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到自然干扰的影响


了解过去的干扰如何影响森林的发展对于破译森林当前的结构和组成以及预测未来的变化至关重要。在这项研究中，应用树木年代学方法来揭示不丹中部以铁杉为主的古老森林的干扰历史。对来自两个不同地形环境的两个古老铁杉林的年轮样本进行分析，确定了间隙相动态在促进补充和生长释放以及随着时间的推移产生复杂的多年龄结构方面的重要性。其中一处遗址显示出 1700 年代末发生过一次近乎林木取代的扰动的证据，而另一处遗址则没有显示出过去 400 年来任何时候发生过严重扰动的证据。在这两个地点，低到中度的扰动主导了扰动状态，其中一些扰动似乎与源自孟加拉湾的气旋有关。铁杉林在旋风发生和生长释放事件之间以及补充脉冲和生长释放事件之间表现出显着的正相关。从 1800 年到 1970 年，大多数地点被子植物树种的补充量有所增加，而针叶树的补充量相应减少。过去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荫被子植物和竹子对林下光照的限制。在各个研究地点观察到扰动动态和补充的显着变化，这表明地形和气候等其他因素可能会影响林分的长期发展模式。 这项研究强调了历史干扰制度和树木补充之间复杂的相互作用，影响着不丹中部古老铁杉林的年龄和规模结构。它还提供了对这些森林动态的新见解，可用于支持未来有效的森林保护和管理。