Species-specific growth patterns of trees neighboring dead oak trees caused by Japanese oak wilt disease

To test whether the effects of mortality caused by Japanese oak wilt disease on the growth patterns of surrounding trees depend on the sizes, densities, and proximities of the dead trees and whether the dependency differs among species, we examined the effects of mortality in the dominant oak species, <i>Quercus serrata</i>, caused by Japanese oak wilt disease on the growth rates of surrounding trees in a temperate forest in Japan. Using data on the diameters at breast height and spatial locations of trees sampled in a 1-ha plot, we evaluated the relationships between the absolute growth rate of 11 dominant species and the competition index (CI) between the neighboring tree and the dead <i>Q. serrata</i> tree. The CI of a focal tree was calculated from the sizes and densities of dead <i>Q. serrata</i> trees within a particular radius (2.5–30 m, 2.5-m intervals) of the focal tree. Of the 11 species, eight shade-tolerant species had significant positive coefficients for CI. Our results indicate that the mortality of the oak trees increased the growth rates of some shade-tolerant species, depending on the sizes and proximities of the dead trees, and that timing of the increases differed among shade-tolerant species.

为探究日本栎枯萎病（Japanese oak wilt disease）引发的林木死亡对周边树木生长格局的影响是否依赖于枯木的个体尺寸、种群密度与空间邻近程度，且该依赖关系是否存在物种间差异，我们以日本温带森林为研究对象，针对由日本栎枯萎病导致的优势栎类物种枹栎（*Quercus serrata*）的死亡事件，分析其对周边树木生长速率的影响。我们基于1公顷样地内采样树木的胸径与空间位置数据，评估了11个优势树种的绝对生长速率与邻株和枯亡枹栎间的竞争指数（CI）之间的关系。目标个体的竞争指数通过计算其特定半径范围（2.5~30米，步长2.5米）内的枯亡枹栎的尺寸与密度得到。在11个供试树种中，有8个耐阴树种的竞争指数系数呈显著正向关联。本研究结果显示，栎树死亡会提升部分耐阴树种的生长速率，且该效应依赖于枯木的尺寸与空间邻近程度；同时不同耐阴树种的生长速率提升时间节点存在差异。