natural World Heritage in 2011. The land snails of the Ogasawaras are an important group of organisms that guarantee their universal value as a World Heritage Site. In particular, the uninhabited island of Ani-Jima has high genetic diversity and is of great importance for conservation. In recent years, however, there has been noticeable damage to the land snails of Ani-Jima caused by rats. The Ministry of the Environment has implemented a rodenticide aerial spraying project for rat control since FY2009. The project failed, however, due to lack of communication with residents and lack of trust. In this study, introducing strategies for measures against alien species and conservation of endemic species by introducing an analysis of residents’ interests and proposals for procedures based on the findings of the rat verification committee, in which the author has been involved as a chairperson. In projects with high uncertainty, such as rat control, it is important to adopt not only the concept of adaptive management but also an adaptive governance approach, which can be used to formulate a decision-making process for community participation that fully takes into account the concerns of the local residents.

Biosphere reserves (BRs) and Natural World Heritage sites (NWHs) both include nature reserves. NWHs are defined by UNESCO’s World Heritage Convention (WHC), while BRs are a UNESCO project. Therefore, Member States need to protect the universal outstanding values of their NWHs in accordance with decisions by the World Heritage Committee. In contrast, recommendations are provided regarding BRs at their registration and every 10 years thereafter. The difference between the two is that World Heritage status helps preserve value, and biosphere reserve status help to create it (UNESCO, 2011). For these purposes, an NWH is a strict nature reserve while a BR is a model site for sustainable development. NWHs consist only of the property surrounded by a buffer zone outside the NWH site, while BRs consist of core areas, buffer zones and transition areas. The core areas are designed to protect nature and eliminate human activity. For BRs, transition areas are as important as core areas. In the case of the Ogasawara Islands NWH, a regional liaison committee was organized to promote smooth and appropriate protection and management of the natural environment through close cooperation and coordination with governments, governmental agencies, islanders and other interested parties. In addition, a wide range of expert advice is available from the Scientific Council for Natural World Heritage in Ogasawara. In this way, participatory approaches are respected in Japan’s Natural World Heritage sites.

The Ogasawara Islands provide interesting examples of ways in which a linguistic ecosystem develops. The natural sciences offer tools, concepts and terminology to help us make sense of an ever-evolving island language. This paper, focuses on processes through which such a linguistic ecosystem expands, and proposes the specific categories of naming, coinage and conceptualization. It also examines ways in which island language can be managed, as other resources are, for the benefit of the islanders.

The relatively short history of the Ogasawara Islands enables us to trace the transmission of songs, dances and musical instruments. Among those from various places, folk songs brought from Hachijo Island, four other songs with Japanese lyrics, Nanyo-odori dances and their accompaniment songs from Micronesia took root and came to be identified as Ogasawaran, especially after their designation as an intangible cultural asset of the Tokyo Metropolitan area in 1987. In addition, foreign materials such as a slit drum called kaka, hula and steelpan were introduced and developed under the Ogasawara brand.

During the past twenty years several surveys have been conducted on the freshwater and brackish-water macroinvertebrates of the Ogasawara Islands. As a result, several species of macroinvertebrates have been described as new species endemic to these islands. Subsequent investigation has shown that some of these endemic species are on the verge of extinction. Consequently, the species are treated as threatened or endangered species in the Red List by the Ministry of the Environment, Japan.

Minami-Iwo-To is a small, isolated member of the Volcano Islands, part of the Ogasawaras. It is a rare example of an island that has maintained a complete original ecosystem without human disturbances or invasive alien species owing to its severe topographical conditions. The most significant feature of Minami Iwo-To is that tens of thousands of seabirds breed there. Seabirds fulfill various ecosystem functions—they disperse seeds, add soil nutrients via their excrement and physically alter habitats. As an ecosystem with seabirds, Minami-Iwo-To can serve as a model for nature restoration programs in the Ogasawara Islands.