Abstract
The relationship between satellite-derived low cloud frequency and the occurrence of tropical montane cloud forest (TMCF) in Taiwan was investigated. From daily MODIS cloud mask products between 2003 and 2012 the low cloud class was extracted and mean low cloud frequency was calculated for Taiwan. This low cloud frequency map was blended with an existing plot-based vegetation classification for Taiwan to analyze the relationship between low cloud frequency and TMCF occurrence. Receiver operating characteristics curves and the area under the ROC curve (AUC) were used to analyze if a relationship exists. No relationship was found for all four TMCF types taken together (AUC = 0.61) and for the dominant TMCF type, Quercus montane evergreen broad-leaved cloud forest (AUC = 0.5). Strong relationships were found for the two spatially-restricted TMCF types, Fagus montane deciduous broad-leaved cloud forest (AUC = 0.91) and Pasania-Elaeocarpus montane evergreen broad-leaved forest (AUC = 0.84), as well as for the second dominant type Chamaecyparis montane mixed cloud forest (AUC = 0.74). The results show that low cloud frequency thresholds might be associated with specific cloud forest types in Taiwan. Further studies should incorporate information about cloud base height, cloud density, and cloud immersion time as well as satellite-based cloud frequency information with a higher temporal resolution. Combination with satellite-based land cover classifications for Taiwan would allow quasi-continuous observation of TMCF changes. Such knowledge would be the precondition for effective protective actions concerning this exceptional but threatened ecosystem.
Highlights
Tropical montane cloud forests (TMCF) represent a rare and exceptional ecosystem of the humid tropics
The aim of the current study is to use the new available vegetation dataset in combination with a ten year time-series of low cloud frequencies from the Moderate-Resolution Imaging Spectroradiometer (MODIS) cloud mask product in 1 km resolution to investigate the relationship between the occurrence of TMCF and low cloud frequencies in Taiwan for the first time
We have used new datasets that have not been explored in Taiwan previously to derive a low cloud frequency map and to analyze the relationship between the calculated low cloud frequency and the occurrence of TMCF based on a new extensive observation dataset of cloud and non-cloud forest classification in Taiwan
Summary
Tropical montane cloud forests (TMCF) represent a rare and exceptional ecosystem of the humid tropics They are generally characterized by the frequent or permanent occurrence of low clouds [1] but their form and appearance varies globally and depends upon latitude, altitude, topography, distance to the ocean, wind direction, and rainfall patterns [2,3]. In addition to their important role regarding regional ecosystem water services (e.g., [4]), they are biodiversity hotspots and known for their exceptionally high endemism (e.g., [5]). The climate of cloud forests is highly variable from forest to forest, with an average rainfall of about 2000 mm per year and an average temperature of 7–17 °C [11]
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