Altitudinal distribution patterns of plant species in Taiwan are mainly determined by the northeast monsoon rather than the heat retention mechanism of Massenerhebung

The objectives of this study are to revisit altitudinal distribution patterns for plant species in the main sections (where the ridges are higher than 2,000 m above sea level) of the Central Mountain Range (CMR) in Taiwan and identify the most influential environmental factor resulting in these patterns. Three east-west oriented sampling belts at regular latitudinal intervals were laid out in the main sections of the CMR. Each belt was further divided into two regions according to the aspect (the east-facing and west-facing aspects). The data of species altitudinal distribution for the six regions were extracted from a dataset of a national vegetation mapping project. On the north and central sampling belts species altitudinal distribution is markedly lower on the east-facing aspect than on the west-facing aspect, whereas on the south belt species altitudinal distribution between the two aspects does not differ significantly. There is an increasing tendency of species altitudinal distribution with the decrease of latitude on the east-facing aspect of the CMR. In contrast, the tendency is barely noticeable on the west-facing aspect. The distinct distribution patterns between the two aspects can be better explained by climatic heterogeneity created by the interaction between the winter northeast monsoon and the topographic effect of the CMR than by the heat retention mechanism of Massenerhebung. The previously-proposed distribution pattern that claimed that species altitudinal distribution descends gradually towards the north and south ends of Taiwan should be revised. On the east-facing aspect of the main sections of the CMR, species altitudinal distribution rises as latitude decreases. On the west-facing aspect, such tendency is not evident.