2019 Volume 23 Issue 1-2 Pages 37-44
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.
