Understanding how past disturbances have influenced the development of forests is critical for deciphering their current structure and composition and forecasting future changes. In this study, dendrochronological methods were applied to uncover the disturbance history of old-growth hemlock-dominated forests in central Bhutan. Analysis of tree-ring samples from two old-growth hemlock stands, located in two different topographic settings, identified the importance of gap-phase dynamics in facilitating recruitment and growth releases and producing complex, multi-aged structures over time. One site showed evidence of a near stand-replacing disturbance in the late 1700s, while the other showed no evidence of high-severity disturbance at any time over the last 400 years. At both sites low-to medium-severity disturbances, some of which appear to be associated with cyclones originating in the Bay of Bengal, dominated the disturbance regime. The hemlock stands exhibited a significant positive association between cyclone occurrence and growth release events and between recruitment pulses and growth release events. From 1800 to 1970 there was an increase in recruitment of angiosperm tree species at most sites and a corresponding decline in conifer recruitment. Over the past 50 years there has been little new recruitment; this may be due to light limitation in the understory from shade-tolerant angiosperms and bamboo in the lower strata of these stands. Significant variations in disturbance dynamics and recruitment were observed across the study sites, suggesting that other factors, such as topography and climate, may be influencing long-term stand development patterns. This study highlights the complex interplay between historical disturbance regimes and tree recruitment in shaping the age and size structures of old-growth hemlock forests in central Bhutan. It also provides new insights into the dynamics of these forests that can be used to support effective forest conservation and management in the future.

中文翻译：

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不丹中部古老铁杉林的林分动态受自然干扰的影响


了解过去的干扰如何影响森林的发展对于破译其当前结构和组成以及预测未来变化至关重要。在这项研究中，应用树木年代学方法揭示了不丹中部以老铁杉为主的森林的干扰历史。对位于两种不同地形环境中的两个古老铁杉林分的树木年轮样本进行分析，确定了间隙相动力学在促进招募和生长释放以及随着时间的推移产生复杂的多龄结构方面的重要性。一个地点在 1700 年代后期显示出近乎林分替代干扰的证据，而另一个地点在过去 400 年的任何时候都没有显示出高度严重干扰的证据。在这两个地点，低到中等严重程度的扰动，其中一些似乎与起源于孟加拉湾的气旋有关，在扰动机制中占主导地位。铁杉林分在气旋发生与生长释放事件之间以及补充脉冲与生长释放事件之间表现出显著的正相关。从 1800 年到 1970 年，大多数地点被子植物树种的补充增加，针叶树的补充相应减少。在过去的 50 年里，几乎没有新的招聘;这可能是由于这些林分下层的耐阴被子植物和竹子在林下层的光线限制。在研究地点观察到干扰动力学和补充的显著差异，表明其他因素，如地形和气候，可能影响林分的长期发展模式。 本研究强调了历史干扰制度和树木招募在塑造不丹中部古老铁杉林的年龄和大小结构方面复杂的相互作用。它还为这些森林的动态提供了新的见解，可用于支持未来有效的森林保护和管理。