Effects of Sika Deer (Cervus nippon) and Dwarf Bamboo (Sasa senanensis) on TrilliumPopulations in Akan National Park, Eastern Hokkaido, Japan

Abstract

The competition between Trillium spp. and other species could modify the utility of Trillium spp. as indicators of the impact of deer on forest vegetation. To evaluate whether Trillium spp. (T. camschatcense and T. tschonoskii) are appropriate indicators of the impact of sika deer (Cervus nippon) in the presence of dwarf bamboo (Sasa senanensis), which competes with Trillium populations, we examined the size class of large-growth-stage Trillium plants, the frequency of the presence of deer pellets and the coverage of S. senanensis in deer-excluded sites (where deer have been eliminated since 1995) and unfenced control sites in Akan National Park, eastern Hokkaido, Japan. The result of a cumulative link mixed model (CLMM) suggests that size class at deer-excluded sites is influenced by competitive understory species, even without deer grazing. The CLMM result for unfenced control sites suggests that C. nippon negatively influences the size class of Trillium populations; however, the negative effect weakened with increasing S. senanensis coverage. Thus, S. senanensis can function as an unpalatable neighbor that makes it difficult for C. nippon to detect Trillium plants. We conclude that the size class structure of Trillium spp. can be a useful index of C. nippon usage under sparse or medium S. senanensis understories; however, it is difficult to use these indices under dense S. senanensis understories because of the weakened negative effect of C. nippon grazing.

Reproductive characteristics in an understory bamboo and gradual environmental changes after its dieback provide an extended opportunity for overstory tree regeneration in a mixed cool‐temperate forest in central Japan

“…The decay of dead culms may facilitate access of sika deer to the study site (Inatomi et al . 2017; Akashi et al . 2021).…”

Response of an Indicator Species, Dryopteris crassirhizoma, to Temporal and Spatial Variations in Sika Deer Density

“…In our study, not only the population-level characteristics (coverage of S. nipponica and plant density of D. crassirhizoma ) but also the morphological characteristics (height of S. nipponica and leaf length of D. crassirhizoma ) did not change significantly with decreasing deer density. The height of Trillium spp., which is often used as an indicator species, can be influenced not only by deer impact in the growing season, but also by legacy impact [ 21 ]. The period of decrease in deer density at WPA may have been too short to detect changes in morphological characteristics.…”

“…However, morphological characteristics such as the height of Trillium spp. can be influenced not only by deer usage in the growing season, but also by historical deer usage [ 21 ]. The grazing intensity with scars only in the growing season may be more sensitive to temporal changes in deer density than morphological and population-level characteristics.…”

Variability in deer diet and plant vulnerability to browsing among forests with different establishment years of sika deer

“…Previous studies have suggested the use of indicator species, which is an approach that monitors plant size or browsing damage of a specific species selected by ungulates, to predict ungulate abundance ( Augustine & DeCalesta, 2003 ; Mysterud et al, 2010 ; Akashi, Unno & Terazawa, 2015 ; Iijima & Nagaike, 2015 ; Inatomi, Uno & Iijima, 2017 ). Waller, Johnson & Witt (2017) have also shown that twig ages provide a direct indicator of browsing on regenerating trees with lower sampling variance, greater sensitivity, and are reliable indicator of deer impacts and habitat conditions.…”