Tropical mountain forests are important biodiversity hotspots, which host disproportionally high number of endemic species. However, the potential impacts of climate change in these areas are uncertain. A key factor contributing to this knowledge gap is that climatic conditions experienced by organisms inside tropical forests (i.e., microclimate) remain largely understudied. Due to the effects of topography and vegetation, the understory microclimate can differ substantially from free-air conditions (i.e., macroclimate). This study aimed at unveiling vegetation structural characteristics and microclimatic patterns along an elevational gradient in a highly diverse tropical mountain ecosystem (Mount Kenya), by combining hundreds of terrestrial laser scanning measurements with a two-year time-series of microclimate observations. Our results showed that macroclimate temperature and elevation contributed >90 % to the microclimate variability in our study area. The influence of vegetation and soil moisture in regulating temperature differed substantially between day and night, as well as in different periods of the year. The contribution of vegetation to microclimate variation during the day was two times higher than that during the night. Soil moisture had a cooling effect on microclimate temperature during daytime, while the opposite pattern was observed at night. These differences affected lapse rates, which showed a clearly seasonal fluctuation during diurnal periods but a relatively stable pattern in night periods. The diurnal temperature range was regulated by combined effects of vegetation structure, elevation, and soil moisture. Finally, we were able to detect subtle changes in forest structure caused by historical selective logging. These changes resulted in a legacy effect on microclimate, thus demonstrating that human-induced disturbances have long-lasting impacts on tropical mountain ecosystems. These results improve our understanding of the climatic conditions experienced by organisms inside highly diverse African mountain forests, as well as how these conditions are regulated by vegetation structure and environmental factors.

中文翻译：

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肯尼亚山沿海拔梯度的森林结构和小气候模式


热带山地森林是重要的生物多样性热点地区，拥有大量特有物种。然而，气候变化对这些地区的潜在影响尚不确定。造成这种知识差距的一个关键因素是热带森林内生物体所经历的气候条件（即小气候）仍然没有得到充分研究。由于地形和植被的影响，林下小气候可能与自然空气条件（即大气候）有很大不同。这项研究旨在通过将数百个地面激光扫描测量与两年时间序列的小气候观测相结合，揭示高度多样化的热带山地生态系统（肯尼亚山）沿海拔梯度的植被结构特征和小气候模式。我们的结果表明，大气候温度和海拔对我们研究区域的小气候变化贡献了>90%。植被和土壤湿度对温度调节的影响在白天和夜间以及一年中的不同时期有很大差异。白天植被对小气候变化的贡献是夜间的两倍。白天土壤湿度对小气候温度有冷却作用，而夜间则相反。这些差异影响了失效率，失效率在白天表现出明显的季节性波动，但在夜间表现出相对稳定的模式。昼夜温度范围受植被结构、海拔和土壤湿度的综合影响。最后，我们能够检测到历史选择性采伐引起的森林结构的微妙变化。 这些变化对小气候产生了遗留影响，从而表明人类引起的干扰对热带山地生态系统具有长期持续的影响。这些结果提高了我们对高度多样化的非洲山地森林中生物体所经历的气候条件的理解，以及这些条件如何受到植被结构和环境因素的调节。