Future Challenges for Research and Management of Sika Deer

Abstract

AbstractA shrinking human population in an area induces changes in land-use patterns; abandoned farmlands across Japan have expanded, which has increased the number and distribution of sika deer populations, resulting in serious damage to agriculture, forestry, and natural vegetation. Deer ranges have expanded close to human settlements, which has increased the risk to human health (deer-vehicle collisions and infectious diseases). Sika deer exhibit high ecological plasticity in movement patterns, density-dependent food switching, and population growth rates depending on habitat quality. Sika deer can survive using low-quality food, and their life history traits such as reproduction rate were rarely affected by their density leading to a sustained high density even in degrading habitats, suggesting that sika deer are highly evolved K-selected species. Under long-term grazing, aboveground body and the seed bank of palatable species will disappear quickly. Thus, the ecosystem resilience will be lost, and the vegetation in the area will not return to its original state even if the deer population is reduced to a lower density by culling. Therefore, the monitoring of forest vegetation and deer population management at low density should be integrated. A wide range of information and evidence-based policymaking should be integrated to successfully manage the highly plastic sika deer populations in a society with a shrinking human population. In the last chapter, we summarized the ecological plasticity of sika deer, focusing on its movement patterns, population dynamics, food habits, and various impacts on ecosystems to deepen our understanding about them. We then considered the role of humans in the ecosystems as users and engineers, which caused drastic changes in deer distribution and population size. The distribution range of deer has expanded to the northern and mountainous areas in response to a decrease in the snow cover period in the past 25 years (Ohashi et al., Ecol Evol 6:7763–7775, 2016). Their distribution range covered 70% of the country as of 2018, and it is expanding at a constant speed, especially in the historical range of the northern part of Honshu (Chap. 2). The expansion of deer distribution is expected to accelerate further with decreasing snow cover period (Chap. 3). In Japan, the human population is shrinking faster than that in the rest of the world. Moreover, the population is concentrated in cities associated with declining primary industries, which has led to a rapid decline in land use and management pressure in rural areas, including a rapid increase in abandoned farmland, a declining hunting population, and an aging population (Tsunoda and Enari, Conserv Biol 34:819–828, 2020). Here, we discuss the future management directions for developing resilient forests and sustainable social-ecological systems in a shrinking society.