雲霧與森林對微氣候時空變異度的影響

Abstract

森林與雲霧之間交互作用對於微氣候的調節，提供了陸域生態系中不可取代的生態棲位，並擁有相當高且獨特的生物多樣性。森林的遮蔽效應和生物量熱儲存，對微氣候的日夜變化有顯著減緩的作用，使其相較於鄰近的開墾地呈現截然不同的日夜變化特性，這進一步增強了近地面微氣候的空間異質性。頻繁的雲霧事件帶來豐沛的水氣以及降低了地表的日輻射量, 造就了特殊的水文氣候特徵。這些生物和非生物的因子藉由水文和能量循環對邊界層發展產生顯著的影響。 本研究結合現地觀測與理想化模式模擬，探討森林生物量的熱儲存、森林遮蔽效應和雲霧事件對陸地與大氣交互作用日變化的影響。從觀測結果可以看到森林的微氣候日夜變化相較於鄰近的開闊地和緩，這不僅僅發生在林下，林上微氣候的日變化也較為穩定。其中，氣候模式的理想實驗說明生物量熱儲存對林上微氣候貢獻了顯著的調節作用。白天的生物量暫時儲存了部分輻射能量，這使得白天氣溫稍微降低；到了夜間，白天儲存在生物量中的能量釋放出來加熱了夜間的氣溫。因此，若模式忽略了生物量熱儲存的能力，將導致日間可感熱通量與潛熱通量被高估，以及低估夜間溫度。這不僅會導致日間地表熱通量的偏差，更容易高估了日最高溫和邊界層發展高度。然而，具有調節作用的森林與鄰近開闊地所形成的氣候空間岐異度, 則會在雲霧事件發生時被有效弭平。雲霧阻擋了進到地表的太陽輻射，進而降低地表熱通量對於近地面微氣候的影響, 進一步降低了大氣垂直不穩定性，同時也有效降低微氣候在空間與時間上的變異度。也就是，雲霧事件的發生暫時停止了陸地與大氣之間能量的交互作用。 為解決目前侷限於近地面觀測，未來將規劃在不同地表條件上進行成對的地表熱通量測量與垂直剖面觀測。此外，未來也將利用全球氣候模型，評估生物量熱儲存對全球氣候的影響。本研究對於雲霧事件改變陸氣交互作用進而弭平微氣候空間歧異度特性的應用，希望可以延伸至全球其他位處不同植被的成對現地觀測通量站。藉由整合模式和觀測，了解雲霧和不同土地利用特性交互作用下，所形成的全球局地微氣候空間與時間的異質性變化。希望能觀測與模擬所建立的完整實驗架構能夠對於氣候變異對水文及生態系統交互作用的影響有更進一步的理解。

Forests-fog interactions play a crucial role in regulating microclimates and contributing to an irreplaceable ecological habitat in montane cloud forests (MCFs). The biomass heat storage and canopy shading effect of forests significantly regulate diurnal variations in microclimate, resulting in distinct differences compared to adjacent open fields. Additionally, frequent fog events bring abundant moisture while reducing solar radiation, thereby creating unique hydroclimatic characteristics of MCFs. These biotic and abiotic factors significantly influence microclimates through hydrological and energy cycles. This study integrates paired in-situ observations and idealized model simulations to examine the impacts of biomass heat storage (BHS), canopy shading, and fog events on the diurnal cycle of land-atmosphere interactions. Analysis of observations demonstrates that forests consistently diminish the diurnal variability of microclimate compared to adjacent open fields. This effect is observed not only within the forest understory but above the forest overstory. Furthermore, idealized climate model experiments highlight the significant role of BHS in microclimate regulation. Biomass absorbs a portion of net radiation as heat flux during the day, inducing a mild cooling effect on air temperature, and subsequently releases the stored heat at night, moderating nocturnal cooling. Thus, omitting BHS in models results in a substantial overestimation of daytime sensible and latent heat fluxes and an underestimation of nighttime temperatures. Meanwhile, cloud and fog events play a crucial role in moderating climatic differences between forests and adjacent open fields. By reducing incoming solar radiation, they lower the influence of surface heat fluxes on near-surface microclimates, thereby decreasing atmospheric vertical instability and stabilizing spatiotemporal variations. Consequently, cloud and fog events temporarily suppress land-atmosphere interactions by altering surface energy balance. By incorporating modeling and observational approaches, this study explores how fog and land-use characteristics shape microclimate spatiotemporal variability. The comprehensive framework established in this study reveals the impacts of climate variability on hydrological and ecosystem interactions. To comprehensively assess boundary layer development, this study recommends expanding paired heat flux measurements and conducting deeper vertical profiling across diverse land types. Additionally, integrating BHS into global climate models will further elucidate a comprehensive understanding of the impact of diverse land types on climate systems. Furthermore, utilizing global paired flux observations across varying vegetation types will enhance the quantification of land-atmosphere interaction intensity at an hourly scale, offering new insights into microclimate variability. This comprehensive approach is expected to provide actionable insights for land-use management and offers a robust foundation for understanding and mitigating the effects of climate change on ecosystems.