Ritter Axel, Regalado Carlos M, Aschan Guido
Instituto Canario de Investigaciones Agrarias (ICIA), Departamento Suelos y Riegos, Apdo. 60 La Laguna, 38200 S/C Tenerife, Spain.
Tree Physiol. 2009 Apr;29(4):517-28. doi: 10.1093/treephys/tpn043. Epub 2009 Jan 20.
The ecophysiologic role of fog in the evergreen heath-laurel 'laurisilva' cloud forests of the Canary Islands has not been unequivocally demonstrated, although it is generally assumed that fog water is important for the survival and the distribution of this relict paleoecosystem of the North Atlantic Macaronesian archipelagos. To determine the role of fog in this ecosystem, we combined direct transpiration measurements of heath-laurel tree species, obtained with Granier's heat dissipation probes, with micrometeorological and artificial fog collection measurements carried out in a 43.7-ha watershed located in the Garajonay National Park (La Gomera, Canary Islands, Spain) over a 10-month period. Median ambient temperature spanned from 7 to 15 degrees C under foggy conditions whereas higher values, ranging from 9 to 21 degrees C, were registered during fog-free periods. Additionally, during the periods when fog water was collected, global solar radiation values were linearly related (r2=0.831) to those under fog-free conditions, such that there was a 75+/-1% reduction in median radiation in response to fog. Fog events greatly reduced median diurnal tree transpiration, with rates about 30 times lower than that during fog-free conditions and approximating the nighttime rates in both species studied (the needle-like leaf Erica arborea L. and the broadleaf Myrica faya Ait.). This large decrease in transpiration in response to fog was independent of the time of the day, tree size and species and micrometeorological status, both when expressed on a median basis and in cumulative terms for the entire 10-month measuring period. We conclude that, in contrast to the turbulent deposition of fog water droplets on the heath-laurel species, which may be regarded as a localized hydrological phenomenon that is important for high-altitude wind-exposed E. arborea trees, the cooler, wetter and shaded microenvironment provided by the cloud immersion belt represents a large-scale effect that is crucial for reducing the transpirational water loss of trees that have profligate water use, such as those of the 'laurisilva'.
在加那利群岛的常绿石南 - 月桂树“拉乌里斯席尔瓦”云雾森林中，雾气的生态生理作用尚未得到明确证实，尽管人们普遍认为雾水对于北大西洋马卡罗尼西亚群岛这一残存古生态系统的生存和分布至关重要。为了确定雾气在该生态系统中的作用，我们将使用格兰尼尔散热探针获得的石南 - 月桂树物种的直接蒸腾测量数据，与在西班牙加那利群岛拉戈梅拉岛加拉霍奈国家公园一个43.7公顷流域内进行的为期10个月的微气象和人工雾收集测量数据相结合。在有雾条件下，环境温度中位数在7至15摄氏度之间，而在无雾时期记录到的温度较高，范围为从9至21摄氏度。此外，在收集雾水的时期，全球太阳辐射值与无雾条件下的辐射值呈线性相关（r2 = 0.831），因此，由于雾气，辐射中位数降低了75±1%。雾天极大地降低了树木日间蒸腾的中位数，蒸腾速率比无雾条件下低约30倍，并且接近所研究的两个物种（针叶叶的树状欧石南 Erica arborea L. 和阔叶的费氏杨梅 Myrica faya Ait.）的夜间蒸腾速率。无论是以中位数表示还是以整个10个月测量期的累积量表示，这种因雾导致的蒸腾大幅下降均与一天中的时间、树木大小和物种以及微气象状况无关。我们得出结论，与雾水滴在石南 - 月桂树物种上的湍流沉积不同，后者可被视为一种对高海拔受风影响的树状欧石南树很重要的局部水文现象，云雾浸没带所提供的更凉爽、更湿润且有遮蔽的微环境代表了一种大规模效应，对于减少像“拉乌里斯席尔瓦”中那些水分利用量大的树木的蒸腾失水至关重要。
