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.

为探明日本栎枯萎病引发的林木死亡对周边树木生长格局的影响是否取决于枯树的体型、密度与空间邻近性，且该影响的物种间差异是否存在，我们以日本某温带森林中的优势栎树种枹栎（*Quercus serrata*）为研究对象，分析其因日本栎枯萎病死亡后对周边树木生长速率的影响。我们利用1公顷样地内抽样调查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目标树周边枯株枹栎之间的竞争指数（Competition Index, CI）之间的关联。目标树的竞争指数通过计算其特定半径范围（2.5~30米，间隔2.5米）内的枯株枹栎的体型与密度得到。在这11个树种中，有8个耐阴树种的竞争指数系数呈显著正相关。研究结果表明，栎树死亡会提升部分耐阴树种的生长速率，且该提升效应依赖于枯树的体型与空间邻近性，同时不同耐阴树种的生长速率提升时机存在差异。