ABSTRACT

Tree-cavities are considered as key components that support multiple species, including endemic ones, in subtropical forests in Yambaru, the northern area of Okinawa Island, Japan. Here, we established two study plots in mature subtropical forests in Yambaru and surveyed for tree-cavities with depths ≥ 10 cm. The density of tree-cavities was 198 per ha, which is exceptionally high compared with tree-cavity densities reported by other studies. Among the three key tree species (Castanopsis sieboldii, Schima wallichii, and Distylium racemosum), no tree-cavities were observed in S. wallichii in the study plots. In both C. sieboldii and D. racemosum, the probability of tree-cavity presence increased as the diameter at breast height (DBH) increased. In addition, the probability of tree-cavity presence on D. racemosum started to increase at smaller DBH stage compared with that on C. sieboldii. Distylium racemosum often had multiple tree-cavities per stem. Excavated cavities were rare across all species, and decay cavities were dominant. We detected the activity of the endangered Ryukyu long-haired rat (Diplothrix legata) in two cavities, both of which had similar features: a stem DBH of about 43 cm and volumes of 0.09–0.16 m³. In the Yambaru area, the preservation of large-diameter stems that will form tree-cavities is critically important for maintaining forest ecosystem health and should be considered when implementing forest management plans, especially for D. racemosum, which is rich in cavities and likely plays multiple ecological roles.

摘要

在日本冲绳岛北部地区山原的亚热带森林中，树洞被认为是支持多种物种（包括特有物种）的关键组成部分。在这里，我们在 Yabaru 的成熟亚热带森林中建立了两个研究地块，并调查了深度 ≥ 10 cm 的树洞。树洞密度为每公顷 198 个，与其他研究报告的树洞密度相比异常高。在三个关键树种（栲、Schima wallichii和Distylium racemosum）中，在研究地块的S. wallichii中没有观察到树洞。在C. sieboldii和D.racemosum 中，随着胸高直径 (DBH) 的增加，树洞存在的可能性增加。此外，与C. sieboldii相比，在较小 DBH 阶段，D.racemosum上出现树洞的概率开始增加。Distylium racemosum每个茎通常具有多个树腔。在所有物种中挖掘的空洞都很罕见，而腐烂的空洞占主导地位。我们在两个洞中检测到濒临灭绝的琉球长毛鼠 ( Diplothrix legata )的活动，这两个洞具有相似的特征：茎 DBH 约为 43 cm，体积为 0.09–0.16 m ³. 在山原地区，保护将形成树洞的大直径茎干对于维持森林生态系统健康至关重要，在实施森林管理计划时应予以考虑，特别是对于富含洞洞和可能发挥作用的D. racemosum。多重生态作用。