Effects of sika deer on tree seedlings in a warm temperate forest on Yakushima Island, Japan

Abstract

High‐density herbivore species often play an important role in forest regeneration. Native sika deer (Cervus nippon yakushimae) inhabit a high density (51.5–63.8 head/km2, estimated by a pellet count method) area in the western part of a lowland natural forest on Yakushima Island, Japan. To test experimentally the impact of sika deer on the mortality and the survivability of current‐year seedlings, which are at a more vulnerable stage than the later stages, we constructed fenced exclosures, planted seeds of nine sapfruit tree species and compared the mortality and the survivability of current‐year seedlings between fenced and unfenced quadrats. Large seeded species had significantly greater survivability in fenced quadrats than in unfenced quadrats. However, the survivability disagreed with feeding preferences. Sika deer activity increased seedling mortality of large‐seeded species more than that of small‐seeded species, and did not decrease much seedling survivability of not‐preferred species. We found that the physical disturbance by the high density of sika deer resulted in mortality for both preferred and not‐preferred species, and that deer herbivory was important for preferred species.